TIMING AND BASIN IMPLICATIONS FOR THE EDEN-COMERONG-YALWAL VOLCANIC ZONE: STRATIGRAPHY, DEPOSITIONAL ENVIRONMENT AND TECTONIC AFFINITY OF THE COMERONG VOLCANIC COMPLEX, NSW

Thomas Cotter (BSc. Geol.)

Submitted in fulfilment of the requirements for the degree of Master of Philosophy (Science)

School of Earth and Atmospheric Sciences Science and Engineering Faculty Queensland University of Technology 2020

Keywords

Put a paragraph of keywords here in alphabetical order (for cataloguing purposes). Comerong Volcanics Lachlan Orogen Paleoenvironment Stratigraphy Intraplate Devonian

Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW i

Abstract

The Lachlan Orogen of New South Wales and Victoria preserves a geological history of Palaeozoic cratonisation of eastern Australia along the paleo-pacific plate boundary. The Lachlan Orogen forms an important crustal feature in eastern Australia because it hosts world-class economic deposits and provides a unique insight into plate tectonic processes active throughout the Palaeozoic. The eastern subdivision of the Lachlan Orogen is comprised of a complex accumulation of volcanic and sedimentary successions, intruded by granitic batholiths. Here I investigate the paleoenvironment, geochemical affinity and timing of the Devonian, Comerong Volcanic Complex on the New South Wales south coast. This investigation demonstrates the Comerong Volcanic Complex consists of alluvial, fluvial and lacustrine sedimentary deposits and bimodal volcanics that were emplaced in a subaerial paleoenvironment. The bimodal volcanics are underlain by a minor accumulation of andesitic lavas that have subduction-related trace element signatures. The bimodal rhyolites and basalts have within-plate geochemical affinities, indicating an intraplate tectonic setting. The basaltic trace element geochemistry displays an enriched mantle source signature with the rhyolites displaying enriched A-type affinity. The bimodal volcanics yielded a zircon U-Pb isotope age range from 392 to 387 Ma in the Eifelian stage of the Middle Devonian. This study shows that the Comerong within-plate rifting and production of A-type felsic volcanics forms part of a short magmatic event in the Early to Middle Devonian, underlain by lavas potentially emplaced as a short period of arc-related volcanism in the Silurian to Early Devonian.

ii Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Table of Contents

Keywords ...... i Abstract ...... ii Table of Contents ...... iii List of Figures ...... v List of Tables ...... xiii List of Abbreviations ...... xiv Statement of Original Authorship ...... xv Acknowledgements ...... xvi Chapter 1: Introduction ...... 17 Chapter 2: Geological Background & Research Aims ...... 20 2.1 Geological Background ...... 20 2.2 Gaps in Knowledge...... 36 2.3 Research Objectives...... 37 Chapter 3: Applied Methods to the Research ...... 39 3.1 Field Geology and Petrographic Analysis ...... 39 3.2 Whole Rock Major and Trace Element Geochemistry ...... 41 3.3 U-P Zircon Geochronology ...... 42 Chapter 4: Field Results ...... 44 4.1 Basement to the Comerong Volcanic Complex: The Ordovician “Mallacoota Beds” .50 4.2 Coherent Lithofacies within the Comerong Volcanic Complex ...... 52 4.3 Fragmental Igneous Lithofacies within the Comerong Volcanic Complex ...... 66 4.4 Sedimentary Lithofacies within the Comerong Volcanic Complex ...... 78 4.5 Lithofacies Associations ...... 88 4.6 Emplacement Mechanisms of the Comerong Volcanic Complex ...... 90 4.7 Paleoenvironment Reconstruction ...... 102 Chapter 5: Geochemical Analysis Results ...... 104 5.1 Alteration ...... 104 5.2 Composition Classification ...... 105 5.3 Major Element Chemistry ...... 107 5.4 Trace Element Chemistry ...... 109 5.5 Relationship Between Mafic and Intermediate Samples ...... 111 5.6 Affinity of Silicic Samples ...... 113 Chapter 6: U-Pb Geochronology Results ...... 116 6.1 Stoney Creek Rhyolite (D9.2) ...... 120

Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW iii

6.2 Buckenbowra River Ignimbrite (D13.1) ...... 123 6.3 Burra Creek Ignimbrite (D17.6) ...... 127 6.4 Emplacement Timing Summary ...... 130 Chapter 7: Discussion ...... 133 7.1 Stratigraphy and Emplacement Model of the Comerong Volcanic Complex ...... 133 7.2 Temporal Relationship within the Eastern Lachlan Orogen ...... 152 Chapter 8: Conclusions and Further Research ...... 156 8.1 Summary and Conclusion ...... 156 8.2 Further Research ...... 157 8.3 Importance of further Research ...... 158 References ...... 159 Appendices ...... 170

iv Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

List of Figures

[The List of Figures can be created automatically and updated with the F9 key – refer to Thesis PAM.]

Fig. 1. Location of the Comerong Volcanics within the Australian states and territories...... 19 Fig. 2. a, Reconstruction of the Gondwana supercontinent depicting the proposed eastern margin. Diagram is modified after Gray and Foster (2004) and Cawood (2005). Diagram taken from Vos et al. (2007). b, The Australian Tasmanides with boundaries from Glen (2005). Diagram taken from Rosenbaum (2018)...... 20 Fig. 3. Timeline of orogenic events recognised in the Lachlan Orogen from: A - Vandenberg et al. (2000); B - Rosenbaum (2018). Timeline constructed from the International Chronostratigraphic Chart after Cohen et al. (2013)...... 23 Fig. 4. a, Exposures of the Tasmanide orogens on the eastern Australian margin displaying the eastern Lachlan subdivision and Wagga-Omeo Metamorphic Belt as the principal surface exposures. b, Lachlan Orogen subdivision into Western, Central and Eastern Lachlan Orogen terranes. Images taken from Gray and Foster (2004)...... 25 Fig. 5. Distribution of major orogenic events across the Lachlan Orogen with locations of original naming exposure abbreviated. Note approximate overlap of events. Major regional fault zones shown as solid lines. Deformation distribution map taken from Gray (1997)...... 27 Fig. 6. Map of the distribution of batholiths and regional basins in the CLO and ELO with reference to Budawang Land and the study area highlighted in red. Figure from from Fergusson (2010)...... 31 Fig. 7. Map of Budawang Synclinorium. Adapted after NSW Geological Survey Wyborn & Owen (1986), McElroy & Rose (1962) and Best et al. (1964)...... 33 Fig. 8. Map of the Budawang Synclinorium taken from Dadd (2011) with locations of mapped Comerong Volcanics in stratigraphic columns. Stratigraphic columns adapted from Dadd (2011) for simplicity. Clear sections indicate covered portions of mapped sections...... 35 Fig. 9. AOI with field sites marked by dashed marker lines on the eastern limb and base camps marked by tent symbol. Regional geology adapted from the Geological Survey of New South Wales Araluen 1:100 000 (Wyborn & Owen, 1986), Canberra 1:250 000 (Best et al., 1964) and Ulladulla 1:250 000 (McElroy & Rose, 1962) geological map sheets...... 40 Fig. 10. Cartoon of Tape Mounted ablation (a) and Polished Mount ablation (b). Length of example crystal set as 100μm...... 43 Fig. 11. Map of Budawang Synclinorium. Adapted after NSW Geological Survey Wyborn & Owen (1986), McElroy & Rose (1962) and Best et al. (1964). Mapped traverses labelled, Belowra Creek (A), Stoney

Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW v

Creek (B), Buckenbowra River (C), Quart Pot Creek (D), and Burra Creek (E). Averaged Dip/Dip Azimuth data displayed alongside field site and compiled as attached steroenet. Trend/Plunge of poles on stereonet plotted as 87/10 for A, 90/51.5 for B, 133/27 for C, 114/38 for D, and 96/25 for E...... 48 Fig. 12. Stratigraphy of the Budawang Synclinorium eastern limb. Outcrop exposure is indicated by greyscale bar adjacent to log. Volcanic crystal size class follows conventions of Cas et al. (2008) with labels as F-Fine, M - Medium, L- Large, E – Extreme, C – Crystals, CC – Coarse Crystals, L – Lapilli. Sedimentary size class follows conventions of Cas et al. (2008) for non-genetic grain size classes for fragmental rocks with labels as Md – Mud/Clay, Slt – Silt, Fs – Fine Sand, Ms – Medium Sand, Cs – Coarse Sand, G – Gravel, P – Pebble. Sample sites indicated opposite stratigraphic log for reference in Appendix C...... 49 Fig. 13. Field photographs of the Massive to fining upward sequenced, Schistic, Foliated, Quartz veined, Metapelite lithofacies. a. Open folding in planar bedded, fine-grained metapelite with quartz veins. b. Metapelite bed (~15 cm thick) with a foliation fabric exposed parallel to hammer head...... 51 Fig. 14. Representative photomicrographs of the Massive, Aphyric Coherent Mafic lithofacies. a. Microlitic groundmass dominated by plagioclase (Pl) and abundant magnetite (Opaque, equant crystals in groundmass). b. Glassy Massive Aphyric Mafic Coherent lithofacies with two plagioclase populations...... 53 Fig. 15. Field photographs of the Massive, Aphyric Coherent Mafic lithofacies. a. Sharp basal contact between the aphyric mafic lithofacies and massive to fining upward sequenced, schistic, foliated, metapelite. b. Clasts of metapelite (Cl) being incorporated locally at the contact interface. c, Deformation fractures with infills of massive calcite and blocky clasts of aphyric mafic wall rock...... 54 Fig. 16. a, Field photo of magma mingling outcrop. Note patchy texture indicated by orange to pink rock in a dominantly dark mafic host rock. b, Cross polarised light (XPL) photomicrograph of representative phaneritic mafic lithofacies with interstitial clinopyroxene (Cpx) and plagioclase (Pl) phenocrysts. c, Magma mingling PPL photomicrograph between mafic (green) and felsic (orange) domains (red dash). Sample D10.7. d, Cross polarised light (XPL) photomicrograph of representative phaneritic mafic lithofacies showing a ophitic texture developed by poikilitic clinopyroxene enclosing acicular plagioclase...... 57 Fig. 17. Representative photomicrographs of the medium-grained, equigranular, mafic lithofacies. a, XPL image showing completely sericite altered plagioclase crystals (Pl) set in a microlitic groundmass of pyroxene (Px) and opaque minerals (most likely Fe-oxide phases). b, PPL image showing chlorite altered vesicles set in an equigranular groundmass (Vs)...... 58

vi Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Fig. 18. Representative photomicrograph of the massive, sparsely porphyritic intermediate coherent lithofacies showing blocky feldspar phenocrysts with moderate sericitic alteration. Alteration has destroyed any primary twinning extinction. Some phenocrysts are locally fractured with infill of chlorite. Spherical, recrystallised quartz occurs as alteration of the groundmass with chlorite (bottom-right)...... 60 Fig. 19. Field photographs of the fine-grained, massive to flow-banded silicic coherent lithofacies. a, Entrained mudstone clast with flow-banding showing a dextral shear sense at Belowra Creek. b, Entrained metapelite clast in flow-banded fine-grained silicic at Belowra Creek. c, Tight, overturned folds in flow-bands, Belowra Creek...... 61 Fig. 20. Field photographs of the fine-grained, massive to flow-banded silicic coherent lithofacies. a, Lenticular features towards the upper margin of silicic cohernet unit at Belowra Creek. Wispy lenticular features are generally aligned but can display rotation away from population alignment. b-c, Columnar joints in thick units of silicic coherent units at Stoney and Quart Pot field sites...... 62 Fig. 21. Representative PPL and XPL photomicrographs of the fine-grained silicic lithofacies. Rounded and embayed quartz crystals comprise cores to sperulites (Sph) and altered feldpsar phenocrysts (Pl, Ksp) are altered by sericite clays. Extensive quartz veining is common throughout all samples and field outcrops...... 63 Fig. 22. Field photograph of the Buckenbowra River magma mingling texture. Guest clasts of the phaneritic to porphyritic mafic coherent lithofacies occur as dark component wthin pink-orange fine-grained, massive to flow-banded silicic coherent lithofacies...... 64 Fig. 23. Photomicrograph of a representative thin section of the pophyritic silicic lithofacies. Weathering has fractured complete feldspar euhedra, encased in a groundmass of micropoikilitic quartz and quartz spherulites...... 66 Fig. 24. Field photographs of the Sediment-hosted, Blocky to fluidal, Monomictic Mafic Breccia. a, Fluidal peperite at Belowra Creek with the mud-rich, polymictic breccia lithofacies with blocky clasts also entrained at the contact. b, Blocky peperite at Belowra Creek with clasts supported within the mud-rich, polymictic breccia lithofacies...... 67 Fig. 25. Field photographs of the sediment-hosted, monomict silicic breccia lithofacies. a-b, Breccia at Stoney creek displaying poorly sorted, angular blocks of fine-grained silicic lithofacies. c, Breccia at Burra creek with in situ fracturing of fine-ash, crystal-rich, fragmental silicic lithofacies. d, Lower contact of fine-ash, crystal-rich, fragmental silicic lithofacies is sharp (red dash)...... 69 Fig. 26. Field photographs of the blocky, monomict mafic breccia at Buckenbowra River. a-b, Matrix (Mx) supported breccia clasts (Cl; dashed outlines) grades into coherent unit of the massive aphyric mafic lithofacies (towards top-right of image). c, Contact (dash) of the blocky, monomictic mafic breccia (M.Br) and the polymictic, pebble to cobble sized para-breccia (Br)...... 70

Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW vii

Fig. 27. Field photograph of the blocky, monomictic silicic breccia lithofacies. a, Unaltered photo of in situ, jigsaw-fit clast (Cl) within a granular matrix of the same compostion (Mx). The clasts and unit are variably weathered (area enclosed by red dash) and show change in colour. b, Greyscale filtered photo of A, with clasts highlighted by red dash...... 71 Fig. 28. Field photograph of coarse, lensoidal pumice lapilli (Pm), subrounded mudstone (Md) and metapelite clasts (Tb) in a fine matrix of the Fine- ash, Crystal-poor, Pumice-rich, Fragmental Silicic at Belowra Creek...... 73 Fig. 29. Field photographs of the fine-ash, crystal-rich, fragmental silicic lithofacies. a, Fiamme textured lapilli (Fm) with high aspect ratios at Buckenbowra River. Image taken through water. b, Weather resistant lapilli at the top of Buckenbowra River displaying low-angle truncations. c, Weather resistant lapilli at Burra Creek, evident as parallel striations perdendicular to hammer head (Image rotated 90°). d, Flow-banding in creek washed outcrop at Burra Creek...... 75 Fig. 30. Representative photomicrograph of the fine-ash, crystal-rich, fragemental silicic lithofacies. a, PPL photomicrograph of compacted, altered glass shards in the fine-ash, crystal-rich, rhyolitic ignimbrite. Some flattened glass shards still show relict triple-junction shards (Gl). b, XPL photomicrograph of compacted, altered glass shards in the fine-ash, crystal-rich, rhyolitic ignimbrite. Some flattened glass shards...... 76 Fig. 31. PPL photomicrograph of welded matrix of glass shards creating eutaxitic texture. a, Note embayed quartz crystal (Qtz), very fine- grained mafic clasts (Bs) and eutaxitic texture flowing around the rounded feldspar phenocryst (Pl). b, Coherent silicic clast (Cl) with perlitic fracturing indicating the quenching was related to hydrated magma...... 77 Fig. 32. Field photographs of the Massively bedded, Polymicitic, Pebble to cobble-sized, Para-Breccia. a, Breccia (Br) deposited atop eroded rocks of the Mallacoota Beds (Tb) at Stoney Creek. b, Clast supported base of the Breccia at Belowra Creek with little matrix (Mx), clasts of silicic coherent (Ry), and mudstone (Md). c, Poorly sorted breccia at Stoney Creek displaying a range of clast sizes. Cobble-sized clasts show greater rounding than pebble-sized clasts. d, Matrix supported Breccia Lithofacies at Stoney Creek...... 79 Fig. 33. Field photographs of the massive to trough crossbedded, polymicitic, pebble to cobble-sized, volcanogenic para-conglomerate. a, Angular mudstone clasts and subangular silicic volcanic (Ry) clasts in a moderate to poorly sorted arrangement within a dark green matrix.b, Large, subrounded silicic volcanic clast and rounded metapelite clast (Tb)...... 81 Fig. 34. Representative photomicrographs of the massive to trough crossbedded, polymicitic, pebble to cobble-sized, volcanogenic para- conglomerate matrix. a, Rounded and partially abraded lapilli clast (Lp), feldspar crystal fragments (Fg) and large scoria fragment with sericite altered, glomeropheric, feldspars with chlorite altered glass. viii Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Alteration has produced recrystallised quartz as speckled patches along rim of scoria clast. b, Photomicrograph of ash shards (Sh)...... 82 Fig. 35. Field photographs of the massively bedded, polymicitic, imbricated, gravel-sized, volcanogenic para-breccia. a, Sharp contact between the porphyritic mafic lithofacies (Bs) and volcanogenic para-breccia (Br). b, Subangular to angular clasts of green-grey, medium to coarse- grained sandstone in the volcanogenic para-breccia. c, Clasts of sericite altered coherent mafic, with local jigsaw-fit texture and fluidal morphology, locally at the contact with the volcanogenic para-breccia...... 83 Fig. 36. Field photographs of the Medium to Coarse-grained, Planar to trough cross-bedded, Sandstone. a-b, Trough cross-bedding at Belwora Creek field site (troughs follow red dash). c, Aphyric mafic clasts at Burra Creek. d, Truncating trough cross-beds at Burra Creek with a western dip azimuth (red needle)...... 85 Fig. 37. Field photographs of the Imbricated, Massive to trough cross-bedded, Polymictic, Para-Conglomerate. a, Imbricated, massive to trough cross-bedded, polymictic, para-conglomerate lithofacies (Cg) scouring underlying sandstone (Ms) at Buckenbowra River (scour red dash). b- c, Field photos showing the poorly sorted, polymict, matrix supported Conglomerate at Belowra (b) and Buckenbowra (c) field sites, with mudstone (Md), nodular quartz (Qtz) and sandstone clasts. d, Enhanced image at Burra Creek, showing the incorporation of dark porphyritic silicic clast (Ry) above field sunglass...... 87 Fig 38. a, ‘Ideal’ internal clast variations within an ignimbrite produced through pyroclastic density current processes, from Sparks (1976). b, Stratigraphic log of the Ora ignimbrite in Italy, from Wilcock et al. (2013). c, Stratigraphic log of the Mt St Helens ignimbrite eruptive units, from Brand et al. (2014)...... 93 Fig. 39. PPL photomicrograph of sintered glass shards with fluidal or plastic forms, from Wilcock et al. (2013)...... 94 Fig. 40. a, Schematic cartoon from McPhie (1993) of subaerial silicic lava flow with a brecciated carapace above and below the flow of rhyolitic lava. b, Subaqueos silicic extrusion diagram showing peperite facies occurring at the basal contact (Rosa, 2016)...... 97 Fig. 41. a. Schematic cartoon of a subaerial rhyolite flow internal variation and associated breccia facies from Fink & Manley (1987). b. Graphic log through the upper exposures of the Sanukayama rhyolite lava on Kozushima Island (Furukawa et al, 2019). c, Generalised graphic log from Hanson et al (2013) through an extremely thick (>300m) rhyolite flow from the Wichita igneous province, USA...... 99 Fig. 42. Schematic cartoon of various environments in which peperite may form with interaction of wet sediment with magma, adapted from White (2000). Labels peperite are of intrusions (1), Feeder dyke intrusions of vent fill deposits (2), partly emergent domes (3), base of lavas (4), and margins of invasive lavas (5)...... 101

Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW ix

Fig. 43. Intermediate and Silicic samples plotted on the LOI vs ANCK (molar Al2O3/ (K2O+CaO+Na2O)) modified from Bull et al. (2008). Samples all plot deep in the Sericite ± Carbonate field indicating sericitic alteration in all intermediate to felsic samples. Sample ID references analyses in Appendix C...... 105 Fig. 44. Comerong Volcanic Complex samples plotted on the Total Alkali Silica (TAS) diagram after Le Bas et al. (1986)...... 106 Fig. 45. Rock classification diagram using the immobile elements Zr/Ti vs Nb/Y, after Pearce (1996). Rhyolitic samples coloured red/pink, andesitic coloured blue and basaltic coloured green...... 107 Fig. 46. Harker diagrams of major elements vs silica. This study’s data points shown as triangles and data from Dadd (2011) shown as diamonds. Data is within 2% error of BCR-2 SRM...... 108 Fig. 47. Harker diagrams of trace elements vs silica. This study’s data points shown as triangles and data from Dadd (2011) shown as diamonds. Standard Reference Material (SRM) percentage error values given for each element. Geological reference materials are USGS SRM AGV-2 and BCR-2. National Institute of Standards and Technology, NIST- 610 glass to complement as a non-geological SRM...... 110 Fig. 48. REE plots of rhyolitic, andesitic and basaltic compositions, normalised to C1 Chondrite after Mcdonough & Sun (1995). Colour key taken from classification plot in Fig. 45...... 111 Fig. 49. a, MORB normalised multi-element variation diagram for andesitic and basaltic compositons. Normalisation values from Pearce (1982). b, Primitive mantle normalised multi-element variation diagram for andesitic and basaltic compositions. Normalisation values from Sun and McDonough (1989). c, Zr/Y vs Zr of Pearce and Norry (1979) to discriminate between Volcanic Arc (VA), Mid-oceanic-ridge-basalt (MORB) and Within-Plate basalts (WPB). d, Th/Yb vs Nb/Yb discrimination diagram from Pearce (2014) separating the MORB- OIB array and subduction-related settings...... 113 Fig. 50. a, A, I, S, M-type melt discriminatory diagram of Whalen et al. (1987). b, A1 and A2 type discriminatory diagram of Eby (1992). c, REE spider diagram normalised to C1 Chondrite after McDonough & Sun (1995). d, Granite discrimination diagram of Pearce et al. (1984), with fields of Within-plate granite (WPG), Oceanic Ridge granite (ORG), and Volcanic Arc Granite + synchronous Collision Granites (VAG + synCOLG). Comerong Volcanics data plotted with data from the Ural and Mt Hope volcanics (Bull et al., 2008), Arbuckle Mountains (Boro, 2015) and Dulladerry volcanics (Raymond et al., 1998)...... 115 Fig. 51. Terra Wasserburg diagrams of raw data of zircons extracted from field samples. York regressions shown as thin red line intersecting lower concordia. Plots generated in Isoplot (Ludwig, 2008). Sample coordinates: D9.2 - 150°03’04”E, 35°27’46”S; D13.1 - 149°58’09.6”E, 35°36’27.1”S ; D17.6 - 149°59’00.8”E, 35°53’57.5”S...... 117

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Fig. 52. TZircsat vs TZircTi plot after Siegel (2018) for concordant tape mounted analyses. Samples are annotated with Stoney Creek Rhyolite in blue, Buckenbowra River Ignimbrite in yellow and Burra Creek Ignimbrite in green...... 120 Fig. 53. Tape mounted concordant analyses for D9.2. a. Linearised probability plot with the youngest population of zircon indicated by black field. b. Weighted mean of the 9 analyses of the youngest population...... 121 Fig. 54. CL images of representative D9.2 zircons showing oscillitry zonations, fluidal melt inclusions and fractures intersecting inner domains. Scale bars represent 20μm...... 122 Fig. 55. Polished zircon concordant rim analyses for D9.2. Weighted mean of the 14 analyses...... 123 Fig. 56. CL images of D13.1 polished zircon. a. Zircon yielding age of ~380 to 395 Ma with large central fracture, typical of the main zircon population. b. Contaminate zircon yielding age of ~273 Ma, showing anhedral, resorbed growth rims and white core. Scale bars represent 30 μm...... 124 Fig. 57. Tape mounted concordant analyses for D13.1. a. Linearised probability plot with the youngest population of zircon indicated by black field. b. Weighted mean of the 4 analyses of the youngest population...... 125 Fig. 58. CL images of representative D13.1 zircon grains and fragments. All grains show oscillitry zonations, fluidal melt inclusions and fractures intersecting inner domains. Scale bars represent 30 μm...... 126 Fig. 59. Polished zircon concordant rim analyses for D13.1. Weighted mean of the 13 analyses, with one rejected age (blue)...... 126 Fig. 60. Tape mounted concordant analyses for D17.6. Linearised probability plot with the youngest population of zircon indicated by black field...... 128 Fig. 61. Polished zircon concordant analyses for D17.6. a. Linearised probability plot with the youngest population of zircon indicated by black field. b. Weighted mean of the 4 analyses of the youngest population...... 129 Fig. 62. CL images of D17.6 zircon. a-b. Interior-Rim analyses with ablation ages indicating zircon growth in one system. c-d. Core-Rim analyses indicating inherited cores with new autocrystic zircon growth. Scale bar represents 30 μm...... 130 Fig. 63. Timeline of orogenic events recognised in the Lachlan Orogen from: A – Vandenberg et al. (2000) and B - Rosenbaum (2018). Comerong Vocanic Complex dates indicated in blue and age error in green dash. Timeline constructed after the International Chronostratigraphic Chart after Cohen et al. (2013)...... 131 Fig. 64. Stratigraphy of the Budawang Synclinorium eastern limb. Correlations shown by highlighted bars and referenced in the legend. Emplacement ages indicated with samples D9.2, D13.1, and D17.6...... 135

Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW xi

Fig. 65. Fence diagram incorporating the stratigraphic packages of this study with block stratigraphy of Dadd (2011). Columns of this study are shown with an asterisk in place of the letters of Dadd (2011)...... 142 Fig. 66. Schematic emplacement model for the Comerong Volcanic Complex from 395 to 385Ma. A1 – IVP lavas with an autobreccia carapace (Ab) emplaced over LBP and basement Mallacoota Beds. B1 – Generalised section through LFP lava with an autobraccia carapace, crystalline core (Cc), and basal peperite with matrix derived from underlying sediments (Pb). B2 – Silicic ignimbrites formed through collapse of eruption columns. B3 – Bimodal magmatism with LMP and LFP magmas mingling (Mm) at depth and in erupted lavas. C1 – UMP basaltic volcanism intruding lake sediments (In). C2 – UFP explosive and effusive volcanism in the southern CVC derived from the same magma source. Colour coding of packages follows stratigraphic log correlations. Note point sources are for illustration and do not indicate true positioning of original volcanic edifices...... 152 Fig 67. Comparison of geological timelines. a, Geological timeline of Palmer (1983). b, Modern geological timeline after Cohen (2013). Columns represent: A – Orogenic events after Vandenberg et al. (2000), B - Orogenic events after Rosenbaum (2018), C – This study CVC dates, D – Interpreted dates of CVC after Schmidt (1986), E - Proposed age of the CVC from Dadd (1992)...... 153 Fig. 68. Map of A-type granites in the Lachlan Orogen dated from Early to Middle Devonian (419<382 Ma). Label numbers as: 1 – Victoria Valley granite (Vandenberg et al. 2000); 2 – Goonmirk Rocks granodiorite and Ellery granite (Vandenberg et al. 2000); 3 – Gabo Island granite suite (Collins, 1977); 4 – Mumbulla granite suite (Collins, 1977); 5 – Wangrah suite A-type granites (King, 1996) ; 6 – Comerong Volcanics, Monga granite, Mongamulla and Coondella Creek adamellites (Wyborn and Owen, 1986); 7 – Wyangala Batholith A-type granites (King, 1996); 8 – Warrumba volcanics, Grenfell granite and Schneiders granite (Wallace, 2000); 9 – Dulladerry volcanics and Bindogandri granite (Lyons et al., 2000); 10 - Mount Mittamatite and Pine Mountian granites (Vandenberg et al. 2000); 11 - Thologolong and Lucyvale granites (Vandenberg et al. 2000); 12 – Ural and Mt Hope volcanics (Bull et al., 2008). Abbreviations are New South Wales (NSW), Victoria (VIC) and Tasmania (TAS)...... 155

xii Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

List of Tables

[The List of Tables can be created automatically and updated with the F9 key – refer to Thesis PAM.]

Table 1. Mineralogy, alteration and composition of the Comerong Volcanics coherent lithofacies...... 45 Table 2. Clast type, matrix and dominant clast composition of the Comerong Volcanics fragmental lithofacies...... 46 Table 3. Clast type, textures/structures and matrix of the Comerong Volcanics sedimentary lithofacies...... 47 Table 4. Lithofacie interpretations from the descriptive lithofacie names with the composition and occurrences in the Comerong Volcanics...... 90 Table 5. Zircon recovery, aspect ratio (AR) range of complete euhedra and percentage of zircon fragments analysed...... 116 Table 6. Zircon ages from tape mounted ablations and polished mount ablations. The accepted emplacement ages are shown in bold. See text for discussion. Abbreviations: TW – Terra Wasserburg; W.Av. – Weighted Average...... 118 Table 7. Plešovice ages in all analytical sessions. The standard age of 337.13±0.37 Ma Slama et al. (2008)...... 119 Table 8. Key trace element ratios characteristic of volcanic arc basalts and ocean island basalts. Ratio ranges taken from Condie (2015). Values highlighted blue relate to volcanic arc ratio ranges and green highlight ocean island basalt ratio ranges...... 145

Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW xiii

List of Abbreviations

Area of Interest: AOI Boyd Volcanic Complex: BVC Eastern Lachlan Orogen: ELO Central Lachlan Orogen: CLO Western Lachlan Orogen: WLO Comerong Volcanic Complex: CVC Eden-Comerong-Yalwal Volcanic Zone: EVZ Management and Assessment of Project Safety: MAPS Central Analytical Research Facility: CARF X-Ray Fluorescence: XRF PPL: Plane Polarised Light XPL: Crossed Polarised Light Inductively Coupled Plasma Mass Spectrometry: ICP-MS Laser Ablation Inductively Coupled Plasma Mass Spectrometry: LA-ICP-MS Lower Breccia Package: LBP Lower felsic Package: LFP Intermediate Volcanic Package: IVP Lower Mafic Package: LMP Upper Felsic package: UFP Upper Mafic Package: UMP

xiv Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW Statement of Original Authorship

The work contained in this thesis has not been previously submitted to meet requirements for an award at this or any other higher education institution. To the best of my knowledge and belief, the thesis contains no material previously published or written by another person except where due reference is made.

Signature: QUT Verified Signature

Date: 06/05/20

Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW xv

Acknowledgements

Thank you to the following for contributions to the fulfilment of this work:

Sarah Lauchs – Field assistant during the geological field season.

Pascal Asmussen – For assisting in the preparation of zircon mounts and for providing guidance during the U/Pb geochronology.

Gus Luthje – Preparing thin sections for petrographic analysis and advice on reducing contamination during sample preparation.

Karine Moromizato – Assistance in analysing XRF disks for bulk-rock major and trace element geochemistry and zircon LA-ICP-MS analysis.

Charlotte Allen - Assistance in zircon LA-ICP-MS analysis and for data reduction of ablation runs.

Crystal Cooper – Imaging of zircon internal domains using CARF’s Zeiss Sigma SEM and Cathodoluminescence detector.

I would also like to thank my supervisory team for guidance throughout my candidature, as this work could not be possible without your expertise. The experience of studying the Comerong Volcanics with you has enriched my short time as a geologist, and I hope to continue working closely in the future.

Thanks, is also directed to my friends and family for support during the difficult times of my candidature. For the past two years, those involved in my life outside of university have enabled me to pursue higher education by offering reassurance, guidance, and opportunities to recharge. For this I am forever grateful.

xvi Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Chapter 1: Introduction

The Australian continental landmass is composed of a complex amalgamation of cratons with a history dated to the Archean. The Palaeozoic era saw the development of eastern Australia with periods of sedimentation and magmatism controlled by orogenesis related to subduction (Miller and Gray, 1997; Rosenbaum, 2018; Vandenberg, 1999). The most exposed and studied orogen is the Lachlan Orogen of New South Wales (NSW) and Victoria (VIC). Previous work on the Lachlan Orogen shows the style of convergent tectonics active during this time is not accurately represented by present-day convergent margins (Collins, 2002; Coney, 1992; Fergusson, 2010). The Lachlan Orogen constitutes an important window into the past tectonics of the Palaeozoic circum-Pacific Ocean due to other ancient margins being destroyed by post-Permian orogenesis or are inaccessible such as exposures in Antarctica (Coney, 1992). Despite the current debate around the exact tectonic setting of the Lachlan Orogen through time, it provides an excellent geological record of convergent and extension tectonics active from the Cambrian to the Carboniferous.

The resolution of the Lachlan Orogen is improving with time as more detailed field mapping is incorporated into existing regional studies. The mapping is then accompanied by the forever improving understanding of volcanic facies and facies associations and access to accurate, reasonably fast geochronological and geochemical analysis techniques. The interpretations made by past and present work on the Lachlan Orogen is critical to understanding the complex interplay between ancient subduction systems and the continental plates. As new studies continue to add spatial, temporal and chemical information on the evolution of the Lachlan Orogen, constraints on tectonic models can be applied. Importantly, the Lachlan Orogen underlies parts of the Murray Basin, Sydney Basin and basins comprising the Great Australian Basin (Coney, 1992; Dadd, 1992; Vandenberg et al. 2000). Furthermore, the importance for ongoing recognition of Lachlan orogenesis phases through structural, geochemical and stratigraphic studies, tightens constraints on periods of metallogenesis with known economic deposits of copper-gold porphyry systems, epithermal gold deposits, and volcanogenic massive sulphide deposits (Vandenberg et al. 2000).

Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW 17

The eastern margin of the Lachlan Orogen is comprised of structurally constrained belts of volcanic, plutonic and sedimentary exposures with deposition and emplacement mechanisms varying in space and time. Outcrop in the eastern margin is dominated by plutonic silicic rocks comprising up to half of the total exposures (Collins, 2002). In the Early Silurian to Middle Devonian, magmatism associated with periods of extension was accompanied by the deposition of deep marine, shallow marine and terrestrial sedimentary facies, illustrating the complex paleotopography that was developing in the eastern Lachlan Orogen (Fergusson, 2010).

The Comerong Volcanics comprise a small crustal feature within the eastern Lachlan Orogen on the NSW south coast (Fig. 1). Depending on the accuracy of the constraining structural and stratigraphic relative ages, the Comerong Volcanics provide an insight into the Australian margin during the Devonian (Schmidt, 1986). This location and period in geological time is recorded by several volcanic centres situated on the South Coast of New South Wales. It has been hypothesised that these centres of volcanic, plutonic and associated sediments form a north-south trending rift zone (McIlveen, 1975). Rift settings are important products of crustal extension episodes that may be produced by a wide range of mechanisms related to the movement of tectonic plates and the dynamics of the underlying mantle. Rifting occurs in many tectonic environments, such as back-arc extensional environments, intraplate rifting in oceanic and continental settings, and at mid-ocean ridges. Each of these rift settings relates to the tectonic setting active at the time of volcanism.

18 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Fig. 1. Location of the Comerong Volcanics within the Australian states and territories.

McIlveen (1975) aptly named this hypothesised rift zone as the Eden-Comerong- Yalwal Rift Zone. Later work by Dadd (1992) renamed the zone as the Eden- Comerong-Yalwal Volcanic Zone (EVZ) as the tectonic affinity of these rocks was not yet heavily accepted, and this conservative approach is adopted here. The Comerong Volcanics are preserved as outcropping limbs on a north-south orientated synclinorium (Glen, 1990). The Comerong Volcanics age constraints dictate that volcanism initiated during mid-late Lachlan orogenesis (Gray, 2004), but the tectonic setting of the volcanic centre is still understudied. The broader regional context and current understanding of the Comerong Volcanics must be investigated on its own without interpretations and extrapolations of stratigraphy and proposed timing from other volcanic centres on the basis of similar lithofacies and stratigraphic horizons. Further understanding on the context and genesis of the Comerong Volcanics will add important information for the evolution of the Lachlan Orogen but also advance the understanding of the EVZ which is prospective for epithermal gold mineralisation such as the Yalwal gold deposit (Glasser, 1988, McIlveen, 1975).

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Chapter 2: Geological Background & Research Aims

2.1 GEOLOGICAL BACKGROUND

Several Palaeozoic orogens comprising the eastern margin of Australia, define a complex and extended history of the Terra Australis Orogen (Cawood, 2005), which comprised the eastern margin of Gondwana and the paleo-Pacific Ocean (Fergusson, 2010; Foster and Gray, 2000; Glen, 2005; Gray & Foster, 2004). The eastern margin included continental landmasses that comprise portions of New Zealand, Antarctica, South America and Australia (Fig. 2a) (Fergusson, 2010; Glen, 2005). In order from oldest to youngest as accepted in the literature, the Delamerian (515-490 Ma), Thomson, Lachlan (485-340 Ma), Mossman, and New England (305-230 Ma) orogens comprise the Australian Tasmanides (Fig. 2b, Tasman Fold Belt System) (Kemp et al., 2009; Leitch et al., 1987; Glen, 1992; Rosenbaum, 2018).

a b

Fig. 2. a, Reconstruction of the Gondwana supercontinent depicting the proposed eastern margin. Diagram is modified after Gray and Foster (2004) and Cawood (2005). Diagram taken from Vos et al. (2007). b, The Australian Tasmanides with boundaries from Glen (2005). Diagram taken from Rosenbaum (2018).

20 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

The Australian Tasmanides is a grouping of recognised orogenic systems within the greater Terra Australis Orogen (Cawood, 2005). Each of the Tasmanide orogens is separated by extensive magnetic, and gravity features visible on regional scale surveys displaying different oroclinal structures (Abdullah and Rosenbaum, 2017; Musgrave, 2015; Rosenbaum, 2018). Each orogen is also defined by granitic batholiths and plutons of metaluminous I-type, peraluminous S-type and minor A-type compositions (Kemp et al. 2009; Musgrave, 2015). A-type intrusive bodies commonly post-date compressional events and are associated with extensional structures and along margins of batholiths (Kemp et al., 2009; King 1996). The Tasmanides are interpreted as a stepped cratonisation of eastern Australia through eastward migration of the Gondwana landmass, initiating progressive compression and extensional deformation events during the Palaeozoic era with an age range from 515 Ma to 230 Ma (Kemp et al., 2009; Gray and Foster, 2004). Today, the Tasmanide boundaries are further debated but can be constrained by structural discontinuities and Precambrian crustal architecture in the west (known as the Tasman line), termination in Papua New Guinea in the north and a rifted margin to the east during the opening of the Tasman sea (Glen, 2005). Most authors are in agreeance that a subduction system was proximal to the Gondwana margin and located west of the Tasmanide exposures (Coney et al., 1990; Kemp et al., 2009; Fergusson, 2010). A general younging of the orogens from west to east also implies the subduction system was located towards the east of the Tasmanides (Gray and Foster, 2004; Rosenbaum, 2018; Scheibner, 1973).

The presence of such a subduction system is indicated by the geochemistry of several volcanic belts with geochemical affinities mimicking modern analogues and the explanation for cyclic volcanic arc, back-arc extension and convergent margin tectonic structures in accretionary complexes (Glen, 2013; Musgrave, 2015). The subduction margin active from the Neoproterozoic until the Triassic is postulated to produce the cyclic volcanic arc volcanism and related rocks through slab roll-back accompanied by periods of compressional deformation through a transition to flat-slab subduction or lithospheric plate re-organisation (Collins, 2002; Collins and Richards, 2008; Cawood et al. 2009; Rosenbaum, 2018).

Other convergent systems in the modern day are accompanied by internal collisional sutures, inboard vergent thrusts or a high-grade metamorphic hinterland

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whereas the Tasmanides lack these large regional scale diagnostic features of ‘classic’ accretionary orogens (Foster and Gray, 2000; Gray and Foster, 2004). The temporal switches from slab roll-back causing trench retreat (Shaanan et al., 2015), to then flat- slab subduction causing trench advance, accounts for the lack of large accreted terranes. It is also evident that each orogen records deformation events that are recognised throughout the Tasmanide orogens (Rosenbaum, 2018). The Lachlan Orogen is one of the most exposed in the Tasman Fold Belt comprising a total of approximately 50% of the Australian Tasmanides (Fig 2); however, it remains enigmatic with changes in tectonic setting throughout time (Gray and Foster, 2004).

The Lachlan Orogen, also described as the Lachlan Fold Belt, was formed by multiple recognised contractional deformation phases (Fig. 3), periods of extension and provided the primary location of volcanism, sedimentary deposition and tectonic deformation after the cessation of the Delamerian orogeny (Gray et al., 1997; Musgrave, 2015). The Lachlan Orogen is subdivided into the Western (WLO), Central (CLO) and Eastern Lachlan Orogen (ELO) from interpretations of geophysical data (gravity, aeromagnetic surveys), and regional oblique over-thrusts termed sutures (Glen, 2005; Gray and Foster, 2004). Other workers discuss a fourth subdivision of the South-western Lachlan Orogen, which is debated on the grounds of geophysical data interpretations (Glen, 2014). The subdivisions of Gray and Foster (2004) is used here to discuss the ELO, which host the Comerong Volcanics (Fig. 4b).

Throughout the exposure of the Lachlan Orogen, turbidite facies rocks of Early to Late Ordovician age conceal basement Cambrian volcanic rocks, also referred to as Cambrian greenstones (Gray and Foster, 2004; Vandenberg, and Stewart, 1992). These greenstones are preserved in regional thrust faults and labelled after the naming convention of the parent thrust fault as the Stavely, Heathcote and Mt Wellington greenstone belts (Coney et al., 1990). The turbidite succession is extensive with dimensions rivalling even the largest, modern submarine megafans, such as the Bengal Fan (Fergusson and Coney, 1992). The paleo-megafan deposits are described as the Adaminaby Group in most present-day literature (Glen et al., 2007). It was directed roughly east, with the source suggested to be originating from the Delamerian Orogen to the west and directed from a southern source, most likely the Ross Orogen in Antarctica, that was connected to the Panthalassan margin and inferred to be the continuation of the Delamerian Orogen (Foden et al., 2006; Vandenberg and Stewart,

22 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

1992). Overlying and intruding these turbidite deposits is a range of magmatic rocks of ages ranging from Silurian to Late-Devonian and compositions of A, I and S-types with volcanic equivalents also exposed.

Fig. 3. Timeline of orogenic events recognised in the Lachlan Orogen from: A - Vandenberg et al. (2000); B - Rosenbaum (2018). Timeline constructed from the International Chronostratigraphic Chart after Cohen et al. (2013).

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2.1.1 Recognised Orogenic Events The Lachlan Orogen has been interpreted to be punctuated by four short, primarily E-W, major contractional episodes, but only recently it is considered to be a progressive contractional event marked by localised deformation events (Gray et al., 1997; Vandenberg 1999; Willman et al., 2002). From the 1970’s until the 2000’s, deformation in the Lachlan Orogen was interpreted as the Benambran, Bindian, Tabberabberan and Kanimblan orogenies and generally referred to as orogen wide events due to unconformable contacts with strata such as the Late-Devonian redbeds unconformably overlying Lower-Devonian rocks in many different localities throughout the Lachlan Orogen, interpreted as the break between the Bindian and Tabberabberan events (Glen, 2005; Vandenberg, 1999). There are still many workers that use this orogenic framework of orogen-wide deformation episodes, however, this framework is challenged by the absence of unconformities and deformation fabrics that have been used to characterise individual episodes of deformation on a Lachlan Orogen scale (Gray and Foster, 2004). More recent work has shown that, not only are these orogenic phases localised and have variable strength across the Lachlan Orogen but these events are recognised in deformation structures in other Tasmanide orogens (Gray et al., 1997; Rosenbaum, 2018). This suggests the evolution of the Lachlan was likely contemporaneous with the development of other Palaeozoic orogens.

24 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Fig. 4. a, Exposures of the Tasmanide orogens on the eastern Australian margin displaying the eastern Lachlan subdivision and Wagga-Omeo Metamorphic Belt as the principal surface exposures. b, Lachlan Orogen subdivision into Western, Central and Eastern Lachlan Orogen terranes. Images taken from Gray and Foster (2004).

The Benambran orogeny is recognised as an orogenic event in the Early-Silurian that affected every orogen in the Tasmanides (Rosenbaum, 2018). In the Lachlan Orogen, the effects of this event are seen east of the Melbourne Zone of the WLO in the form of E-W trending folds in the Wagga-Omeo Metamorphic Belt and Tabberabberan Zone (Fergusson, 2010; Gray, 1997). The Benambran event comprises the Quidongan “orogeny” of early work from Gray (1997; Fig. 5), but it is now grouped as part of the Benambran event because the hiatus encompasses the proposed timing of the Quidongan event (Fergusson and Coney, 1992). Minor effects are noted in the ELO, in parts of the Macquarie Arc and bounding Ordovician-Silurian turbidite sediments (Glen, 1992). The Benambran event also produced marked sedimentation effects for the Lachlan Orogen. Following the Early-Silurian, black shales (Bendoc Group) were the dominant sedimentation product across the ELO and effectively

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marks the cessation of Adaminaby Group turbidite sedimentation (Glen et al., 2007; Vandenberg, 1999).

The Bindian orogeny (420-410 Ma; Fergusson, 2017) was an active deformation event in the Late-Silurian to Early-Devonian as shown by cross-cutting relationships of Early-Devonian granitoids and weakly deformed Late-Silurian Grampians Group (Fergusson, 2010; Fergusson and Coney, 1992). Some revision has been advocated for the exact nature of deformation as either contractional or transpressional-transtentional due to later interpretations that the discordancies and positions of the Bindian structures occurred as syn-rift rotations on regional listric faults (Glen, 1992). This event is recognised in the CLO and ELO (with localised areas in the WLO) and best preserved as Early-Devonian volcanics overlying foliated, Silurian strata (Gray, 1997). The Bindian event overprinted previous Benambran deformation structures in the Wagga-Omeo and Tabberabberan Zones of the CLO and increases in deformation intensity towards the east with shortening up to 60% in localised places (Fergusson and Coney, 1992; Glen, 1992). This event coincides with a major increase in silicic magmatism in the ELO and WLO during the Late-Silurian to Early-Devonian (Collins, 2002; Fergusson and Coney, 1992).

26 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Fig. 5. Distribution of major orogenic events across the Lachlan Orogen with locations of original naming exposure abbreviated. Note approximate overlap of events. Major regional fault zones shown as solid lines. Deformation distribution map taken from Gray (1997). The Tabberabberan orogenic event (380-370 Ma; Vandenberg, 1999) was the second last contractional event and most widely recognised deformation pulse across the Lachlan Orogen, with the exception of the Stawell Zone in western Victoria (Fergusson and Coney, 1992; Gray et al., 1997). It is generally viewed as a very short- lived episode of compressional deformation producing tight to isoclinal, meridional folding by E-W shortening (Fergusson, 2017; Vandenberg, 1999). Basin-inversions and strike-slip tectonics were highly active in the ELO during the Tabberabberan event (Glen, 2005). It was first defined as terrestrial Late-Devonian to Early-Carboniferous successions unconformably overlying older rocks of Early-Ordovician (Gray, 1997). There is a consensus that during the mid-Devonian, the Eastern Lachlan Orogen (ELO) saw a thermal event characterised by A-type magmatism coincident with the Tabberabberan orogeny (Glen and Watkins, 1999). Importantly, the Tabberabberan event is closely associated with the Comerong Volcanics. This contractional event is thought to pre-date the emplacement of the Comerong Volcanics and is responsible for the deformation of underlying Ordovician turbidites (Dadd, 1992).

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The Early-Carboniferous saw deformation owed to the Kanimblan orogeny (Gray & Foster, 2004; Schmidt, 1986). The Kanimblan event (340 Ma) has been shown to have variable intensity across the orogen and mimicks the E-W contraction of the Tabberabberan event (Fergusson, 2017) with a locus to the north-east of the ELO (Glen, 2005; Gray, 1997). It is best identified by folded Late-Devonian rocks, overlain by Permian sedimentary successions of the Sydney Basin (Gray, 1997). The Budawang Synclinorium comprising the Comerong Volcanics and Merimbula Group sediments is interpreted as a high-strain product of the Kanimblan event due to the N- S trend in meridional folding (Glen, 2005). The Kanimblan contractional event marks the cessation of Lachlan orogenesis and quiescence of magmatic activity (Gray, 1997). These deformation events have had variable impacts on the western, central and eastern subdivisions of the Lachlan Orogen.

2.1.2 Structural Subdivisions of the Lachlan Orogen The Lachlan Orogen subdivisions represent key structural domains hosting a common assemblage of volcanic, volcaniclastic and sedimentary sequences, commonly with unique deformation fabrics formed by the multitude of deformation events previously discussed. These subdivisions are important in the context of continuing orogenesis through time and the eventual emplacement of the Comerong Volcanics in the ELO subdivision.

Throughout the Silurian to Devonian, the WLO experienced multiple phases of compression and extension deformation. Bounding regional faults or fault zones include the Stawell-Ararat and Mt Useful Fault Zones (Fig. 4b)(Gray and Foster, 2004). The western subdivision hosts the Stawell, Bendigo-Ballarat, and Melbourne Zones of deformed turbidites with northeast to east thrusting regional faults and 30- 70% shortening variations with the greatest shortening in the west (Foster, 2000; Vandenberg and Stewart, 1992). These thrusts are argued by many authors as the evidence for an accretionary complex produced by the subduction margin during the Late Ordovician-Early Silurian (Fig 3)(Gray and Foster, 2004). Several exposures of ophiolites in major thrust faults, as well as relict blueschist metamorphic rocks and mélanges, indicate underthrusting related to subduction during WLO formation (Gray and Foster, 2004). Other deformation structures characteristic of the WLO associated with the eastward thrust faulting are slightly overturned, west-dipping, chevron folds

28 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

with variable axial planar cleavage and regional anticlinoria and synclinoria (Foster, 2000). The east-vergent fold-thrust belts are intruded by S-type, late Early to Late Devonian granitoids constraining the age of deformation (Vandenberg and Stewart, 1992). The rocks of the WLO subdivision shows a basement of Cambrian metavolcanics, in the form of tholeiitic basalts and boninitic rocks, with exposure decreasing from west to east (Glen, 2015; Musgrave, 2015). These Cambrian basalts are overlain by several kilometres of quartz-rich turbidites with black shale and massive mudstones with abundant graptolite and phllocarid fossils of Early to Late Ordovician age (Foster and Gray, 2000; Vandenberg and Stewart, 1992). The western subdivision largely consists of this Ordovician turbidite succession which is later intruded by S-type, granitic bodies (Foster and Gray, 2000). Exposures in the WLO are largely confined to the southwest of the Lachlan Orogen, with northern exposures concealed under Murray Darling Basin sediments (Collins, 2002).

The CLO contains the Wagga-Omeo Metamorphic Belt and the Tabberabberan Zone, both of which are dominated by the Cambrian-Ordovician turbidity current deposits and minor black shale observed through the WLO (Fergusson, 2010; Vandenberg and Stewart, 1992). The CLO is bounded by the Mt Useful Fault Zone in the west and the Gilmore Fault Zone in the east (Fig 2 b)(Gray and Foster, 2004). A general widespread, north-south trending crenulation cleavage defines the deformation of turbidite sequences in the Wagga-Omeo belt with the timing of deformation in the range of Late Ordovician to Early Silurian (Fergusson, 2010). The turbidite sequence is largely intruded by S-type granite batholiths related to a high temperature-low pressure metamorphic event which partially melted the Ordovician metasediments producing the sediment-signature granitoids and migmatites (Flood and Vernon, 1978). This greenschist to upper amphibolite facies metamorphism is not repeated in the Tabberabberan Zone directly west of the Wagga-Omeo Metamorphic Belt. Localised rift-related rocks of dominantly silicic composition occur in several basin successions with evidence for uplift to marine and subaerial depositional environments in the Late Silurian to Early Devonian (Fergusson, 2010).

The eastern Lachlan subdivision is constrained by the Gilmore Fault Zone on the western flank until exposures cease at the coast (Gray and Foster, 2004). The structural grain of the ELO is preserved in the Ordovician turbidite sequence with an increase in cleavage development eastwards and open folding bounded by east and west-dipping

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reverse faults (Foster and Gray, 2000). Several troughs characterise the ELO and are interpreted as the products of a fold-thrust zone with periods of extension in the Silurian (Fergusson, 2010). The basement rocks consist only of the Ordovician quartz- rich turbidites and minor Early Ordovician volcanics as no exposures of Cambrian greenstones have been found throughout the eastern subdivision (Fergusson. 2010; Foster and Gray, 2000; Wyborn and Owen, 1986). However, it is expected that these greenstones continue in the subsurface underneath the Ordovician turbidites due to small exposures of Cambrian basaltic breccias, highly deformed mafic rocks and OIB- like basalts at Melville Point, in the Batemans Bay region (Fergusson, 2010; Stokes et al., 2014). The turbidites in the ELO are similar in composition to the rocks described by Vandenberg (1992) in the western and central Lachlan and have been interpreted to be part of the deep-marine, Ordovician megafan. The eastern Lachlan exposures consist of granitic batholiths of Silurian-Devonian age, mafic-silicic volcanics, associated volcaniclastics and deep marine to subaerial siliciclastic sedimentary deposits (Collins, 2002; Foster, 2000). This change in the deposition, from turbidites to magmatic products marks a major change in the evolution of the Lachlan Orogen (Coney et al., 1990). In particular, the change shows the eastern subdivision underwent strong extensional phases producing a flare-up event in the Middle to Late Silurian and emplacement of I-type granitic batholiths in the Early Devonian (Rosenbaum, 2018). Multiple rift basins occur within the ELO. These basins include the Cowra, Hill End and Tumut troughs (Fig. 6). A general trend has been recognised consisting of continental uplift gradually changing the depositional environment from dominantly deep marine during the Cambrian-Ordovician, to a variety of transitional marine environments during the Silurian, into fluvial and shallow marine environments by the Late Devonian-Early Carboniferous (Coney, 1990; Glen, 1992; Gray, 1997). This uplift also caused widespread erosion across the orogen, leading to extensive sedimentary basin infill (Coney et al., 1990). Later uplift and km-scale erosion events have affected the ELO during the Mesozoic (O’Sullivan et al., 1996).

30 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Fig. 6. Map of the distribution of batholiths and regional basins in the CLO and ELO with reference to Budawang Land and the study area highlighted in red. Figure from from Fergusson (2010).

2.1.3 Previous Work on the Comerong Volcanics The Comerong Volcanics are shown to comprise the limbs of a 120km, N-S striking, discontinuous, synclinorium (Glen & Lewis, 1990; Dadd, 2011). From 1990 until the present day, the number of studies either directly focused on the Comerong Volcanics or referencing it in regional interpretations of ELO history has been scarce with the exception of work conducted by Kelsie Dadd (1992a, 1992b, 2011) and Richard Glen (1990). Initial work in the region was conducted as state government surveys, with the bulk of the work focusing on the structure of the synclinorium and infill of Devonian, fluvial to shallow marine sedimentary rocks (McElroy & Rose, 1962). The relative timing of the volcanics has been interpreted to be between Middle to Late Devonian based upon conodont fossils found in the overlying sedimentary

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succession dated as Frasnian (Late-Devonian) by Pickett (1972), and regional faults crosscutting through the Early-Devonian Merricumbene Granodiorite (Biotite K-Ar: 400±6 Ma, Rb-Sr: 394±6 Ma; Wyborn and Owen, 1986). In fault contact with the Comerong Volcanics are the Monga, Merricumbene, Mongamulla and Coondella granitoids and intruding Donovan basic complex (Fig. 7) (Wyborn & Owen, 1986). Collins (1977) and Beams (1980) have interpreted the A-type Gabo Island granite of the Eden area to be comagmatic with the rhyolite of the Comerong Volcanics. Based upon the similarity in petrography and geochemistry it has been hypothesised that the Monga A-type granite, dated at 376±6 Ma by K-Ar biotite dating methods and 371±6 Ma by Rb-Sr dating by biotite-whole-rock dating methods, is comagmatic with the Comerong rhyolite and hence was emplaced at a similar time (Wyborn and Owen, 1986).

32 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Fig. 7. Map of Budawang Synclinorium. Adapted after NSW Geological Survey Wyborn & Owen (1986), McElroy & Rose (1962) and Best et al. (1964).

North of the Budawang Synclinorium is a sequence of volcanics in the Yalwal and Morton townships, up to approximately 1200 m thick of altered mafic rocks, rhyolite, ignimbrite and intercalated terrestrial sediments proposed as part of a similar volcanic event to the Comerong Volcanics (McIlveen, 1975).

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West of the Donovan Fault, separating the western limb of the Budawang Synclinorium from the Coondella Creek and Mongmula adamellites is a gently to open folded or tilted rhyolite sheet. This is considered to be an extension of the Comerong Volcanics based on field and petrographic evidence (Wyborn and Owen, 1986).

Approximately 40 km south of the Comerong Volcanics are the Bunga Beds coastal exposures of subaqueous rhyolite domes and basalt with intercalated lacustrine sediments (Cas, 2009; 1990). This is considered as the northern extent of the Boyd Volcanics Complex (BVC) of the Eden area, comprising extrusive and partly intrusive, terrestrial bimodal volcanics of rhyolite with minor sedimentary rocks of terrestrial origin, with a Late-Devonian age indicated by fossils recovered from interbedded sediments (Fergusson et al., 1979; Steiner, 1972). The BVC is considered to be the southward continuation of volcanism comprising the Comerong Volcanics (McIlveen, 1975).

A block stratigraphy for the Comerong Volcanics has been produced by Dadd (2011) for the northern half of the Budawang Synclinorium (Fig. 8). The base of the volcanics is marked by monomict breccia derived from the basal metasedimentary rocks (Dadd, 2011). The volcanics are a bimodal suite of largely basalt and rhyolite with intercalated fluvial redbeds marking the final horizon before being overlain by sedimentary sequences of the Merimbula Group (Schmidt, 1986). The rhyolite units within the volcanic pile constitute the most voluminous outpourings with a thickness reaching 350 m (Dadd, 1992). Pyroclastics within the rhyolite units are rarely observed by Dadd (2011) but are indicated to constitute roughly 50% of the Comerong Volcanics, according to Wyborn and Owen (1986). Dadd (2011) proposed three basalt members and a member of intermediate volcanics that only outcrop on the east limb with rhyolite lava flows. Unit thicknesses and limb dips are highly variable along strike (Dadd, 1992, 2011; McIlveen, 1975; Schmidt, 1986). The Comerong Volcanics constitute an accumulation of bimodal volcanic and sedimentary units further referred to here as the Comerong Volcanic Complex (CVC).

34 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Fig. 8. Map of the Budawang Synclinorium taken from Dadd (2011) with locations of mapped Comerong Volcanics in stratigraphic columns. Stratigraphic columns adapted from Dadd (2011) for simplicity. Clear sections indicate covered portions of mapped sections.

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2.2 GAPS IN KNOWLEDGE

2.2.1 Paleoenvironment of the CVC The stratigraphy produced to date within the Budawang Synclinorium has been conducted on the basis of identifying the main sedimentary formations of the overlying sediments (Glen and Lewis, 1990) which are considered to be an extension of the Merrimbula Group of the Eden area (Giordano and Cas, 2001; McIlveen, 1975). Work on the volcanics has focused on establishing the compositional variation (Dadd, 1992a, 1992b, 2011) and identifying the nature of bounding regional faults (Glen and Lewis, 1990). The most recent work in the area described the CVC as having intercalated sediments of fluvial and lacustrine origin (Dadd, 1992). Current understanding of the CVC stratigraphy is the superposition of volcanic and sedimentary members illustrated in Fig. 8.

Understanding of the emplacement mechanisms for the volcanics and the contact relationships with sedimentary units is critical to evaluating the depositional setting at the time of volcanism (McPhie et al., 1993). Addition to the previous studies on the CVC would benefit from a volcano-sedimentary facies analysis to provide a robust interpretation for the CVC paleoenvironment. This will further add resolution to the overall tectonic environment active in the ELO towards the final stages of Lachlan orogenesis.

2.2.2 Geochemical Affinity The geochemistry of the Comerong Volcanics has been rarely focused on with a small dataset available from previous work. Several geochemical samples of the CVC felsic rocks were collected by Wyborn & Owen (1986), which yielded major element oxide and limited trace element chemistry. The lack of trace element data was likely a consequence of the limited availability of specialist equipment that has become more available since the 1980s. Dadd (2011) investigated the Comerong Volcanic mafic suite with evidence for a within-plate setting and bimodality of the CVC expressed as major wt% element SiO2 (Dadd, 1992). Felsic data has not been utilised on discriminatory diagrams or investigated further for the CVC in conjunction with mafic geochemical data. Discrimination of felsic rocks has matured since the early

36 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

geochemistry work of the CVC was examined in the 1980s and early 1990s. This thesis will incorporate all available geochemistry data with the addition of new felsic, intermediate and mafic data to discriminate with current geochemical classifications. This will utilise the whole available geochemistry of the volcanics to provide a robust geochemical affinity for the CVC.

2.2.3 Temporal Relationship in the Region Regional mapping conducted by workers in the south coast region has provided constraints upon the timing of Comerong volcanism. These constraints represent a total age range between the Middle and Late-Devonian of twenty-three million years (according to fossil dates) according to the current International Chronostratigraphic Chart (Cohen et al., 2013). Many plutonic bodies proposed to be comagmatic with the CVC are dated using K-Ar dating techniques (Wyborn and Owen, 1986) measured on biotite phenocrysts which were commonly reported to be altered in response to widespread regional metamorphism. The use of these dates must be taken with caution as these isotopic systems may develop open-system behaviour (Bull et al., 2008). These emplacement dates include the Merricumbene Granodiorite and Monga Granite adjacent to the Budawang Synclinorium which have been used as timing constraints for the Comerong Volcanics. The timing of the Comerong volcanic event is important in correlating the volcanism to either a Late-Silurian to early Devonian ‘flare-up’ event or a later thermal event in the Late Devonian. The correlation of coeval volcanism and plutonism in the ELO requires accurate dates produced by reliable, absolute dating methods.

2.3 RESEARCH OBJECTIVES

This investigation aims to establish a robust history for the CVC building upon previous work, including an assessment of the temporal relationship with coeval volcanism in the ELO, the establishment of the CVC’s tectonic affinity using modern discriminatory criteria and the development of detailed stratigraphic architecture. This can be achieved by providing:

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1. The paleoenvironment for the volcanics through detailed stratigraphic logging of the sedimentary and volcanic facies and facies associations.

2. Absolute age dates for the Comerong Volcanic Complex gathered through U-Pb dating techniques.

3. Determination of the tectonic setting of the Comerong Volcanic Complex using felsic and mafic geochemical affinities.

This theoretical test surrounds this study’s hypothesis that the Comerong Volcanic Complex formed in an intermountain continental setting as part of a back- arc rifting event in Givetian time and constitutes an extension to other temporal basins across the ELO not formally recognised as part of the EVZ by McIlveen (1975).

38 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Chapter 3: Applied Methods to the Research

The Comerong Volcanics were analysed from the regional scale to the microscale, with field mapping providing the context to correlate lithofacies and interpret the evolution of the CVC. All sample preparation and analysis was conducted with QUT equipment and technical staff at the Central Analytical Research Facility with the exception of the zircon separation which was conducted at Geotrack International Pty Ltd. The methods are given below, and a stepped procedure with instruments used is available in Appendix A.

3.1 FIELD GEOLOGY AND PETROGRAPHIC ANALYSIS

The geological field season is designed to encompass the available outcrop along the entire eastern limb. This would provide a stratigraphic view of the CVC from the farthest northern exposure to the southernmost exposure. Stratigraphic logs of the eastern limb provide a stratigraphy slice through the depositional basin to investigate the nature of deposition/emplacement and the relationships between volcanic and sedimentary facies. The positions of the limb traverses are shown in Fig. 9. The results from the field season were used to select samples of interest for petrographic analysis and construct stratigraphic logs.

The geographic information system, ArcGIS was used for digitising the area of interest (AOI) map area using New South Wales geological survey maps and for providing accurate measurements between GPS locations for true thickness measurements taken in the field. The sampling of volcanic lithofacies was carried out with care to minimise the impact of weathering and to provide a representative sample of the outcrop. The true thickness was calculated for each field site by averaging dip measurements taken from contacts and interbedded sedimentary units and applying trigonometric calculations to find the true thickness of strata. True thickness calculation overview is supplied in Appendix B.

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Fig. 9. AOI with field sites marked by dashed marker lines on the eastern limb and base camps marked by tent symbol. Regional geology adapted from the Geological Survey of New South Wales Araluen 1:100 000 (Wyborn & Owen, 1986), Canberra 1:250 000 (Best et al., 1964) and Ulladulla 1:250 000 (McElroy & Rose, 1962) geological map sheets.

40 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

3.2 WHOLE ROCK MAJOR AND TRACE ELEMENT GEOCHEMISTRY

Geochemical methods used in the collection of geochemistry results include X- ray fluorescence (XRF) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). These quantitative methods provide the major and trace element chemistry of samples collected in the field. Geochemistry sample locations are provided in the Field Results chapter. Whole-rock geochemical data is given in Appendix C.

Whole-rock major element geochemistry was collected via X-Ray fluorescence analysis and was conducted at QUT’s CARF laboratory by Dr Karine Moromizato. XRF glass disks were prepared by fusing 1.15 g of sample with 8.85 g of high purity flux, homogenised and fused in a Claisse ‘TheOx’ Advanced Fusion Instrument. Following fusion, each disk was wiped with ethanol to clean the analysis surface and loaded into a PANalytical AXIOS Wavelength X-ray Fluorescence (WD-XRF) Spectrometer. Each sample disk was analysed twice along with USGS standards AGV- 2 and BCR-2, and two blank flux disks. The accuracy and precision of the major element results were within 1% error from the secondary standard.

Whole-rock trace element geochemistry was conducted by ablating XRF glass disks in an Agilent 8800 Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICP-MS). The XRF glass disks were stacked in order and sawed in half, with the exposed inner disk used as the ablation surface. Trace element ablations used a spot size of 100μm with a dwell time of 25 seconds at 2.5J/cm2, at a rate of 11Hz and with a Helium flow rate of 600ml/min. The same laser system parameters were used for REE data collection with the exception of an increased spot size of 110μm. Accuracy was measured with USGS standards, NIST SRM-610, BCR-2, and AGV-2 for data quality assurance. BCR-2 was used as a primary standard with AGV- 2 and SRM-610 measured as unknowns. Silica and Calcium are used as internal standards based upon data collected from major element XRF analysis. Accuracy to the secondary standard AGV-2 was within 10%, with the majority within 5% analytical error.

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3.3 U-P ZIRCON GEOCHRONOLOGY

Comerong Volcanic zircons were analysed at the Queensland University of Technology’s Central Analytical Research Facility (CARF). The zircons analysed for U-Pb isotope ages are from rock units at the base and capping felsic units. This provided age determination of the lower and upper felsic stratigraphy. The zircons were analysed by tape mounting on a glass plate. The tape mounted ablations were collected in two separate sessions. Polished mounts were prepared by mounting the same zircons in epoxy and polishing to reveal internal domains. Some zircons were lost in the polishing process, which reduced the total number of available zircons for dating. Polished zircons were measured in session three with ablation sites selected by Cathodoluminescence imaging of internal zircon domains.

Zircon ablation took place in an Agilent 8800 Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICP-MS) using tape mounted zircon and polished mounted zircon arranged in rows. The zircons were observed under a plane polarised light image map processed on a Leica DM6000 light microscope to target zircon surfaces free of fractures and inclusions. Zircon standards Temora 2 (Black, 2004) and Plešovice (Slama et al., 2008) were used to correct U-Pb geochronological systematics, where Temora 2 and USGS glass standard NIST 610 was used as a primary standard, and Plešovice treated as an unknown. Ablation procedure analysed ten unknowns, followed by a set of zircon standards. Two sets of zircon standards were analysed before and after to check for an age drift effect throughout the experiment.

The Agilent 8800 LA-ICP-MS operated with a dwell time of 30 seconds at 2.0J/cm2. The rate was 7Hz in an ablation cell with a Helium atmospheric flow rate of 600ml/min. Zircon trace element chemistry was collected for all tape mounted zircon analyses using a spot size of 30μm. Trace elements were used as a set of criteria in assigning concordance (P<2500 ppm, La<7 ppm, Ti<110 ppm, Pb206<5% ppm). Thirty seconds between ablations provided background recording to extract a baseline data reduction in the Iolite software package (Paton et al., 2011). Session three was not able to collect trace elements on polished zircon mounts as the laser diameter of 30μm was too large to ablate thin rim domains. Instead, a 20μm spot size was chosen to sample zircon interior-rim domains (Fig. 10). The use of different spot sizes was not able to definitively eliminate contaminants such as inclusions and internal fractures, as

42 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

illustrated in Fig. 10, however the targeted zircon domains were able to avoid these contaminant sources for the majority of ablations.

Data collected was processed through a reduction process in Iolite were isotope peaks were trimmed, and a common Pb correction applied in excel. The youngest population of autocrystic zircon for each tape mounted sample was constrained using a linearised probability plot (Bryan et al., 2004), and final age determined using the weighted average function in Isoplot 4.15 (Ludwig, 2008) or using the Isoplot “unmixing” function after Sambridge & Compston (1994) if the concordant data does not define a young population on the linearised probability plot. The tape mounted ages were then crosschecked with the weighted average of polished mounted rim ages to provide robust confidence to the final age. Concordant zircon data is supplied in Appendix D.

Fig. 10. Cartoon of Tape Mounted ablation (a) and Polished Mount ablation (b). Length of example crystal set as 100μm.

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Chapter 4: Field Results

The Comerong Volcanic Complex (CVC) within the eastern limb of the Budawang Synclinorium comprises intercalated felsic and mafic volcanic and intrusive units, with minor sedimentary units. The CVC is underlain by deformed metapelites (Ordovician Mallacoota Beds; Wyborn & Owen, 1986) and overlain by gravel to cobble-grained, polymict, conglomerates. The CVC on the eastern limb is mapped up to 1.2km in true thickness and 58 km laterally along a N-S strike within this study’s AOI but extends further based upon NSW Geological Survey mapping completed by Wyborn & Owen (1986) and McElroy & Rose (1962) (Fig. 11). The volcanic outcrop extends for approximately 40 km strike length further north and 2 km further south. The true extent of the Comerong Volcanics is unknown due to concealment under Permian sediments of the Sydney Basin (Wyborn & Owen, 1986).

Five east-west oriented traverses at Belowra Creek, Stoney Creek, Buckenbowra River, Quart Pot Creek, and Burra Creek, show the orientations of the volcanic units are variable within 177-223° strike orientation and 38.5-80° of dip angle (Fig. 12). Stoney Creek true thickness has been extrapolated along with regional features associated with weather- resistant silicic units at Belowra and Buckenbowra field sites (dashed line, Fig. 12). This extrapolated thickness result has been collected due to the inaccessibility of the Stoney Creek field site. Younging direction on the eastern limb is considered westerly from early mapping carried out by Wyborn and Owen (1986) based upon the sedimentary succession overlying the volcanics. Regional metamorphism within the CVC is pervasive in mafic units with lower greenschist alteration exhibited by chloritisation of groundmass/matrix with minor calcite and titanite. Felsic units are affected with sericitic alteration of plagioclase phases. Minor sedimentary units of sandstone, mudstone and conglomerate are intercalated with the CVC volcanic units, with variations in sediment size, clast abundances and depositional style.

Geology was exposed intermittently within watercourses and cliff faces, generally with less than 5 m in outcrop height. Changes in watercourse direction and transition from areas of high and low relief commonly denoted changes in lithology, such as coherent silicic lithofacies to mudstone lithofacies. The following sections present the facies and facies

44 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

associations observed within the CVC volcanic and sedimentary lithologies, including a description of the basement to the volcano-sedimentary succession. A summary for the coherent, fragmental and sedimentary lithofacies are presented in Table 1, Table 2 and Table 3. Physical volcanology nomenclature for the characterisation of fragmental and coherent rocks follows Cas et al. (2008). All reported facies thicknesses are true thickness calculated from outcrop exposure and taking into account local and regional dip orientation. The following dip azimuth and dip measurements are shown as ###/## unless specified as a strike measurement.

Table 1. Mineralogy, alteration and composition of the Comerong Volcanics coherent lithofacies. Coherent Phenocryst, Size, Alteration Groundmass Mineralogy Composition Lithofacie Type Abundance

Massive, Fine- Scarce phenocrysts Minor Chlorite and Plagioclase, <0.5mm, 40- Intermediate/Mafic grained, Aphyric <1%, rare phenocrysts up to Sericite with Calcite 50%, Pyroxene <0.4mm, 5- Mafic Coherent 1.5mm. veining. 10%, Magnetite 0.2mm, 15%, Unit Intersertal glass, 30%

Massive, Sub- Coarse-grained Plagioclase Moderate to strong Plagioclase 0.2mm, 0-10%, Mafic ophitic, Phaneritic 1.5mm, 40%, Very Coarse- sericite + calcite Pyroxene 0-10%, Magnetite, to Porphyritic grained Pyroxene <2mm, alteration of <5%, Intersertal glass, 20% Mafic Coherent 20% plagioclase. Chlorite alteration of pyroxene Unit and glass. Calcite veining common. Massive, Medium- Medium grained Plagioclase Heavily sericitised Plagioclase, 0-10%, Pyroxene Mafic grained, 1mm, 45%, Rare Coarse feldspar, sepentenised 0.2mm, 10%, Magnetite Equigranular, Olivine 2mm, <1% rare olivine and 0.25mm, 15%, Intersertal Plagioclase-rich chloritised glass, 15% groundmass. Mafic Coherent Unit

Massive, Sparsely Very coarse-grained Strong Chlorite and Plagioclase, <0.1mm, 60%, Intermediate/Mafic Porphyritic Plagioclase on av.2mm, up to Sericite alteration of Quartz 0.05mm, 15%, Intermediate 4mm crystals, 5% groundmass minerals Magnetite 0.2mm, <5%, and glass. Intersertal glass, 10-15% Coherent Unit

Fine-grained, Medium-grained K-spar (av. Moderate sericitic Microlitic feldspar in Felsic Massive to flow- 0.25mm) <5%, and rare alteration of feldspar micropoikilitic quartz, <1mm, banded Silicic coarse feldspar, 2mm, and groundmass 90%, Opaques/Magnetite Coherent Unit Embayed Quartz 2mm, <5% microlites. Pervasive <0.2mm, <1% quartz veining.

Porphyritic, Coarse Quartz 1mm, 10%, Sericitic alteration of Microlitic feldspar in Felsic Massive textured Very coarse K-spar 2-3.5mm, feldspar. Weak micropoikilitic quartz, 1mm, Silicic Coherent 5% chloritisation of glass. 70%, Opaques/Magnetite Unit Pervasive quartz <5%, Fluorite euhedral veining. 0.1mm, <1%

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Table 2. Clast type, matrix and dominant clast composition of the Comerong Volcanics fragmental lithofacies. Fragmental Clast/Fragment, Size, Clast/Fragment textures Matrix Composition Lithofacie Type Abundance

Sediment-hosted, Gradational abundance, Angular, blocky clasts or Black to dark grey, very Mafic Blocky to fluidal, Blocky 0.1-1m, Fluidal lensoidal/bulbous clasts. fine to clay-sized Monomictic Mafic 3cm Clast to matrix-supported sediment. Breccia variations. In situ jigsaw-fit texture in small clasts. Sediment-hosted, Gradational abundance, Angular to irregular blocky Grey to cream, fine- Silicic Blocky, Monomictic Blocky 30cm clasts. Clast to matrix- grained sediment. Silicic Breccia supported variations. Jigsaw-fit textures are common. Blocky, Monomictic Blocky clasts 95% Aphyric massive textured Gravel to granule-sized Mafic Mafic Breccia clasts or sparse phenocrysts monomictic clasts. of altered feldspar common.

Blocky, Monomictic Blocky clasts 95% Flow-banding to massive Gravel to granule-sized Silicic Silicic Breccia textures common in clasts. monomicitic clasts.

Fine-ash, Crystal- Coarse Quartz 1mm, Weak sericitic alteration of Feldspar fragments30%, Silicic poor, Pumice-rich, 5%, Medium grained feldspar. Quartz veins are Quartz 20%, Glass Fragmental Silicic Feldspar fragments common. Shards/Ash 30-40% 0.5mm, <5%

Fine-ash, Crystal- Embayed coarse Quartz Sericitic alteration of Feldspar fragments, 20%, Silicic rich, Fragmental 1mm, 5%, Very coarse, feldspar. Chloritisation of Quartz fragments 0.1mm, Silicic resorbed K-spar <3mm, small clasts (<5mm). 15%, Glass/Ash shards 10% 50%

46 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Table 3. Clast type, textures/structures and matrix of the Comerong Volcanics sedimentary lithofacies. Fragmental Clast, Size, Abundance Texture & Structures Matrix Lithofacie Type

Massively bedded, Clasts: Silicic Volcanics (10%), Massive fining upward Grey, lithic-rich, angular, sand with grain Polymicitic, Pebble Metapelitic Rock (10%), Mudstone sequence. size ranging from 0.2-0.5 mm to cobble-sized, (<5%), Nodular Quartz (<5%) Para-Breccia Size: 2<20cm Subrounded to Subangular Massively bedded, Clasts: Silicic Volcanics (<5%), Massive, structureless Very to extremely fine matrix (<0.01mm). Mud matrix- Metapelitic Rock (<5%), Nodular supported, Quartz (<5%) Polymictic, Gravel Size: 2<15mm, commonly 2<4mm. Subrounded to Angular to pebble-sized, para-Breccia Finely laminated, NA Laminated beds. Very to extremely fine matrix (<0.1mm). silt to clay-grained, Mudstone

Massive to planar Clasts: Fine-grained Silicic Poorly sorted, Massive Very fine-grained ash matrix. bedded, Polymicitic, Volcanics (<5%), Fine-grained Mafic tabular bedding. <0.5mm Pebble to cobble- Volcanics, Metapelitic Rock (<5%), sized, Volcanogenic Mudstone (<5%), Nodular Quartz (<5%) para-Conglomerate Size: 0.5<8cm, Exception <20cm Silicic Clasts Rounded to Subangular Fine to Medium- NA Massive planar bedding. Quartz (90%), Lithics (10%) grained, Massive to Size: 0.25<0.5 mm planar-bedded, Angular Sandstone

Massively bedded, Clasts: Scoria (30%), Fine-grained Massively bedded, Very fine-grained sediment. Quartz and Polymicitic, Mafic Volcanics (<5%), Metapelitic imbricated clasts. feldspar. Imbricated, Gravel- Rock (<5%) Size: 0.5<8cm, <0.5mm sized, volcanogenic Subangular to Angular Para-Breccia Medium to Coarse- Fine-grained Mafic Volcanics (<1%), Well sorted, Trough Quartz (80%), Feldspars (15%), Lithics grained, Planar to Nodular Quartz (<1%) crossbedding. (5%) trough cross-bedded, Size: 2 cm Size: 0.5 mm Sandstone Subangular Subangular to Angular Commonly Maroon Coloured Imbricated, Massive Sandstone (20%),, Fine-grained Massive fining upward Quartz (80%), Feldspars (15%), Lithics to trough cross- Mafic Volcanics (<5%), Mudstone sequence. (5%) bedded, Polymictic, (<5%), Porphyritic Silicic Volcanics Trough crossbedding. Size: 0.5 mm Para-Conglomerate (<5%) Subangular to Angular Size: 5<15 cm Maroon Coloured Rounded to Well-Rounded

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Fig. 11. Map of Budawang Synclinorium. Adapted after NSW Geological Survey Wyborn & Owen (1986), McElroy & Rose (1962) and Best et al. (1964). Mapped traverses labelled, Belowra Creek (A), Stoney Creek (B), Buckenbowra River (C), Quart Pot Creek (D), and Burra Creek (E). Averaged Dip/Dip Azimuth data displayed alongside field site and compiled as attached steroenet. Trend/Plunge of poles on stereonet plotted as 87/10 for A, 90/51.5 for B, 133/27 for C, 114/38 for D, and 96/25 for E.

48 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Fig. 12. Stratigraphy of the Budawang Synclinorium eastern limb. Outcrop exposure is indicated by greyscale bar adjacent to log. Volcanic crystal size class follows conventions of Cas et al. (2008) with labels as F- Fine, M - Medium, L- Large, E – Extreme, C – Crystals, CC – Coarse Crystals, L – Lapilli. Sedimentary size class follows conventions of Cas et al. (2008) for non-genetic grain size classes for fragmental rocks with labels as Md – Mud/Clay, Slt – Silt, Fs – Fine Sand, Ms – Medium Sand, Cs – Coarse Sand, G – Gravel, P – Pebble. Sample sites indicated opposite stratigraphic log for reference in Appendix C.

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4.1 BASEMENT TO THE COMERONG VOLCANIC COMPLEX: THE ORDOVICIAN “MALLACOOTA BEDS”

4.1.1 Massive to fining upward sequenced, Schistic, Foliated, Metapelite Metapelite lithofacies are in unconformable or faulted contact with the basal CVC deposits, and therefore this study uses them to denote the stratigraphic base. The true thickness and geographic extent was not constrained due to the kilometre-scale exposure outside of the study region. The metapelite lithofacies comprises foliated, quartz-rich slate to phyllite with a distinct schistosity produced by the alignment of muscovite and minor biotite. Fresh surfaces display schistosity via a phyllic sheen on appearance. Outcrops weakly displayed bedding via subtle grain size changes, with upward fining beds (fining approx. west), up to 20 cm thick (Fig. 13). Quartz grains ranged in size from 0.2 mm to 1 mm. A foliation fabric was present in the form of cross-cutting striations indicating a period of intense compression. This fabric is noted in all metapelite exposures. Original bedding is not reliable due to local folding producing a range of orientation measurements with an average dip azimuth at Belowra Creek of 136° (strike NE-SW), 279° at Stoney Creek (strike N-S) and 294° at Burra Creek (strike NNE-SSW).

At Stoney Creek, one locality (150°03’14.2”E, 35°27’40.4”S) preserves a low angle, erosional unconformity contact between the metapelites and westward titled (Dip/dip azimuth: 253/38°, 253/39°) conformable beds of pebble to cobble-sized, para-breccia. The breccia lithofacies does not exhibit poly-phase deformation or schistosity defined by metamorphic mineral growth, thus an angular unconformity relationship is inferred. At Quart Pot Creek the metapelitic rocks outcrop adjacent to a fault margin indicated by talc-altered rock with extensive veining, juxtaposing the metapelites with a porphyritic, massive silicic volcanic lithofacies unit.

50 Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Fig. 13. Field photographs of the Massive to fining upward sequenced, Schistic, Foliated, Quartz veined, Metapelite lithofacies. a. Open folding in planar bedded, fine-grained metapelite with quartz veins. b. Metapelite bed (~15 cm thick) with a foliation fabric exposed parallel to hammer head.

Ordovician rocks of deep marine origin are found throughout the Lachlan Orogen and commonly form the bedrock juxtaposed to younger rocks by a regional unconformity (Vandenberg and Stewart, 1992). In the eastern subdivision of the Lachlan Orogen, and adjacent the Budawang Synclinorium, the underlying turbidite deposits are considered to be of Ordovician age (Dadd, 1992; Glen, 1990; Miller and Gray, 1997). Graptolite fossils recovered during regional mapping by Wyborn and Owen (1986) suggest an oldest age of Eastonian (Late- Ordovician). Wyborn and Owen (1986) also interpreted the contact between the Ordovician turbidites and overlying units to be represented by an angular unconformity. Work in the Eden- Merrimbula area of the NSW south coast region, describes the Ordovician turbidite deposits as the Mallacoota Beds, following early regional mapping by Hall (1957). The metapelite rocks

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observed in this study that comprise the basement to the CVC are in accordance to the regional mapping of Wyborn and Owen (1986) and McElroy and Rose (1962) and mimic the Mallacoota Beds described in more recent work by Steiner (1972) and Fergusson et al. (1979). The metapelite basement to the CVC is further referred to as the Mallacoota Beds in accordance with the current understanding of the stratigraphic framework for the NSW south coast.

4.2 COHERENT LITHOFACIES WITHIN THE COMERONG VOLCANIC COMPLEX

4.2.1 Massive, Fine-grained, Aphyric Mafic Coherent Unit A dark grey to black, very fine-grained, aphyric coherent mafic lithofacies is observed with a thickness ranging from 20 to 85 m. This lithofacies is very poorly vesicular (0-5%) and preserves a massive texture. The primary mineral assemblage consists of acicular, euhedral plagioclase microlaths in two crystal populations (Fig. 14)( Michel-Levy Extinction Values labelled as ‘An’, An55<70, <0.5 mm at 40-50%, <1.5 mm at <1%) and interstitial clinopyroxene (<0.4 mm) with abundant magnetite (0.2mm) up to 20% (modal estimate, Table.1). Groundmass comprises up to 90% of the rock which consists of glass and microlitic plagioclase, pyroxene and magnetite. Some plagioclase phenocrysts from the larger 1.5 mm population show sieve texture, rounded vertices and sericite alteration increasing in intensity towards rims. Phenocrystic and microlitic plagioclase variably display weak to strong flow alignment displaying a trachytic texture in thin section.

Most primary contacts associated with this lithofacies are now concealed; however one lower contact exhibits a sharp base which erodes into an underlying fine-grained, lithified sedimentary unit (Buckenbowra River; 149°58’33.2”E, 35°36’59.2”S; Fig. 15a). Regional stratigraphic orientation indicates a westwards younging direction and is used to infer this as a basal contact. The rough orientation of the strike of this contact is 258° indicating a SSW-NNE strike. The fine-grained, aphyric mafic lithofacies commonly preserve clasts incorporated from underlying units at observed contacts. For example, in Fig. 15b, angular, fine-grained sedimentary clasts (<5 cm) are integrated into a thin contact margin approximately 10cm wide. Other exposures at Buckenbowra River show the fine-grained coherent aphyric lithofacies grading into a fragmented base comprised of the poorly sorted, monomictic, mafic breccia lithofacies with clasts texturally and compositionally derived from the bulk of the coherent mafic lithofacies.

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Fig. 14. Representative photomicrographs of the Massive, Aphyric Coherent Mafic lithofacies. a. Microlitic groundmass dominated by plagioclase (Pl) and abundant magnetite (Opaque, equant crystals in groundmass). b. Glassy Massive Aphyric Mafic Coherent lithofacies with two plagioclase populations.

Overprinting veins are prevalent with upper and lower margins of the aphyric mafic lithofacies. Deformation was observed at Buckenbowra River (149°58’28.3”E, 35°36’48.7”S) where a large sinistral carbonate filled vein was exposed towards the upper margin (Fig. 15c). Notably, the fracture displays a ductile form with smooth arcuate edges and sharp terminations indicating shear sense. Pervasive epidote veining was noted above the basal contact in Fig. 15a. The epidote veining is branched and in random orientations with overturned to convoluted folding parallel to the contact margin. Greenschist alteration occurs as fine chlorite replacing glass and thin calcite veins commonly occurring along the faces of sericite altered plagioclase crystals. At Buckenbowra River the greenschist alteration varies throughout the massive, fine- grained, aphyric mafic lithofacies. This results in a patchy outcrop texture which may give a clastic appearance on first observation.

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Fig. 15. Field photographs of the Massive, Aphyric Coherent Mafic lithofacies. a. Sharp basal contact between the aphyric mafic lithofacies and massive to fining upward sequenced, schistic, foliated, metapelite. b. Clasts of metapelite (Cl) being incorporated locally at the contact interface. c, Deformation fractures with infills of massive calcite and blocky clasts of aphyric mafic wall rock.

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4.2.2 Massive, Sub-ophitic, Phaneritic to Porphyritic Mafic Coherent Unit The dark grey, massive, sub-ophitic, phaneritic to porphyritic mafic lithofacies is between 20 to 150 m in thickness. This lithofacies exhibited outcrops up to 30 m in thickness. The dominant outcrop texture was of a massive, structureless interior with irregularly spaced joints oriented roughly east-west. The lithofacies is composed of acicular to tabular, euhedral plagioclase up to 1.5 mm (An60<70) and poikilitic orthopyroxene and clinopyroxene (<2 mm) with accessory magnetite present in the groundmass (Fig. 16b-d, <5%, 0.2 mm) (Table.1). The larger plagioclase crystals and occasionally pyroxene phases are characteristic of this lithofacies. In the lower margins of the sub-ophitic, phaneritic to porphyritic mafic lithofacies, phenocrysts (1-2mm) are present but in lower abundance to unit interiors. Plagioclase crystals display a felty texture in massive textured outcrops and are tangential to amygdales towards upper margins. The mineral assemblage includes un-altered clinopyroxene crystals (2 mm), interstitially surrounding plagioclase phenocrysts, and in some cases is common enough to produce a granular, sub-ophitic texture in fresh outcrop. Olivine is notably, rare to absent. This lithofacies is weakly to non-magnetic, indicating a reduced magnetite abundance in contrast to other mafic lithofacies.

At Buckenbowra River, this lithofacies displays a magma mingling character of a felsic guest component creating a ‘marble cake’ texture in fresh samples (Fig. 16a, 149°58’20.7”E, 35°36’45”S). It is not characterised by magma mixing, because the guest and host domains retain sharp boundaries however both mafic and felsic domains display a porphyritic texture with tabular feldspar phenocrysts up to 1.5 mm set in a glassy, aphyric groundmass. Felsic domains can range in size from several millimetres to 20cm with rounded edges and a fluidal character. Host domains have a feldspar abundance of 30%, and an aspect ratio range of 1:1.5 to 1:6.1. Guest domains have a feldspar abundance of 15%, and an aspect ratio range of 1:2.7 to 1:3.6. In addition, the alteration of both domains has sharp boundaries with the host being dominantly chlorite altered and guest having intense sericitic alteration of both phenocrysts and groundmass (Fig. 16c). These domains were picked for geochemical analysis, but due to the random, fluidal morphology, it is presumed some cross-contamination has occurred between the separates. Chlorite and calcite alteration of groundmass glass and sericite alteration of feldspar is common in the massive, sub-ophitic, phaneritic to porphyritic mafic lithofacies however fresh basalt occurs at Belowra Creek and Quart Pot Creek which has preserved primary major mineral assemblages.

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Lower margins to the phaneritic mafic lithofacies include wet sediment interactions. At Belowra Creek, lower margins of the coherent crystal-rich mafic lithofacies grade into a sediment-hosted, monomictic breccia lithofacies. The gradation commonly takes place in less than one meter of unit thickness, whereby variably sized (1<20 cm), blocky to bulbous clasts of the coherent mafic unit increase in abundance towards the overlying coherent body with a decrease in the sedimentary matrix. In some places, small tapered fingers of the coherent facies intrude the sediment. Many outcrops of the sub-ophitic, phaneritic to porphyritic mafic lithofacies have concealed upper margins, which includes their primary contact relationship with overlying lithofacies; however, at Belowra Creek vesiculation within the sub-ophitic, phaneritic to porphyritic mafic coherent unit provided a younging direction (westward) via an increasing abundance of vesiculation in an individual outcrop. The vesiculation occurs as elongated amygdales with quartz and plagioclase rims encompassing cores of chlorite. The amygdales within the top 5 m range in size from 1 to 3 mm set in a glassy groundmass. At Quart Pot Creek, an upper contact and contact margin is preserved in two places. The first is a contact with a finely laminated mudstone lithofacies (149°57’1.4”E, 35°42’9.7”S). The mudstone laminations are set parallel to the contact with no disturbance (folding, mixing) of laminations indicated. No laminated mudstone clasts were observed within the coherent mafic lithofacies at the margin. The second upper margin is a sharp contact with a polymictic gravel breccia lithofacies (149°56’58”E, 35°42’9.2”S). Clasts of the gravel breccia are incorporated into the upper margin as subrounded to subangular clasts.

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Fig. 16. a, Field photo of magma mingling outcrop. Note patchy texture indicated by orange to pink rock in a dominantly dark mafic host rock. b, Cross polarised light (XPL) photomicrograph of representative phaneritic mafic lithofacies with interstitial clinopyroxene (Cpx) and plagioclase (Pl) phenocrysts. c, Magma mingling PPL photomicrograph between mafic (green) and felsic (orange) domains (red dash). Sample D10.7. d, Cross polarised light (XPL) photomicrograph of representative phaneritic mafic lithofacies showing a ophitic texture developed by poikilitic clinopyroxene enclosing acicular plagioclase.

4.2.3 Massive, Medium-grained, Equigranular, Plagioclase-rich Mafic Coherent Unit The grey, medium-grained, equigranular, plagioclase-rich mafic lithofacies is only found at Buckenbowra River where it is largely concealed beneath the riverbed. True thickness is roughly 45 m. No unit geometry was observed; however, small lobes were preserved in a riverbank outcrop with sizes up to 30 cm across (149°58’6.3”E, 35°36’21.3”S). The lobes

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truncated each other and were positioned atop a massive interior, devoid of internal structures before outcrop was concealed under the riverbed. The unit is notably vesicle poor in outcrop with vesicles infilled by pale green chlorite in fresh samples. This lithofacies consists of equigranular, coarse-grained, acicular plagioclase that averages 1 mm in length (Fig. 17) (45%). Fine-grained clinopyroxene and orthopyroxene up to 0.1 mm are present in the groundmass, comprising up to 25% (Table. 1). The remainder of the groundmass comprises interstitial glass (25%) and anhedral, microlitic opaque minerals interpreted as late-stage magnetite (<5%). Alteration in outcrop and under thin section is intense. All plagioclase phases have been psuedomorphed by sericite clays, and primary glass has been completely altered to chlorite. Vesicles are sub-parallel to plagioclase laths and associated with secondary calcite growths along vesicle rims.

The lower contact with the porphyritic, massive silicic lithofacies was more poorly exposed than the uppermost contact with the medium-grained, trough cross-bedded sandstone lithofacies of the capping sedimentary sequence. Package thickness is defined by the first observed outcrop until the exposure of fine-grained sandstone.

Fig. 17. Representative photomicrographs of the medium-grained, equigranular, mafic lithofacies. a, XPL image showing completely sericite altered plagioclase crystals (Pl) set in a microlitic groundmass of pyroxene (Px) and opaque minerals (most likely Fe-oxide phases). b, PPL image showing chlorite altered vesicles set in an equigranular groundmass (Vs).

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4.2.4 Massive, Sparsely Porphyritic Intermediate Coherent Unit The sparsely porphyritic intermediate lithofacies occurs only at Buckenbowra River (149°58’30.7”E, 35°36’53.9”S). It has a minimum thickness of 20 m with upper and lower contacts concealed. In outcrop, this lithofacies features a clast rich basal margin (<1 m) with a vesiculated layer leading into a texturally massive interior. The clasts at the basal margin include mafic volcanic clasts, nodular quartz, silicic volcanic clasts and medium-grained metapelite sedimentary clasts. The largest clast population are angular, mafic volcanic clasts up to 5 cm. Silicic, metapelite and nodular quartz clasts are found up to several centimetres. The mineralogy of the massive, sparsely porphyritic intermediate lithofacies is characterised by blocky plagioclase phenocrysts (<5%) from 2 to 4 mm in size, evenly distributed throughout the outcrop. Absence of pyroxene and olivine and small quartz crystals in thin section argue for an intermediate composition. Under thin section, the plagioclase phenocrysts show moderate sericitic alteration with rounded crystal edges (Fig. 18). Very few plagioclase phenocrysts are broken with some crystals missing fragments of euhedra. The phase composition of plagioclase could not be determined due to sericitic alteration destroying twinning extinction patterns for reliable Michel-levy methods. The groundmass is composed of microlitic quartz (10%), feldspar (55%) and indistinguishable altered mafic minerals (20%) below 0.05 mm (Table. 1). Glass is also present in the groundmass as interstitial patches of chlorite, occurring with opaque minerals (<15%). The sericitic and chloritic alteration has replaced much of the groundmass excluding small quartz crystals.

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Fig. 18. Representative photomicrograph of the massive, sparsely porphyritic intermediate coherent lithofacies showing blocky feldspar phenocrysts with moderate sericitic alteration. Alteration has destroyed any primary twinning extinction. Some phenocrysts are locally fractured with infill of chlorite. Spherical, recrystallised quartz occurs as alteration of the groundmass with chlorite (bottom-right).

4.2.5 Fine-grained, Massive to flow-banded Silicic Coherent Unit The fine-grained, massive to flow-banded silicic lithofacies is one of the most common lithofacies encountered throughout the field sites. It has a maximum true thickness of 170 m. Most outcroppings of this lithofacies are between the ranges of 100 to 150 m true thickness at Belowra Creek, Stoney Creek, Buckenbowra River and minor units at Quart Pot Creek. Flow- band deformation is a common feature within the interior of fine-grained, massive to flow- banded silicic coherent bodies (Fig. 19). Flow-banding is discriminated as alternating fluidal- form layers with distinct colour contrast. The layers may be completely or locally deformed (as in Fig. 19c) and are continuous throughout the exposed outcrop. Spherulites are found in the interior of silicic bodies and can dominate groundmass, creating a granular appearance. Spherulites at Stoney Creek are up to 1mm with a core of volcanic quartz. At Belowra Creek the lithofacies is largely concealed, however good exposure of a granular textured outcrop exhibits a spherulitic rich interior of 40% radial spherulites up to 3mm in diameter. Small to large lenticular features are common towards upper margins of coherent felsic bodies (Fig. 20a). These lenticular clasts are white to grey, up to 8 cm long, elongate to equant, exhibit vesiculated internal domains and have pinched terminations. At Stoney Creek and Quart Pot Creek, crude to perfect columnar joints (oriented E-W) are exposed with sizes of joint widths from 10 cm to

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4 m with the diameter increasing with proximity towards the centre of the unit body Fig. 20b- c). The Stoney Creek columnar joints perfectly exposed laminar flow-bands consistently perpendicular to the joint fractures with an orientation of 188° (150°3’4.23”E, 35°27’46.1”S). This lithofacies displays abundant devitrification textures such as micropoikilitic quartz producing outcrop ‘snowflake’ texture. Spherulites with quartz cores are common in all thin sections up to 1 mm in diameter. Feldspar phenocrysts are tabular to blocky with rounded vertices and scarce (<2 mm, averaging 0.25 mm), constituting less than 5% of the total rock (Table. 1). The groundmass is completely devitrified by micropoikilitic quartz, defined as optically continuous host quartz (<0.5 mm) surrounding internally altered, guest feldspar needles with a rim growth of pale brown sericite in plane polarised light (Fig. 21).

Fig. 19. Field photographs of the fine-grained, massive to flow-banded silicic coherent lithofacies. a, Entrained mudstone clast with flow-banding showing a dextral shear sense at Belowra Creek. b, Entrained metapelite clast in flow-banded fine-grained silicic at Belowra Creek. c, Tight, overturned folds in flow-bands, Belowra Creek.

Alteration in the form of sericite clays is moderate in feldspar crystals and groundmass. Weathering is strong in thin section, with fractures infilled with quartz and late-stage opaque oxides preferentially occurring with feldspar phenocrysts. Weathering fractures work to fracture feldspar phenocrysts with a jigsaw-fit arrangement displayed in multiple crystals. Infill consists of oxides and heavy sericitic alteration.

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Fig. 20. Field photographs of the fine-grained, massive to flow-banded silicic coherent lithofacies. a, Lenticular features towards the upper margin of silicic cohernet unit at Belowra Creek. Wispy lenticular features are generally aligned but can display rotation away from population alignment. b-c, Columnar joints in thick units of silicic coherent units at Stoney and Quart Pot field sites.

The lithofacies has been observed to be in direct contact with a sediment-hosted monomictic, silicic breccia at Stoney Creek. Clasts from the breccia are not observed above the basal margin of approximately 2 m but within this margin locally display clast-supported to rare matrix- supported jigsaw-fit texture. Other indicators of lower contact margins are the increase in abundance and size of foreign clasts. Fig. 19a-b shows entrainment of angular mud (<4 cm) and metapelite clasts (<10 cm) at Belowra Creek, with fluidal flow-bands encasing the clasts producing a dextral (northerly) shear sense direction. Upper margins in the lithofacies are defined by contacts with a monomictic, silicic breccia which differs from the basal margins because the matrix is derived from a granule sized matrix of the same composition, rather than a sedimentary origin. The monomictic silicic breccia is not found at all field sites due to concealment.

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Fig. 21. Representative PPL and XPL photomicrographs of the fine-grained silicic lithofacies. Rounded and embayed quartz crystals comprise cores to sperulites (Sph) and altered feldpsar phenocrysts (Pl, Ksp) are altered by sericite clays. Extensive quartz veining is common throughout all samples and field outcrops.

A magma mingling texture was observed with the massive, sub-ophitic, phaneritic to porphyritic mafic coherent lithofacies (Fig. 22). This exposure occurs in proximity to the magma mingling exposure within the phaneritic to porphyritic mafic coherent lithofacies lying stratigraphically above. Guest mafic and host silicic domains retain sharp boundaries but have a smooth, irregular morphology.

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Fig. 22. Field photograph of the Buckenbowra River magma mingling texture. Guest clasts of the phaneritic to porphyritic mafic coherent lithofacies occur as dark component wthin pink-orange fine-grained, massive to flow- banded silicic coherent lithofacies.

4.2.6 Porphyritic, Massive textured Silicic Coherent Unit The porphyritic, massive textured, silicic lithofacies is found at Buckenbowra River and Burra Creek field sites. It has a true thickness of 240 m at Buckenbowra River and a minor occurrence at Burra Creek presumably above 30 to 40 m in outcrop thickness but was not adequately constrained with regards to thickness limits. Individual flow units could not be established; however, outcrops are continuous for up to 30 m and display macroscopically similar, massive texture and phenocryst abundance of 15% (Feldspars 10%, Quartz 5%). Contacts involving this lithofacies were rare due to concealment and erosion; however, the interior of the units are exposed and was adequately sampled. At Buckenbowra River, the porphyritic silicic lithofacies displays a massive, ‘snowflake’ texture composed of quartz

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spherulites and evenly distributed, blocky to tabular, sub-euhedral, commonly unbroken, feldspar phenocrysts with an average length of 2.5 mm. Burra Creek outcrops display a granular texture with larger quartz phenocrysts up to 1<1.5 mm. The feldspar macrocrysts reach a size of up to 3.5 mm at both field sites. Petrographic analysis reveals all phenocrysts exhibit rounded to sub-rounded crystal edges with some larger phenocrysts displaying zonation of sieve texture with outer rims of crystalline feldspar. Phenocrysts of feldspar comprise 10% of the rock with a minor crystal component of <5% quartz (<1 mm). The quartz phenocrysts are rounded with micropoikilitic quartz growths conforming to the crystal faces. The micropoikilitic quartz patches are dominant in the groundmass (50%) with an average size of 0.3 mm (Fig. 23). Margins between the micropoikilitic quartz patches commonly display a thin edge of sericite alteration. Sericitic alteration is moderate to strong in feldspar phenocrysts, and weathering occurs in the form of fractures with oxide and quartz infills.

At Burra Creek an upper contact is seen between the porphyritic, massive textured silicic coherent lithofacies and the blocky, monomictic silicic breccia lithofacies (149°58’54.1”E, 35°53’53.6”S). The contact is gradational, with the breccia grading into a fractured margin of the porphyritic, massive textured silicic coherent lithofacies. The contact is tens of centimetres thick (10-50 cm) within the exposed outcrop.

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Fig. 23. Photomicrograph of a representative thin section of the pophyritic silicic lithofacies. Weathering has fractured complete feldspar euhedra, encased in a groundmass of micropoikilitic quartz and quartz spherulites.

4.3 FRAGMENTAL IGNEOUS LITHOFACIES WITHIN THE COMERONG VOLCANIC COMPLEX

4.3.1 Sediment-hosted, Blocky to fluidal, Monomictic Mafic Breccia The blocky to fluidal monomictic mafic breccia is found at Belowra Creek field site, observed as intermittent exposures for approximately 30 m along strike. The breccia has a thickness of no greater than 2 m with a lower gradational contact with a massively bedded, mud-rich, polymictic, gravel to pebble-sized, para-breccia lithofacies. The contact orientation is 267/80 (150°4’35.4”E, 35°24’21.4”S). Gradation of clasts from matrix-supported to clast supported occurs before an upper contact into a horizon of a fractured parental coherent lithofacies.

The breccia clasts are angular, embayed, blocky clasts or have a shattered appearance with small lensoidal/bulbous clasts dispersed throughout the matrix, which here are termed fluidal clasts (Fig. 24a). The matrix is composed of a mud-rich, polymictic breccia. The monomictic mafic breccia is dominantly matrix-supported, commonly 60-80% matrix, before

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passing into mud-rich, polymictic breccia lithofacies or the fractured parental mafic coherent lithofacies. Fluidal clasts range in size up to 3 cm with highly irregular shapes. The fluidal clasts are not confined as their own occurrence because they commonly are found mixed with blocky clasts of the same composition. Blocky breccia clasts can be up to 1 m, and display jigsaw-fit texture in matrix-supported breccia (Fig. 24b). The blocky clasts are distinctly angular. Large blocky (>10 cm) clasts may also have a jointed appearance in outcrop. Alteration is pervasive in the fluidal and blocky clasts with all primary feldspar phases almost indistinguishable due to sericitic and carbonate alteration. Millimetre scale, calcite and chlorite veining is present in all clasts.

Fig. 24. Field photographs of the Sediment-hosted, Blocky to fluidal, Monomictic Mafic Breccia. a, Fluidal peperite at Belowra Creek with the mud-rich, polymictic breccia lithofacies with blocky clasts also entrained at the contact. b, Blocky peperite at Belowra Creek with clasts supported within the mud-rich, polymictic breccia lithofacies.

4.3.2 Sediment-hosted, Blocky, Monomictic Silicic Breccia The blocky, monomictic silicic breccia is found at Burra Creek and Stoney Creek. At Stoney Creek, the breccia is best exposed where it outcrops in the creek bed (150°03’07.6”E,

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35°27’45.8”S). The breccia is clast supported (75%) with a matrix of fine-grained, grey sand (25%). The clasts are angular, with local in-situ jigsaw-fit texture, whereby clasts may fit together with locally fractured clasts of the same composition (Fig. 25.a-b). Blocky clasts of up to 30 cm exist with the dominant clast size of 10 cm. At Burra Creek, jigsaw-fit clasts of the fragmental lithofacies comprise a unit of the sediment-hosted, blocky, monomictic silicic breccia lithofacies (Fig. 25c-d). This outcrop is supported by a matrix (80%) similar to the Stoney Creek matrix, of fine-grained, grey to cream sand. The jigsaw-fit texture is common with clasts up to 8 cm observed.

At Burra Creek, a sharp basal contact is poorly preserved. At Stoney Creek, the breccia has a lower gradational contact with a grey to cream, fine-grained massive sandstone lithofacies. Both the Stoney Creek and Burra Creek sediment-hosted, blocky, monomictic silicic breccia outcrop with a minimum thickness of 1 m. Exposures of the sedimentary lithofacies that comprise the parent to the matrix are not exposed.

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Fig. 25. Field photographs of the sediment-hosted, monomict silicic breccia lithofacies. a-b, Breccia at Stoney creek displaying poorly sorted, angular blocks of fine-grained silicic lithofacies. c, Breccia at Burra creek with in situ fracturing of fine-ash, crystal-rich, fragmental silicic lithofacies. d, Lower contact of fine-ash, crystal- rich, fragmental silicic lithofacies is sharp (red dash).

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4.3.3 Blocky, Monomictic Mafic Breccia The monomictic mafic breccia is found at Stoney Creek (150°03’11.6”E, 35°27’43.5”S) and Buckenbowra River (149°58’30.2”E, 35°36’59.8”S). It occurs as a small, poor outcrop of 1 m maximum thickness. It is a thin unit of angular, blocky clasts up to 20 cm but commonly below 5 cm (Fig. 26). The lithofacies is commonly clast supported (<30% matrix) and occurs in sharp contact with the pebble to cobble-sized, polymictic breccia lithofacies and gradational contact with the aphyric mafic lithofacies. The clasts are of the same composition as the fractured aphyric coherent mafic lithofacies that overlie the units.

Fig. 26. Field photographs of the blocky, monomict mafic breccia at Buckenbowra River. a-b, Matrix (Mx) supported breccia clasts (Cl; dashed outlines) grades into coherent unit of the massive aphyric mafic lithofacies (towards top-right of image). c, Contact (dash) of the blocky, monomictic mafic breccia (M.Br) and the polymictic, pebble to cobble sized para-breccia (Br).

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4.3.4 Blocky, Monomictic Silicic Breccia The blocky monomictic silicic breccia is found at Buckenbowra River, Quart Pot Creek and Burra Creek field sites. It is commonly 2 m thick and dominantly clast supported. The clasts are up to 30 cm in size, with a coherent, glassy groundmass. Individual clasts may show jigsaw- fit texture in outcrop with good exposure at Buckenbowra River (149°58’24.1”E, 35°36’45.9”S; Fig. 27). The clasts also display varying textures. At Quart Pot Creek the breccia clasts show flow-banding or massive textures with irregular or blocky forms. At Burra Creek and Buckenbowra River, the clasts show only massive, glassy textures with 1 mm quartz phenocrysts embedded in glassy, pink to light brown groundmass.

Fig. 27. Field photograph of the blocky, monomictic silicic breccia lithofacies. a, Unaltered photo of in situ, jigsaw-fit clast (Cl) within a granular matrix of the same compostion (Mx). The clasts and unit are variably weathered (area enclosed by red dash) and show change in colour. b, Greyscale filtered photo of A, with clasts highlighted by red dash.

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The breccia is always proximal with a gradational contact into a coherent silicic lithofacies in which the clasts are the same composition and texture. Contacts with other lithofacies occur at Burra Creek, where an irregular sharp, upper contact exists with the polymictic para-conglomerate lithofacies. The breccia is discoloured at the contact only with a white to grey, leached appearance whereby silicic clasts are heavily fractured, quartz veined and display abundant clay alteration. The leached breccia cap is no more than 20 cm in total thickness and is the only contact observed with the sedimentary sequence overlying the CVC.

4.3.5 Fine-ash, Crystal-poor, Pumice-rich, Fragmental Silicic The fine-ash, crystal-poor, pumice rich, fragmental silicic lithofacies is found at Belowra Creek. The largest true thickness calculated for this lithofacies is 27 m. The lithofacies can be described as a pink to maroon, poorly to moderately sorted, very crystal poor, fine-grained ash, fragmental silicic rock. All contacts for this lithofacies are concealed. The basal concentration of lithic clasts and pumice lapilli displays a crude upward fining. Increase in size indicates proximity to unit margins. Lithics are comprised of mudstone (<2 cm) and metapelite clasts (<5 cm) and generally constitute 5 to 15% of the unit. The unit is moderately sorted with large, lenticular pumice compacted in a fine to very fine matrix grading into an interior of smaller, moderately-flattened, pumice lapilli. Sub-rounded to rounded clasts of very fine-grained to aphyric mafic clasts no greater than 10 cm (av. 1cm) are incorporated in the basal margin. All pumice clasts have high aspect ratios of width ranges from 2 up to 10 mm and lengths from 5- 10cm (Fig. 28). Discontinuous bands, wisped terminations and glassy cores with small crystal fragments all produce a fiamme structure. Elongated vesicles up to 2 cm long and several millimetres wide are commonly sub-parallel with fiamme structures. Interior welded pumice clasts are within the same fine to very fine-grained, maroon matrix as the larger basal pumice outcrop.

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Fig. 28. Field photograph of coarse, lensoidal pumice lapilli (Pm), subrounded mudstone (Md) and metapelite clasts (Tb) in a fine matrix of the Fine-ash, Crystal-poor, Pumice-rich, Fragmental Silicic at

Belowra Creek.

4.3.6 Fine-ash, Crystal-rich, Fragmental Silicic The fine-ash, crystal-rich, fragmental silicic lithofacies outcrops at Burra Creek and Buckenbowra River field sites. It has a maximum thickness calculated at 383m. At Buckenbowra River, the lower margin (<5 m) is composed of a glassy, dense, very fine-grained matrix with fiamme-like lapilli clasts up to 10 cm long with aspect ratios typically above 8 (Fig. 29a). Above the lapilli rich zone is a zone of weakly defined, 1<2 mm flow-bands with blocky feldspar crystals (<3 mm) and crystal fragments (Modal <5% total crystal/crystal fragment, 1:4

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respectively) irregularly spaced throughout the matrix. Below this lower margin, the contact was concealed. The upper margin at Buckenbowra River is defined by glassy, weathering resistant, sub-parallel, pumice-lapilli clasts forming a pseudo-bedding foliation at an average of 124/51 (Fig. 29b). The pumice is vesicular with elongate ovoid structures infilled with creamy silica. The best-preserved outcrop of this lithofacies is seen at Burra Creek, where it exhibits a distinctive, massive to flow-banded, dense texture. Within the interior of the Burra Creek outcrop are zones of glassy, parallel, striations which mimic flattened pumice-lapilli (fiamme). These zones are exposed as weather-resistant, parallel foliations with an average orientation of 255/76 (Fig. 29c). Flow-banding structures are common throughout the interior of the unit with banding consistent for several meters until outcrop was concealed or inaccessible (Fig. 29d). Quartz veining is common in outcrop and thin section with the veins generally very thin (0.5-2 mm wide). On a microscale, the matrix is dominated by compacted glass shards that adhere to one another (Fig. 30). Coarse glass shards (0.5-1 mm) are rare in the matrix and exhibit non-flattened forms. Average glass shards in the matrix below 0.1 mm, are annealed into sub-parallel bands. Sub-angular phenocryst fragments, quartz fragments, recrystallised quartz and sericite altered ash shards comprise the bulk of the matrix. Phenocrysts up to 3.5 mm display rounded edges and commonly fractured with missing vertices (Fig. 31a). Phenocrysts are rarely preserved as complete euhedra. Embayed quartz phenocrysts (<2 mm) are rare (<1%) and comprise the cores of radial spherulites (3-4 mm). Opaque oxides are also present in the matrix with a prismatic habit, and angular lithic clasts (<5 mm) have also been identified under thin section, showing lower greenschist alteration to muscovite and very fine- grained quartz. Accessory clasts exhibit relict, perlitic fractures defined by arcuate, concentric fractures altered to silica and sericite (Fig. 31b). Moderate sericitic alteration of feldspar phenocrysts and phenocryst fragments is common. Many feldspar and quartz phenocrysts are hosts to inclusions of opaque oxide minerals.

The Buckenbowra River contacts are concealed or heavily eroded. At Burra Creek, a sharp basal contact is poorly preserved (149°59’02.2”E, 35°53’55”S). The contact could not be traced further than 20 m across strike.

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Fig. 29. Field photographs of the fine-ash, crystal-rich, fragmental silicic lithofacies. a, Fiamme textured lapilli (Fm) with high aspect ratios at Buckenbowra River. Image taken through water. b, Weather resistant lapilli at the top of Buckenbowra River displaying low-angle truncations. c, Weather resistant lapilli at Burra Creek, evident as parallel striations perdendicular to hammer head (Image rotated 90°). d, Flow-banding in creek washed outcrop at Burra Creek.

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Fig. 30. Representative photomicrograph of the fine-ash, crystal-rich, fragemental silicic lithofacies. a, PPL photomicrograph of compacted, altered glass shards in the fine-ash, crystal-rich, rhyolitic ignimbrite. Some flattened glass shards still show relict triple-junction shards (Gl). b, XPL photomicrograph of compacted, altered glass shards in the fine-ash, crystal-rich, rhyolitic ignimbrite. Some flattened glass shards.

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Fig. 31. PPL photomicrograph of welded matrix of glass shards creating eutaxitic texture. a, Note embayed quartz crystal (Qtz), very fine-grained mafic clasts (Bs) and eutaxitic texture flowing around the rounded feldspar phenocryst (Pl). b, Coherent silicic clast (Cl) with perlitic fracturing indicating the quenching was related to hydrated magma.

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4.4 SEDIMENTARY LITHOFACIES WITHIN THE COMERONG VOLCANIC COMPLEX

4.4.1 Massively bedded, Polymicitic, Pebble to cobble-sized, Para-Breccia The massively bedded, polymictic, pebble to cobble-sized, para-breccia is found as the first outcropping units at Belowra Creek and Stoney Creek. Unit thickness has a maximum of 80 m at Belowra Creek. The base of the breccia is clast supported for approximately 3m (Fig. 32b). Outcrop consists of a structurally massive unit displaying a crude fining upward sequence of poorly sorted clasts. Clast size ranges from 2-20 cm (Fig. 32c) before grading into finer clasts of pebble-grained, matrix-supported material (Fig. 32d). Exceptions include sub-rounded, boulder-sized (30 cm) clasts at Stoney Creek. Angular clasts up to 20 cm, of altered silicic volcanics mimicking the fine-grained silicic lithofacies is common (10%) with small rounded clasts of mudstone and nodular quartz up to 5 cm. The metapelite clasts are commonly subrounded but can also be subangular in pebble-sized clasts and comprise 10% of the breccia. The breccia clasts are poorly imbricated and poor to very poorly sorted. Large clasts are commonly silicic volcanic clasts with sub-rounded to subangular surfaces. Under thin section, the silicic clasts are fine pebble-sized with 0.2 mm quartz spherulites. Breccia matrix is a grey, lithic-rich, angular, sand with grain size ranging from 0.2-0.5 mm.

At Stoney Creek, a sharp, lower contact outcrops atop an erosional surface which truncates the Mallacoota Beds (Fig. 32a). This contact is also observed at Belowra Creek but is very poorly preserved. These contacts with the Mallacoota Beds comprise two of three contacts, with the third at Buckenbowra River (Fig. 15a). No upper contacts are preserved in outcrop.

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Fig. 32. Field photographs of the Massively bedded, Polymicitic, Pebble to cobble-sized, Para-Breccia. a, Breccia (Br) deposited atop eroded rocks of the Mallacoota Beds (Tb) at Stoney Creek. b, Clast supported base of the Breccia at Belowra Creek with little matrix (Mx), clasts of silicic coherent (Ry), and mudstone (Md). c, Poorly sorted breccia at Stoney Creek displaying a range of clast sizes. Cobble-sized clasts show greater rounding than pebble-sized clasts. d, Matrix supported Breccia Lithofacies at Stoney Creek.

4.4.2 Massively bedded, Mud matrix-supported, Polymictic, Gravel to pebble-sized, para-Breccia The massively bedded, mud matrix, polymictic, gravel to pebble-sized, para-breccia outcrops only at Belowra Creek with a maximum thickness of 35 m. This lithofacies comprises

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the matrix to the sediment-hosted monomictic mafic breccia lithofacies (Fig. 24). Clasts within the breccia are incorporated in a mud-rich, black matrix with no imbrication alignment. Matrix dominates this lithofacies, comprising above 95% of the unit with clasts dispersed in a poorly sorted arrangement. Clasts are comprised of nodular quartz, metapelite, and coherent silicic clasts with sizes ranging from 2 to 15 mm, however, are generally grit/granule sized (2 to 4 mm). Clasts have subrounded to subangular rounding with some metapelite clasts being distinctly angular. The outcrop displays a massive texture with no distinguishable laminations, bedding or sedimentary structures.

4.4.3 Finely laminated, silt to clay-grained, Mudstone Very fine-grained sedimentary rocks occur as massive to laminated (0.5<5 mm laminations), black to dark grey outcrop at Quart Pot Creek (grain size <0.06 mm). Laminations at Quart Pot Creek are continuous for tens of meters until across-strike outcrop was concealed. The largest and best exposed outcrop of the massive to finely laminated, mudstone lithofacies is at Quart Pot Creek where it has a maximum true thickness of 120 m with interbeds of the fine to medium-grained, massive to planar-bedded, sandstone. These laminations also provided reliable dip and dip azimuth measurements for Quart Pot Creek, with an average of 294/52 (149°57’1.1”E, 35°42’9.5”S). The massive to finely laminated, silt to clay-grained, mudstone lithofacies also outcrops as minor interbedded units within the overlying sedimentary sequence at Belowra Creek, Buckenbowra River and Burra Creek field sites.

4.4.4 Massive to planar bedded, Polymicitic, Pebble to cobble-sized, Volcanogenic para- Conglomerate This conglomerate lithofacies is found only in Buckenbowra River where it is interbedded between units of the massive, fine-grained, aphyric mafic coherent lithofacies (149°58’30.2”E, 35°36’52”S). This lithofacies has an estimated thickness of up to 20 m. Clast sizes are variable, consisting of nodular quartz, fine-grained silicic clasts, fine-grained mafic clasts, mudstone clasts, and metapelite clasts derived from the basement (Fig. 33). The clasts are all well rounded with the exception of subangular, fine-grained mafic clasts which mimic the fine-grained, aphyric, mafic coherent lithofacies. Clasts are matrix-supported and in a poorly sorted arrangement. The matrix consists of a very fine-grained ash matrix altered to chlorite and sericite (75%), with crystal fragments comprising 10% of the matrix (Fig. 34). Scoria fragments

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are common in the matrix with elongate, flattened morphology, tabular feldspar glomerocrysts (<1.5 mm) and relict vesicles infilled with chlorite. The lower and upper contacts of the main exposure at Buckenbowra River were concealed beneath the riverbed.

Fig. 33. Field photographs of the massive to trough crossbedded, polymicitic, pebble to cobble-sized, volcanogenic para-conglomerate. a, Angular mudstone clasts and subangular silicic volcanic (Ry) clasts in a moderate to poorly sorted arrangement within a dark green matrix.b, Large, subrounded silicic volcanic clast and rounded metapelite clast (Tb).

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Fig. 34. Representative photomicrographs of the massive to trough crossbedded, polymicitic, pebble to cobble- sized, volcanogenic para-conglomerate matrix. a, Rounded and partially abraded lapilli clast (Lp), feldspar crystal fragments (Fg) and large scoria fragment with sericite altered, glomeropheric, feldspars with chlorite altered glass. Alteration has produced recrystallised quartz as speckled patches along rim of scoria clast. b, Photomicrograph of ash shards (Sh).

4.4.5 Fine to Medium-grained, Massive to planar-bedded, Sandstone Sandstone occurs as a fine to medium-grained, grey to cream, massive-bedded, sublitharenite at Stoney Creek, Buckenbowra River, Quart Pot Creek and Burra Creek field sites. It has a maximum estimated true thickness of approximately 30 m but is more commonly found to be less than 10 m at Buckenbowra River and Burra Creek field sites. Planar bedded outcrops occur at Quart pot creek where beds up to 20 cm but more commonly 5cm thick occur in a sequence with the finely laminated mudstone lithofacies. Quartz is the dominant matrix component, with angular grains in a size range of 0.25 to 0.5 mm with 10% accompanying angular, lithic grains (1 mm). The massively bedded outcrops have not been found with lower contacts but do outcrop with upper contacts preserved at Burra Creek Stoney Creek and Buckenbowra River field sites. These are sharp contacts with the sediment-hosted, blocky, monomictic silicic breccia lithofacies.

4.4.6 Massively bedded, Polymicitic, Imbricated, Gravel-sized, volcanogenic Para- Breccia This breccia lithofacies is found only at Quart Pot Creek where it overlies and is intruded by the porphyritic mafic lithofacies (Fig. 35a, 149°56’57.8”E, 35°42’9.3”S). The estimated

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minimum thickness of this unit is approximately 5 m, but no upper contact has been found. Clasts range in size from several millimetres to 8 cm. All clasts are subangular to angular in shape (Fig. 35b) and well imbricated to produce alignment of all clast sizes. The dominant clast type is of highly vesicular, subangular, scoria clasts (<4mm, 30%). Where the scoria is altered, glass is replaced by chlorite, and vesicles are infilled with carbonate or zeolite growths. Small clasts of mafic volcanics also occur in the matrix (1.5-3 mm), and rare larger clasts up to 2 cm are also present comprising 5% of the breccia (Fig. 35c). These mafic clasts resemble the massive, medium-grained, equigranular, plagioclase-rich mafic coherent lithofacies in that the plagioclase laths are acicular and equigranular (1mm), and the clasts exhibit the presence of olivine (Calcite + oxide alteration). Larger clasts are of a sedimentary origin as a green-grey, medium to coarse-grained sandstone with a schist-like sheen from the alignment of secondary muscovite. The matrix to the breccia is a dark black, very fine-grained sediment consisting of quartz grains and feldspar crystal fragments (50%).

Fig. 35. Field photographs of the massively bedded, polymicitic, imbricated, gravel-sized, volcanogenic para-breccia. a, Sharp contact between the porphyritic mafic lithofacies (Bs) and volcanogenic para-breccia (Br). b, Subangular to angular clasts of green-grey, medium to coarse-grained sandstone in the volcanogenic para-breccia. c, Clasts of sericite altered coherent mafic, with local jigsaw-fit texture and fluidal morphology, locally at the contact with the volcanogenic para-breccia.

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4.4.7 Medium to Coarse-grained, Planar to trough cross-bedded, Sandstone Sandstone occurs as a medium to very coarse-grained, grey to violet, trough cross- bedded, sub-arkosic unit at Belowra Creek, Buckenbowra River, Quart Pot Creek and Burra Creek field sites (Fig. 36a-b). The sandstone outcrops as a stacked unit of 1 to 4 m beds, with scoured basal contacts and a common gravel lag. Clasts comprise pebble-sized, angular quartz with the addition of aphyric mafic clasts (<2 cm) at Burra Creek (Fig. 36c-d). All grains are sub-angular and well sorted. Quartz grains comprise 80% of the units with a ‘milky’, grey to cream colour. Alteration of feldspar fragments produces orange, angular grains with some relict cleavage present in less-exposed outcrop and constitute 15% (modal estimates).

This lithofacies is exclusively found as part of a capping sediment sequence to the CVC and is regularly found in scoured contact with the imbricated, massive to trough cross-bedded, polymictic, para-conglomerate. The maximum true thickness for this sedimentary lithofacies is recorded as 50 m at Burra Creek, before grading into an overlying mudstone sequence. At Belowra Creek and Buckenbowra River field sites, the sandstone is in scoured contact with units of the finely laminated, mudstone lithofacies.

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Fig. 36. Field photographs of the Medium to Coarse-grained, Planar to trough cross-bedded, Sandstone. a-b, Trough cross-bedding at Belwora Creek field site (troughs follow red dash). c, Aphyric mafic clasts at Burra

Creek. d, Truncating trough cross-beds at Burra Creek with a western dip azimuth (red needle).

4.4.8 Imbricated, Massive to trough cross-bedded, Polymictic, Para-Conglomerate Polymict conglomerate is the dominant lithofacies in the capping sedimentary sequence overlying the CVC. It is found at every mapped traverse except for Stoney Creek and rests atop an erosional surface best observed at Burra Creek. The maximum true thickness for the

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conglomerate lithofacies is 25 m, comprising a stacked sequence of on average 2 m thick, scoured, predominantly trough cross-bedded, conglomerate with minor interbeds of the medium to coarse-grained, massive to trough cross-bedded, sandstone. The clasts are matrix- supported and constitute up to 30% of the units. The dominant clasts are cobble-sized, poorly sorted, moderately to well-rounded maroon coloured sandstone with a size range of 8-15 cm (Fig. 37b-c). The clasts are well imbricated with the long axes of the clasts following the basal trough orientations.

Other clasts include gravel-sized aphyric mafic clasts, pebble-sized rounded mudstone and rare, dark black to maroon coloured, porphyritic silicic volcanic clasts only at Burra Creek (Fig. 37d). The matrix is a fine to medium-grained, violet to maroon sand. The sand matrix exhibits a similar composition to the sandstone interbeds. The conglomerate can occur as structurally massive or trough cross-bedded in outcrop. The only direct contact with the volcanics is observed at Burra Creek where the conglomerate overlies the blocky, monomictic silicic breccia (149°58’53.8”E, 35°53’53.9”S). The conglomerate lithofacies is a re-occurring sedimentary unit further up in the capping sedimentary where it defines a fining-upward sequence with the associated sandstone and mudstone lithofacies (Fig. 37a).

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Fig. 37. Field photographs of the Imbricated, Massive to trough cross-bedded, Polymictic, Para- Conglomerate. a, Imbricated, massive to trough cross-bedded, polymictic, para-conglomerate lithofacies (Cg) scouring underlying sandstone (Ms) at Buckenbowra River (scour red dash). b-c, Field photos showing the poorly sorted, polymict, matrix supported Conglomerate at Belowra (b) and Buckenbowra (c) field sites, with mudstone (Md), nodular quartz (Qtz) and sandstone clasts. d, Enhanced image at Burra Creek, showing the incorporation of dark porphyritic silicic clast (Ry) above field sunglass.

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4.5 LITHOFACIES ASSOCIATIONS

4.5.1 Coherent Igneous – Fragmental Lithofacies Associations Many primary associations were observed between coherent and fragmental lithofacies in the Comerong Volcanics. Most frequent are monomictic breccias at the margins of associated coherent igneous lithofacies. For example, the fine-grained, massive to flow-banded, silicic lithofacies and the porphyritic, massive silicic lithofacies are closely associated with the blocky, monomictic breccia lithofacies. Both these coherent silicic lithofacies outcrop with the breccia units occurring stratigraphically above and below them and occasionally as localised pockets within the interiors. The sediment-hosted, monomictic, silicic breccia is also associated with both the coherent silicic lithofacies. However, the sediment-hosted breccias are only found stratigraphically below the coherent units and have not been found contacting laterally or above them (Fig. 25a-b).

Mafic coherent lithofacies display similar facies associations with monomictic mafic breccias; comparable to the observed associations with the coherent silicic lithofacies. The blocky, monomictic mafic breccia is found at the base of the Stoney Creek massive, aphyric mafic lithofacies unit. At Buckenbowra River, the breccia is observed outcropping above the aphyric mafic lithofacies. The blocky monomictic mafic breccia is not regularly seen with the coherent mafic lithofacies as often as the equivalent silicic associations. The second association is the sediment-hosted, blocky to fluidal, monomictic breccia, which underlies the massive, porphyritic mafic lithofacies at Belowra Creek (Fig. 24).

4.5.2 Coherent Igneous – Sedimentary Lithofacies Associations Coherent igneous and sedimentary lithofacies associations are few in the CVC. Most coherent igneous lithofacies are associated with one or more breccia lithofacies prior to the contact with sedimentary units. However, minor coherent igneous-sedimentary associations are observed adjacent to mafic coherent lithofacies.

At Quart Pot Creek, a unit of the finely laminated mudstone lithofacies overlies a body of the massive, phaneritic mafic lithofacies. No disturbance of the mudstone laminations was observed. Additionally, no mudstone clasts were seen incorporated towards the upper margin of the mafic unit.

This coherent mafic lithofacies also is seen with a sharp upper and lower contact with the polymictic, imbricated, gravel-sized, volcanogenic para-breccia lithofacies. This is a distinct

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upper contact which is the only upper conformable contact with a sedimentary unit found within the CVC. The Quart Pot Creek field site is the only field site displaying multiple coherent- sedimentary contacts for all mafic units found.

A unit of the massive, aphyric mafic lithofacies is in sharp contact above the massive to fining upward sequenced, schistic, foliated, metapelite lithofacies at Buckenbowra River. Small fingers of the mafic rock can be seen locally penetrating the sediment along small fractures. The contact is not planar, with the aphyric mafic lithofacies emplaced atop an eroded surface and locally fracturing gravel-sized angular clasts from the underlying metapelite unit (Fig. 15a).

4.5.3 Fragmental – Sedimentary Lithofacies Associations The lithofacies associations between fragmental and sedimentary lithofacies are common for silicic units. The associations are commonly gradational, especially for sediment-hosted breccias. Gradational contacts for all fragmental lithofacies and sedimentary lithofacies are no more than 2 m in thickness.

The sediment-hosted, blocky, monomictic silicic breccia lithofacies is associated with the fine to medium-grained, massive to planar-bedded, sandstone lithofacies at Burra Creek and Stoney Creek. The sediment forms the matrix to the breccia and can be clast supported or matrix-supported. Contacts between these lithofacies types are always proximal to coherent silicic lithofacies that occur above them. The coherent silicic lithofacies represents the parent to the breccia clasts.

4.5.4 Sedimentary Associations At every field site, there is an association of the trough cross-bedded, para-conglomerate lithofacies, the medium to coarse-grained, planar to trough cross-bedded, sandstone lithofacies and minor laminated mudstone lithofacies. This association forms a sedimentary sequence above the CVC that is present at all field sites. The sequence indicates a westward younging indicated by the up-direction in excellent exposures of trough cross-beds. This sedimentary association rarely has the contact with the lower volcanics preserved except for at Burra Creek where an irregularly surfaced, leached cap of the monomictic silicic breccia is overlain by the trough cross-bedded, para-conglomerate. The conglomerate and sandstone lithofacies in this association dominate the association characterised by an upward-fining sequence of meter scale, trough cross-bedded conglomerate, passing into medium-grained sandstone trough cross-

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beds and upper planar bedded sandstone. Beds of trough cross-beds are typically 10’s of centimetres up to 3 m thick. Lenses of conglomerate are common within thick accumulations of meter-scale trough cross-beds of the sandstone lithofacies. Conglomerate beds are always observed to scour underlying sandstone beds at basal contacts.

4.6 EMPLACEMENT MECHANISMS OF THE COMERONG VOLCANIC COMPLEX

The CVC preserves silicic and mafic volcanics with coherent and fragmental lithofacies variations. Physical volcanological characteristics associated with coherent lava flows, intrusions and pyroclastic density currents are used here to discriminate the primary volcanic facies observed. Primary magma interactions with interbedded sedimentary lithofacies herein provide insight into the paleoenvironment during emplacement of the CVC. Final interpreted lithofacies names for this study are summarised in Table 4, along with the descriptive lithofacies name, composition, occurrence and interpreted genesis throughout the study area.

Table 4. Lithofacie interpretations from the descriptive lithofacie names with the composition and occurrences in the Comerong Volcanics. Descriptive Lithofacies Name Lithofacies Interpretation Composition Occurrence Genesis

Massive, Fine-grained, Massive, Fine-grained, Aphyric Mafic Stoney, Lava Aphyric Mafic Coherent Unit Basalt Buckenbowra

Massive, Sub-ophitic, Massive, Sub-ophitic, Phaneritic Mafic Belowra, Lava, Shallow Phaneritic to Porphyritic Mafic to Porphyritic Basalt Buckenbowra, Intrusion Coherent Unit Quart Pot Massive, Medium-grained, Massive, Medium-grained, Mafic Buckenbowra Lava Equigranular, Plagioclase-rich Equigranular, Plagioclase-rich Mafic Coherent Unit Basalt Massive, Sparsely Porphyritic Massive, Sparsely Porphyritic Intermediate Buckenbowra Lava Intermediate Coherent Unit Andesite

Fine-grained, Massive to flow- Fine-grained, Massive to flow- Felsic Belowra, Stoney, Lava banded Silicic Coherent Unit banded Rhyolite Buckenbowra, Quart Pot, Burra Porphyritic, Massive textured Porphyritic, Massive textured Felsic Buckenbowra, Lava Silicic Coherent Unit Rhyolite Quart Pot, Burra

Fine-ash, Crystal-poor, Fine-ash, Crystal-poor, Pumice- Felsic Belowra Pyroclastic Pumice-rich, Fragmental rich, Fragmental Silicic Rhyolitic Density Silicic Unit Ignimbrite Current Fine-ash, Crystal-rich, Fine-ash, Crystal-rich, Rhyolitic Felsic Buckenbowra, Pyroclastic Fragmental Silicic Unit Ignimbrite Quart Pot, Burra Density Current

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4.6.1 Pyroclastic Deposits of the CVC Explosive Eruption Lithofacies Pyroclastic deposits are formed by the rapid vesicle exsolution and resultant fragmentation of magma during explosive volcanic eruptions (Brown and Andrews, 2015; Houghton et al., 2015). Explosive eruptions commonly form eruption columns consisting of hot air, gases and pyroclasts with the column comprised of a gas thrust region, convection region and umbrella region (Sparks, 1986; Woods and Wohletz, 1991). These eruption columns can collapse due to negative buoyancy contrasts with the surrounding atmosphere to form pyroclastic density currents and/or disperse in the atmosphere to settle as pyroclastic fall deposits (Brown and Andrews, 2015; Ishimine, 2006). Eruption column collapse has been documented in recent explosive eruptions (Brand et al., 2014) and studied in ancient pyroclastic deposits (Maeno & Taniguchi, 2009; Willcock et al., 2013).

The clast types produced during explosive volcanic eruptions are variable but are dominantly derived from the primary magma in the form of juvenile clasts, such as pumice lapilli, crystals, accretionary lapilli and ash shards (McPhie et al., 1993). Other clasts include accidental clasts from the depositional surface and accessory clasts from the conduit walls (McPhie et al., 1993). These clast types may occur together in a pyroclastic deposit but are commonly dominated by pyroclasts derived from the original magma. Under thin section, pyroclastic deposits are characterised by ash-sized, glass shards in the matrix, with pumice clasts and accessory or accidental clasts (Maeno & Taniguchi, 2009). The deposits can be subjected to welding processes during and after emplacement (Quane and Russell, 2005). In contrast, coherent lithofacies show interlocking grain boundaries and have a higher percentage of complete phenocryst euhedra (Allen and McPhie, 2003). Pyroclastic deposits occur in three main deposits styles originating from fallout, and high to low concentration pyroclastic density currents.

Explosive Eruption Processes and Products Pyroclastic fall deposits are produced from the rain out of pyroclasts from the eruption column due to buoyancy contrast with the atmosphere as cooling progresses in the umbrella region (Ishimine, 2006). Fall deposits are commonly formed with pyroclastic density current deposits (Sparks, 1976). Deposits are generally characterised by well to moderately-sorted, planar bedded deposits of dominantly juvenile clasts with variations of sorting and particle size

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dispersion between wet and dry eruptions (Houghton et al., 2015). Proximal to source vents, pyroclastic fall deposits may be poorly sorted, but a general characteristic of fall deposits rather than ignimbrite deposits is due to the well-sorted character (Sparks, 1976). Bedding is commonly parallel and mantles the topography it is deposited upon, with the thickness of fall deposits uniform at outcrop scale and waning exponentially on a regional scale (Houghton et al., 2015).

Eruptions that form highly concentrated pyroclastic density currents produce ignimbrite deposits, commonly consisting of fine-grained pumice and ash (Brown, 2015). The high- concentration pyroclastic density current is formed by a negative buoyancy contrast in the gas thrust region of the eruption column, thereby collapsing down the flank of the volcano in a dense, hot and turbulent pyroclastic flow (Woods and Wohletz, 1991). Ignimbrite deposits can be formed as pulsed units as the Mt St Helens ignimbrite (Brand et al., 2014) or as a large single unit with its own textural variations as shown by the Ora ignimbrite in Italy (Pittari et al., 2006; Willcock et al., 2013). Generalised stratigraphic logs of ignimbrites in Fig 38 display the variability in internal texture, structures and unit thicknesses. Pyroclastic density currents are topographically controlled by preferentially filling depressions in topography but may also completely bury entire landscapes when volumetrically large (Brown, 2015; Wright et al., 1980). Ignimbrite deposits are generally poorly sorted (Sparks, 1976), may be weakly or distinctly graded, and typically host a variety of lithic clasts (McPhie et al., 1993). A singular unit may be constructed of multiple lithofacies types including massive ignimbrite, pumice-rich ignimbrite, stratified to cross-stratified ignimbrite, massive agglomerate, massive or stratified lithic breccias and accretionary lapilli-bearing ignimbrite (Brown and Andrews, 2015).

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Fig 38. a, ‘Ideal’ internal clast variations within an ignimbrite produced through pyroclastic density current processes, from Sparks (1976). b, Stratigraphic log of the Ora ignimbrite in Italy, from Wilcock et al. (2013). c, Stratigraphic log of the Mt St Helens ignimbrite eruptive units, from Brand et al. (2014).

Ignimbrites also may be completely, partly or variably welded (McPhie et al., 1993; Quane and Russell, 2005). Welding exhibits sintered clasts aligned into fabrics (Fig. 39) and an overall decrease in unit porosity (Quane and Russell, 2005). The intensity of welding may be variable throughout an ignimbrite unit due to depth within the pyroclastic flow and lateral distance from source vent (Quane and Russell, 2005). Welding textures on their own are not characteristic of subaerial pyroclastic density current deposits; however, subaqueous welded pyroclastic deposits are rare and should be accompanied by water supported debris flows or turbidites comprised of the pyroclastic detritus (Cas and Giordano, 2014). Field outcrop of strongly welded ignimbrite may also exhibit flow banding texture, stretched vesicles and rotation of clasts defining rheomorphism of the matrix (Brown and Andrews, 2015). Highly welded to rheomorphic ignimbrite outcrops can mimic the same textures and morphology of effusive volcanic facies (e.g. lavas) which make them difficult to distinguish in the field (Anderson, 1969; Brown and Andrews, 2015). Basal and upper margins may also exhibit rubble to blocky, carapace breccia, such as the Greys Landing ignimbrite, USA (Brown and Andrews,

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2015) and units within the Kathleen Ignimbrite, Australia (Medlin et al., 2015). Field observations such as structures, textures, components and grading (Brown and Andrews, 2015) must be used with microscopic observations when interpreting ignimbrites from silicic lavas, especially exposures that have undergone devitrification, recrystallisation, metamorphism and are poorly exposed. A common ignimbrite matrix may be composed of broken crystals which formed through abrasion, explosive discharge from the source vent through decompression of vesiculating magma and violent tumbling of crystals upon deposition (Best & Christiansen, 1997; Allen & McPhie, 2003). Other indications of the fragmented nature of the rock is the incorporation of high percentages of juvenile clasts.

Fig. 39. PPL photomicrograph of sintered glass shards with fluidal or plastic forms, from Wilcock et al. (2013).

Well-defined, cross-stratification or dune bedding is associated with low-concentration, turbulent pyroclastic density currents that are described as pyroclastic surge deposits (Maeno & Taniguchi, 2009; Sparks, 1976; Willcock et al., 2013). Expansion of external water and interacting with the erupting magma works to inflate the resultant surge allowing the deposition of pulsed, massive, planar, cross-stratified and dune-like bedforms (Maeno & Taniguchi, 2009; Wohletz and Sheridan, 1979). Pyroclastic surge deposits contrast with ignimbrites in that they are commonly crystal and lithic-rich with associated bedding structures (Sparks, l976). Bedding thicknesses of pyroclastic surge deposits are typically thin, have variable sorting of lithic and

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juvenile clasts (Brown, 2015), and many occur at the base of overlying ignimbrite deposits (Sparks, 1976).

CVC Pyroclastic Deposits The lithofacies identified in the CVC characterise typical features of ignimbrite and pyroclastic surge deposits, with an absence of pyroclastic fallout deposits. The two fine-ash fragmental silicic lithofacies are interpreted as the products of explosive fragmentation of silicic magma deposited from a rhyolitic, high-particle concentration pyroclastic density current (sections 4.3.5, 4.3.6). Observed structures within the fine-ash, crystal-rich, fragmental silicic lithofacies show low angle truncations of cross-stratified, welded, pumice-rich bedding (Fig. 30). The bedding structures indicate a pulsed, turbulent deposition of a pyroclastic surge deposit.

Tabular feldspar phenocrysts rarely are preserved as complete crystals in the CVC fragmental silicic lithofacies, with fragments of acicular quartz and feldspar phenocrysts forming a significant proportion of the matrix (>35%; Fig. 31a). The Belowra Creek exposure of the fine-ash, crystal-poor, pumice-rich, rhyolitic ignimbrite exhibits lapilli-sized pumice clasts that are flattened to form a fiamme texture, with wispy to sharp terminations and collapsed vesicles (Fig. 28). Lithics of mudstone and metapelitic sedimentary rock are common throughout the outcrop and have a larger proportion towards the base (15% modal). The majority of exposed crystal-rich rhyolitic ignimbrite presents massively textured, dense, structureless internal body with tabular to broken feldspar crystals (<3 mm), quartz spherulites (0.5 mm) and fiamme structures (1x5 mm) (Fig. 29).

The ignimbrites under thin section display compaction of glass shards, and in densely welded variations, the glass shards are completely flattened and arranged into a flow-like alignment characterising a well-defined eutaxitic texture (Fig. 30a). Fragments of quartz and feldspar phenocrysts make up a significant part of the ash matrix in the fine-ash, crystal-rich, fragmental silicic lithofacies (35%) with the large feldspar crystals generally stubby, tabular or equant (Table 2). In the crystal-rich fragmental lithofacies, angular fragments of coherent clasts of similar composition are common.

These characteristics provide evidence that the two fine-ash fragmental silicic lithofacies are rhyolitic ignimbrite deposits formed through explosive eruption processes and deposited by

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high concentration pyroclastic density currents with minor low-angle, cross-stratified pyroclastic surge deposits.

4.6.2 Coherent Volcanic Lithofacies of the CVC Effusive Eruptions Terrestrial lavas of all compositions form lava bodies with associated lithofacies which are generated from air-magma interactions at their top margins and substrate-lava interactions at their base. Lavas erupted subaerially form carapace breccia commonly described as autobreccia; formed due to the cooling of outer margins during flow (Fig. 40a). Autobreccia is monomictic and occurs as angular, blocky clasts or subrounded, rubble clasts up to several meters in diameter (Harris and Rowland, 2015; McPhie et al., 1993). Low viscosity volcanic extrusions (basaltic to intermediate composition) may also exhibit autobreccia margins; however, the breccia textures can exhibit spiny or scoriaceous-like textures, termed clinker clasts (Loock et al., 2010). Subaerial lavas may have associated quenched basal lithofacies due to interactions with paleosurfaces laden with water or water-saturated sediments (White, 2000). Quench breccias are dominantly formed by subaqueously erupted lavas.

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Fig. 40. a, Schematic cartoon from McPhie (1993) of subaerial silicic lava flow with a brecciated carapace above and below the flow of rhyolitic lava. b, Subaqueos silicic extrusion diagram showing peperite facies occurring at the basal contact (Rosa, 2016).

Subaqueously erupted lavas are characterised by the formation of associated breccias which form by quenching of the flow margins and can form pillow structures which are diagnostic of subaqueous emplacement (McPhie et al., 1993). Quench textures such as perlitic fracturing, curviplanar blocky clasts, and jigsaw-fit glassy clasts, indicate rapid cooling of hot magma (McPhie et al., 1993). Where quenching textures are preserved, and the matrix to the clasts is the parent lava, the breccia is interpreted as hyaloclastite. The textural differences between autobreccia and hyaloclastite can be subtle (McPhie et al., 1993). Hyaloclastite is the dominant breccia facies when formed in subaqueous environments due to extensive hydration

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of volcanic glass (Rosa, 2016), whereas autobreccia is expected to dominate the associated breccia facies when water is absent in subaerial emplacement environments. Where lavas flow into unconsolidated wet sediment, quenching and mingling of the magma with the sediment occurs at the basal contact (Fig. 40b) forming sediment-hosted breccia (Cas and Giordano, 2014; White, 2000). On margins of coherent igneous units where associated breccia lithofacies are sediment-hosted, show evidence of contact ‘baking’, exhibit gradation into fractured coherent lavas, and destruction of primary sedimentary structures, the breccia is interpreted as peperite breccia (White, 2000). Importantly, peperite breccia contacts represent marginal facies to coherent igneous rocks of any composition (White, 2000) and have been documented in modern and ancient volcanic fields (McPhie et al., 1993; Polo, 2018; Rosa, 2016).

CVC Volcanic Lavas Both the coherent silicic lithofacies and associated silicic breccia lithofacies exhibit associations of subaerially erupted rhyolite lavas on paleoground influenced by water and water laden sediments. Basal lava flow contacts are characterised by quench fragmentation of the coherent lava into monomictic breccias. Basal silicic peperite, with sediment-hosted monomictic rhyolitic breccia, is described at Stoney Creek (Fig. 24a). Hyaloclastite is observed at the basal contact at Buckenbowra River, where fine-grained rhyolite lava clasts are commonly preserved with a jigsaw-fit arrangement (Fig. 26) and displaying micro-scale quench textures such as perlitic fractures in thin section. The perlitic fracturing is indicative of silicic glass quenching on contact with water (McPhie et al., 1993).

Thin (<5 m) autobreccia units are preserved as monomictic breccias at the top of coherent silicic outcrops at Belowra Creek, Buckenbowra River, Quart Pot Creek and Burra Creek field sites. Thick autobreccia carapaces (>10m) are not observed in this study. Internal textures leading into the upper and lower margins of breccia facies include pumiceous lava (Fig. 20a) and massive to flow-banded glassy rhyolite (Fig. 19). Each coherent silicic lithofacies display a population of euhedral, tabular, unbroken (95%), feldspar phenocrysts of different size and percentage proportions, in a devitrified groundmass of micropoikilitic quartz and feldspar. The lack of peperite breccia at the upper contacts, the formation of blocky, poorly sorted, clast supported breccia as autobreccia carapaces, and the occurrence of hyaloclastite at the base of the outcrops indicate that the fine-grained, massive to flow-banded silicic coherent lithofacies and the porphyritic, massive textured silicic coherent lithofacies have erupted as subaerial rhyolitic flows on a paleosurface influenced by water. Analogous monomictic breccia

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associations are seen with other silicic lava flow models and examples (Fig. 41) from exceptionally exposed flows such as the Puy de Cliergue in southern France (Latutrie et al., 2017) and rhyolite flows of the Snake River Plain, USA (Bonnichsen and Kauffman, 1987).

Fig. 41. a. Schematic cartoon of a subaerial rhyolite flow internal variation and associated breccia facies from Fink & Manley (1987). b. Graphic log through the upper exposures of the Sanukayama rhyolite lava on Kozushima Island (Furukawa et al, 2019). c, Generalised graphic log from Hanson et al (2013) through an extremely thick (>300m) rhyolite flow from the Wichita igneous province, USA.

Coherent mafic lithofacies exhibit massively textured, crystalline cores with upper and lower margins commonly concealed. The mafic lithofacies are almost all interpreted as

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subaerial basalt flows due to the composition of the rock described by thin section analysis and associated fragmental and sedimentary lithofacies defining upper and lower contacts. Basal contacts display either sharp (Fig. 14a) or brecciated characters with the best exposure of basal peperite at Belowra Creek (Fig. 22). Upper margins of the coherent mafic lithofacies increase in fine vesicularity; however, upper contacts are rarely exposed. Other upper margins are marked by monomictic mafic breccia (Fig. 24) which is interpreted as autobrecciation of the coherent unit due to rubbly, poorly sorted, dominantly matrix poor, monomictic breccia. The internal domains of the basalts are homogenous and non-vesiculated with crude joints roughly perpendicular to regional strike. Such internal features of basaltic flows are common in documented subaerial flows (Barreto et al, 2014; Passey & Bell, 2007; Thordarson and Self, 1998). The field observations indicate that both mafic coherent lithofacies and intermediate coherent lithofacies erupted as subaerial lava flows. One exposure at the top of Buckenbowra River forms massive textured, bulbous structures, mimicking the idealised cross-section through basaltic pillow lava (section 4.2.3). The pillow structures indicate the possibility that this unit was emplaced subaqueously, but quench textures could not be defined due to advanced weathering.

4.6.3 Intrusions of the CVC Intrusive Bodies Intrusive igneous units have been documented in modern and ancient volcanic fields and can range from any composition (ultramafic to felsic), variably thick (0.5<100’s m), may or may not be conformable, display a range of internal textures similar to extrusive units, and are commonly associated with breccia facies with the clasts derived from the coherent igneous body (McPhie et al., 1993). Critical criteria for an intrusive origin is the igneous unit must have a primary upper contact or contact margin with overlying strata (McPhie, 1993; White, 2000). When intrusion into unconsolidated, wet sediment occurs, upper peperite contacts along top contacts are critical evidence of an intrusive origin for coherent units (Rosa, 2016; White, 2000).

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Fig. 42. Schematic cartoon of various environments in which peperite may form with interaction of wet sediment with magma, adapted from White (2000). Labels peperite are of intrusions (1), Feeder dyke intrusions of vent fill deposits (2), partly emergent domes (3), base of lavas (4), and margins of invasive lavas (5).

CVC Intrusions Intrusive units within the Comerong Volcanic Complex are rare with only one confirmed intrusive unit at the Quart Pot Creek field site. It involves the massive, sub-ophitic, phaneritic to porphyritic mafic coherent lithofacies with a sharp upper contact with a gravel-sized, polymictic, volcanogenic para-breccia (Fig. 34c). The basal contact of the basalt unit is not exposed. Small clasts of the basalt (<5 cm) are arranged in a jigsaw-fit texture with the sediment infilling fractures that grade into patches of jigsaw-fit, poorly sorted, matrix poor basaltic breccia with discoloured clast edges interpreted as hyaloclastite. The sediment-basalt mingling in this upper contact indicates syn-depositional emplacement and is critical evidence that this basaltic unit occurred as a shallow intrusion into unconsolidated sediment (McPhie et al., 1993; White, 2000).

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4.7 PALEOENVIRONMENT RECONSTRUCTION

The paleoenvironment of the CVC can be determined by the evidence from sedimentary and volcanic lithofacies. The interbedded sedimentary lithofacies within the CVC are a volumetrically small but important in providing a constraint on the environments responsible for their deposition. Similarly, the volcanic units that interact with these interbedded sediments also provide evidence through the emplacement mechanisms described previously.

4.7.1 Sedimentary Constraints on the CVC Paleoenvironment The massively bedded, polymictic, pebble to cobble-sized, para-breccia lithofacies comprises a mixed texture of pebble-sized subangular to subrounded clasts and angular matrix comprised of sand to gravel-sized clasts. This implies that the catchment area is sourcing detritus from both proximal and more distal sources. The large sizes of clasts and the dominant angularity within the unit suggest a terrestrial origin with proximal high topography close to deposition (Bowman, 2019). Sandstone units such as the fine to medium-grained, massive to planar-bedded, sandstone lithofacies indicate periods of traction controlled current flow. Terrestrial water-controlled deposition of sands is constrained to fluvial depositional environments such as braided and meandering river systems (Nichols, 2009). Mudstones such as the finely laminated mudstone lithofacies are constrained by low to very low energy deposition via settling from a standing water column. Terrestrial settings whereby low energy settling of fine-grained detritus can occur as overbank flood deposits in fluvial systems and lacustrine depositional environments (Nichols, 2009).

Overlying the CVC, the sedimentary facies association between the trough cross-bedded, para-conglomerate lithofacies, the medium to coarse-grained, planar to trough cross-bedded, sandstone lithofacies and minor laminated mudstone lithofacies indicates deposition in high energy, upper flow regime depositional environment. This is shown by the cross-cutting trough structures, the scarcity of fine-grained sediment interbeds, large individual bed thicknesses and coarse grain-size consistency throughout all field sites. The well-rounded clasts of nodular quartz and sandstone in the conglomerate indicate that transport of these clasts is distal from the originating source. The conglomerate lithofacies within the association occurs as truncating, lensoidal beds and also occurs interbedded within the trough cross-bedded sandstones. This is representative of a fluvial deposition rather than gravity-flow deposition. The outcrop section exhibits an absence of thick accumulations of ripple, planar fine sedimentary deposits but rather

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are scarce interbeds of planar laminated mudstone. These minor mudstone units are typical of braided river systems rather than thick accumulations of floodplain deposits of meandering river systems (Miall, 1977; Boggs, 2014). The thick accumulations of stacked trough cross-beds and erosive basal lags seen in outcrops are characteristic of channelised bar deposits within a braided (high-bedload) fluvial depositional system (Nichols, 2009). These associated lithofacies define a braided river association above the CVC.

4.7.2 Volcanic Constraints on the CVC Paleoenvironment A terrestrial paleoenvironment is indicated by the dominant air-magma breccia facies associations with the CVC lavas. The absence of pillow structures throughout the CVC lavas and the occurrence of quench breccias (hyaloclastite and peperite breccia) only as basal facies associations exemplifies a terrestrial paleoenvironment. The sedimentary lithofacies describe high proximal topography and water-controlled deposition of sands and settling of very fine- grained sand and mud. A terrestrial paleoenvironment comprising these sedimentary units can be ascribed to fluvial and lacustrine depositional environments. Both fluvial and lacustrine depositional environments are common in modern volcanic terranes (Riggs, 2001), with examples such as the Western Snake River Plain, USA, the East African Rift and the Taupo Volcanic Zone, NZ.

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Chapter 5: Geochemical Analysis Results

Twenty-two rock samples were analysed for whole-rock major and trace element geochemistry. Lithofacies that have been sampled for geochemical analysis include rhyolitic lavas, rhyolitic ignimbrites, intermediate lavas and basaltic lavas. The samples are here referred to as silicic, intermediate and mafic compositional groups. Three of the silicic samples are derived from ignimbrite and have been sourced from texturally massive, unstratified, interiors of ignimbrite units that are largely absent of lithic clasts to ensure that stratification bias and contamination is limited. All samples have been prepared with care to remove heavily weathered sections, and for ignimbrites, the presence of foreign clasts. Some samples comprise high percentages of greenschist facies alteration minerals. These altered samples are marked in the tabulated whole-rock geochemistry in Appendix C, with Weak, Moderate and Strong used to describe the intensity of alteration. Location of sample sites is given in Fig. 12.

Two samples constitute handpicked separates from the magma mingling outcrop at Buckenbowra River (10.7 P&D; Appendix C). The two handpicked separates have been excluded from trace element results due to the small amounts of cross-contamination.

5.1 ALTERATION

Alteration in Comerong Volcanic Complex samples is variable with loss of ignition (LOI) in the samples ranging from 0.63 to 4.52% with an average LOI of 2.4%. Mafic samples all have variable chlorite alteration identified by petrography. The chemistry of the intermediate and silicic samples plot in the field for sericite and carbonate in the LOI vs ANCK plot from Bull (2008; Fig. 43).

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Fig. 43. Intermediate and Silicic samples plotted on the LOI vs ANCK (molar Al2O3/ (K2O+CaO+Na2O)) modified from Bull et al. (2008). Samples all plot deep in the Sericite ± Carbonate field indicating sericitic alteration in all intermediate to felsic samples. Sample ID references analyses in Appendix C.

The chemical index of alteration (CIA) after Nesbitt and Young (1982), calculated for the mafic, intermediate and silicic samples give ranges of 54.5 to 60.7, 55.2 to 64.4 and 56.5 to 64, respectively. These range values for the compositional groups indicate that all samples have undergone a degree of weathering in mobile major elements (Nesbitt and Young, 1982). Classification and interrogation studies with the use of mobile elements (K, Na) should be considered with caution for those samples showing large scatter and hence use of immobile trace elements is preferred.

5.2 COMPOSITION CLASSIFICATION

The three compositional groups identified through petrology for the Comerong Volcanics are visible on the Total Alkali Silica (TAS) diagram (Fig. 44). Because of the potential spread in alkali elements, the TAS diagram may be unreliable. Immobile element classification is preferred in order to geochemically classify the CVC samples. The elements of interest are Zr, Nb, Y, Ti and Ga, which are shown to be resistive to alteration under greenschist facies conditions (Morisson, 1978; Floyd and Winchester, 1975).

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Fig. 44. Comerong Volcanic Complex samples plotted on the Total Alkali Silica (TAS) diagram after Le Bas et al. (1986).

The classification plot of Pearce (1996) discriminates the three petrographic groupings (Fig. 45). The mafic samples plot in the field for basalts (green). The intermediate samples mostly plot in the andesitic fields, with one sample in the basalt field (blue). Four of the silicic samples plot in the field for rhyodacites and two samples plot in the field of alkali rhyolite (red/pink). The three compositional groups are further referred to by these new naming terms (rhyolite, andesite, basalt) and used to interrogate the geochemistry dataset.

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Fig. 45. Rock classification diagram using the immobile elements Zr/Ti vs Nb/Y, after Pearce (1996). Rhyolitic samples coloured red/pink, andesitic coloured blue and basaltic coloured green.

5.3 MAJOR ELEMENT CHEMISTRY

The data from this study is shown on Harker diagrams where silica is used as the fractionation index in Fig. 46, with additional rhyolite data from Wyborn and Owen (1986), and basalt to andesite data from Dadd (2011). The dataset shows more mobile elements such as

P2O5 and CaO have a larger spread than the more immobile TiO2 and Fe2O3 major elements.

The basalts have a narrow range in silica from 45 to 52%. The elements TiO2, MgO and

Fe2O3 are more tightly clustered with positive trends for TiO2 and Fe2O3 and a negative trend for MgO. The CaO results show a large scatter between 45 to 54% with no fractionation trend. The basalts of this study are similar to the Currowan Creek Basalt Member (CCBM) and Dingo

Road Basalt Member (DRBM) low-Ti endmembers of Dadd (2011), with TiO2 no greater than

2.5%. All basalt data clusters on the P2O5 vs SiO2 well, with the exception of the DRBM high- Ti endmembers.

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Fig. 46. Harker diagrams of major elements vs silica. This study’s data points shown as triangles and data from Dadd (2011) shown as diamonds. Data is within 2% error of BCR-2 SRM.

The andesitic samples have a large range in silica from 50.6 to 63% (silica range from basalt to andesite). Negative fractionation trends are shown for all major elements except MgO, which shows a flat trend between the BAM samples of Dadd (2011) and this study’s andesitic samples. The samples collected in this study form the negative trends in contrast to the BAM samples which cluster tightly.

The rhyolite samples of this study and Wyborn and Owen (1986) show negative to flat trends in the major elements with greater scatter in Al2O3. Separation of two groups of rhyolitic

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samples is apparent within the silica range of 68 to 78%. The TiO2 and Fe2O3 Harker plots show greater negative slopes with CaO and MgO showing flat trends.

5.4 TRACE ELEMENT CHEMISTRY

Trace element Harker diagrams are presented where silica is used as the fractionation index in Fig. 47, with additional data from Wyborn and Owen (1986), and basalt to andesite data from Dadd (2011). For all compositional groups Zr, Nb, Cr, and La cluster the data well or define clear fractionation trends.

Basalt samples of the CVC exhibit immobile element ratios of Zr/Nb ratios of 0.62 to 0.68, Th/Ta ratios of 1.6 to 2.3, and Nb/Y ratios of 2.3 to 2.95. The basaltic data collected in this study is uniform with only small differences in Cr, Sr and Al2O3. All basaltic data clusters well on the Y, Nb and Zr Harker plot with the DRBM high-Ti member clearly separated from the dataset (Fig. 47). The basalt trace element chemistry shows a large scatter in Cr.

The andesitic samples do not cluster well with the BAM of Dadd (2011) due to the larger range in silica. The basaltic andesites with SiO2 concentrations below 52% (similar silica to basalt samples) have immobile element ratios of Zr/Nb ratios of 0.14, Th/Ta ratios of 5 to 6.2, Nb/Y ratios of 1.9 to 2.2 and have MgO values from 2.8 to 4.2. These immobile element ratios contrast with those of the CVC basalts. Andesitic samples show flat fractionation trends against silica for Cr, Ta, Nb and La with negative trends in Y and Zr (Fig. 47). The plagioclase compatible elements, Sr and Eu, are also negatively correlated with silica.

Rhyolitic samples of the CVC have high Zr (270<370 ppm, av. 393 ppm), Y (44<97 ppm, av. 66 ppm), Nb (13.6<51.6 ppm, av. 26 ppm), and moderate Ga (13.4<16.7 ppm, av. 16.1 ppm) compared to I-Type granite compositions of the Bega Batholith (Collins et al., 1982). The elements of Al2O3 and Zr are negatively correlated with increasing silica. Enrichment of highly charged elements such as Zr, Nb, Y, and most REE’s is characteristic of the CVC rhyolites. Most trace elements show large scatter on against silica (Fig. 47), with a negative trend in Zr.

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Fig. 47. Harker diagrams of trace elements vs silica. This study’s data points shown as triangles and data from Dadd (2011) shown as diamonds. Standard Reference Material (SRM) percentage error values given for each element. Geological reference materials are USGS SRM AGV-2 and BCR-2. National Institute of Standards and Technology, NIST-610 glass to complement as a non-geological SRM.

Rare earth element (REE) plots normalised to C1 Chondrite after Mcdonugh & Sun (1995) show enrichment of light rare earth elements (LREE) and flattened heavy rare earth

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elements (HREE) for all samples (Fig. 48). Basalt samples are slightly LREE enriched (La/Yb; 3.2<4.8) with one sample exhibiting a negative Eu anomaly (0.88). Andesitic samples are overall more enriched in all REE relative to the mafic samples, but with near identical LREE enrichment (La/Yb; 4.3<7) and more pronounced negative Eu anomalies (0.72). Rhyolitic samples mostly overlap the LREE of the intermediate samples but have lower HREE (La/Yb; 7<11.2) and with more significant Eu anomalies (0.40). Two silicic samples have anomalously low LREE.

Fig. 48. REE plots of rhyolitic, andesitic and basaltic compositions, normalised to C1 Chondrite after Mcdonough & Sun (1995). Colour key taken from classification plot in Fig. 45.

5.5 RELATIONSHIP BETWEEN MAFIC AND INTERMEDIATE SAMPLES

Primitive mantle normalised multi-element variation diagrams demonstrate significant differences between the andesitic and basaltic units of the CVC (Fig. 49 a-b). The mafic rocks show a relatively smooth trend with anomalies only present in elements expected to be affected by alteration such as Cs and Rb. In contrast, the intermediate samples demonstrate negative Nb, Ta, Sr and Ti and positive anomalies in Th, Pb and Zr and Hf.

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The discriminatory diagram of Pearce and Norry (1979) show the CVC basaltic samples plot in the within-plate field (Fig. 49c). Also plotted are the basaltic andesites and basalts of Gamble et al. (1993) representing samples from a continental arc to back-arc rift setting. CVC andesite plots adjacent to the Within Plate Basalt (WPB) field whereas the Taupo Volcanic Zone (TVZ) back-arc samples show a spread from volcanic-arc to Mid-Ocean-Ridge Basalt (MORB), with some minor overlap with the WPB field. The within-plate field characterises rocks erupted from intraplate settings such as oceanic island basalts and continental basalts (Pearce and Cann, 1973; Pearce and Norry 1979). The plot of the mantle array of Pearce (2008) allows for an assessment of whether volcanic rocks are derived from mantle melting versus volcanic arcs and/or have undergone crustal contamination. The CVC basalts plot near Enriched MORB (E-MORB) compositions and are displaced towards the volcanic arc array with a distinct curvature towards the deep crustal recycling domain whereas the andesitic samples plot in the volcanic arc array (Fig. 49d). The basaltic data of Dadd (2011) shows considerable spread from this study’s basaltic samples, whereas the andesite samples agree well with this study’s andesitic samples and cluster within the volcanic arc array.

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Fig. 49. a, MORB normalised multi-element variation diagram for andesitic and basaltic compositons. Normalisation values from Pearce (1982). b, Primitive mantle normalised multi-element variation diagram for andesitic and basaltic compositions. Normalisation values from Sun and McDonough (1989). c, Zr/Y vs Zr of Pearce and Norry (1979) to discriminate between Volcanic Arc (VA), Mid-oceanic-ridge-basalt (MORB) and Within-Plate basalts (WPB). d, Th/Yb vs Nb/Yb discrimination diagram from Pearce (2014) separating the MORB-OIB array and subduction-related settings.

5.6 AFFINITY OF SILICIC SAMPLES

Discriminatory diagrams and REE plots of silicic CVC samples show similarities to other studies on voluminous rhyolitic volcanism both regionally in the Lachlan Orogen and from studies in the Southern Oklahoma Rift Zone, USA (Boro, 2015, Bull et al., 2008, Raymond et al., 1998). REE of the Comerong Volcanic Complex overall displays a similarity to these other regions with both datasets showing enrichment of LREE and flattened HREE (Fig. 50c). The CVC and Ural Volcanics both display negative Eu anomalies that are equally depleted.

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All rhyolitic samples plot as A-type on the Zr vs Ga/Al plot of Whalen et al. (1987) along with the Ural and Mt Hope Volcanics, Arbuckle Mountains and averaged Dulladerry Volcanics samples (Fig. 50a). The A-type classification of Whalen et al. (1987) is used to define a compositional type of magmatism related to the melting of anhydrous, salic crustal sources. The dataset plots within the A2 field of Eby (1992) and the ‘Within-plate Granite’ and A2 classification field of Pearce et al. (1984) (Fig. 50b,d). The A2 classification characterises silicic rocks from magmas that are derivatives of continental crust or produced through magmatic underplating during orogenesis or subduction complexes. In contrast, the A1 classification suggests magmas derived from mantle sources with similar trace element abundances to Oceanic Island Basalt.

The Comerong Volcanic Complex rhyolitic samples are majority ferroan based upon Fe* number, have Alumina Saturation Index values of 1.3 to 1.7 (ASI), and a Modified Alkali Lime Index (MALI) range of 5.69 to 11.17, following the classification schemes of Frost and Frost (2001). The samples show these are A-type, ferroan, calc-alkalic, peraluminous rhyolites with A2 type affinities.

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Fig. 50. a, A, I, S, M-type melt discriminatory diagram of Whalen et al. (1987). b, A1 and A2 type discriminatory diagram of Eby (1992). c, REE spider diagram normalised to C1 Chondrite after McDonough & Sun (1995). d, Granite discrimination diagram of Pearce et al. (1984), with fields of Within-plate granite (WPG), Oceanic Ridge granite (ORG), and Volcanic Arc Granite + synchronous Collision Granites (VAG + synCOLG). Comerong Volcanics data plotted with data from the Ural and Mt Hope volcanics (Bull et al., 2008), Arbuckle Mountains (Boro, 2015) and Dulladerry volcanics (Raymond et al., 1998).

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Chapter 6: U-Pb Geochronology Results

Three samples sites were used for zircon sampling. The lowermost sample in the stratigraphy is located at the base of the fine-grained, massive to flow-banded rhyolite at Stoney Creek (sample D9.2). The uppermost sample is from the fine-ash, crystal-rich, rhyolitic ignimbrite at Buckenbowra River (sample D13.1). The third sample is from the fine-ash, crystal-rich, rhyolitic ignimbrite at Burra Creek (sample D17.6). Sample positions are also displayed in Fig. 12. These ranged from good to poor with total sample weights, and zircons picked in Table 5. The samples separated for zircon collectively provided a total of 364 grains for analysis by tape mounted ablation.

Of the zircon fraction analysed via tape mounting, 18% were identified as concordant from the Stoney Creek Rhyolite, 13% from the Buckenbowra River Ignimbrite and 37% from the Burra Creek Ignimbrite. The very low concordance of these results can be attributed to the intersection of contaminants, as the majority of imaged zircons revealed melt inclusions and fractures observed under transmitted light microscopy and cathodoluminescence response. The discordancy is produced from the disruption of the uranium and lead isotope ratios by the intersection of the laser with radiogenic Pb enriched inclusions and fractures with initial non- radiogenic Pb (Seydoux-Guillaume, 2015). The Pb enrichment can be visually shown by using the whole dataset for each sample on Tera Wasserburg Concordia plots, where a model 1 fit (York regression) of the discordant points trends towards a 207Pb/206Pb ratio of 1 and a lower crystallisation discordia intersection (Villa and Hanchar, 2017)(Fig. 51). All zircon populations, Concordia and Discordia ages are summarised in Table 6.

Table 5. Zircon recovery, aspect ratio (AR) range of complete euhedra and percentage of zircon fragments analysed. Sample ID Sample Weight (g) Recovered Zircon Range of AR % Zircon Fragment 9.2 420 103 2.2-5 22% 13.1 550 121 1.4-4.5 38% 17.6 410 140 1.8-3.4 47%

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Stoney Creek Rhyolite

Buckenbowra River Ignimbrite

Burra Creek Ignimbrite

Fig. 51. Terra Wasserburg diagrams of raw data of zircons extracted from field samples. York regressions shown as thin red line intersecting lower concordia. Plots generated in Isoplot (Ludwig, 2008). Sample coordinates: D9.2 - 150°03’04”E, 35°27’46”S; D13.1 - 149°58’09.6”E, 35°36’27.1”S ; D17.6 - 149°59’00.8”E, 35°53’57.5”S.

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Polished zircons for analysis of interior to rim domains record more concordant analyses with 90 from 160 analyses returning as concordant. The definition of interior and core domains is adopted from Storm et al., (2011) and Asmussen (2018) where interiors are undefined central zones with inconclusive boundaries identified by cathodoluminescence response or under transmitted light microscopy, whereas cores are identifiable by the same means.

The secondary zircon standard Plešovice ages indicate that session’s one and two are within analytical error, however the third analytical session is elevated with an age difference of 2Ma out of error range (Table 7). This difference in analytical age shows there is the possibility of a small age drift in session 3 results.

Table 6. Zircon ages from tape mounted ablations and polished mount ablations. The accepted emplacement ages are shown in bold. See text for discussion. Abbreviations: TW – Terra Wasserburg; W.Av. – Weighted Average. Session Sample Sampled Sample TW W.Av. Age Inherited Rejected % ID Lithofacies Preparation Discordia grains/ Analyses Concordance Age populations of Total

1 D9.2 Fine- Tape 392.2 ± 8.1 391 ± 3.7 Ma 414 ± 7 Ma 380 ± 9 18% grained, Mount Ma (MSWD=0.92, (MSWD=1.2, Ma (n=1) Massive to (MSWD=14, n=9, n=3, flow- n=103) POF=0.49) POF=0.29), banded 434 ± 7.2 Ma Rhyolite (MSWD=0.33, n=4, POF=0.81), 452 ± 16 Ma, 544 ± 24 Ma (n=1) Polished 388 ± 4 Ma 554 ± 21 Ma 54% Mount (MSWD=0.99, (n=1) n=14, POF=0.46)

2 D13.1 Fine-ash, Tape 384 ± 13 Ma 380.5 ± 4 Ma 837 ± 30 Ma 273 ± 8 13% Crystal- Mount (MSWD=35, (MSWD=1.6, (n=1) Ma (n=1), rich, n=119) n=4, 353 ± 9 Rhyolitic POF=0.19) Ma (n=1) Ignimbrite Polished 387.3 ± 4.5 897 ± 27 Ma 67% Mount Ma (n=1) (MSWD=1.4, n=12, POF=0.15)

3 D17.6 Fine-ash, Tape 388.1 ± 18.5 384.1 ± 5.6Ma 504 ± 37 Ma, 350 ± 18 37% Crystal- Mount Ma (Relative 624 ± 33 Ma, Ma, rich, (MSWD=23, Misfit =0.933) 630 ± 77 Ma, 354 ± 18 Rhyolitic n=140) 785 ± 47 Ma Ma, Ignimbrite (n=4), 364 ± 36 398 ± 4 Ma Ma, (MSWD=0.49, (n=1) n=31, POF=0.49) Polished 388.7 ± 7.4 507 ± 21 Ma, 62% Mount Ma 615 ± 19 Ma, (MSWD=0.13, 727 ± 38, n=4, 1030 ± 140 POF=0.94) Ma, (n=4)

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Field samples chosen for zircon extraction were also tested for the potential to promote new autocrystic zircon growth upon emplacement. This check is important to determine if the measured zircon rim domains record the emplacement age of the zircon and do not represent earlier stages of growth (antecrystic/xenocrystic). It is expected that the samples chosen for zircon separation are from zircon saturated melts since all samples are high silica melts

(SiO2<70%; Siegel, 2018), and show abundant zircon crystals present under thin section. Fig.

52 shows that all samples plot within the Antecrysts + Autocrysts field of the TZircsat vs TZircTi plot after Siegel (2018) assuming a Ti activity of 1. Following the zircon saturated character of the host rocks, the high silica content and abundance of zircon identified under thin section, it can be confidently determined that the original melt of all rhyolitic samples separated for zircons could grow autocrystic zircon upon final emplacement (c.f. Siegel, 2018).

Table 7. Plešovice ages in all analytical sessions. The standard age of 337.13±0.37 Ma Slama et al. (2008). Session Plešovice Age Sample Preparation Samples Analysed 1 340 ± 6 Ma Tape Mount D9.2, D13.1 2 339 ± 5 Ma Tape Mount D13.1, D17.6 3 341 ± 2 Ma Polished Mount D9.2, D13.1, D17.6

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Fig. 52. TZircsat vs TZircTi plot after Siegel (2018) for concordant tape mounted analyses. Samples are annotated with Stoney Creek Rhyolite in blue, Buckenbowra River Ignimbrite in yellow and Burra Creek Ignimbrite in green.

6.1 STONEY CREEK RHYOLITE (D9.2)

Zircons from the fine-grained, massive to flow-banded rhyolite sample at Stoney Creek (D9.2) are larger on average (150 μm) than zircons from the Buckenbowra River and Burra Creek Ignimbrite samples. Complete euhedra range in aspect ratio (AR) from 1:1.5 to 1:5 with 22% of the picked grains fragmented or broken. Notably, there are several very large complete crystals (200-350 μm, 2.2-3.3AR) with distinct cores in contrast to the main population lacking distinct core domains. The zircons show abundant melt inclusions with roughly one-third of all complete zircon crystals fractured through the centre domains/cores (Fig. 54). In contrast to other samples derived from fragmental lithofacies, the Stoney Creek Rhyolite sample incorporates a population of relatively large (130 μm), high aspect ratio (1:3<) zircon and

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fragments with diameters sharply contrasting with all other zircon samples (60 μm). High aspect ratio zircon crystals are expected from the rapid cooling conditions of extruded lavas (Corfu et al., 2003).

6.1.1 Tape Mount Age From the 103 grains prepared on a tape mount, 19 analyses met analytical criteria for concordance. The sample provided 18 analyses to discriminate emplacement age with one analysis returned with an age of 544±24 Ma. This analysis at 544 Ma is excluded from further consideration because it plots as an outlier with respect to the bulk of analyses within 380-450 Ma and is considered as an inherited age. The youngest population of zircons are shown by the linearised probability plot in Fig. 53. Each analysis in this youngest population has shown through uncorrected 238U/206Pb ages and corrected 238U/206Pb ages to be concordant in both cases with the exception of one age at 380±9 Ma which has been excluded (youngest age point on Fig. 53a). This population produces a weighted average age of 390.7±3.7 Ma (MSWD=0.92). The remaining eight analyses show a spread of ages from 405 to 450 Ma and are interpreted to be the result of mixed ages from partially ablating antecrystic zones beneath thin autocrystic rims during analyses.

a b

Fig. 53. Tape mounted concordant analyses for D9.2. a. Linearised probability plot with the youngest population of zircon indicated by black field. b. Weighted mean of the 9 analyses of the youngest population.

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6.1.2 Polished Mount Age Cathodoluminescence imaging of polished zircons from this sample reveals thin autocrystic rims along the long axes of complete zircon crystals with an average thickness of 10μm (Fig. 54). Melt inclusions are rounded and associated with the interior of most crystals. Darker interior domains are recognised and are associated with fractures propagating through the crystal (Fig. 54b). Thirty polished zircons were analysed with 69 ablations yielding 37 concordant analyses. Targeted ablation of zircon rim domains provides an age of 387.6±4.1 Ma (MSWD=0.99) from 14 concordant analyses (Fig. 55).

The polished age is within error of the age provided by the tape mounted analyses. The polished mount ablations are restricted to the 20μm laser spot size, and some mixing of antecrystic zones may have occurred as shown by Fig. 54. Due to this possibility the age of emplacement is recognised as the tape mounted weighted average age of 390.7±3.7 Ma, which is almost identical to the discordia intercept age of 391.2±8.1 Ma (Fig. 51a).

381±14 Ma 390±16 Ma 385±15 Ma 554±21 Ma

a b

387±18 Ma 396±14 Ma 398±16 Ma 394±17 Ma

c d

Fig. 54. CL images of representative D9.2 zircons showing oscillitry zonations, fluidal melt inclusions and fractures intersecting inner domains. Scale bars represent 20μm.

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Fig. 55. Polished zircon concordant rim analyses for D9.2. Weighted mean of the 14 analyses.

6.2 BUCKENBOWRA RIVER IGNIMBRITE (D13.1)

The fine-ash, crystal-rich, rhyolitic ignimbrite sample at Buckenbowra River (D13.1) yielded 121 grains from a 550g sample. The zircon range in size from 60 to 150 μm with aspect ratios 1:1.4 to 1:4.5. The zircons are commonly fractured or have sharp, irregular breakages. The majority of the zircon grains rarely exhibit euhedral/unbroken crystal morphologies and are typically 80 to 100 μm with aspect ratios of 1:2. The zircons within this sample are expected to have a higher percentage of fragments due to the explosive processes involved during pyroclastic density currents (section 4.6.1). It is also expected that this sample may contain xenocrystic zircon which can be attributed to the incorporation of accidental lithic clasts during deposition of the ignimbrite unit.

6.2.1 Tape Mount Age From the D13.1 sample separated for zircon, 121 grains were recovered and analysed via on-tape ablation. The analysed zircons had the lowest recorded concordance, with only 14 analyses meeting analytical criteria. Such low percentages of concordance are attributed to the ablation of heavily fractured grains intersected from the 30μm spot size. One analysis yielded

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an age of 837±30 Ma interpreted as an inherited grain from Neoproterozoic rocks. Two analyses record young ages of 273.3±7.7 Ma and 353±9.4 Ma. The ~273 Ma zircon is interpreted as sample preparation contamination as it is the only grain exhibiting a younger age inconsistent with the bulk majority of concordant ages. Cathodoluminescence imaging confirms the morphology of this zircon differs from the remaining population with a rounded, resorbed core and equally rounded growth zonation (Fig. 56). This young grain is therefore not considered further. The ~353 Ma grain is considered to have suffered from subtle Pb loss due to the accidental intersection of a large central fracture that crosscuts the body of the crystal.

Of the eleven tape mounted concordant analyses, four provide a young population on the linearised probability plot with a weighted mean of 381±4 Ma (MSWD=1.6)(Fig. 57a). The slightly elevated MSWD may indicate that these analyses represent two subpopulations, but due to the small number of concordant results, it cannot be constrained further on tape mounted ablation results. The 381±4 Ma age population also has a larger spread on the probability density plot, potentially indicating Pb loss. The other concordant analyses plot as a spread of ages from 390Ma to 420 Ma (Fig. 57a), likely to be the result of mixed ages between thin autocrystic rims and antecrystic zircon.

395±17 Ma 270±10 Ma 380±16 Ma 278±14 Ma

a b

Fig. 56. CL images of D13.1 polished zircon. a. Zircon yielding age of ~380 to 395 Ma with large central fracture, typical of the main zircon population. b. Contaminate zircon yielding age of ~273 Ma, showing

anhedral, resorbed growth rims and white core. Scale bars represent 30 μm.

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a b

Fig. 57. Tape mounted concordant analyses for D13.1. a. Linearised probability plot with the youngest population of zircon indicated by black field. b. Weighted mean of the 4 analyses of the youngest population.

6.2.2 Polished Mount Age Cathodoluminescence images of Buckenbowra River Ignimbrite zircons show melt inclusions are common throughout the picked grains, which influenced the spot sites for targeting rim and interior/core domains (Fig. 58). Zircon rim ablations provided thirteen concordant analyses with one analysis at 357 Ma, statistically rejected in the Isoplot processing due to the function identifying it as an outlier to the main population. The remaining twelve analyses have a weighted mean of 387.3±4.5 Ma (MSWD=1.4) (Fig. 59).

This rim age is within error overlap of the tape mounted age of 381±4 Ma and the discordia age indicated by the whole tape mounted dataset (Fig. 51b). The emplacement age of this ignimbrite is accepted as the polished mount weighted average age of 387.3±4.5 Ma due to the larger number of analyses considered (relative to the tape mount age), the successful ablation of rim domains and the lowered MSWD.

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378±12 Ma 386±17 Ma 389±12 Ma 397±15 Ma

a b

396±20 Ma 385±15 Ma 389±14 Ma

c d

Fig. 58. CL images of representative D13.1 zircon grains and fragments. All grains show oscillitry zonations, fluidal melt inclusions and fractures intersecting inner domains. Scale bars represent 30 μm.

Fig. 59. Polished zircon concordant rim analyses for D13.1. Weighted mean of the 13 analyses, with one rejected age (blue).

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6.3 BURRA CREEK IGNIMBRITE (D17.6)

Zircons extracted from the fine-ash, crystal-rich, rhyolitic ignimbrite sample at Burra Creek (D17.6), show a large proportion of zircon crystal fragments (47%), similar to Buckenbowra River Ignimbrite zircons. There are two crystal morphologies observed within this sample. One population (9%) is translucent under transmitted light microscopy, large relative to the overall grain population (135 μm) and displays dark cores with planar growth rims. The cores of this large population display rounded boundaries indicating periods of resorption (Corfu et al., 2003). Rim domains on this population have a similar luminescence response to the main population and maintain tetragonal crystal morphology. The dominant population (91%) comprises euhedral, stubby grains with aspect ratios from 1:1.7 to 1:2.4 and lengths from 70 to 100 μm. The interior domains of this population have a similar luminescence during cathodoluminescence imaging to the zircon rim domains.

6.3.1 Tape Mounted Age From the 140 tape mounted zircons, 52 met the analytical criteria for concordance. Four of the analyses are inherited zircons with ages of 504±37 Ma, 624±33 Ma, 630±77 Ma, and 785±47 Ma and thus are not considered further. The remaining 48 concordant results plotted as a weighted average produce a 390± .1 Ma age with an MSWD of 3.6 and a zero probability of fit. The elevated MSWD suggests that the analytical errors are underestimated or there is non- analytical scatter indicative of multiple age populations (Ludwig, 2008). The linearised probability plot of the 48 points shows a small younger population of five analyses (Fig. 60). The significant spread of young ages in this indicated population with the absence of clustered points might indicate Pb loss or an inadequate common Pb correction for these analyses (Bryan et al., 2004). Inspection of this population shows the accidental intersection of large fractures identified by transmitted light microscopy and cathodoluminescence response; hence they are rejected. The remaining concordant analyses provide a Gaussian distribution with the absence of a clear youngest population. The “unmix” function after Sambridge & Compston (1994) is used here to determine the youngest and oldest age population within these data. The unmixing function yielded an age of 384.1±5.6 Ma and 410.7±7.5 Ma with a relative misfit of 0.933. The unmix function has identified the youngest population from results obtained from on tape ablation conducted to intersect autocrystic zircon rims. However, laser drilling of antecrystic domains beneath thin autocrystic rims is the likely cause of the older age spread in the results.

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The conventional method of targeting autocrystic rims on polished mounted zircon is consequently required to provide confidence to this ‘unmixed’ youngest age.

Fig. 60. Tape mounted concordant analyses for D17.6. Linearised probability plot with the youngest population of zircon indicated by black field.

6.3.2 Polished Mount Age Polished grains gave thirty-seven analyses of which six analysed the outermost rims. The linearised probability plot shows a small population of four analyses providing a weighted mean of 388.7±7.4 Ma (MSWD=0.13) (Fig. 61). The small number of analyses combined with the errors produces a low MSWD of 0.13. Interrogation of the whole D17.6 dataset, including core and interior analyses, was required to resolve the lack of reliable age data. Interior analyses yield a weighted average age of 388.4±8.3 Ma (MSWD=2.6, n=10, POF=0.005) suggesting the interiors of analysed zircon are either autocrystic or subtly antecrystic. Fig. 62a-b shows representative cathodoluminescence images of zircon with rim-interior analyses of the same age and inherited zircon with autocrystic rims (within sessional error). The cathodoluminescence images show that grains yielding young ages are typically characterised by thick autocrystic zircon growth on the apex of crystals whereas inherited zircon is

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characterised by low aspect ratio interiors/cores or a resorbed rounded morphology indicative of stages of zircon undersaturated conditions (Fig. 62c-d). In most cases, cores are luminescent with or without small dark centres.

a b

Fig. 61. Polished zircon concordant analyses for D17.6. a. Linearised probability plot with the youngest population of zircon indicated by black field. b. Weighted mean of the 4 analyses of the youngest population.

Excluding inherited ages of 1030±140 Ma (rim), 615±19 Ma (interior), and 727±38 Ma (Interior), the eighteen concordant analyses of interior and rim ablations were processed via the “unmix” function in Isoplot (Sambridge & Compston, 1994), following the method outlined by Siegel (2018). The function provided a youngest age of 388.3±4.2 Ma and older age of 412.5±10 Ma with a relative misfit of 0.894. The youngest unmixed age agrees with the suggested youngest age from the tape mounted analyses (384.1±5.6 Ma) and is almost identical to the weighted average of the rim analyses (388.7±7.4 Ma). Owing to the high probability of mixed ages impacting tape mounted age data, the almost identical age indicated by the unmix age function and the similarity to the whole population discordia age (Fig. 51c), the emplacement age for the Burra Creek Ignimbrite is accepted as the weighted average of 388.7±7.4 Ma (MSWD=0.13) from targeted zircon rim analyses.

Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW 129

386±17 Ma 389±15 Ma 397±12 Ma 396±15 Ma

a b

392±14 Ma 387±14 Ma 615±19 Ma 507±21 Ma

c d

Fig. 62. CL images of D17.6 zircon. a-b. Interior-Rim analyses with ablation ages indicating zircon growth in one system. c-d. Core-Rim analyses indicating inherited cores with new autocrystic zircon growth. Scale bar represents 30 μm.

6.4 EMPLACEMENT TIMING SUMMARY

The Comerong Volcanics Complex 238U/206Pb dates of 390.7±3.7 Ma for sample D9.2, 387.3±4.5 for D13.1, and 388.7±7.4 for D17.6 indicates that the volcanism occurred within a four million year period in the early-Eifelian (Fig. 63). The synchronicity of these dates shows the volcanics were emplaced rapidly because the sample sites for the extracted zircons are located at the basal and capping felsic units, thus timing the duration of felsic and intercalated sedimentary and basaltic volcanic units.

The Eifelian stage is proposed as occurring from 393.3±1.2 Ma until 387.7±0.8 Ma referencing the International Chronostratigraphic Chart (Cohen et al., 2013). The error proposed by these dates indicates that the Comerong volcanism could extend into the Emsian stage (Early Devonian) and the Givetian stage (late-Middle Devonian). There is some overlap

130Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

of the age errors and the proposed dates for the Tabberabberan Orogeny from Vandenberg et al. (2000) and Rosenbaum (2018). The age overlap with the deformation ages of Rosenbaum (2018) suggests the CVC volcanism is syn-Tabberabberan, however, the main age period proposed by the CVC samples is pre-Tabberabberan orogenesis when considered against the more constrained age of Tabberabberan deformation from Vandenberg’s (2000) work in the Tabberabberan Zone of the CLO.

Comerong Volcanic Complex

Fig. 63. Timeline of orogenic events recognised in the Lachlan Orogen from: A – Vandenberg et al. (2000) and B - Rosenbaum (2018). Comerong Vocanic Complex dates indicated in blue and age error in green dash. Timeline constructed after the International Chronostratigraphic Chart after Cohen et al. (2013).

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Chapter 7: Discussion

7.1 STRATIGRAPHY AND EMPLACEMENT MODEL OF THE COMERONG VOLCANIC COMPLEX

7.1.1 Stratigraphic Architecture of the Comerong Volcanics on the Eastern Limb of the Budawang Synclinorium The results of this study show similar thickness and lithologies to the fence diagram of Dadd (2011) for the Budawang Synclinorium eastern limb (Fig. 8), which is the only other stratigraphic study of the Comerong Volcanics. However, there are some differences in the occurrence of rhyolite and basalt units as well as the extent of the CVC’s basal breccia to the fence diagram of Dadd (2011). The stratigraphy produced in this study (Fig. 64) is subdivided into six packages comprising different stages of distinctive sedimentation and volcanism. The CVC packages, from oldest to youngest, are the Lower Breccia Package, Intermediate Volcanic Package, Lower Felsic Package, Lower Mafic Package, Upper Felsic Package and the Upper Mafic Package. The compiled CVC stratigraphy occurs between the basal Ordovician metapelite lithofacies of the Mallacoota Beds and an overlying braided river association described in section 4.7.1.

The Comerong Volcanic Complex has an unconformable contact with the underlying Mallacoota Beds. This is shown by the deposition on an erosional surface by the massively bedded, polymicitic, pebble to cobble-sized, para-breccia (Stoney and Belowra Creek) and the massive, fine-grained, aphyric basaltic andesite (Fig. 32a; Fig. 15a). This observed unconformity is noted by many studies throughout the ELO where Ordovician, fine to medium- grained turbidite and shale deposits are overlain by Silurian to Devonian sediments and volcanics (Fergusson et al., 1979; Giordano and Cas, 2001; Glen, 1990; McIlveen, 1975; Steiner, 1972).

The overlying braided river sedimentary deposits closely compare to the work of Glen (1990) in the Budawang synclinorium, where a braided fluvial sequence was described, comparable to the Twofold Bay Formation described by Steiner (1972) in the Eden area to the south of the CVC. The depositional environment of the Twofold Bay Formation is interpreted as an alluvial fan overlain by a transitioning braided to meandering river sequence (Steiner, 1972). Wyborn and Owen (1986) also recognised a conglomerate unit overlying the Comerong Volcanics, which passes into a sequence of purple, quartzo-feldspathic, lithic arenite and red

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shale or siltstone in fining upward cycles. Although this conglomerate and fining upward cycle of medium-grained arenite and siltstone was observed, Wyborn and Owen (1986) made no formal interpretation on the depositional environment except indicating that it was similar to the Late Devonian Gundillion conglomerate. The braided river association identified through this study is interpreted as part of the Two Fold Bay Formation (TFBF) of Steiner (1972) for simplicity, however the recognition of this fluvial system may not be directly linked with TFBF sediments of the Eden-Merrimbula area until a detailed provenance study combining data from both regions can be accomplished.

The CVC is also in unconformable contact with overlying para-conglomerate lithofacies comprising the base of the TFBF. This is shown by the leached cap of the Burra Creek porphyritic, massive textured rhyolite, described in section 4.3.4. This weathered (and/or eroded) contact is interpreted as a time break between the emplacement of the volcanics and the deposition of the TFBF. Conjecture surrounds the contact between the Merrimbula Group and Boyd Volcanic Complex in the Eden area, and similarly several authors disagree whether the CVC upper contact is conformable or at least disconformable (McIlveen, 1975). Due to the observations of the contact at Burra Creek, and the abrupt change in sedimentation, the contact between the CVC and the overlying TFBF is interpreted as a disconformity.

Stratigraphic sections throughout the eastern limb of the Budawang Synclinorium show variable thicknesses in correlated volcanic and sedimentary lithofacies. The thickest mapped traverse is at Buckenbowra River (1196 m), where all stratigraphic packages can be found and ordered into relative age. Each package is interpreted in order from oldest to youngest with mention of defining lithofacies and the distribution along the eastern limb of the Budawang Synclinorium.

134Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

Fig. 64. Stratigraphy of the Budawang Synclinorium eastern limb. Correlations shown by highlighted bars and referenced in the legend. Emplacement ages indicated with samples D9.2, D13.1, and D17.6.

Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW 135

Lower Breccia Package The Lower Breccia Package (LBP) comprises the massive bedded, polymictic, pebble to cobble-sized, para-breccia lithofacies (section 4.4.1). The package extends from Belowra Creek to Stoney Creek, encompassing a strike distance of at least 6.9km and a thickness ranging from 40 to 80 m. The LBP is missing from Buckenbowra River, Quart Pot Creek and Burra Creek field sites. It is possible the LBP underlies the Quart Pot Creek stratigraphy because the contact with basement Mallacoota Beds is marked by an interpreted fault (fault zone <5 m thick). Similarly, deposition of the LBP could extend as far south as Burra Creek because all outcrop beneath the volcanic units was eroded or concealed.

The massive bedded, polymictic, pebble to cobble-sized, para-breccia lithofacies is interpreted as forming from a proximal region of high topography with mixed source components. This lithofacies reflects high energy deposition and restricted extent throughout the volcanic field. The LBP deposit characteristics are consistent with an alluvial fan depositional environment. Current understanding on alluvial fan proximal to distal facies defines the deposits as proximal to a high-topography source basin (Bowman, 2019) as evidenced by the meter-sized clasts and clast angularity (section 4.4.1). Alluvial fans are dominated by coarse-grained sediment and may have fan head radii from 1 to 20 km from the source and thicknesses up to several hundred meters (Hartley et al. 2010), which is consistent with the 6.9 km strike distance observed between Stoney Creek and Belowra Creek and maximum thickness of 80 m.

Steiner (1972) has described a basal conglomerate with interbeds of lithic arenite overlying the Mallacoota Beds in the Eden area on the NSW south coast, which he named the Quarantine Bay Member and interpreted as forming in a talus slope or alluvial fan to braided stream depositional environment. The LBP in this study is unlikely related to the Steiner’s Quarantine Bay Member due to the distance from Eden but may relate to a similar period of uplift and erosion along the NSW south coast.

Intermediate Volcanic Package The Intermediate Volcanic Package (IVP) consists of basaltic andesite and andesite flows of the massive, fine-grained, aphyric basaltic andesite (section 4.2.1) and minor massive, sparsely porphyritic andesite (section 4.2.4) and the massive to planar bedded, polymicitic, pebble to cobble-sized, volcanogenic para-conglomerate (section 4.4.4). This package is

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thickest at Buckenbowra River with a total stratigraphic thickness of 220 m and also occurs as a 20 m thick lava flow unit at Stoney Creek where it overlies the LBP (Fig. 26c). The IVP is distinguished from the LBP by the presence of andesitic flows and volcanoclastic debris flows. The IVP lavas are interpreted to be emplaced as low volatile, crystal-poor lava flows emplaced onto a terrestrial paleosurface as evidence by sharp contacts observed between the alluvial fan deposits of the LBP (terrestrial) and absence of pillow structures indicating a subaqueous emplacement.

The interbedded massive to planar bedded, polymicitic, pebble to cobble-sized, volcanogenic para-conglomerate incorporates clasts of silicic volcanics, basement metapelite and minor mudstone clasts. This indicates silicic volcanics, mudstones and metapelite were being actively eroded and redeposited with the emplacement of the andesitic volcanic units. The silicic volcanic clasts are very similar in colour and texture to the fine-grained, massive to flow-banded rhyolite lithofacies; however, this cannot be interpreted as direct evidence of synchronous volcanism, as no underlying silicic lithofacies are known and there is no geochemical or geochronological evidence to link these clasts to CVC rhyolites.

Lower Felsic Package The fine-grained, massive to flow-banded rhyolite (section 4.2.5) and fine-ash, crystal- poor, pumice-rich, rhyolitic ignimbrite (section 4.3.5) with minor units of the fine to medium- grained, massive to planar-bedded, sandstone, constitute the Lower Felsic Package (LFP). This silicic volcanic package records a maximum thickness at Belowra Creek of 380 m with a total strike length of 25.5 km. The package is dominated by rhyolite lava flows of the fine-grained, massive to flow-banded rhyolite with the fine-ash, crystal-poor, pumice-rich, rhyolitic ignimbrite comprising only 15% of the total stratigraphic thickness. At Stoney Creek and Buckenbowra River, the rhyolitic ignimbrite is absent. These silicic lithofacies are notably aphyric in most outcrops with rare, tabular feldspar phenocrysts only within the interior of the Stoney Creek rhyolite. This observation distinguishes the LFP from UFP. The LFP behaves like the LBP, thinning southward where it is last recorded as two rhyolite lava flows comprising a 112 m thick stack at Buckenbowra River.

The rhyolite lavas of the LFP indicate a subaerial emplacement onto paleoground influenced by water, as evidenced by peperite and hyaloclastite breccias in the basal contacts (section 4.6.2, Fig. 25, Fig. 27). The contacts are with the fine to medium-grained, massive to

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planar-bedded, sandstone lithofacies at Stoney Creek and Buckenbowra River interpreted as the result of a fluvial depositional environment (4.7). At Buckenbowra River, sandstone is interbedded between two rhyolite flow units indicating that fluvial sedimentation was occurring between stages of volcanism.

Lower Mafic Package The Lower Mafic Package (LMP) extends 25.5 km in strike length, between Belowra Creek in the north to Buckenbowra River in the south. The thickest outcrop occurs at Belowra Creek with a thickness range of 270 m and thinnest exposure at Buckenbowra River of 80 m. This package thins from north to south, similar to the LBP and LFP. At Belowra Creek, the LMP includes the the massive, sub-ophitic, phaneritic to porphyritic basalt (section 4.2.2), minor mud-rich, matrix-supported, polymictic breccia (section 4.4.2), and one minor outcrop of fine-grained, massive to flow-banded rhyolite (section 4.2.5). Other LMP exposures consist of the sub-ophitic, phaneritic to porphyritic basalt. Synchronous felsic and mafic flows characterise the LMP, with intercalated, lateral emplacement of basalt and rhyolite flows at Belowra Creek and magma mingling textures of both compositions identified at Buckenbowra River.

The Belowra Creek LMP comprises the best-preserved outcrop of peperite in the study area. Peperite is direct evidence for synchronous volcanism emplaced into a water-saturated environment (White, 2000). Most other upper and lower contacts from basalt flows of the LMP are concealed however a westward younging of the outcrops is supported by an increase in amygdale abundance and size towards the west and therefore the inferred upper margins of basalt outcrops. An increase in vesicularity towards the upper margins of basalt lava flows (pahoehoe and A’ā) has been modelled from ancient and current volcanic fields (c.f. Loocke et al., 2010; Passey and Bell, 2007; Thordarson and Self, 1998).

Upper Felsic Package The Upper Felsic Package (UFP) is the thickest (646 m, Buckenbowra River) of the CVC packages and overlies the LMP, with a strike length of 57 km. The UFP is inferred to have a larger strike extent based upon distinctive topographic ridges identified in high-resolution satellite imagery. The package is found at every field site; thickening towards the centre of the eastern limb at Buckenbowra River. The Buckenbowra exposures record a total thickness of

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630 m of the porphyritic, massive textured rhyolite and fine-ash, crystal-rich, rhyolitic ignimbrite lithofacies. In the northern exposure of Belowra Creek, the UFP consist of 50 to 80 m thick units of the fine-grained, massive to flow-banded rhyolite lithofacies. The southern field sites of Burra Creek, Quart Pot Creek and Buckenbowra River all display a composite stratigraphy of lavas and ignimbrites indicating that mechanisms for pyroclastic eruptions were more common in the southern CVC during this phase of felsic volcanism. Poorly exposed, minor fluvial deposits of the fine to medium-grained, massive to planar-bedded, sandstone are found at the base of Burra Creek and overlying the rhyolite volcanic package at Quart Pot Creek (Fig. 64).

Upper Mafic Package The massive, sub-ophitic, phaneritic to porphyritic basalt and massive, medium-grained, equigranular, plagioclase-rich basalt lithofacies comprise the Upper Mafic Package (UMP). It has a thickness at Quart Pot Creek of 120 m comprised of lava flows and an intrusion of the phaneritic to porphyritic basalt with sedimentary units of the finely laminated, silt to clay- grained, mudstone (section 4.4.3) and polymictic, imbricated, gravel-sized, volcanogenic para- breccia lithofacies (section 4.4.6). Buckenbowra River is the only other site with this package, where it has a thickness of 45 m. The UMP occurs within the central part of the study area and is absent in the northern and southern extensions of the eastern limb.

Past work on the CVC at Quart Pot Creek by Wyborn and Owen (1986) noted that pillow basalts were exposed along with fine clastics, such as shales, siltstones and sandstones. Pillow structures were not observed at Quart Pot Creek during this study; however, the porphyritic basalt lithofacies was exposed with undisturbed laminated mudstones conformably overlying the unit. Further up stratigraphy the massive, sub-ophitic, phaneritic to porphyritic basalt forms a dyke intrusion into the overlying gravel-sized, volcanogenic para-breccia lithofacies (Fig. 64). This study cannot determine if the UMP basalt at Quart Pot Creek was subaqueously emplaced due to the absence of pillow structures and associated quench breccias.

Extensions to Known Stratigraphy This stratigraphic study of the eastern limb of the Budawang Synclinorium is similar to the study of Dadd (2011) and observations by Wyborn and Owen (1986). However, there are some variances that are important in the interpretation of the CVC volcanic event. These

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similarities and differences are summarised in a block fence diagram for each CVC package in Fig. 65, and discussed below by examining each interpreted package.

Breccia at the base of the Comerong Volcanics has been noted by Conolly et al. (1969) and McIlveen (1975) where it is described as a fine to medium-grained conglomerate or boulder conglomerate with intercalated arkosic sandstone. Alternatively, Dadd (1992) noted a sedolithic breccia-conglomerate-sandstone facies at the base of the volcanic sequence. The matrix to the LBP breccia comprise gravel to pebble-sized clasts of the basement Mallacoota Beds, and a significant proportion of the breccia also comprise silicic volcanic clasts indicating the presence of a pre-CVC silicic volcanic event.

The IVP of this study is comparable to the Buckenbowra Andesite Member (BAM) of Dadd (2011), however the IVP extends to the Stoney Creek field site, whereas Dadd mapped the extent of the BAM to the centre of the CVC with outcrops extending for a 3 to 4 km strike length on the Budawang eastern limb. In this study, the tuff breccia, lapilli tuff and fine-grained chloritic tuff facies of Dadd, (2011) were not recognised but may comprise variances in the volcanogenic para-conglomerate lithofacies recorded as part of this study.

The LFP shows both thickness variations and lithology variation in comparison to the Lower Rhyolite Lava of Dadd (2011). This study identified a fine-ash, crystal-poor, pumice- rich, rhyolitic ignimbrite lithofacies at Belowra Creek, in addition to rhyolite lava flows. All studies show that the lower rhyolitic phase in the Comerong stratigraphy is dominated by coherent rhyolite lava flows.

The LMP closely resembles the Dingo Road Basalt Member (DRBM) described by Dadd (2011) as sparsely amygdaloidal, sparsely porphyritic to porphyritic and intercalated with lacustrine sedimentary deposits. One difference is that in this study, a 20 to 30 m thick unit of the fine-grained, massive to flow-banded rhyolite is recorded at Belowra Creek. This rhyolite unit had no preserved marginal contacts and may be an intrusion associated with the UFP or as a lava flow that was synchronous with the emplacement of the LMP basaltic lava flows. It is a minor constituent of the LMP and is an additional observation to the comparable DRBM.

The UFP has a number of distinct differences to the Upper Rhyolite Lava described by Dadd (2011). The thickness and occurrence of ignimbrite units are described as rare, whereas this study has identified large (>300 m) occurrences of the fine-ash, crystal-rich, rhyolitic ignimbrite at Burra Creek and Buckenbowra River with minor units at Quart Pot Creek. Wyborn and Owen (1986) mapped the Comerong Volcanics in the south of the Budawang Synclinorium

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and proposed that there was approximately a 1:1 ratio of rhyolitic ignimbrites and lavas. This observation is supported by this study’s results in the UFP southern field sites (Burra and Quart Pot Creek).

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Fig. 65. Fence diagram incorporating the stratigraphic packages of this study with block stratigraphy of Dadd (2011). Columns of this study are shown with an asterisk in place of the letters of Dadd (2011).

142Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

7.1.2 Implications of the Comerong Volcanic Complex Geochemistry The Comerong Volcanic Complex details a history of volcanic phases that have geochemical affinities indicative of the tectonic environment responsible for their generation. The CVC rhyolite and basalt define a bimodal suite of volcanics with magma mingling at Buckenbowra River in both rhyolite and basalt units (sections 4.2.2 and 4.2.5) and interfingering volcanism at Belowra Creek. The phases of volcanic activity propose a multi- stage history of volcanism overlying the Mallacoota Beds unconformity.

The basalts of the CVC show slight plagioclase fractionation indicated by Al2O3 and strong olivine fractionation indicated by steep negative trends in Cr ppm. Most scatter is seen in CaO, likely due to the observed alteration (Fig. 46; Fig. 47). Basalt samples in this study are similar to the DRBM low-Ti and CCBM members of Dadd (2011) and show weak evidence for crystal fractionation trends with the exception of Al2O3. The CCBM displays considerable variability in comparison to this study’s basalts. The DRBM high-Ti of Dadd (2011) clearly separates from the majority of basalt samples on all major and trace element Harker plots and commonly is comparable to andesitic samples with very similar MgO, Al2O3, Cr, and Y. This indicates the high-Ti DRBM had a similar fractionation history to the andesitic samples.

Bimodal Rhyolitic and Basaltic Volcanism Bimodal volcanism is a characteristic of rift settings in many tectonic environments including continental rifts (Bonnichsen and Kauffmann, 1987; Hughes et al., 2002; Mazzarini et al., 2004). The Comerong Volcanics have been considered as part of a rift structure since the work of McIlveen (1975). Two rift settings could fit proposed models of the Lachlan Orogen environment of a west-dipping subduction system. The models consist of a continental back- arc rifting setting, comparable to the Taupo Volcanic Zone of New Zealand or a continental (intraplate) rift setting away from plate margins such as the Snake River Plain of the western USA. The lack of data for the position of the subduction system active at the time of late- Lachlan orogenesis has been identified by detailed reviews on the Lachlan Orogen evolution (Coney, 1992). The position of the volcanic arc during the Devonian has been suggested as offshore of the current NSW coast, but if it was proximal to the CVC, a back-arc rift tectonic setting would be plausible. Determining the CVC tectonic affinity as either arc-related rifting or within-plate rifting is consequently important for interpreting the cause of magmatism.

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The basalt and rhyolites of the CVC are distinct in that the chemistry indicates a within- plate tectonic affinity (section 5.5 and 5.6). The rhyolites are classified as A-type, ferroan, calc- alkalic, peraluminous rhyolites. A-type silicic rocks in southeastern Australia have had a major focus on plutonic bodies, with weakly peraluminous, A-type granites interpreted as the products of high temperature, small partial melts of a crustal source via mantle upwelling (King et al., 1997). A-type plutons and lavas have been linked with within-plate, extensional geodynamic settings (Bonin, 2007; Frost, 2011). Furthermore, they are generally associated with mantle- derived mafic rocks (Grebennikov, 2014) or have isotopic compositions indicative of a large mantle input (Bonin, 2007).

The A2 classification of Eby (1992) indicates that the source for the A-type rhyolites is derived from melting of a crustal source that had undergone modification due to magmatic underplating from continental collision or arc-related volcanism. This signature is plausible since the I-type Bega Batholith was emplaced prior to the rifting of the Comerong Volcanics and the region was expected to have experienced a subduction history during the Ordovician to Silurian. The Ural and Mt Hope volcanics have been suggested as a within-plate rift based upon the volcanic facies, 238U/206Pb isotope ages and bulk rock geochemistry (Bull et al., 2008). These magmas also plot in the A2 classification of Eby (1992) and have comparable enrichment of incompatible REE to the CVC rhyolites (Fig. 50). While the classification scheme of Eby (1992) is not diagnostic on its own, as shown by Medlin (2015), and the classification cannot always clearly discriminate rocks of intraplate settings (as shown by Arbuckle Mtns samples; Boro, 2015), it does provide information on the melt source for the rhyolitic lavas. In addition, the zircon inheritance of Precambrian core ages (Table 6) shows that melting sampled a Precambrian crustal source to produce the A-type, CVC rhyolites (>540 Ma).

Observed flow distances for rhyolite domes rarely exceed several kilometres from the source vent (Bonnichsen and Kauffmann, 1987) and there has been past conjecture of long transport distances for silicic lava flows (Manley, 1996). The CVC rhyolite lava flows contrast with short flow lengths typical of high silica lavas in that they have been interpreted to flow lengths greater than 18 km (Dadd, 1992b). The high-temperature magmas with long distance transport of the CVC rhyolite is interpreted by Dadd (1992b), due to low bubble content in outcrop, and proposed comagmatism with A-type plutons characterised by an anhydrous melt composition, high F contents and high Zr-saturation temperatures (e.g. Monga, Mongmulla granitoids; Wyborn and Owen, 1986). Similarly, the paucity of vesicles or vesicular horizons found in this study, with high (>850°C) zircon saturation temperatures (Fig. 52) agrees with

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previous interpretations that the CVC rhyolites erupted as high temperature, low volatile lavas capable of long transport from source vents. Furthermore, the low crystal contents of both coherent rhyolite lithofacies identified in this study and the thickness of the lavas likely due to high-topography ponding of the lava flows would also contribute to the low-viscosity rheology, allowing them to flow further than typical rhyolite lava flows.

The basaltic geochemistry supports a mantle-derived source composition. This is shown by the similarities to enriched mantle source compositions such as E-MORB and OIB, without the strong negative Nb-Ta, Ti, Zr and Hf anomalies characteristic of island arc tholeiite (Fig. 49a-b; Condie, 2015; Gamble, 1993; Pearce, 1982). There is a weak Nb-Ta anomaly in CVC basalts on the MORB and Primitive mantle normalised multielement variation diagrams. However, this anomaly contrasts with the pronounced Nb-Ta depletion of the CVC andesitic compositions. The plot of the CVC basaltic compositions on the mantle array of Pearce (2008) in Fig. 49d, suggests a crustal contamination component displacing the data towards the transitional field with a vector towards the deep crustal recycling domain. Crustal contamination modelling by Pearce (2008) of enriched mantle source compositions supports this observation (Fig. 49d). Traditional trace element ratios from Condie (2015), such as Zr/Nb, Th/Ta and Nb/Y ratios (Table 8), fail to unequivocally determine if the basalts fall within the ranges of volcanic arc basalts (subduction influenced) or ocean island basalts (intraplate). It should also be noted that the oceanic island basalt ratios are built from empirically constrained values from magmas that have no influence from contamination effects of continental crust. Contamination of continental crust is expected to preferentially enrich LREE and LIL elements such as Ba, Th, Pb and Rb. This would explain the inconclusive indications from classical trace element ratios used to differentiate intraplate from subduction-related magmas.

Table 8. Key trace element ratios characteristic of volcanic arc basalts and ocean island basalts. Ratio ranges taken from Condie (2015). Values highlighted blue relate to volcanic arc ratio ranges and green highlight ocean island basalt ratio ranges. Sample ID Nb/Th Zr/Nb Th/Ta Nb/Y Nb/La La/Yb La/Nb FeOT D5.6 8.2 15.944 1.791 0.344 0.731 4.381 1.368 9.339 D5.6B 6.898 17.383 2.065 0.271 0.65 4.884 1.54 10.015 D6.6 6.762 17.138 2.037 0.3 0.653 4.697 1.533 9.651 D6.7 7.012 17.603 2.013 0.3 0.934 3.196 1.071 10.1265 D15.6 6.367 16.877 2.356 0.338 0.732 4.15 1.366 10.857 D16.11B 5.821 16.933 2.633 0.334 0.697 4.603 1.435 11.992 D7.3 2.087 24.926 5.555 0.225 0.520 4.371 1.922 12.279 D11.2B 1.797 29.908 6.908 0.265 0.512 5.061 1.952 13.805

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The CVC basalts are similar to the incompatible trace element signature of the Grande Ronde basalt flows which comprise the bulk of the Columbia River Basalt Province (CRBP) in the western USA (Hooper & Hawkesworth, 1993). The CRBP shows enrichment of LIL elements in comparison to HREE, and weak Nb and Ta values, which has been attributed to melt contamination by a subcontinental lithospheric mantle component (Hooper and Hawkeworth, 1993; Wolff and Ramos, 2013). The CRBP is interpreted as the manifestation of extensive asthenospheric melting via the upwelling of a mantle plume head. Such an interpretation for the CVC was first suggested by Dadd (1992) and applied as a regional hypothesis for the EVZ. Key characteristics such as radial dyke swarms, uplift and doming of the region and recognition of a hotspot track are absent in both the preserved outcrop of the CVC and in the Lachlan Orogen. Despite the lack of evidence for the melting mechanism, the basaltic chemistry implies an enriched mantle source lacking in strong subduction signatures that has experienced a degree of crustal contamination.

Significance of the Intermediate Volcanic Package The IVP comprises a unique part of the CVC with andesitic lavas interpreted to be generated by convergent margin processes. The composition of some IVP lavas is within 3wt% silica of the CVC basalts and displays different trace element signatures. The lavas of the IVP show key subduction-related influences on incompatible trace element variations, exhibited by strong negative Nb, Ta and Ti anomalies (Pearce, 1982). The trace element signatures of arc magmas are understood to be generated by fluid-flux melting of the mantle wedge in subduction complexes (Condie, 2015; Gamble, 1993). The absence of outcropping contacts between the IVP and LFP units makes identifying conformable or unconformable relationships difficult. The stratigraphy shows the IVP lavas are not a reoccurring lithofacies, do not interfinger with the overlying bimodal volcanics or constitute part of the uppermost stratigraphy. Whether these lavas constitute a remnant volcanic arc, post-exhumation of the basement Mallacoota Beds and prior to CVC bimodal volcanism is difficult to indicate confidently. Incompatible element chemistry may provide valuable information to either separate or incorporate the flows of the IVP into the same volcanic event through genesis as a hybrid magma through mixing.

Dadd (2011) interpreted the andesites of the CVC as highly fractionated equivalents to the CVC basalt. The emplacement of the most evolved mafic lavas before the most primitive

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would be less likely as the most evolved, fractionated melts of CVC basalts would be expected to erupt after the most primitive because the andesites would require residence time to fractionate in the crust before reaching the surface. If the IVP lavas are derived from fractionation of the basaltic compositions, the depletions in Nb, Ta and the variable enrichment in LIL elements cannot be explained by the strong fractionation of olivine, pyroxene and plagioclase as evidenced by the large Sr and Cr depletions (Dadd, 2011). Harker plots crudely suggest plagioclase, olivine and Fe-Ti oxide fractionation trends in the elements Al2O3, Fe2O3 and Cr from CVC basalts to andesites. Higher degrees of crustal contamination with fractionation of Fe-Ti oxides would be required to satisfy the positive LIL element anomaly (Fig. 49b) and the negative Nb-Ta anomaly. The trace element chemistry would require either a complex interplay between crustal contamination of a basaltic parental magma and the fractionation of plagioclase, olivine and Fe-Ti oxides or formation in a convergent margin with a long residence time in the crust to fractionate plagioclase.

Field observations such as the magma mingling, ‘marble cake’ texture observed at Buckenbowra River in both rhyolitic and basaltic outcrops suggest the two bimodal end- member magmas were unable to homogenise to form andesitic, hybrid compositions prior to cooling. Mixing of the basalt and rhyolite is therefore considered unlikely. Furthermore, the overlap in enrichment between the CVC rhyolitic and andesitic samples argues against a mixing model from parental basaltic compositions and therefore the IVP lavas are considered to be a separate magmatic event to the other CVC packages (Fig. 48).

Reference to the Stratigraphic Architecture The stratigraphy of the CVC in relation to the geochemistry results shows that volcanism was periodical with synchronous (magma mingling) and interfingering phases of intraplate mafic and silicic volcanics, underlain by a period of possible arc-related, andesitic volcanism. The IVP intermediate volcanics are a minor stratigraphic component in contrast to the bimodal CVC volcanics. The IVP age must be older than the CVC rhyolite (390.7±3.7 Ma, LFP sample D9.2) and younger than 467 to 443 Ma Mallacoota Beds fossil ages (McIlveen, 1975).

The bimodal volcanism was active in the northern margin of the Comerong basin as rhyolite and basalt lava flows that thin towards the south. In the south of the study area, the rhyolitic volcanism is marked by an increase in explosive rhyolitic volcanism and decreasing mafic volcanism. This trend is also reflected by the regional mapping of Wyborn and Owen

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(1986). The explosive rhyolitic volcanism is accompanied by perlitic fractures in cognate clasts within the fine-ash, crystal-rich, rhyolitic ignimbrite (section 4.3.6) indicating the hydration of cooling glass (McPhie et al., 2003). This is evidence for water entrainment in the pyroclastic density currents during the eruption and reinforces the interpretation that the CVC ignimbrites where produced by phreatomagmatic activity which requires magma interaction with surficial or groundwater sources (Lorenz, 1987). Phreatomagmatic activity is also supported by the dominant ash-rich matrix of the CVC ignimbrites due to the efficient fragmentation of magma during interactions with superheated water (Brown, 2015). At Burra Creek the very thick, fine- ash, crystal-rich, rhyolitic ignimbrite with well-developed eutaxitic texture (moderate to intensely welded), flow-banding structures in outcrop, and the very high temperatures indicated by zircon saturation temperatures (D17.6, Fig. 52) indicate a hot, high concentration pyroclastic density current that was proximal rather than distal to the source vent (Gooday et al., 2018; McPhie et al., 1993). Analogous examples to the CVC ignimbrites, of proximal, thick (>100 m), welded ignimbrites, include the Ora Ignimbrite, in Italy (Willcock and Cas, 2014) and the ignimbrite deposits of the Arran caldera, in Scotland (Gooday et al., 2018).

7.1.3 Emplacement Model for the Comerong Volcanic Complex The emplacement model for the Comerong Volcanic Complex incorporates the spatial distribution of the stratigraphic packages from north to south along the eastern limb of the Budawang Synclinorium. The correlated western limb data from Dadd (2011) indicates that the UMP is much thicker to the west with minor occurrences of the LFP and LMP. The development of the CVC stratigraphy through time and the depositional model reflects the superposition of the stratigraphic packages.

Small, incipient back-arc rift basins are proposed to have formed as part of a Late Silurian subduction system west of Canberra, approximately 150 km west of the present CVC (Dadd, 1998). There is evidence of an accretionary complex on the NSW south coast, which is postulated to have formed in the Silurian subduction system, post-Benambran Orogeny (Miller and Gray, 1996; Miller and Gray, 1997). The position of the arc front is not mentioned by any study; however, this short-lived Late Silurian subduction system may provide a candidate for the small accumulation of andesitic IVP lavas emplaced before the bimodal CVC volcanics and after exhumation of the basement Mallacoota Beds.

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Following the Bindian-Bowning orogenic event, the ELO experienced an extensional period lasting until the Tabberabberan Orogeny (Glen, 2013). Glen (2013) calculated a minimum regional extension of approximately 260 km from trench retreat until the subduction zone was offshore of the NSW coast by the Early to Middle Devonian (Rosenbaum, 2018). This would create a large area of thinned lithosphere in a broad continental back-arc basin with very high heat flow, similar to the western USA (Hyndman, 2005). There is not enough evidence from this study to determine the likely mantle mechanism for melting; however, the CVC basalts indicate a clear within-plate signature, distal from the effects of subduction. This interpretation is reinforced by the absence of key subduction related signatures such as strong Nb, Ta and Ti negative trace element anomalies (Fig. 49), lack of widespread high-alumina basalt characteristic of back-arc-basin basalts (>17wt%; Gamble, 1993), elevated incompatible REE’s between E-MORB and OIB compositions, within-plate basalt classification and the bimodal association with rhyolites characterised as A-type, intracontinental felsic melts.

The model of the CVC rift is interpreted as part of a larger Silurian-Devonian basin described by Fergusson (2010) as the Newell Basin. The Newell Basin theory recognises Silurian-Devonian sedimentary deposition and volcanic emplacement was widespread in the ELO, and that the remnants of the past volcano-sedimentary successions are confined to basins formed by younger deformation events and eroded to produce the present topography (Fergusson, 2010). The CVC would occupy the eastern extent of the proposed Newell Basin. The mountainous region proposed to occur east of the CVC and source for the LBP deposits, is recognised as part of a basement high existing on the edge of the ELO (Fergusson, 2010).

The CVC packages are interpreted to fill an extensional rift basin with bounding regions of high topography to the east-northeast of the study area that was responsible for the development of the LBP deposits observed at Belowra and Stoney Creek (Fig. 66). These deposits are overlain by the andesitic arc-related volcanics of the IVP that were potentially emplaced during a magmatic event related to subduction from the Early Silurian (~444 Ma) to Early Devonian (~419 Ma). These andesitic lavas were emplaced as thick lava flows (10-30 m) on Ordovician Mallacoota Beds (section 4.2.1) and in sharp contacts with LBP sedimentary breccias (section 4.3.3).

The bimodal volcanism of the CVC begun in the earliest Middle Devonian with early rhyolitic (LFP) and mafic (LMP) subaerial volcanism active in the north. The lavas are characterised by autobreccia carapaces and basal quench breccias as a result of interactions with water-saturated sediments deposited in a terrestrial setting with an active fluvial depositional

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environment (sections 4.3.4, 4.3.1). The extreme thicknesses of the rhyolite lava flows are likely the result of high topography (evidenced by LBP deposits) in the rift zone that ponded the lavas, similar to well documented examples of very thick, extensive and ponded felsic lava flows (c.f. Bonnichsen and Kauffman, 1987; Parker et al., 2017; Polo et al., 2018; Silva, 1994). Furthermore, the rhyolites were likely erupted from fissure vents as has been shown to be effective at erupting rhyolite lavas effusively rather than explosively (Loewen et al., 2017). The rhyolite lava flows were subject to slow cooling in the extremely thick units, evidenced by the wide (>2 m) columnar joints and pervasive devitrification textures under thin section (section 4.2.5). The magma mingling of the rhyolite and basalt lava flows indicates the volcanic plumbing system was linked at depth, with periodical volcanism possibly caused by new injections of mantle derived mafic melts below the rift.

This transitioned to a later phase of explosive rhyolitic volcanism in the south with a higher proportion of ignimbrites with associated lava flows (UFP), overlain by variably thick (5-30 m) accumulations of subaerial basaltic lavas and dykes (UMP). The ignimbrites were emplaced as very to extremely thick (100-300 m), variably to intensely welded, rheomorphic ignimbrites characteristic of proximal, plinian to phreatoplinian sized eruptions, which fed pyroclastic density currents by a fountaining eruption column. This emplacement mechanism is interpreted as comparable to the intra-caldera Ora Ignimbrite eruption (Wilcock et al., 2013) due to the high-grade of welding, unit thicknesses (> 200 m), rheomorphism and dominance of ash-sized pyroclasts. Extra-caldera deposits of the Ora ignimbrite and other distal ignimbrite deposits commonly range in thicknesses from 5-100 m (Milner et al., 2002; Moran-Zenteno et al., 2004; Riggs and Busby-Spera, 1991; Wilcock et al., 2013) which contrast with the thick ignimbrite deposits of the CVC. Lacking the remnant topography of an ancient caldera landform, the CVC ignimbrites are here interpreted as proximal to the source vent/vents rather than an inferring the ignimbrites as intra-caldera deposits.

Following a depositional hiatus, the first of the Merrimbula Group sediments were deposited as a fining-upward sequence, braided river system over the rift basin prior to E-W contraction in the Kanimblan orogenic event to form the Budawang Synclinorium (Glen and Lewis, 1990). The sediment source for the Merrimbula Group is unknown, but it is expected to be a distant source region demonstrated by clast maturity of large, rounded, nodular quartz clasts in the basal conglomerate (4.4.8) and was possibly initiated by Tabberabberan orogenic uplift of the source region.

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Fig. 66. Schematic emplacement model for the Comerong Volcanic Complex from 395 to 385Ma. A1 – IVP lavas with an autobreccia carapace (Ab) emplaced over LBP and basement Mallacoota Beds. B1 – Generalised section through LFP lava with an autobraccia carapace, crystalline core (Cc), and basal peperite with matrix derived from underlying sediments (Pb). B2 – Silicic ignimbrites formed through collapse of eruption columns. B3 – Bimodal magmatism with LMP and LFP magmas mingling (Mm) at depth and in erupted lavas. C1 – UMP basaltic volcanism intruding lake sediments (In). C2 – UFP explosive and effusive volcanism in the southern CVC derived from the same magma source. Colour coding of packages follows stratigraphic log correlations. Note point sources are for illustration and do not indicate true positioning of original volcanic edifices.

7.2 TEMPORAL RELATIONSHIP WITHIN THE EASTERN LACHLAN OROGEN

Comparisons with past Chronostratigraphic Chart The international chronostratigraphic chart of Cohen et al. (2013) used in this study is the modern age chart used to categorise the emplacement age of the Comerong Volcanic Complex. Past literature commonly utilises age name nomenclature to describe the timing of the CVC and other plutonic and volcanic exposures. There are problems with describing the age of volcanism as a period name such as Silurian with the prefix’s ‘late’, ‘middle’ or ‘early’. Furthermore, there has been subdivision of periods with stage names such as Ludlow or Wenlock (Silurian stages). These descriptions in the literature commonly lack numerical age dates and authors do not provide the geological timeline in order to reference the nomenclature. The evolving understanding of the geological timeline continues to reformat the period dates and the divisions within these periods. This lack of chronological information makes it difficult when attempting to understand the temporal relationships between regional events such as sedimentation, volcanism and plutonism (Vandenberg et al. 2000). The need for a standard timeline is imperative before further use of the terms such as Middle Devonian can be confidently applied to the CVC. The geological timeline of Cohen (2013) used in this study is selected on the basis that it is a current international standard.

The CVC ages indicate that the volcanism was Eifelian (392 to 387 Ma) on the modern geological timeline (Fig. 63). For comparison, the geological timeline of Palmer (1983) is used to represent numerical dates for the 1980’s nomenclature (Fig 67). Dates for the Comerong Volcanics are overlain on both timelines to show the difference between the stages. An important observation is that past interpreted dates for the Comerong Volcanics suggest a younger onset of volcanism (Dadd, 1992; Schmidt et al., 1986). The timing difference exhibited by these results also highlights the need for revision of K-Ar and Rb-Sr isotopic dates assigned

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to plutonic bodies adjacent to the CVC, because these have been used as timing constraints through fault relationships (Schmidt et al., 1986) and these elements are subject to open system behaviour under metamorphic conditions.

Fig 67. Comparison of geological timelines. a, Geological timeline of Palmer (1983). b, Modern geological timeline after Cohen (2013). Columns represent: A – Orogenic events after Vandenberg et al. (2000), B - Orogenic events after Rosenbaum (2018), C – This study CVC dates, D – Interpreted dates of CVC after Schmidt (1986), E - Proposed age of the CVC from Dadd (1992).

Coeval Volcanism in the Lachlan Orogen The EVZ tectono-magmatic correlation made by McIlveen (1975) for rift volcanics within the Merrimbula Group and Mallacoota Beds stratigraphic horizons is more complex than previously considered. The dates for the rift volcanics were considered as Givetian to Frasnian (McIlveen, 1975)) based upon fossil evidence and this may reflect the onset of the Boyd Volcanic Complex where these fossils were found well preserved. The numerical age of 380 to 367 Ma is inferred from the proposed Givetian-Frasnian time range (Palmer, 1983). If the BVC is understood as being within 380 to 367Ma, the CVC then exhibits a volcanic event 10 Ma separate from the BVC. However, the tectonic setting generating the magmatism and mechanisms for BVC volcanism displays a striking similarity in volcanic phases with a rhyolitic phase termed the Eden Rhyolite comparable to the LFP and UFP, overlain by a thick accumulation of basalt flows termed the Lochiel Formation, comparable to the UMP (Fergusson, 1979; Steiner, 1972).

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Plutonic A-type units provide evidence that A-type magmatism is not localised to the NSW south coast region but instead constitutes a regional thermal event (Glen and Watkins, 1999). Within the Eastern Lachlan Orogen (ELO), felsic magmatism during 400 to 390 Ma was I-type in composition with the intrusion of the Bega Batholith to the west of the CVC (White et al., 2001). The occurrence of A-type plutonic and volcanic rocks in the Lachlan Orogen generally is of Devonian age (Fig. 68) with the exception of Ordovician A-type granites in Victoria (Vandenberg et al. 2000). The A-type Dulladerry volcanics have been regarded as related to the CVC magmatic event (Lyons et al., 2000; Dadd, 2011). The Dulladerry volcanics have ages from 387 to 376 Ma (Atton, 2013; Lyons P. et al., 2000) which post-date the 392<387 Ma age for the CVC but are within age error. South of the Dulladerry volcanics are the Warrumba A-type volcanics which have an age of 384 Ma (Lyons et al., 2000). The A-type Gabo Island granite suite of the Eden area has been interpreted by Wyborn and Owen (1986) to be comagmatic with the CVC rhyolite based on similar geochemistry and mineral assemblage. The Gabo Island granite suite comprises the Watergums granite dated at 395 Ma with zircon saturation temperatures ranging from 885 to 893°C (King, 1996). The age and high zircon saturation temperature calculated for the Watergums granite is comparable to the lower age range of 392 Ma and high temperatures (860°C) of the CVC rhyolites.

Other A-type granites and volcanics occurring in the Early to Middle Devonian are found throughout the Lachlan Orogen with other synchronous units in the Delamerian and Thomson Orogen. In Queensland, new data from the Thomson Orogen suggests Early Devonian volcanism was A-type with the emplacement of the Gumbardo formation at 398 Ma (Asmussen, 2018). In Victoria, the occurrence of A-type Devonian granites includes the Victoria Valley granite in the Delamerian Orogen (392±5 Ma), Ellery granite (386±3 Ma), Murrungowar granodiorite (387±8 Ma), Goonmirk Rocks granodiorite (Early Devonian 420<410 Ma), and the Thologolong granite (Early Devonian 420<410 Ma) (Vandenberg et al. 2000). The A-type Grenfell granite (384±3.4 Ma), Wirrinya granite (possibly 395 Ma), Bindogandri granite (390<370 Ma), and Ganantagi granite (390<370 Ma) occur in NSW as part of the ELO (Lyons P. et al., 2000).

Based upon the ages of A-type plutonic and volcanic units throughout the Lachlan Orogen and the CVC, a short magmatic event, pre and post-Tabberabberan Orogeny, produced A-type magmatism, primarily in the ELO. The dates occur within a time range of 395 to 375Ma which includes the A-type CVC rhyolites and groups the CVC magmatism into a discrete magmatic event from Early to Middle Devonian.

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Fig. 68. Map of A-type granites in the Lachlan Orogen dated from Early to Middle Devonian (419<382 Ma). Label numbers as: 1 – Victoria Valley granite (Vandenberg et al. 2000); 2 – Goonmirk Rocks granodiorite and Ellery granite (Vandenberg et al. 2000); 3 – Gabo Island granite suite (Collins, 1977); 4 – Mumbulla granite suite (Collins, 1977); 5 – Wangrah suite A-type granites (King, 1996) ; 6 – Comerong Volcanics, Monga granite, Mongamulla and Coondella Creek adamellites (Wyborn and Owen, 1986); 7 – Wyangala Batholith A-type granites (King, 1996); 8 – Warrumba volcanics, Grenfell granite and Schneiders granite (Wallace, 2000); 9 – Dulladerry volcanics and Bindogandri granite (Lyons et al., 2000); 10 - Mount Mittamatite and Pine Mountian granites (Vandenberg et al. 2000); 11 - Thologolong and Lucyvale granites (Vandenberg et al. 2000); 12 – Ural and Mt Hope volcanics (Bull et al., 2008). Abbreviations are New South Wales (NSW), Victoria (VIC) and

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Chapter 8: Conclusions and Further Research

8.1 SUMMARY AND CONCLUSION

This study has shown the Comerong Volcanic Complex comprises six stratigraphic packages here termed the Lower Breccia Package, Intermediate Volcanic Package, Lower Felsic Package, Lower Mafic Package, Upper Felsic Package and the Upper Mafic Package. These packages show volcanism was periodical with the evolution of the rift progressing southward with an increase in explosive rhyolitic volcanism. The sedimentary and volcanic lithofacies comprise ignimbrite deposits and lava flows that were erupted and emplaced in a subaerial paleoenvironment with evidence for water-saturated sediment interaction in a fluvial depositional environment. Lacustrine sedimentary deposits are spatially restricted within the CVC. The subaerial lava flows are characterised by associated autobreccia carapaces and basal peperite and hyaloclastite breccias (section 4.6.2). The geochemistry of the rhyolite and basaltic compositions of the bimodal CVC volcanic suite characterise magmas derived from intraplate extensional environments (Fig. 49, Fig. 50). The basalts also show evidence for crustal contamination with elevated Nb/Yb and Th/Yb ratios (Fig. 49). This indicates the rift was sourcing mantle derived mafic melts that were distal from convergent margin processes and lack the depleted mantle signatures of MORB. The timing of the volcanics is early-Middle Devonian (Eifelian) with errors extending into the Emsian (407<393 Ma) and Givetian (387<382 Ma) stages. This age pre-dates the currently proposed timing of the Boyd Volcanic Complex and the regionally recognised Tabberabberan orogenic event (Vandenberg, 2000). This implies that the CVC magmatism was not synchronous with the BVC magmatic event as suggested by McIlveen (1975), but they may be compositionally similar.

These findings have challenged the hypothesis (section 2.3) that the Comerong Volcanic Complex was part of a back-arc rift setting in the Late Devonian. The geochemistry indicates a within-plate rift setting rather than a proximal back-arc rift and the 238U/206Pb isotope dates indicate an earlier volcanic event contrasting with previous interpretations for the CVC’s inception. The lithofacies and lithofacies associations observed in this study confirm that the CVC formed as a terrestrial rift.

This study has shown the potential for a separate volcanic event underlying the bimodal CVC volcanics, that has previously not been recognised in past studies. This volumetrically minor basaltic andesite and andesite has trace element geochemistry exhibiting subduction-

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related enrichment and depletion signatures. Contacts between the andesitic volcanics and the bimodal volcanics were not observed; however, the andesitic magmatism is interpreted to pre- date the bimodal, intraplate magmatic event.

8.2 FURTHER RESEARCH

The findings of this study raise questions for further investigation, whilst serving as a platform for continued research on the Comerong Volcanic Complex. Further research on the CVC will continue to add information on this volcanic field which forms part of an enigmatic period in Lachlan Orogen evolution. From the findings of this study, several further research topics are proposed.

The provenance of the Merrimbula Group sediments is largely unknown but can provide information on the size and distance of the source regions during this dynamic period of sedimentation and magmatism in the ELO. Detrital zircon dates would temporally relate the period of uplift and erosion of the source region and allow reconstructions of the ELO.

The geochemistry of the CVC bimodal volcanics can be further investigated through magma petrogenesis studies. A possible candidate for the parental magma to the basalts could be modelled from the gabbroic intrusion at Mt Donovan, located on the southern extent of the Budawang Synclinorium’s western limb. The Mt Donovan basic complex is postulated to be the intrusive equivalent to the basalts (Wyborn and Owen, 1986). Geochemical sampling of the basic complex should be carried out with care as it has been shown there are considerable fractionated components within the intrusion (Wyborn and Owen, 1986). The utilisation of isotopic ratios, such as Sr, Nd and Pb isotopes, would be able to evaluate the mantle source melts for the basalts but would require a broad sampling program to collect samples with minimal alteration and weathering. Melts modelling studies would also be able to definitively conclude whether the IVP lavas are a fractionated and heavily contaminated CVC basalt derivative that experienced a long residence time in the crust, or as a separate melt produced through convergent margin processes in an earlier volcanic event.

Accompanying the mafic petrological study, a comagmatic study should be investigated between the A-type Monga, Coondella and Mongmulla intrusive bodies with the CVC rhyolite and new isotopic age dates for these intrusive bodies should be produced, as the Rb-Sr and K- Ar ages of Wyborn and Owen (1986) may have experienced open system behaviour under the regional greenschist metamorphic conditions. In addition to the revision of age dates for

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adjacent intrusive units, 238U/206Pb zircon age dates for the Yalwal rhyolite and Eden rhyolite would serve to definitively correlate or disprove a synchronous magmatic event with the CVC. There is also scope for this study’s emplacement ages to be further constrained with more dates for other felsic units within the CVC during future investigations on the Yalwal and Eden rhyolites.

The presence of older Precambrian zircons analysed as xenocryts in CVC zircons assumes these xenocrysts were imparted from their host rock during the melting of a crustal source. The Precambrian zircons could be used as the focus of further research by using geochronological data from basement rocks in the Lachlan Orogen, such as the Cambrian greenstones found throughout the CLO, to provide answers to source crustal regions of melting during the later I and A-type magmatism in the ELO.

8.3 IMPORTANCE OF FURTHER RESEARCH

The further questions this study proposes will add resolution to the Comerong Volcanic Complex, which is important in understanding the timing and emplacement mechanisms of regional and local magmatism. The rift in which the CVC formed and the later burial and deformation to produce the Budawang Synclinorium has experienced a long history of gold prospectivity.

The history of gold and copper prospects in the Budawang Synclinorium incited a PhD at the University of Melbourne conducted by Glasser (1988), who found that epithermal gold mineralisation was present along the margins and hosted within the CVC rhyolite. The mineralisation of the rhyolites is suggested to have occurred by the reactivation of rift graben faults. It was also the view of McIlveen (1975) that the rhyolites provide an excellent exploration target for massive, low-grade gold mineralisation. Modern exploration techniques such as aeromagnetic surveys, induced polarisation, and soil sampling may help identify mineralisation targets below the surface and outside of the current national park borders encompassing parts of the Comerong Volcanic Complex.

158Timing and basin implications for the Eden-Comerong-Yalwal Volcanic Zone: Stratigraphy, Depositional Environment and Tectonic Affinity of the Comerong Volcanic Complex, NSW

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Appendices

Appendix A Methods, Instrumentation, Sample Preparation and Procedures

Methods The field season consisted of four weeks of field mapping and sampling from late April to May, 2018. There were two campgrounds which provided base camps to access the northern and southern extents of the Budawang Synclinorium. The first two weeks was situated at Yadboro Flats campground in the north of the study area. This provided access to Belowra and Stoney Creeks, which are the two northern field sites. The following two weeks were spent at Deua River campground in the south of the study area, providing access to Buckenbowra River, Quart Pot Creek and Burra Creek field sites. Each field site was chosen based on accessibility, historically available outcrops, coverage of the eastern limb and proximity to the base camp. Fire trails enabled the field team to reach hiking trails, connecting river/creek beds or in general hiking proximity of the field site. Mapping began at the first noticeable lithology change from schistic, foliated, metapelite lithofacies until the volcanic units terminated with an overlying fining-upward sequence of polymictic, para-conglomerate and medium to coarse-grained, sandstone lithofacies. Observations of the outcrop were noted with “spots of interest” referred to as “S#. ##” in field notes. Spots of interest included stratigraphic contacts, lithology changes, lithology structures, changes in the orientation of bedding/flow-foliation and changes in the outcrop occurrence. The observations were formatted into field notes and drafted into stratigraphic logs. These field logs are used as the initial basis for the finalised stratigraphic logs displayed in the results chapter. The sampling of stratigraphy was carried out with care to minimise the impact of weathering and to provide a representative sample of the outcrop. Field samples were catalogued for descriptions, and preliminary interpretations applied. The true thickness was calculated for each field site by averaging dip measurements taken from contacts and interbedded sedimentary units and applying trigonometric calculations. Data, samples and observations were brought back to QUT to be tabulated and digitised. The geographic information system, ArcGIS was used for digitising the AOI map area using New South Wales geological survey maps and to provide accurate measurements between GPS locations for revision of true thickness measurements taken in the field.

Instruments The equipment utilised by this study has been chosen with care and within the cost of the project. All instruments were owned by QUT and operated by technical staff or with technical assistance unless otherwise stated in the “Procedure and Timeline” section of the thesis document.

170 Appendices

Freiberg Compass The compass type used in the field season was a Freiberg geological compass. The compass is commonly used in geological fieldwork to assess dip and dip azimuth of stratigraphy and also as a positioning device. The compass also has a declination indicator and was set to the appropriate degree for the AOI. The declination set on the compass was 13 degrees in accordance with the Australian Geomagnetic Reference Field Values available through Geoscience Australia (12.728 deg).

Garmin Handheld 64ST GPS The Garmin GPS used in the field, collected coordinates for locations of interest and important spot locations used to work out the true thickness of stratigraphy. Coordinates for samples and spot locations are available in field notes.

Leica DM750P Light Microscope The bulk of petrographic work conducted on thin sections was carried out using a Leica light microscope capable of transmitted and reflected light operation. Magnification lenses used consisted of x4, x10 and x40. Reflected light petrography was carried out with the primary purpose of locating in-situ thin section zircon.

Leica DM6000 Light Microscope The DM6000 allowed thin section mapping of zircons in situ. It also provided the image mosaics that are discussed in the discussion section of this thesis. It was a useful tool to image zircon before LA-ICP-MS analysis and navigate around the zircon mount.

Retsch Steel Jaw Crusher BB 200 Primary crushing was done using a Retsch steel jaw crusher at QUT’s Banyo Pilot facility. Great care was used with regards to cleaning and maintaining this equipment. The jaw crusher has many small divets and crevices in which contaminants could accumulate. Cleaning consisted of air blasting with a compressed air gun, ethyl alcohol scrubbing and silica sand crushing between very 3rd sample run.

Steel Sieves Sample preparation used several steel sieves to treat samples. These were selected to separate appropriate chip and powder sizes depending on the preparation stage. A 1cm and 4mm sieve was used to separate chips used for contaminant picking. Two sieves were used in the milling preparation step. A 500μm sieve attached above a 90μm sieve was the setup used to separate powders ready for further preparation steps. The sieves were rust-free, largely un-scratched and carefully cleaned between each sample preparation using an ultrasonic bath, ethyl alcohol scrubbing, and blasting with compressed air.

Rocklabs Swing Mill with Tungsten Carbide Millhead Samples in this study were pulverised using a swing mill, fitted with a Tungsten Carbide mill head. The milling stage of sample preparation is critical because sample powders must be micronized to appropriate sizes in order to effectively prepare XRF disks, and digest ICP-MS

Appendices 171

solutions. The Tungsten Carbide mill head was chosen because it is the most effective at crushing hard quartz-rich samples and contaminants such as tungsten, carbon, and cobalt are not elements of importance to this study. The mill head was thoroughly cleaned by compressed air blasting, scrubbing and ethyl alcohol washing to remove former samples.

Quantachrome Micro Rotary Riffler The rotary riffler was used to provide a representative sample for later fusion and digestion sample preparation steps. It is important for this study that a representative sample is prepared correctly as this may impact on the chemistry collected in later analysis. The feeder and rotary outlets were thoroughly cleaned by ethanol scrubbing and blasting with compressed air between each sample riffling.

Claisse TheOx Advanced Fusion Instrument XRF disks were fused using a Claisse advanced fusion instrument at QUT’s Central Analytical Research Facility. Fusion was conducted using platinum crucibles and platinum disk moulds. Crucibles were inspected for contaminants and cleaned in an acidic ultrasonic bath. This instrument is responsible for preparing XRF disks used for major element analysis and therefore has a vital role in sample preparation. The machine was within the servicing period and functioned properly.

Carbolite High-Temperature Box Furnace Loss of Ignition was carried out in a Carbolite Box Furnace operating at 1050°C to remove volatiles. Samples were fired in ceramic crucibles. Loss of Ignition (LOI) analysis is important for calculations automatically carried out by software during XRF analysis and in plotting data on geochemical ternary diagrams.

Agilent 8800 Laser Ablation Inductively Coupled Plasma Mass Spectrometer (LA-ICP-MS) The Agilent 8800 LA-ICP-MS was used on sampled zircon populations for U-Pb isotopes and whole-rock trace element geochemistry. This machine is critical to the geochronology and trace element analysis detailed in this thesis. The machine was calibrated using international standards and unknowns throughout the ablating runs. The machine was operated with guidance from Dr Karine Moromizato and Dr Charlotte Allen (See acknowledgements).

PANalytical AXIOS Wavelength X-ray Fluorescence (WD-XRF) Spectrometer Major trace elements were measured using a PANalytical x-ray fluorescence spectrometer at QUT’s Central Analytical Research Facility. The machine is calibrated each morning using approximately one hundred permanently supplied standards to ensure the best measurements possible. It uses LOI values with flux and sample weights to calculate major element oxide percentages from glass disks prepared from the Claisse Fusion Instrument previously mentioned. Each analysis run was conducted by Dr Karine Moromizato (see acknowledgements). XRF major elements are important for whole-rock geochemistry analysis to determine lithology and for plotting discriminatory diagrams.

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Sample Preparation Sample preparation is a major part of the study procedure. It has been conducted with care to ensure the field samples are representative of the field outcrop from which it has been sourced. Sample preparation is described in the order in which it was completed. Since each analytical method requires the completion of the previous, it has governed the order of sample preparation.

Petrographic thin section preparation was completed at QUT’s Banyo Pilot Facility. Samples were each prepared by the stepped procedure below. 1- The hand sample was first cut with a rock saw and ground to reveal fresh rock faces. This ensured textures observable in thin-section would be free from the effects of weathering. 2- From the fresh faces observed, a face was chosen as a representative surface of the rock texture. Secondary faces were also chosen for samples displaying one or more interesting textures that were to be studied. 3- From the chosen face, a billet of the sample was slabbed using a precision rock saw to a rough dimension of 28x48mm and lapped with a diamond tip, fine grit grinder polisher. The dimension of the billet ensured the finished thin sections were small enough to fit inside the mounts of the Agilent 8800 LA-ICP-MS to ablate zircons in-situ. Polishing the face of interest ensured firm contact on the glass slide. Billets with vesicular or porous faces were filled with epoxy to seal the billet to the glass slide. 4- Sample billets were then dried on a hot plate overnight. 5- The following steps were conducted by Gus Luthje, a technician specialising in the preparation of thin sections. Following drying the billets were then mounted onto glass slides with an epoxy resin. 6- Billets mounted on glass slides were then polished down to approximately 30μm thickness. 7- Polished slides were then dried and placed in a protective case until used in the binocular microscope laboratory.

Sample powders were prepared using several instruments. Care was taken to clean each piece of equipment before each sample run. The sample powders prepared in the stepped procedure below were used for XRF preparation. 1- Hand sample was inspected for weathering. Weathered surfaces and large veins were removed using a rock saw and ground down with a coarse grit grinder polisher. Part of the sample was slabbed and set aside for further thin-sectioning or as a representative of the final milled powder. 2- The sample was then dried by blasting with compressed air. This ensured the sample would not cake on any instruments or equipment. 3- Treated hand sample was then crushed using a Retsch Steel Jaw Crusher and sieved to a chip size of 0.4<1cm. Chips and powder that was smaller than 4mm was retained but not used further. Before each crushing run, the instrument was inspected for contaminants, such as previous samples or particulates from cleaning equipment. Between each crushing run, the jaw of the crusher was removed and thoroughly cleaned via scrubbing with a plastic scrubber, wiping with paper towel soaked in ethanol and blasting with compressed air. The same

Appendices 173

cleaning procedure was used to decontaminate the inside chamber of the crusher and the catch box. For every three crushing runs, a high purity silica sand was passed through the jaw crusher to remove lodged particulates. 4- The sample chips were then picked for contaminants. Contaminants included foreign clasts, veining and well-developed discolouration evident of weathering. Chips picked for further preparation had to be free from these contaminants but also be representative of the original sample set aside in step 1. Sample D10.7 was picked into two visible populations after washing the chips with water. The chips were dried in an oven at 60° before picking. 5- The picked chips were then weighed out to approximately 100g or up to this amount and placed into a Tungsten Carbide (WC) mill head. 6- The sample was then milled in a Rocklabs swing mill for approximately fifteen seconds at 750RPM. 7- The milled sample was handled by emptying the powder onto A4 paper and poured into a sieving stack comprised of a 500μm sieve atop a 90μm sieve. Inspections throughout the sieving process helped to identify any anomalous particulates with clear contrast to the sample material. Material that did not pass through the 90μm sieve was then re-milled for a further ten seconds. If coarse material was greater than 20g, the sample was re-milled for another 10 seconds. The resulting sample powder was then stored in a zip-lock plastic bag. The WC mill head and internal disks were cleaned in an ultrasonic bath, scrubbed with a plastic scrubber, ethanol wiped, and air blasted with compressed air until dry. Each sieve was de-contaminated using the ultrasonic bath and blasted with compressed air until dry. Care was taken to dry each instrument due to the risk of sample caking and contaminating further samples. 8- Sample splitting was conducted with a rotary riffle splitter. The powder was poured into the vibrating hopper feeding eight rotating glass test tubes. Each sample split was bagged separately. The hopper and glass test tubes were rinsed, ethanol wiped and blasted with compressed air. The glass test tubes were dried in a 60°C oven before splitting the following sample.

X-ray fluorescence disks were prepared with the same sample to flux ratio as standards unless indicated otherwise. The disks were prepared in the procedure below. 1- Exactly 1.15g of the sample was mixed with 8.85g of high purity flux (Claisse Flux: Lithium tetraborate with Lithium metaborate 50:50 + 0.5% Lithium Iodide) into plastic vials. The vials were shaken thoroughly to mix sample and flux. 2- The mix was poured in platinum crucibles and mounted in a Claisse Fusion Instrument. Six samples at a time were fused for thirty minutes by which point the sample is completely melted. The melted sample and flux was moulded in platinum disk moulds for the venting period of five minutes. 3- Melted sample which did not fully encompass the mould were re-annealed by restarting the melting cycle. The platinum crucibles were cleaned with a 5% Nitric acid, ultrasonic bath for three minutes followed by rinsing and drying with a tissue. Platinum moulds were cleaned by running through a melt cycle using 100% flux. Cleaning procedure flux disks were discarded.

174 Appendices

4- Loss of Ignition was measured with 2g of sample ignited in a Carbolite furnace at 1050°C for three hours. Samples were left overnight at 500°C until weighing after cooling to 70°C. The results were then used in conjunction with the XRF disks to produce major element chemistry.

The zircons used in this study for geochronological analysis were separated from field samples by Geotrack International Pty Ltd. The separates were collected by methyl iodide heavy liquid separation techniques and magnetic separation from a Frantz Isodynamic separator. Handpicking was conducted at QUT. 1- Zircon was handpicked from concentrate and magnetic fractions under a binocular microscope. 2- Crystals were mounted on adhesive tape attached to a glass plate. 3- Mounted zircons were then imaged under reflected light with a Leica DM6000 light microscope. This enabled internal domains, melt inclusions and fractures to be imaged and avoided during ablation. 4- Following ablation on tape mounts, the zircons were then mounted in epoxy resin and polished to expose internal domains. The polished zircons were then imaged via a Zeiss Sigma SEM, using an AsP Cathodoluminescence detector to observe internal zircon morphology and place spot locations for core-rim analysis.

Analysis Methods Petrographic Analysis All thin-sections were examined on a Leica DM750P light microscope. Each slide represented a hand sample collected from a field outcrop. In order to accurately characterise each thin- section, a stepped procedure was used to provide as much detail about the host lithology as possible. Through examination, it is the goal to either confirm or re-interpret field lithology and correlate units between field sites. Petrographic descriptions are very important to this study because the outcrops dominantly consisted of fine-grained to aphyric rocks with minerals largely unidentifiable at macroscale viewing. 1- The thin-section was examined for structures such as clast contacts, textures and crystal morphology. This first step provides a large scale view of the thin-section. If domains were identified, they are characterised separately with their specific mineralogy. 2- Each thin-section was examined for the mineral assemblage. The mineral assemblage provides the major mineral components responsible for the rocks lithological classification. Each major mineral population was measured, described and quantified via percentage estimate. 3- Accessory minerals were described and recorded for their abundance and size. Accessory minerals include zircon, which is a mineral of interest in this study. All zircon are noted and positions within the thin-section mapped. 4- The thin-section name uses the naming convention described in Cas et al. (2008). 5- Representative thin-sections were imaged using a Leica DM6000 light microscope for in-text discussion.

Appendices 175

Whole-rock Major Element XRF Geochemistry X-Ray fluorescence analysis was conducted at QUT’s CARF laboratory by Dr Karine Moromizato. Each disk was wiped with ethanol to clean the analysis surface and loaded into a PANalytical AXIOS Wavelength X-ray Fluorescence (WD-XRF) Spectrometer. Each sample disk was analysed twice along with two rhyolite and basalt standards and two blank flux disks. This ensured the accuracy and precision of the major element results.

Whole-rock LA-ICP-MS Trace Element Geochemistry Trace element geochemistry was acquired through the ablation of pre-prepared XRF fused glass disks. The following procedure was conducted by Dr Karine Moromizato at CARF. Fused disks were stacked together with epoxy resin and cut in half. The cut was then ablated using a spot size of 100μm with a dwell time of 25 seconds at 2.5J/cm2, at a rate of 11Hz and with a Helium flow rate of 600ml/min for trace elements. The same system parameters were used for REE data collection with the exception of an increased spot size of 110μm. Analyses were complemented with USGS standards, NIST SRM-610, BCR-2, and AGV-2 for data quality assurance. BCR-2 was used as a primary standard with AGV-2 and SRM-610 measured as unknowns. Silica and Calcium are used as internal standards based upon data collected from major element XRF analysis.

LA-ICP-MS Zircon Geochronology Zircon ablation took place on an Agilent 8800 Laser Ablation Inductively Coupled Plasma Mass Spectrometer (ICP-MS) using tape mounted zircon arranged in rows. The tape mounted zircons were analysed in two separate sessions using a plane polarised light image map processed on a Leica DM6000 light microscope. The image map identified outer crystal surfaces required for ablation as some grains displayed fractured surfaces. Zircon standards Temora 2 (Black, 2004) and Plešovice (Slama et al., 2008) were used to correct U-Pb geochronological systematics, where Temora 2 and glass standard NIST 610 was used as a primary standard, and Plešovice was treated as an unknown standard. Ablation procedure analysed ten unknowns, followed by ablation of a set of standards. Two sets of standards were used before the session and as final ablations. The tape mounted ablations were collected in two separate sessions. Polished zircons measured in session three were recorded with the same procedure and standards with mapped ablation sites obtained through Cathodoluminescence imaging. For all sessions, the laser operated with a dwell time of 30 seconds at 2.0J/cm2. The rate was 7Hz in an ablation cell with a Helium atmospheric flow rate of 600ml/min. Spot size for the two tape mounted sessions was 30μm and 10μm for the third session. Thirty seconds between ablations provided background recording to extract a baseline data reduction in Iolite.

176 Appendices

Appendix B True Thickness Calculation

Averaged dip represented by ϴ. Averaged dip azimuth represented by Red arrow. TT = True Thickness MT = Mapped Thickness

 •‹ ԕ ൌ 

 ൌ  ൈ •‹ ԕ Please note*

-This calculation assumes the averaged dip azimuth and dip angle is representative of all dipping stratigraphy at the field site in question.

-This calculation assumes that across strike variations in dip azimuth within the proximity of the field site are negligible to the averaged field dip azimuth.

- This calculation assumes that across strike variations in dip within the proximity of the field site are negligible to the averaged field dip azimuth.

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Appendix C Major and Trace Element Chemistry

Whole-rock geochemistry for the Comerong Volcanics. Lithofacies labelled as Porphyritic Mafic Lithofacies (PML), Aphyric Mafic Lithofacies (AML), Fine-grained Silicic Lithofacies (FSL), Porphyritic Silicic Lithofacies (PSL). Coordinates are given using geocentric GDA1994.

Sample 5.6 5.6B 6.6 6.7 7.3 9.2 10.2 10.5 10.7P 10.7D 11.2 Lithofacies PML PML PML PML AML FSL AML AML PSL PML AML Coordinate Long. 150.080 150.079 150.080 150.079 150.054 150.051 149.976 149.753 149.972 149.972 149.975 Coordinate Lat. -35.405 -35.405 -35.405 -35.405 -35.461 -35.463 -35.616 -35.615 -35.613 -35.613 -35.616 Alteration Mod Mod Mod Mod Mod Weak Mod Weak Strong Strong Mod XRF wt% Oxide SiO2 49.12 47.08 47.56 49.47 50.66 75.73 55.47 61.78 75.58 48.85 63.48 TiO2 2.04 2.05 2.06 2.21 3.03 0.20 1.92 1.30 0.97 1.43 1.49 Al2O3 16.06 16.21 15.60 14.45 13.83 13.05 13.53 12.76 11.17 17.83 13.02 Fe2O3 10.38 11.13 10.73 11.25 13.65 1.31 13.33 10.52 2.63 13.56 9.25 Mn2O3 0.37 0.19 0.19 0.17 0.26 0.00 0.21 0.19 0.03 0.20 0.08 MgO 7.34 6.95 7.26 7.19 4.22 0.26 2.53 2.64 0.73 5.11 2.02 CaO 5.01 9.16 9.22 6.21 6.45 0.02 5.56 1.71 1.58 2.45 1.13 Na2O 5.17 3.17 3.20 5.18 3.10 4.22 3.32 2.33 3.13 3.11 1.47 K2O 0.19 0.50 0.39 0.13 0.59 4.23 1.19 3.29 2.75 2.31 4.60 PsO5 0.39 0.41 0.41 0.43 0.54 0.02 0.77 0.46 0.28 0.44 0.47 LOI 3.67 2.93 3.14 3.15 3.36 0.84 1.98 2.69 1.01 4.52 2.70 Total 100.00 100.00 100.00 100.00 100.00 100.02 100.00 100.01 100.00 100.00 100.01 Trace Elements ppm Sc 32.868 33.5464 34.7991 34.3741 36.0895 11.165 24.9943 19.0151 14.0967 23.3173 22.1548 V 267.40 258.17 255.76 235.21 378.56 2.78 128.81 94.93 71.51 155.52 103.22 Cr 191.25 195.23 198.69 211.73 24.70 5.46 5.77 9.35 16.56 24.60 10.72 Ni 42.09 44.18 45.07 39.75 14.88 6.50 7.35 8.13 13.31 8.18 Cu 48.25 30.48 28.44 39.46 30.42 6.71 20.39 15.08 27.91 5.77 14.86 Zn 106.21 102.71 98.92 111.45 148.28 62.26 131.46 108.14 27.06 178.57 88.95 Ga 14.80 20.51 19.73 15.62 22.37 20.42 23.79 21.89 10.76 31.47 22.81 Rb 9.67761 16.4598 11.7513 4.0669 45.0918 158.33 74.0379 114.392 97.0868 123.777 173.148 Sr 691.11 413.55 465.19 190.79 251.88 36.73 241.22 49.78 175.87 163.11 51.18 Y 30.90 39.47 35.61 38.19 62.90 58.78 62.33 52.77 40.94 52.76 66.71 Zr 169.57 186.45 183.36 202.05 352.21 312.07 505.80 375.73 254.23 314.42 464.32 Nb 10.64 10.73 10.70 11.48 14.13 27.68 16.84 14.87 11.68 18.76 17.57 Cs 3.11 4.98 3.89 1.21 20.35 2.42 12.49 0.61 1.37 3.60 1.31 Ba 85.77 269.61 275.86 74.85 492.61 437.28 367.59 732.11 499.99 400.23 868.12 La 14.54 16.51 16.40 12.29 27.16 45.58 35.96 37.50 23.78 40.93 39.71 Ce 37.58 39.17 39.11 35.23 61.95 107.55 82.69 81.02 53.89 111.74 100.01 Nd 24.15 25.65 25.74 23.76 37.79 45.32 43.60 39.96 25.58 49.05 47.67 Sm 6.16 6.01 6.49 6.61 10.31 10.62 11.18 9.38 6.26 12.01 11.77 Eu 1.95 2.08 2.21 1.61 3.22 1.47 3.08 2.15 1.13 2.27 2.53 Gd 6.85 6.78 7.40 6.99 11.54 10.15 12.32 10.44 7.16 11.70 13.32 Tb 1.06 1.07 1.07 1.07 1.77 1.46 1.75 1.49 1.00 1.57 1.95 Dy 6.31 6.84 7.02 7.28 11.68 11.80 11.85 10.24 6.44 10.82 12.37 Ho 1.33 1.28 1.42 1.54 2.35 2.29 2.44 2.05 1.36 1.94 2.60 Er 3.69 3.65 4.17 4.19 7.14 6.77 7.13 5.82 3.77 5.69 7.20 Tm 0.43 0.44 0.48 0.54 0.91 0.90 0.92 0.76 0.49 0.71 0.99 Yb 3.32 3.38 3.49 3.84 6.22 6.50 6.40 5.36 3.09 5.25 6.72 Lu 0.57 0.60 0.65 0.65 1.09 1.24 1.13 0.95 0.60 0.88 1.12 Hf 4.66 4.61 4.83 5.21 9.22 10.09 12.91 10.48 6.28 8.70 12.31 Ta 0.72 0.75 0.78 0.81 1.22 2.32 1.43 1.32 1.01 1.48 1.52 Pb 3.20 4.04 4.28 3.83 8.82 8.42 13.34 5.25 27.35 12.26 8.54 Th 1.30 1.56 1.58 1.64 6.77 21.45 9.80 10.59 12.15 15.54 12.66 U 0.39 0.35 0.33 0.35 1.88 3.66 2.68 3.14 2.56 3.97 3.87 Eu/Eu* 0.911 0.989 0.969 0.716 0.896 0.424 0.797 0.660 0.512 0.575 0.615

178 Appendices

Sample 11.2b 11.3 11.4 13.1 13.2 13.3 15.1E 15.2 15.6 16.11B 17.6 Lithofacies AML AML AML PSL PSL CML PSL FSL PML PML PSL Coordinate Long. 149.974 149.975 149.753 149.969 149.969 149.969 149.956 149.955 149.951 149.950 149.983 Coordinate Lat. -35.616 -35.615 -35.615 -35.405 -35.605 -35.605 -35.705 -35.704 -35.703 -35.703 -35.899 Alteration Weak Weak Weak Strong Mod Mod Strong Strong Weak Weak Weak XRF wt% Oxide SiO2 51.36 59.54 61.83 71.34 70.72 48.16 68.63 78.30 48.09 47.14 78.32 TiO2 2.23 1.53 1.42 0.23 0.61 1.69 0.63 0.23 2.15 2.09 0.20 Al2O3 13.83 13.26 12.84 14.58 12.94 15.21 14.22 10.80 15.28 14.81 10.80 Fe2O3 15.34 11.01 9.89 1.37 4.71 10.35 5.06 2.10 12.07 13.33 1.75 Mn2O3 0.26 0.18 0.18 0.01 0.06 0.18 0.06 0.04 0.18 0.19 0.01 MgO 2.87 2.60 2.82 0.25 0.66 7.53 0.59 0.69 6.18 7.13 0.28 CaO 6.37 2.20 1.88 0.01 0.80 8.19 0.55 0.32 7.02 6.17 0.09 Na2O 2.76 1.85 2.46 2.23 3.53 3.27 6.09 2.66 4.16 4.00 1.90 K2O 2.07 4.11 3.29 8.96 4.72 1.23 1.33 3.35 1.02 0.82 5.83 PsO5 0.80 0.57 0.56 0.03 0.15 0.34 0.16 0.03 0.49 0.47 0.03 LOI 1.89 2.81 2.53 0.80 0.91 3.60 1.56 1.33 3.05 3.60 0.63 Total 100.00 100.00 100.00 100.01 100.00 100.00 100.01 100.01 100.00 100.00 100.01 Trace Elements ppm Sc 28.5133 21.8488 19.2734 9.51048 11.8223 33.0569 10.2807 5.50483 29.9687 29.6768 11.506 V 174.84 103.29 94.42 5.81 33.21 239.05 20.29 13.98 244.32 248.59 8.22 Cr 8.71 12.30 9.38 3.11 5.98 199.10 9.40 8.00 128.50 127.31 4.93 Ni 7.42 10.03 8.22 6.28 57.86 10.84 41.10 46.04 24.28 Cu 22.08 19.28 9.76 43.62 14.55 40.10 8.74 41.01 45.77 Zn 165.51 125.56 99.41 66.40 54.81 83.56 369.92 40.46 87.31 107.88 207.89 Ga 23.75 21.80 20.70 13.47 16.33 36.08 15.84 13.94 18.74 18.52 16.70 Sr 275.75 89.40 50.36 43.39 142.95 559.08 57.70 62.71 343.32 347.03 157.47 Y 71.22 64.56 60.34 44.58 60.41 29.75 63.48 73.68 38.23 37.37 97.90 Zr 564.39 472.33 433.96 351.91 446.24 170.46 332.83 274.44 218.70 211.60 645.13 Nb 18.87 17.34 17.65 32.71 17.30 11.47 16.42 13.67 12.96 12.50 51.68 Cs 3.45 1.78 0.62 4.28 1.96 7.15 3.97 1.94 4.22 14.46 Rb 82.8971 162.363 115.42 273.326 153.002 45.3757 32.111 138.61 20.859 21.8739 195.917 Ba 378.52 690.60 558.19 1096.90 1036.76 351.38 324.74 591.90 258.94 284.70 1707.75 La 36.84 37.07 37.85 50.45 38.42 34.19 5.87 61.55 17.70 17.93 17.23 Ce 82.68 87.07 89.91 104.36 85.55 83.93 13.84 101.74 43.82 43.54 36.03 Nd 45.49 43.55 41.60 42.85 41.50 46.93 11.47 55.63 27.65 26.89 17.38 Sm 12.29 11.25 10.20 8.31 9.54 11.77 4.00 12.45 7.00 6.85 4.53 Eu 3.34 2.62 2.44 0.91 1.50 3.52 0.60 1.49 2.02 2.08 0.69 Gd 13.03 12.70 11.77 6.65 9.10 13.94 5.50 12.65 7.78 7.09 5.49 Tb 1.89 1.85 1.68 1.09 1.41 1.71 1.11 1.92 1.11 1.10 0.99 Dy 13.23 12.43 11.85 7.54 10.32 13.30 9.26 12.54 7.66 7.59 8.12 Ho 2.65 2.54 2.29 1.66 1.82 2.58 1.96 2.32 1.56 1.54 1.69 Er 7.52 7.13 6.73 5.27 5.20 7.23 5.82 6.16 4.25 4.03 5.16 Tm 1.03 1.00 0.93 0.85 0.86 0.98 0.82 0.69 0.61 0.58 0.89 Yb 7.28 6.84 6.47 6.07 5.08 7.01 6.07 5.47 4.26 3.89 5.46 Lu 1.17 1.08 1.02 0.89 0.75 0.98 0.86 0.79 0.63 0.60 0.96 Hf 14.24 12.24 11.59 10.66 9.90 8.89 7.59 6.93 5.25 4.76 8.53 Ta 1.52 1.49 1.41 2.33 1.26 1.57 1.17 0.86 0.86 0.82 1.82 Pb 12.64 17.85 6.40 6.44 32.11 5.42 4.93 101.45 8.14 5.04 38.90 Th 10.50 11.55 11.01 22.70 18.07 1.99 15.69 14.28 2.04 2.15 39.29 U 2.74 3.45 3.39 5.19 4.28 0.69 4.29 3.69 0.57 0.53 10.92 Eu/Eu* 0.799 0.665 0.677 0.362 0.483 0.837 0.389 0.357 0.829 0.900 0.424

Appendices 179

Appendix D U/Pb Zircon Geochronology Data

Concordant zircon data for three Comerong Volcanic Complex samples. Spot ID describes the polished mounted zircon ablation sites as rims (r), interiors (i) or cores (c).

Tape/ Final Final Sample Ablation Best Err- Final Final Error Spot ID Polished Age Type 207_235 206_238 ID ID Age selected 207_235 206_238 Corel (R, I, C) Mount Prop2SE Prop2SE

D9.2 Tape D9_2_16 380 9.3 Pbcor.6/38 0.61 0.066 0.0618 0.0028 0.38625 NA D9.2 Tape D9_2_3 384 9.9 6/38 0.505 0.052 0.0613 0.0028 0.40549 NA D9.2 Tape D9_2_29 386 9.6 6/38 0.482 0.051 0.0617 0.0028 0.39417 NA D9.2 Tape D9_2_99 391 11 6/38 0.546 0.071 0.0626 0.003 0.3458 NA D9.2 Tape D9_2_79 388 11 6/38 0.469 0.043 0.0621 0.0029 0.45386 NA D9.2 Tape D9_2_80 390 11 6/38 0.497 0.054 0.0624 0.0029 0.39327 NA D9.2 Tape D9_2_18 393 11 6/38 0.484 0.054 0.0629 0.003 0.39308 NA D9.2 Tape D9_2_53 397 11 6/38 0.498 0.052 0.0636 0.003 0.41168 NA D9.2 Tape D9_2_55 398 11 6/38 0.517 0.054 0.0637 0.003 0.41105 NA D9.2 Tape D9_2_88 399 20 6/38 0.527 0.07 0.0639 0.0041 0.43496 NA D9.2 Tape D9_2_52 406 14 6/38 0.567 0.074 0.065 0.0034 0.37202 NA D9.2 Tape D9_2_4 415 12 Pbcor.6/38 0.652 0.073 0.0673 0.0032 0.39089 NA D9.2 Tape D9_2_61 420 11 6/38 0.558 0.056 0.0674 0.0031 0.41663 NA D9.2 Tape D9_2_90 431 13 6/38 0.577 0.072 0.0691 0.0034 0.36683 NA D9.2 Tape D9_2_92 431 14 6/38 0.551 0.056 0.0693 0.0035 0.44502 NA D9.2 Tape D9_2_91 437 16 6/38 0.585 0.07 0.0702 0.0037 0.4031 NA D9.2 Tape D9_2_40 439 15 6/38 0.598 0.079 0.0705 0.0037 0.3692 NA D9.2 Tape D9_2_31 452 16 6/38 0.582 0.066 0.0726 0.0038 0.41907 NA D9.2 Tape D9_2_51 544 24 6/38 0.727 0.072 0.0881 0.0053 0.51916 NA D13.1 Tape D13_1_37 273 7.7 6/38 0.314 0.035 0.0433 0.002 0.38282 NA D13.1 Tape D13_1_102 353 9.4 Pbcor.6/38 0.567 0.06 0.0576 0.0027 0.40501 NA D13.1 Tape D13_1_47 373 8.2 Pbcor.6/38 0.797 0.095 0.0622 0.0027 0.34219 NA D13.1 Tape D13_1_69 382 6.3 Pbcor.6/38 0.674 0.068 0.0625 0.0026 0.3812 NA D13.1 Tape D13_1_64 383 10 6/38 0.492 0.05 0.0612 0.0029 0.42259 NA D13.1 Tape D13_1_30 384 9.2 Pbcor.6/38 0.741 0.084 0.0635 0.0028 0.36252 NA D13.1 Tape D13_1_5 391 9.7 6/38 0.472 0.045 0.0625 0.0028 0.42529 NA D13.1 Tape D13_1_89 395 9.8 Pbcor.6/38 0.528 0.062 0.0632 0.0029 0.36397 NA D13.1 Tape D13_1_110 400 9.9 6/38 0.462 0.042 0.064 0.0029 0.44609 NA D13.1 Tape D13_1_31 405 9.9 6/38 0.525 0.056 0.0649 0.0029 0.38638 NA D13.1 Tape D13_1_99 408 12 Pbcor.6/38 0.617 0.071 0.0661 0.0032 0.38778 NA D13.1 Tape D13_1_81 415 10 Pbcor.6/38 0.642 0.076 0.0673 0.003 0.3524 NA D13.1 Tape D13_1_13 422 16 Pbcor.6/38 0.507 0.061 0.0677 0.0037 0.41358 NA D17.6 Tape D17_6_1 396 31 6/38 0.468 0.09 0.0634 0.005 0.37943 NA D17.6 Tape D17_6_2 386 30 6/38 0.57 0.12 0.0619 0.005 0.35822 NA D17.6 Tape D17_6_3 373 27 6/38 0.492 0.081 0.0596 0.0044 0.40917 NA D17.6 Tape D17_6_7 366 28 Pbcor.6/38 0.356 0.091 0.058 0.0046 0.29633 NA D17.6 Tape D17_6_10 397 29 Pbcor.6/38 0.524 0.1 0.064 0.0047 0.35914 NA D17.6 Tape D17_6_12 404 39 6/38 0.62 0.16 0.065 0.0064 0.35647 NA D17.6 Tape D17_6_14 423 37 6/38 0.68 0.15 0.0681 0.0062 0.38151 NA D17.6 Tape D17_6_16 444 54 6/38 0.63 0.22 0.0718 0.0089 0.33451 NA D17.6 Tape D17_6_18 391 34 6/38 0.57 0.13 0.062 0.0054 0.35676 NA D17.6 Tape D17_6_21 416 40 6/38 0.54 0.17 0.0668 0.0067 0.30356 NA D17.6 Tape D17_6_22 630 99 6/38 2.45 0.59 0.188 0.018 0.36945 NA D17.6 Tape D17_6_29 504 47 6/38 0.62 0.13 0.0817 0.0079 0.41878 NA D17.6 Tape D17_6_30 397 33 6/38 0.474 0.1 0.0637 0.0054 0.37285 NA D17.6 Tape D17_6_32 353 28 6/38 0.462 0.078 0.0564 0.0046 0.43499 NA D17.6 Tape D17_6_33 389 34 6/38 0.63 0.15 0.0624 0.0057 0.3582 NA D17.6 Tape D17_6_34 361 30 6/38 0.433 0.083 0.0578 0.0049 0.40447 NA D17.6 Tape D17_6_37 396 30 6/38 0.56 0.14 0.0629 0.0053 0.31939 NA D17.6 Tape D17_6_38 449 39 6/38 0.78 0.19 0.0724 0.0065 0.34583 NA D17.6 Tape D17_6_42 624 49 6/38 0.88 0.15 0.1019 0.0084 0.43537 NA D17.6 Tape D17_6_43 386 34 6/38 0.5 0.11 0.0619 0.0056 0.38032 NA D17.6 Tape D17_6_51 431 41 6/38 0.72 0.19 0.0694 0.0068 0.34808 NA D17.6 Tape D17_6_52 364 42 6/38 0.58 0.16 0.0584 0.0069 0.39371 NA D17.6 Tape D17_6_59 401 31 6/38 0.63 0.12 0.0636 0.0048 0.36836 NA D17.6 Tape D17_6_65 395 44 6/38 0.65 0.18 0.0635 0.0074 0.38788 NA D17.6 Tape D17_6_68 401 32 Pbcor.6/38 0.59 0.15 0.0644 0.0053 0.30797 NA D17.6 Tape D17_6_71 420 43 6/38 0.67 0.18 0.0676 0.0071 0.36411 NA

180 Appendices

D17.6 Tape D17_6_73 429 39 Pbcor.6/38 0.57 0.21 0.0693 0.0064 0.24315 NA D17.6 Tape D17_6_76 399 42 6/38 0.55 0.15 0.0641 0.0069 0.36713 NA D17.6 Tape D17_6_79 386 36 6/38 0.5 0.13 0.0618 0.0059 0.34469 NA D17.6 Tape D17_6_85 373 28 Pbcor.6/38 0.553 0.092 0.0598 0.0043 0.39675 NA D17.6 Tape D17_6_86 379 28 Pbcor.6/38 0.65 0.11 0.0611 0.0046 0.40647 NA D17.6 Tape D17_6_87 378 30 Pbcor.6/38 0.56 0.12 0.0606 0.005 0.35932 NA D17.6 Tape D17_6_90 420 34 6/38 0.58 0.13 0.0675 0.0057 0.35256 NA D17.6 Tape D17_6_93 411 31 6/38 0.61 0.12 0.066 0.0051 0.36561 NA D17.6 Tape D17_6_94 785 65 Pbcor.6/38 1.63 0.3 0.1306 0.011 0.41613 NA D17.6 Tape D17_6_95 402 45 6/38 0.58 0.23 0.0648 0.0074 0.27673 NA D17.6 Tape D17_6_107 413 45 6/38 0.76 0.21 0.0665 0.0075 0.3779 NA D17.6 Tape D17_6_113 354 27 6/38 0.467 0.078 0.0565 0.0045 0.43042 NA D17.6 Tape D17_6_114 388 30 6/38 0.62 0.12 0.0622 0.0049 0.37699 NA D17.6 Tape D17_6_116 391 29 6/38 0.462 0.1 0.0626 0.0048 0.33392 NA D17.6 Tape D17_6_117 377 27 6/38 0.443 0.08 0.0602 0.0045 0.38246 NA D17.6 Tape D17_6_118 402 29 6/38 0.53 0.11 0.0644 0.0048 0.33799 NA D17.6 Tape D17_6_119 404 31 6/38 0.45 0.12 0.0647 0.005 0.27835 NA D17.6 Tape D17_6_121 405 28 Pbcor.6/38 0.579 0.1 0.0652 0.0047 0.38517 NA D17.6 Tape D17_6_127 405 37 6/38 0.47 0.14 0.0651 0.0061 0.30007 NA D17.6 Tape D17_6_137 444 54 6/38 0.61 0.21 0.0718 0.0089 0.33877 NA D17.6 Tape D17_6_138 447 44 Pbcor.6/38 0.46 0.13 0.0719 0.0074 0.3422 NA D17.6 Tape D17_6_140 385 30 6/38 0.55 0.11 0.0617 0.005 0.37553 NA D9.2 Polished D9_2_1 381 14 6/38 0.481 0.056 0.0609 0.0033 0.42196 D92_00R D9.2 Polished D9_2_2 385 15 6/38 0.459 0.044 0.0616 0.0034 0.49898 00I D9.2 Polished D9_2_4 381 14 Pbcor.6/38 0.445 0.051 0.0604 0.0032 0.41961 01C D9.2 Polished D9_2_6 374 14 6/38 0.45 0.052 0.0597 0.0033 0.43152 002I D9.2 Polished D9_2_7 390 16 6/38 0.528 0.058 0.0625 0.0035 0.45418 003R D9.2 Polished D9_2_8 554 21 Pbcor.6/38 0.685 0.054 0.0892 0.005 0.57949 003C D9.2 Polished D9_2_9 387 17 Pbcor.6/38 0.516 0.044 0.0621 0.0037 0.57276 004R D9.2 Polished D9_2_10 389 13 Pbcor.6/38 0.495 0.037 0.062 0.0032 0.5682 004I D9.2 Polished D9_2_11 382 16 Pbcor.6/38 0.611 0.096 0.0615 0.0035 0.34056 0051I D9.2 Polished D9_2_12 380 14 Pbcor.6/38 0.487 0.04 0.0606 0.0033 0.55258 0052R D9.2 Polished D9_2_13 388 15 Pbcor.6/38 0.631 0.063 0.0632 0.0034 0.47435 0052I D9.2 Polished D9_2_14 394 16 6/38 0.499 0.047 0.0632 0.0036 0.51749 006I D9.2 Polished D9_2_15 396 14 6/38 0.52 0.061 0.0634 0.0033 0.40558 0071R D9.2 Polished D9_2_16 394 17 6/38 0.527 0.053 0.0632 0.0037 0.50309 0071C D9.2 Polished D9_2_19 401 14 6/38 0.531 0.067 0.0642 0.0034 0.38702 0081R D9.2 Polished D9_2_20 388 14 6/38 0.502 0.047 0.0622 0.0034 0.5042 0081C D9.2 Polished D9_2_23 387 13 6/38 0.489 0.039 0.062 0.0032 0.5433 009C D9.2 Polished D9_2_25 386 14 6/38 0.508 0.048 0.0618 0.0033 0.492 010I D9.2 Polished D9_2_26 387 18 Pbcor.6/38 1 0.17 0.065 0.004 0.34038 0111R D9.2 Polished D9_2_27 398 16 Pbcor.6/38 0.837 0.086 0.0663 0.0037 0.47729 0111I D9.2 Polished D9_2_30 397 18 Pbcor.6/38 0.79 0.13 0.0653 0.0039 0.34117 006R D9.2 Polished D9_2_31 370 17 6/38 0.573 0.093 0.0591 0.0037 0.35989 0131I D9.2 Polished D9_2_34 381 14 6/38 0.514 0.044 0.061 0.0033 0.53423 0141I D9.2 Polished D9_2_37 391 17 6/38 0.548 0.073 0.0626 0.0038 0.41466 0151I D9.2 Polished D9_2_42 388 14 6/38 0.478 0.048 0.062 0.0033 0.46832 016C D9.2 Polished D9_2_44 380 11 Pbcor.6/38 0.747 0.082 0.0631 0.0031 0.4085 0201R D9.2 Polished D9_2_49 386 17 Pbcor.6/38 0.631 0.091 0.0637 0.0038 0.38224 024R D9.2 Polished D9_2_50 375 12 6/38 0.464 0.048 0.0599 0.0031 0.44741 024I D9.2 Polished D9_2_51 383 13 Pbcor.6/38 0.582 0.074 0.062 0.0032 0.37612 025R D9.2 Polished D9_2_52 383 12 Pbcor.6/38 0.53 0.058 0.0622 0.0032 0.42545 025I D9.2 Polished D9_2_53 386 19 Pbcor.6/38 1.02 0.16 0.0648 0.004 0.36619 027R D9.2 Polished D9_2_56 379 13 Pbcor.6/38 0.548 0.061 0.0612 0.0032 0.42516 D92_2_9I D9.2 Polished D9_2_59 386 17 Pbcor.6/38 0.69 0.1 0.0636 0.0037 0.37252 D92_2_7R D9.2 Polished D9_2_60 397 15 6/38 0.496 0.043 0.0636 0.0034 0.52488 D92_2_7I D9.2 Polished D9_2_62 403 18 6/38 0.497 0.058 0.0646 0.0039 0.45948 D92_2_6I D9.2 Polished D9_2_65 402 21 Pbcor.6/38 0.8 0.12 0.0667 0.0042 0.38707 D92_2_4R D9.2 Polished D9_2_69 394 19 6/38 0.52 0.058 0.0632 0.0039 0.4841 D92_2_1I D13.1 Polished D13_1_1 378 12 Pbcor.6/38 0.625 0.08 0.0612 0.0031 0.36797 D131_1R D13.1 Polished D13_1_2 389 12 6/38 0.489 0.042 0.0623 0.0031 0.50129 D131_1I D13.1 Polished D13_1_4 393 9.9 6/38 0.491 0.046 0.0629 0.0029 0.44155 D131_3I D13.1 Polished D13_1_7 382 16 6/38 0.483 0.069 0.0612 0.0035 0.37165 D131_6C D13.1 Polished D13_1_10 372 15 Pbcor.6/38 0.457 0.056 0.0597 0.0034 0.42147 D131_9R D13.1 Polished D13_1_11 383 23 6/38 0.513 0.086 0.0613 0.0045 0.40112 D131_9I D13.1 Polished D13_1_14 395 14 6/38 0.538 0.051 0.0633 0.0034 0.49298 D131_10I D13.1 Polished D13_1_15 393 18 6/38 0.479 0.063 0.063 0.0038 0.41686 D131_11I D13.1 Polished D13_1_16 390 15 Pbcor.6/38 0.64 0.1 0.0633 0.0035 0.3336 D131_12R D13.1 Polished D13_1_19 386 15 Pbcor.6/38 0.657 0.096 0.0631 0.0035 0.3549 D131_14I D13.1 Polished D13_1_20 395 25 Pbcor.6/38 0.92 0.23 0.0662 0.0049 0.28389 D131_15R D13.1 Polished D13_1_22 403 18 Pbcor.6/38 0.79 0.12 0.0664 0.0039 0.36065 D131_17R

Appendices 181

D13.1 Polished D13_1_23 393 13 6/38 0.516 0.05 0.0628 0.0032 0.46543 D131_17I D13.1 Polished D13_1_24 384 15 Pbcor.6/38 0.746 0.1 0.0631 0.0035 0.38235 D131_18R D13.1 Polished D13_1_25 376 14 6/38 0.48 0.037 0.0602 0.0032 0.5677 D131_18C D13.1 Polished D13_1_26 397 18 Pbcor.6/38 0.673 0.089 0.0658 0.0039 0.40899 D131_19R D13.1 Polished D13_1_27 385 15 6/38 0.466 0.047 0.0617 0.0035 0.49022 D131_201R D13.1 Polished D13_1_28 380 14 Pbcor.6/38 0.551 0.06 0.0611 0.0033 0.44434 D131_202R D13.1 Polished D13_1_29 389 12 6/38 0.495 0.054 0.0622 0.0031 0.41555 D131_19C D13.1 Polished D13_1_31 385 20 Pbcor.6/38 0.86 0.18 0.0644 0.0041 0.29101 D131_21I D13.1 Polished D13_1_33 357 12 6/38 0.499 0.05 0.0571 0.003 0.46438 D131_23R D13.1 Polished D13_1_34 396 17 Pbcor.6/38 0.685 0.087 0.0648 0.0038 0.4192 D131_24I D13.1 Polished D13_1_36 374 14 Pbcor.6/38 0.509 0.061 0.0599 0.0033 0.41768 D131_25I D13.1 Polished D13_1_39 396 20 Pbcor.6/38 0.89 0.17 0.0666 0.0042 0.31351 D131_27R D13.1 Polished D13_1_40 389 14 Pbcor.6/38 0.529 0.061 0.0623 0.0034 0.42779 D131_27I D13.1 Polished D13_1_41 897 27 6/38 1.853 0.085 0.182 0.0086 0.71752 D131_28I D13.1 Polished D13_1_43 389 14 Pbcor.6/38 0.554 0.048 0.0629 0.0033 0.51797 D131_29I D13.1 Polished D13_1_44 395 17 Pbcor.6/38 0.706 0.093 0.0646 0.0038 0.40775 D131_30R D13.1 Polished D13_1_45 380 16 6/38 0.467 0.071 0.0609 0.0035 0.35359 D131_30I D13.1 Polished D13_1_46 401 17 6/38 0.501 0.038 0.0643 0.0038 0.61462 D131_33I D13.1 Polished D13_1_47 270 10 Pbcor.6/38 0.443 0.078 0.0439 0.0024 0.29653 D131_35R D13.1 Polished D13_1_48 278 14 Pbcor.6/38 0.287 0.043 0.0438 0.0028 0.39245 D131_35I D13.1 Polished D13_1_50 396 15 Pbcor.6/38 0.512 0.044 0.0636 0.0035 0.53927 D131_361I D13.1 Polished D13_1_51 389 12 Pbcor.6/38 0.439 0.047 0.0622 0.0031 0.42203 D131_362C D13.1 Polished D13_1_52 396 14 6/38 0.506 0.05 0.0634 0.0034 0.47699 D131_37R D13.1 Polished D13_1_53 397 13 6/38 0.58 0.077 0.0633 0.0034 0.37505 D131_37I D13.1 Polished D13_1_55 403 14 Pbcor.6/38 0.483 0.061 0.0643 0.0034 0.3862 131_rI D17.6 Polished D17_6_4 727 38 6/38 1.15 0.1 0.1198 0.0081 0.61383 D176_002I D17.6 Polished D17_6_5 389 15 6/38 0.549 0.063 0.0619 0.0034 0.43174 D176_003R D17.6 Polished D17_6_6 397 15 Pbcor.6/38 0.552 0.058 0.0638 0.0036 0.47312 D176_003I D17.6 Polished D17_6_8 378 15 6/38 0.508 0.068 0.0605 0.0034 0.3871 D176_004I D17.6 Polished D17_6_11 387 14 Pbcor.6/38 0.605 0.073 0.0627 0.0033 0.39981 D176_006R D17.6 Polished D17_6_12 507 21 6/38 0.654 0.055 0.082 0.0048 0.57129 D176_006C D17.6 Polished D17_6_13 420 13 Pbcor.6/38 0.637 0.047 0.068 0.0034 0.56098 D176_007C D17.6 Polished D17_6_14 392 14 6/38 0.529 0.052 0.0628 0.0033 0.47144 D176_008R D17.6 Polished D17_6_15 615 19 6/38 0.898 0.07 0.1002 0.0051 0.54672 D176_008I D17.6 Polished D17_6_16 412 15 Pbcor.6/38 0.86 0.11 0.0688 0.0036 0.37863 D176_009R D17.6 Polished D17_6_17 396 14 Pbcor.6/38 0.52 0.054 0.0637 0.0033 0.4464 D176_009I D17.6 Polished D17_6_19 384 15 Pbcor.6/38 0.577 0.084 0.0622 0.0035 0.36053 D176_010I D17.6 Polished D17_6_21 368 14 Pbcor.6/38 0.68 0.13 0.0607 0.0033 0.27353 D176_011I D17.6 Polished D17_6_22 409 15 Pbcor.6/38 0.772 0.091 0.0678 0.0036 0.41071 D176_CL01R D17.6 Polished D17_6_23 400 16 6/38 0.504 0.069 0.0642 0.0036 0.37903 D176_CL01I D17.6 Polished D17_6_25 400 15 Pbcor.6/38 0.546 0.056 0.0646 0.0036 0.47742 D176_2_1I D17.6 Polished D17_6_27 376 13 Pbcor.6/38 0.583 0.068 0.0614 0.0032 0.40796 D176_2_2I D17.6 Polished D17_6_29 386 17 6/38 0.472 0.061 0.0618 0.0037 0.42035 D176_5C D17.6 Polished D17_6_30 1030 140 7/6 2 0.14 0.1853 0.01 0.61057 D176_6R D17.6 Polished D17_6_34 386 17 Pbcor.6/38 0.616 0.083 0.0634 0.0037 0.39745 D176_10R D17.6 Polished D17_6_35 397 12 6/38 0.482 0.033 0.0636 0.0031 0.57997 D176_10I D17.6 Polished D17_6_37 390 16 Pbcor.6/38 0.593 0.077 0.0637 0.0036 0.39908 D176_12I

182 Appendices