Petrogenesis of Eclogite and Mafic Granulite Xenoliths from South

Petrogenesis of eclogite and mafic

granulite xenoliths from South

Australian Jurassic kimberlitic

intrusions: Tectonic Implications

Thesis submitted in accordance with the requirements of the University of Adelaide for an Honours Degree in Geology

Angus Tod November 2012

PETROGENESIS OF GITE ECLO AND MAFIC GRANULITE XENOLITHS FROM SOUTH AUSTRALIAN JURASSIC KIMBERLITIC TRUSIONS: IN TECTONIC IMPLICATIONS

ANGASTON, EL ALAMEIN AND PITCAIRN ECLOGITES AND MAFIC TES GRANULI

ABSTRACT

Jurassic kimberlites in South Australia have entrained sub lithospheric mafic granulites and eclogites from the eastern margin of the Australian Craton. This thesis looks at these rocks as a unique window into the sub-lithospheric mantle beneath the south eastern margin of Gondwana. Samples collected from Angaston, El Alamein and Pitcairn included eclogites, amphibole eclogites, amphibole granulites and feldspar rich granulites. These samples were prepared for analytical work at the University of Adelaide. Whole rock geochemistry was collected from x-ray fluorescence in the Mawson Laboratories. Mineral identification and geochemistry was determined by the Cameca SX 51 microprobe at Adelaide Microscopy. Geothermobarometry showed pressures between 6-30kbar, which represent 15-90km of depth and temperatures between 620-1200oC. These rocks experience very high pressure and temperatures and show petrological evidence of isobaric cooling path from the adiabat to the stable geotherm. Magma crystallisation models using MELTS program helped to determine the protoliths that appear to represent mafic underplates. The cumulate and melts that make up these xenoliths have been shown in this thesis to most likely have been derived from a MORB source that crystallised at high pressures (up to 30kbar). Pseudosections produced with the Theriak-Domino program were used to produce a metamorphic path and show that rock type is closely linked to emplacement depth and bulk composition. Radiogenic dating using Neodymium and Samarium system created isochron’s using IsoPlot and gave ages supporting protolith emplacement during the Neoproterozoic (≈670Ma) around the breakup Rodinia.

KEYWORDS: ECLOGITES, TES, GRANULI EMAC, PETEROGENESIS AND METAMORPHISM

TABLE OF CONTENTS Angaston, El Alamein and Pitcairn Eclogites and Mafic Granulites ...... 1 Abstract ...... 1 Keywords: Eclogites, granulites, EMAC, Peterogenesis and metamorphism ...... 1 List of Figures and Tables ...... 3 Introduction ...... 8 Background ...... 10 Setting ...... Error! Bookmark not defined. Petrology ...... 14 Methods ...... 22 Observations and Results ...... 23 Discussion ...... 47 Conclusions ...... 58 References ...... 60 Appendix A: Methods ...... 64 Appendix B Average garnet and clinopyroxene data (see extended appendix for all data) ...... 66 appendix C Hand Sample descriptions ...... 68 appendix DThinsection Descriptions ...... 69

LIST OF FIGURES AND TABLES

Figures Figure 1 Location map for the xenoliths which also shows locations of relevant locations for this thesis such as the Australian Craton, Tasman line and Kayrunnera xenoliths. Map adapted from Tappert et al (2011)...... 9 Figure 2 Modal percentages of minerals garnet (Gt), pyroxene (Px) and Feldspar (Fd) for the South Australian xenoliths. Xenoliths are distinguished by rock type is Figure 2.A and location of kimberlitic pipe withe two areas being El Alamein and Pitcairn in Figure 2.b. The rock type definitions are found in table 1 ...... 15 Figure 3 Photomicrographs of the three main types of textural xenoliths from Angaston, El Alamein and Pitcairn. Image A shows the common eclogitic texture such as triple points in plain polarised light (PPL) (Ai) and cross Polarised light (CPL) (Aii) in sample PA 6x2, Image B shows the common granulite texture and the main metamorphic reaction that defines theses suites of mafic rocks in PPL and CPL (Bii) in smaple Pit- M25, Image C shows gabbroic texture of xenoliths within a matrix of fine grained plagioclase and pyroxene in PPL (Ci) and CPL (Cii) in sample PA 7x9...... 17 Figure 4 Photomicrographs of important textures found within the studied xenoliths. Image (A) shows the metamorphic reaction plagioclase + pyroxene ↔ garnet + quartz as seen at El Alamein. Exsolution features such as vermicular exsolution of clinopyroxene of garnet and orthopyroxene exsolution of clinopyroxene in plane polarised light (PPL) (Ai) and cross polarised light (CPL) in sample PA 7x1. Image (B) shows garnet mineral relationships within the granulites in the Pitcairn xenoliths. Garnets form as blebs around pyroxene in PPL (Bi) and CPL (Bii) in sample JS Kim. Image (C) shows the metamorphic reaction Plagioclase + pyroxene ↔ garnet + quartz as seen at El Alamein. Exsolution features such as garnet exsolution of clinopyroxene and orthopyroxene exsolution of clinopyroxene in PPL and CPL (Cii) in sample PA 7x1...... 20 Figure 5 Photomicrograph of orthopyroxene crystal core of a complex carona structure in plane polarised light (PPL) (i) and cross polarised light (CPL) (ii) in sample PA 7x1...... 21 Figure 6 Modal percentages of end members for garnet of the South Australian xenoliths. The iron end member is almandine (Al), magnesium end member is pyrope (Py) and calcium end member is grossular (Go), xenoliths are distinguished by rock type in diagram 6a and xenolith location 6b ...... 23 Figure 7 Modal percentages of end members for pyroxene of the South Australian xenoliths. The iron end member is Forsterite (Fs), iron calcium end member is Hedenbergite (Hd), magnesium end member is Enstatite (En) and the magnesium calcium end member is diopside (Di). Xenoliths are distinguished by rock type in diagram 6a and xenolith in location 6b...... 24 Figure 8 Graph of Jadeite cation % vs pressure. Pressure was calcutalted using Nimmis and Taylor (2000) clinopyroxene barometer. Data taken from table 2 and table 6...... 25 Figure 9 Modal percentages of end members for feldspars of the South Australian xenoliths. The Sodium end member is albite (Ab), calcium end member is anorthite (An) and potassium end member orthoclase (Or). Xenoliths are distinguished by rock type in diagram 6a and xenolith location 6b...... 25 Figure 10 Plotted amphiboles from Pitcairn xenoliths using A-site occupancy by alkalis (Na + K) vs SiO2 to discriminate between the end members (HAWTHORNE et al.

1997) pargasite (Pa), edenite (Ed), tschermakite (Ts), hornblende (Hb) and tremolite (Tr)...... 26 Figure 11Alkalis (Na2O + K2O) vs SiO2 whole rock geochemistry for the xenoliths plotted using IgPet (Carr 2002). Rock type boundaries described by Cox et al (1979). The South Australian xenoliths plot within the Basaltic region. This shows Angaston (red circles and blue squares) (Segui 2010), El Alamein (yellow crosses) and Pitcairn (green triangles) ...... 34 Figure 12 (A) Calculated CIPW Norm for the South Australian xenoliths, the proposed classification by Thompson (1984) for basalt based on their normative proportions of nepheline (Ne), olivene (Ov), albite (Ab), hypersthenes (Hy) and quartz (Qt). Red circles represent South Australian xenoliths (Segui 2010) which plot within the silica saturated and silica undersaturated portions. Green circles represent MORB (Jenner & O'Neill 2012) which plot in the silica oversaturated and silica saturated parts of the diagram. (B) Mole percent diagram (petrogenetic grid) relevant to variable precent melting (5% to the point where clinopyroxene disappears from the residue) of lherzolite over a pressure range of 0.5 to 3GPa (i.e., about 15-90km depth; pressure shown in bold). Each dashed line at a given pressure represents loci of melt compositions (molar normative) generated by progressive partial melting of lherzolite assemblage (ol + opx + cpx + melt) at that pressure (melt % increasing from left to right on each dashed curve). Each continuous line represents a fixed %melting curve. Aldo shown is the cpx out line. A lherzolitic source rock will lose cpx to the melt beyond this line. Sources of data: Takahashi and Kushiro (1983), Hirose and Kushiro (1993), and Baker and Stopler (1995). Note that it is mainly schematic and does not take into account the changing source composition that must happen as the melt in removed from the source...... 35 Figure 13 Plate of whole rock geochemical graphs of South Australian xenoliths (Segui 2010) with MORB (Jenner & O'Neill 2012) for comparison. Graphs A, B, C and D are MgO vs SiO2, CaO, TiO2 and Al2O3 respectively. Diamonds on Graph A and B show mineral compositions plagioclase (PLAG), clinopyroxene (CPX), orthopyroxene (OPX) and the mid ocean ridge basalt (MORB) melt composition, with two distinct trends; 1) a trend towards orthopyroxene showing orthopyroxene crystallisation driving the melt and 2) a trend clinopyroxene + plagioclase showing clinopyroxene + plagioclase driving crystalisation. Black arrow shows igneous variation trends, “M” is the direction towards melt differentiation and “C” is towards the cumulates or crystal extracts that must drive the magmatic trend...... 36 Figure 14 Graph of barium (Ba) vs wt% MgO for the South Australian xenoliths (Segui 2010) (red circles) with MORB (Jenner & O'Neill 2012) (blue circle). South Australian xenoliths show a several order magnitude higher amounts...... 37 Figure 15 Isochrons calculated using IsoPlot (Ludwig 2003) graphs show 143Nd/144Nd vs 147Sm/144Nd (A) represents whole rock isotope data for the South Australian xenoliths from Angaston (Segui 2010), El Alamein and Pitcairn and gives an age 739±680Ma. (B) South Australian xenoliths (Segui 2010) (green triangles) and Neoproterozoic Cambrian and South Australian Adelaidean basalts (John Foden, per comms) (Blue diamond’s) and gives an age of 656 ± 92Ma...... 39 Figure 16 Pseudosection calculated for Pit M22 (see table 2) using THERIAK- DOMINO program (De Capitani & Petrakakis 2010), for the geologically realistic chemical system SiO2-Al2O3-FeO-Fe2O3-MgO-CaO-Na2O-K2O-H2O-TiO2 (NCKFMASHTO). The dataset used compiles the following a-x models which incorporate Fe3+ end-member minerals: garnet, biotite and melt (White et al. 2007),

5 orthopyroxene and magnetite (White et al. 2002), amphibole (Diener et al. 2007), clinopyroxene (Green et al. 2007), K-feldspar and plagioclase (Holland & Powell 2003) and ilmenite (White et al. 2000). Mn is not considered for the reasons given by White et al (White et al. 2007). Blue lines represent major introduction of a mineral to the assemblage (amphibole, garnet and plagioclase), arrow represent direction on pseudosection the mineral labled is introduced. The introduction of garnet to the assemblage turns to Gabbroic rock to granulite and the loss of plagioclase turns granulite to eclogite. Blue shaded polygon represents the mineral assemblage seen for Pit M22 and the blue star represents the pressure and temperature estimations for the sample (see table 6)...... 43 Figure 17 Pseudosection calculated for Pit M25 (see table 2) using THERIAK- DOMINO program (De Capitani & Petrakakis 2010), for the geologically realistic chemical system SiO2-Al2O3-FeO-Fe2O3-MgO-CaO-Na2O-K2O-H2O-TiO2 (NCKFMASHTO). The Dataused compiles the following a-x models which incorporate Fe3+ end-member minerals: garnet, biotite and melt (White et al. 2007), orthopyroxene and magnetite (White et al. 2002), amphibole (Diener et al. 2007), clinopyroxene (Green et al. 2007), K-feldspar and plagioclase (Holland & Powell 2003) and ilmenite (White et al. 2000). Mn is not considered for the reasons given by white et al (2007). Red lines represents major introductions of mineral to an assemblage (amphibole, garnet and plagioclase), arrows represent direction on pseudosection the mineral in labled is introduced. The Introduction of garnet to the assemblage turns Gabbroic rock to granulite and the loss of plagioclase turns granulite to eclogite. Red shaded polygon represents the mineral assemblage seen for Pit M25 and the red star represents the pressure and temperature estimations for the sample (see table 6)...... 45 Figure 18 Pressure and temperature plot of geothermobarometry estimations for the SEA (O'Relly & Griffin 1985), EMAC (Pearson & O'REILLY 1991), Monk Hill (Tappert et al. 2011), Angaston (Segui 2010) and Pitcairn and El Alamein. Pressure and temperature estimations using garnet-clinopyroxene Fe-Mg thermometer (Ellis & Green 1979, Krogh 1988) and clinopyroxene barometer (Nimis & Taylor 2000). Data for UHP metamorphic rocks Refrence) schematic subduction metamorphic path taken from Agard (2009) and subduction data points taken from numerous sources(Gao 1999, Dale 2003, Janak 2004). Arrows right of Monk Hill Geotherm (Tappert et al. 2011) show the metamorphic path for the South Australian xenoliths...... 47 Figure 19 Ni-Cr (ppm) variation of the South Australian mafic xenoliths (Segui 2010) (red circles) and MORB data (Jenner & O'Neill 2012) (green circles). Trends on this Figure show melt fractionation curves for high pyroxene/olivene (high pressure) (blue line) and lower pyroxene/olivene trends (black line with yellow triangles) and the complimentary cumulate trend for a high pressure (black line with orange circles). Trends created using MELTS (Ghiorso & Sack 1995). The specific chosen starting basalt used was an olivene tholeiite from the Adelaidean Smithon basin in N.W. Tasmania. This was chosen as it clearly had experienced no crustal contamination (John Foden, per comms) ...... 51 Figure 20 % of melt remaining vs Temperature showing melt evolution path (red crossed) and the complimentary solid cumulate path (black dashes) created from the results of MELTS (Ghiorso & Sack 1995) modelling on the specific chosen starting basalt, an olivene tholeiite from the Adelaidean smithton basin in N.W. Tasmania. This was chosen as it clearly had experienced no crustal contamination (John Foden, per comms). The most favourable run made at pressure 8.5 kbar, low water content and

6 oxygen fugacity of QFM + 1as seen in the MELTS list. Minerals crystallised orthopyroxene (OPX), clinopyroxene (CPX), spinel (SP) and plagioclase (PLAG) ..... 53 Figure 21 MELTS (Ghiorso & Sack 1995) modelling of the south Australian xenoliths on Wt% MgO vs Wt% CaO (A) and SiO2 (B). Melt evolution path (blue crosses) and the complimentary solid cumulate path (black dashes) are shown on the diagram. Starting compostion is shown to be the orthopyroxenite (sample EA08 6)...... 54

Tables Table 1 Distinguishing characteristics for xenoliths different rock types...... 14 Table 2Whole rock major element geochemistry collected using XRF ...... 29 Table 3Whole rock trace element geochemistry collected using XRF ...... 31 Table 4 Radiogenic Isotope data ...... 38 Table 5 Equations used for Geothermobarometry ...... 41 Table 6 Presure and temperature estimates where TEG79 Ellis ( & Green 1979), T K88(Krogh 1988) and PNT95(Nimis & Taylor 2000)...... 44

INTRODUCTION

Jurassic kimberlites occur at a number of locations in the mid north of South Australia.

They have transported a diverse range of lower crustal and upper mantle xenoliths.

Studies of these will help to explain the thermal and compositional evolution of the lithosphere of South Eastern Gondwana. These xenoliths include mafic eclogite and granulite, garnet peridotite (Tappert et al. 2011) and xenocrysts including diamonds

(Tappert et al. 2009), Cr diopside, garnet, picroilmenite and spinel. The mineral assemblages of the eclogites range from garnet + clinopyroxene eclogite to amphibole + garnet + clinopyroxene eclogite. The mineral assemblages of the granulites range from

Feldspar rich (Fd rich) to amphibole rich granulites but both granulite and eclogite generally have a garnet and clinopyroxene dominated mineralogy. This project aims to identify the protolith of the kimberlite transported eclogites and the pressure, temperature and timing of their metamorphic evolution. This will lead to a better understanding of the paleo-geotherm and structure along the south eastern margin of

Australian Craton. These xenoliths are unique samples of the lithospheric mantle beneath the important transition zone between Precambrian craton and the Paleozoic fold belt of Eastern Australia (Figure 1). We will test the hypothesis that these eclogites and granulites are mafic under plates recording mantle derived magmatism supplied to the evolving crust. It is possible they originated during Late Proterozoic rifting and early Proterozoic subduction.

This Thesis focuses on xenoliths from kimberlitic intrusions at three localities; El

Alamein, Pitcairn and Angaston (Figure 1). In this study we used a number of techniques to help constrain the P-T-t path and the possible protoliths of the mafic

Figure 1 Location map for the xenoliths which also shows locations of relevant locations for this thesis such as the Australian Craton, Tasman line and Kayrunnera xenoliths. Map adapted from Tappert et al (2011). xenoliths. Bulk geochemistry analysis were used to constrain the pressure, temperature and time paths through the production of a pseudosection using the program

THERIAK-DOMINO program (De Capitani & Petrakakis 2010). Bulk geochemistry was also used to make comparisons with other data sets. Mineral comparison analyses were done using the electron microprobe to provide mineral geochemistry and geothermobarometry determination. Geothermometry determination were based on the exchange of Mg-Fe2+ between garnet (gt) and clinopyroxene (cpx) (Ellis & Green 1979,

Krogh 1988) and geobarometry estimations were made using the clinopyroxene site

10 occupancy barometer formulated by Nimis and Taylor (2000). The most common mineral assemblage was Gt-cpx-rutile±kyanite±plag and made up the bulk of the mafic xenolith mineral assemblage’s prograde and retrograde metamorphic reactions and metamorphic/igneous textures were used to show the infered metamorphic path through the pseudosections (Pearson et al. 1991, Jacob 2004).

BACKGROUND

Kimberlites are volatile rich, highly potasic, ultra mafic rock that ascend from the deep mantle/lithospheric mantle (Sparks et al. 2006). Rocks from the mantle lithosphere and lower crust, such as peridotite, granulite and eclogite, are commonly sampled as xenoliths by the ascending kimberlites. Kimberlites have been studied due to their association with diamonds for their economic importance; but also to provide rare sampling windows into the lower crust and upper mantle. Eclogitic and granulitic xenoliths are believed to form in three different ways (Jacob 2004, Griffin & O'Reilly

2007).

1) As a high pressure cumulate from ascending mafic magma.

2) Whole-sale under plating of ascending mafic magma at the Moho; forming

Gabbro, which eventually cools first into garnet granulite field then into the

eclogite facies.

3) Oceanic crust subducted at a convergent margin and converted to eclogite during

subduction, which is then tectonically accreted to the base of the lithosphere.

Many eclogites show MORB like chemistry and P-T values like the upper subducted slab. This has led to many papers linking eclogites to kimberlite subduction processes

(Jacob 2004). Kimberlitic eclogites are thought to experience exceptionally high

11 pressures and temperatures when compared to eclogites that occur in glaucophane schist terrain and those within crustal migmatite gneissic terrains (Coleman et al. 1965) that are commonly associated with subduction zones. Eclogites found entrained within kimberlites can be referred to as high Temperature (HT) and ultra high pressure eclogites due to the forming temperatures of T>900oC and pressures P> 36Kbar.

Geological setting

The Precambrian Australian Craton is made up of a mosaic of Archean and Proterozoic crustal elements on the western side of Australia. The Eastern side of Australia is made up of the Paleozoic to Mesozoic Tasman fold belt, which shows a thinner crustal package. The Tasman Line defines the boundary between these two building blocks that make up Australia (Veevers & Conaghan 1984) (Figure 1). Xenoliths from kimberlite pipes and dykes have been found in a number of places in south and south-eastern

Australia (O'Relly & Griffin 1985, Pearson . 1991, Song 1994, Segui 2010, Tappert.

2011). South Australian Kimberlites occur in the Mid North of South Australia at Port

Augusta, Eurelia, Terowie, Orroroo and in the Adelaide Hills (Figure 1). The Eurelia and Adelaide Hills kimberlites have diamonds as xenocrysts and have, therefore, been well studied. South Australian kimberlites intrude the Burra and Umbertana sequences of the Adelaidean sediments (Colchester 1972, McCulloch 1982). They occur as pipes with N.W.-S.E. trending dykes that are deeply weathered and have been dated to the

Jurassic (~180Ma) by Stracke et al (1979) and Tappert et al (2011). Xenoliths found in

South Australia are a mixture of country rock and nodules of ultra mafic to felsic rocks derived from upper and lower lithosphere.

Paleogeothermal gradients have been determined at various locations on both sides of the Tasman line in Australia where data is available. Xenolith suites from East of the

Tasman Line have been extensively studied by a number of previous authors

(Sutherland & Hollis 1982, O'Relly & Griffin 1985, Pearson & O'REILLY 1991,

Pearson et al. 1991, Pearson et al. 1995).These studies have led to the definition of the

South-eastern Australian geotherm (SEA). They concluded that the protoliths for these mafic xenoliths were a number of mafic underplates from magmatic plumes that rose during the opening of the Tasman sea (O'Relly & Griffin 1985). Pearson et al (1991) studied xenoliths from the Pine Creek and Calcutteroo kimberlites and from the New

South Wales Kayrunnera alkali basalt (Tappert et al. 2011). These lie on the eastern margin of the Australian Craton (EMAC) just to the west of the Tasman Line. They used this data to define the EMAC geotherm, which appeared slightly cooler than the

SEA geotherm (REFRENCE). They concluded that the EMAC defined geotherm started out with a similar crust-mantle boundary as seen in the SEA geotherm but have now cooled due to equilibrations under different pressure and temperature conditions closer to the Australian Craton (Pearson & O'REILLY 1991).

Song (1994) collected a number of kimberlitic xenoliths from Culcutteroo, Pine Creek and Port Augusta (Figure 1) for geochemical and pressure temperature analysis for his study on the evolution of the lithospheric mantle below S.E. South Australia. His work concluded that the South Australian xenoliths reflected several periods of underplating by basaltic liquids derived from deep lithosphere or athenosphere, subsequent metamorphism, and metasomatism of the original melt (Song 1994). He also concluded that his calculated P-T estimates illustrate that the lithosphere beneath the Paleozoic

Adelaide geosyncline is cooler than that of the Phanerozoic eastern Australia; indicating of different petrology or geochemical composition, which is also shown between the

EMAC and SEA geotherms. Tappert et al (2011) in addition conducted research into the

Monk Hill garnet peridotites xenoliths (Figure 1) and xenocrysts. This locality is on the eastern margin of the Australian Craton. Monk Hill P-T estimations also defined a significantly lower geothermal gradient (40mW/m2) than that under south-eastern

Australia. However the estimates of Song (1994) and Tappert et al (2011) show a much lower geotherm than the EMAC model of Pearson et al (1991). This may indicate that the EMAC and SEA estimations are both still re-equilibrating to the stable geotherm in the Jurassic, shown by the Monk Hill geotherm.

Tappert et al (2011) have showed the differences in goetherms are due to the

Kayrunnera volcanic rocks used in the Pearson et al (1991) P-T estimations. The volcanic hosts for these xenoliths have Permian emplacement age, compared to the

Jurassic kimberlites in South Australia (Gleadow & Edwards 1978, Stracke et al. 1979), and their geochemistry indicates they are alkaline basalts rather than kimberlites

(Ferguson & Sheraton 1979). Therefore, the earlier transport of the Kayrunnera volcanic rocks reveals a different, and in this case, a hotter geothermal gradient compared to the

South Australian kimberlitic xenoliths.

The El Alamein and Pitcairn kimberlites are both located along the EMAC and are assumed to be Jurassic in age (Stracke et al. 1979, Tappert et al. 2011). El Alamein is the most northern and western kimberlite locality studied within the central Adelaide fold belt of South Australia and was chosen to investigate any possible regional trends

in locality in mantle P-T conditions and mafic magma composition. Only limited prior

studies have been made at Pitcairn. The geochemistry and petrography is hoped to help

better constrain the paleogeotherm along the EMAC and to define the age, source and

tectonic signatures of their mafic protoliths. The inferred depth to the Moho in the Mid

North of South Australia is 35km (Branson et al. 1968)

Petrology Nineteen samples were collected for petrological descriptions from the Pitcairn and El

Alamein kimberlites (Figure 1) and were combined with 18 petrographical descriptions

of Angaston xenoliths from Segui (2010). The xenoliths were divided into five

lithological groups based on their mineral assemblage, mineral chemistry and textures.

The ratio Al(6)/Al(4) is a ratio used to distinguish eclogites from granulites based on the

clinopyroxene chemical composition and represents the ratio of Tschermaks to Jadeite

molecule within the mineral (Jacob 2004).

Table 1 Distinguishing characteristics for xenoliths different rock types.

Lithology Mineralogy Chemistry Texture Triple point equi- to sub Eclogitic rock Gt+ CPX±Qt±OPX±Am Al(6)/Al(4) ≥2 (CPX) granular euhedral texture

Triple point equi- to sub Amphibole CPX+Gt+Am±Qt±OPX Al(6)/Al(4) <2 (CPX) granular euhedral texture Eclogite Modal Am≥10% _ Orthopyroxenite OPX+CPX±Am±Gt Modal OPX>70%

Diverse stages of exsolution Feldspar rich Pl+CPX+Kfd±Opx±Gt±Am±Qt Modal Pl+K+Fd 40-50% textures, rutile inclusions granulite within garnet and or clinopyroxene Diverse stages of exsolution Amphibole Pl+Am+CPX+Kfd±Opx±Gt±Qt Modal Pl+K+Fd 40-50% textures, rutile inclusions granulite and Am >10% within garnet and or clinopyroxene Doleritic microstructure, Gabbroic Rock Pl+CPX+OPX+Am±Il±Ru lath shaped plagioclase, clinopyroxenes showing an intergrowth with amphibole and minor ilmenite

The El Alamein (Figure 1) xenoliths were collected from weathered kimberlitic sills near Port Augusta in the South Australian Mid North. Ten samples were examined and used for petrological description and mineral geochemistry. The Pitcairn xenoliths

(Figure 1) were collected from a location 160km East S.E. of Port Augusta. Nine samples were examined and used for peterological descriptions and mineral geochemistry and whole rock geochemistry.

Figure 2 Modal percentages of minerals garnet (Gt), pyroxene (Px) and Feldspar (Fd) for the South Australian xenoliths. Xenoliths are distinguished by rock type is Figure 2.A and location of kimberlitic pipe withe two areas being El Alamein and Pitcairn in Figure 2.b. The rock type definitions are found in table 1

Eclogitic Rock

The Eclogitic rocks are dominantly composed of garnet (30-60%), clinopyroxene (20-

40%, with essential rutile (1-10%) ± ilmenite ± spinel (Figure 2). They have equigranular textures with well-equilibrated triple point grain boundary textures indicative of equilibrated rocks (Figure 3A). These rocks show unstrained textures with clinopyroxene and garnet making up 90% of the rocks composition. Rutile is in abundance within this rock type and occurs at the junction between clinopyroxene and garnet. The little amount of plagioclase that is present (0-3%) exists as small crystals

Figure 3 Photomicrographs of the three main types of textural xenoliths from Angaston, El Alamein and Pitcairn. Image A shows the common eclogitic texture such as triple points in plain polarised light (PPL) (Ai) and cross Polarised light (CPL) (Aii) in sample PA 6x2, Image B shows the common granulite texture and the main metamorphic reaction that defines theses suites of mafic rocks in PPL and CPL (Bii) in smaple Pit-M25, Image C shows gabbroic texture of xenoliths within a matrix of fine grained plagioclase and pyroxene in PPL (Ci) and CPL (Cii) in sample PA 7x9. with their shape dictated by the other surrounding minerals. Alteration within the eclogite rock type is readily seen along fractures and mineral boundaries. The Alteration minerals are carbonates and micas.

Amphibole Eclogite

The amphibole eclogite rocks are dominantly composed of garnet (30-50%), clinopyroxene (20-40%,), Amphibole (>10%) with essential ruitle (1-10%) ± ilmenite ± spinel (Figure 2). These rocks show triple point textures indicative of equilibrated rocks

(Figure 3A). They also show layering textures defined by garnet-rich layers and then clinopyroxene rich layers. Amphibole demonstrates a strong relationship to rutile forming as inclusions within amphibole. The low amounts of plagioclase (0-3%) within this rock type is rimmed by garnet.

Feldspar (Fd) rich Granulite and Amphibole Granulite

These Fd-rich granulite and amphibole granullite rocks are mafic rocks. The Fd-rich granulites are composed of clinopyroxene (20-45%), garnet (15-40%), plagioclase (20-

55%) ± ilmenite ± rutile (Figure 2). The amphibole granulites are composed of clinopyroxene (20-40%), garnet (15-35%), plagioclase (20-55%), Amphibole (>10%) ± ilmenite ± rutile (Figure 2). They are characterised by fine to medium grained interlocking sub- to equiangular textures (Figure 3B). The diagnostic mineral for these rock types is large elongate plagioclase which display simple and multiple twinning.

Reddish-pyrope garnet occurs as sub to euhedral grains that form rings around the clinopyroxenes, llmenite and plagioclase. Clinopyroxene are subhedral and dark green, their boundaries with plagioclase are straight and curved with garnet. Ilmenite, pyroxene, amphiboles and garnets all show exsolution textures implying the breakdown of this mineral assemblage. Within this rock type we see three types of exsolution: 1) garnet and amphibole exsolution from clinopyroxenes (Figure 4C and 5); 2) clinopyroxene as vermicular exsolution in garnet (Figure 3A), and; 3) clinopyroxene exsolution from orthopyroxene (Figure 5). These textures are believed to show the transition from primary igneous (gabbroic rock) textures towards granulite metamorphic textures under static stress.

Orthopyroxenite1

There was one orthopyroxenite sample found from El Alamein (EA 08 6) with 70% orthopyroxne (OPX) and 10% clinopyroxene (CPX) and minor Garnet. Orthopyroxenite are formed as early high pressure cumulates from fractionated magmas

Gabbroic rock

These xenoliths show plagioclase laths and prismatic clinopyroxenes that are intergrown with amphibole and minor illmenite and rutile (Figure 3C). Garnet rings encompass the clinopyroxenes in some of these rock type.

1 No thin section was created for this sample so the petrography was concluded from the hand sample only.

Figure 4 Photomicrographs of important textures found within the studied xenoliths. Image (A) shows the metamorphic reaction plagioclase + pyroxene ↔ garnet + quartz as seen at El Alamein. Exsolution features such as vermicular exsolution of clinopyroxene of garnet and orthopyroxene exsolution of clinopyroxene in plane polarised light (PPL) (Ai) and cross polarised light (CPL) in sample PA 7x1. Image (B) shows garnet mineral relationships within the granulites in the Pitcairn xenoliths. Garnets form as blebs around pyroxene in PPL (Bi) and CPL (Bii) in sample JS Kim. Image (C) shows the metamorphic reaction Plagioclase + pyroxene ↔ garnet + quartz as seen at El Alamein. Exsolution features such as garnet exsolution of clinopyroxene and orthopyroxene exsolution of clinopyroxene in PPL and CPL (Cii) in sample PA 7x1. Mineral Relationships

Several of the xenoliths studied from El Alamein contain microstructures that show evidence of arrested local equilibrium and re-equilibrium in different locations throughout the slide. Evidence for this includes: 1) Double and single corona of garnet/garnet + CPX around OPX on the boarder of plagioclase that is readily seen in the garnet granulites from El Alamein (Figure 3B, 4A and 4B) and within the Pitcairn xenoliths. 2) Garnet and pyroxene exsolution of relict pyroxenes’ (Figure 4A and 4B).

3) The replacement of plagioclase by garnet and quartz assemblage (Figure 3A, 4A and

4B).

Pearson and O’Reilly (1991) also noted these microstructures and deduced that they were the result of the breakdown of the primary assemblages, mainly olivine + plagioclase and pyroxene + plagioclase as a response to cooling from igneous temperatures. Garnet coronas can be explained by Equation (1):

(1)

𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 + 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 = 𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔 + 𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞 The garnets form as blebs or rims around pyroxenes or as lamellae or blebs in pyroxenes (Figure 4B). Garnet-clinopyroxene symplectites also form at the interface of plagioclase OPX relict boundaries and can be expressed in Equation 2 that depicts the transition from granulite to eclogite.

(2)

𝑜𝑜𝑜𝑜𝑜𝑜ℎ𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 + 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 = 𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔 + 𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐𝑐 + 𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞 This reaction also shows the compositional change from a more jadeite-rich pyroxene to a more omphacite-rich pyroxene due to the breakdown of albite.

Figure 5. Photomicrograph of orthopyroxene crystal core of a complex carona structure in plane polarised light (PPL) (i) and cross polarised light (CPL) (ii) in sample PA 7x1.

Slide PA78X shows an OPX crystal at the core of a complex corona structure and may illustrate either re-equilibration of primary Al-rich orthopyroxene with garnet, or an intermediate stage in the transformation of olivene + plagioclase to garnet + clinopyroxene (Pearson et al. 1991) (Figure 5).

Segui (2010) discussed a similar group of rocks located within the Angaston kimberlite dykes and diatremes which also lies on the eastern margin of the Australian Craton

(Figure 1). The Angaston mafic xenoliths however had an important addition to their suite, the inclusion of kyanite. This inclusion of kyanite to the assemblage was in the form of fine grained crystals that make up a matrix and symplectites with clinopyroxene

22 that aid in the breakdown of plagioclase with garnet (Segui 2010). Re-equilibration textures mainly that of garnet corona and garnet and pyroxene exsolution were also discussed.

METHODS

Samples were collected in the field from locations labelled (Angaston, El Alamein and

Pitcairn) and transported in clear bags to Mawson Laboratories. Sample descriptions were made at location sites.Sample preparation was conducted at Adelaide University

Mawson Laboratories. A diamond saw, stainless steel jaw crusher, tungsten mill and

Franz separator were used to preparethe samples for major element geochemistry, trace element geochemistry and radiogenic isotope geochemistry.

Major mineral geochemistry was conducted on in-situ mineral grains using the Cameca

SX 51 microprobe at Adelaide Microscopy. Whole rock major element analysis was conducted using fused glass discs and x-ray fluorescence (XRF). Total FeO was determined by the digestion in HCl in the presence of CO2 with the solution then being titrated using potassium di-chromate with BADS as an indicator. Whole rock trace element geochemistry was obtained by using pressed pellets and XRF.

Phase diagram calculations are based on whole-rock compositional data. Water content is based of weight loss on ignition. Analysis via titration methods provides the concentration of ferric iron. Due to the inevitable hydration and oxidation of the sample during retrogression and/or weathering at the surface, the H2O and Fe2O3 values of the composition used for phase diagram calculations should be considered a maximum estimate.

Radiogenic Isotope work was carried out on seven whole rock samples which were prepared at the Mawson Laboratories. Neodymium and Samarium analysises were carried out on a Finigan MAT 262 TIMS at Adelaide University. The Nd and Sm values were calculated using depleted mantle values (from Goldstein et al 1984).

OBSERVATIONS AND RESULTS

Mineral Geochemistry

Mineral geochemistry was collected using the SX 51 microprobe at Adelaide

Microscopy and used to help with geothermobarometry, mineral identification and end members.

Figure 6. Modal percentages of end members for garnet of the South Australian xenoliths. The iron end member is almandine (Al), magnesium end member is pyrope (Py) and calcium end member is grossular (Go), xenoliths are distinguished by rock type in diagram 6a and xenolith location 6b

Garnet

The garnets analysed from both localities were homogenous throughout with no zonation along the rims. Figure 6 shows garnets plotted within a compositional end member triangle with almandine (Fe), pyrope (Mg) and grossular (Ca) end members.

The Almandine composition of all garnets is roughly <50% with most differences occurring within the pyrope and gossular end member for garnet. Pitcairn displays a more pyrope-rich end member for garnet and El Alamein towards the Almandine end member. The rock types ternary diagram also depicts subtle differences in garnet end member compositions of garnet. The Fd-rich granulites display a higher amount of pyrope and gossular than the other rock types. The rock types that have >10% amphibole also display a trend towards the almandine end member, away from the samples with <10% amphibole.

Figure 7. Modal percentages of end members for pyroxene of the South Australian xenoliths. The iron end member is Forsterite (Fs), iron calcium end member is Hedenbergite (Hd), magnesium end member is Enstatite (En) and the magnesium calcium end member is diopside (Di). Xenoliths are distinguished by rock type in diagram 6a and xenolith in location 6b.

Pyroxene

The pyroxenes found in all samples were homogenous, showing no zoning. The dominant clinopyroxene throughout all samples was a type of clinopyroxene with a high diopside (Ca) (Figure 7). No systematic difference can be seen between the compositions of clinopyroxene through location of xenolith or type of xenoliths.

Orthopyroxene is only present in two samples from El Alamein and show enstatite as the dominating end member. Figure 8 shows a plot of pressure (Nimis & Taylor 2000) vs Jadeite (table 6) which illustrates a positive correlation, where omphacite is

25 consumed by jadeite during increased metamorphism (Fleet & Zussman 2003). The percentage of Jadeite was calculated as the sodium cation amount.

0.45

0.4

0.35

0.3

0.25

0.2 Jadeite % 0.15

0.1

0.05

0 0 5 10 15 20 25 30 35 Pressure (kbar)

Figure 8 Graph of Jadeite cation % vs pressure. Pressure was calcutalted using Nimmis and Taylor (2000) clinopyroxene barometer. Data taken from table 2 and table 6.

Figure 9 Modal percentages of end members for feldspars of the South Australian xenoliths. The Sodium end member is albite (Ab), calcium end member is anorthite (An) and potassium end member orthoclase (Or). Xenoliths are distinguished by rock type in diagram 6a and xenolith location 6b. Feldspar

The composition of feldspars in the Pitcairn and El Alamein xenoliths lay within the plagioclase feldspar series. Feldspars were not identified within the eclogitic rock type

26 group. The majority of plagioclase plot towards the albite (Na) end member (Figure 9).

Regional differences can be seen between El Alamein and Pitcairn feldspars. Pitcairn feldspars display a broader range of plagioclase compositions (30-90%albite), with some plotting towards the orthoclase (K) end member. El Alamein Feldspars all plot along the plagioclase series and have a much tighter range of composition (55-75%).

Figure 10 Plotted amphiboles from Pitcairn xenoliths using A-site occupancy by alkalis (Na + K) vs SiO2 to discriminate between the end members (HAWTHORNE et al. 1997) pargasite (Pa), edenite (Ed), tschermakite (Ts), hornblende (Hb) and tremolite (Tr). Amphibole

There is a large difference in abundance of amphibole between the Pitcairn and El

Alamein xenoliths, as El Alamein displays significantly lower amounts of amphibole if any at all. The chemistry of Amphibole is very important due to its component of water, which may indicate that Pitcarin mantle may have been more volatile enriched. The composition of the amphiboles found at Pitcairn display a trend towards pargasite (Pr), which is the silica-poor Alkali (Na+KA-site) high end member (Figure 10). Pargasite is known to form in high temperature metamorphic regions such as in contact aureoles

27 with igneous intrusions (HAWTHORNE et al. 1997). The samples also seem to show trends towards the pargasite end member as you move from the core of the mineral to the rim of the mineral.

Whole Rock Geochemistry

Whole-rock geochemical analyses were conducted on selected xenoliths from the

Pitcairn, El Alamein and Angaston localities. These added to the existing data set of whole rock analyses of Angaston xenoliths produced by Segui (2010). Candidate samples for these analyses were restricted by the availability of sufficiently large and homogeneous samples (usually those larger than ~ 300 gms). Such candidates are far more abundant at Angaston than at other localities. These data are reported in Table 2

Although most of these xenoliths are now dominated by metamorphic mineralogies and textures (though as discussed earlier there are good examples where some xenoliths and some textures are in transition from igneous to metamorphic), a key issue is the nature and age of their protoliths. It seems likely they have mafic igneous precursors and if this is the case then key questions include: what is the age and tectonic significance of the igneous event? Do they have equivalent volcanic suites recognizable in the geological record of S.E. Gondwana?

Amongst the samples analysed were a few examples of the host kimberlite (Angaston

Kim, EA08 2 and EA08 4). These are ultramafic rocks characterized by having very low

SiO2 and Al2O3 and very high MgO and moderate to high TiO2. They have very high ignition loss, dominated by CO2. Their trace elements are characterised by high Ni and

Cr and high light rare earth element (LREE) and high LREE/ heavy rare earth elements

(HREE) and very high Ba and Sr. One sample analysed is a lower crustal garnet gneiss

(CAX-M10), with a psamo-pelitic composition.

Table 2. Whole rock major element geochemistry collected using XRF

SiO2 Al2O3 TiO Fe O T FeO Fe O MnO MgO CaO Na O K O P O SO LOI Total Sample Mg# 2 2 3 2 3 2 2 2 5 3 % % % % % % % % % % % % % % % Metapelite CAX-‐M10 0.53 63.47 19.48 0.83 6.14 2.27 3.62 0.08 2.55 0.59 0.81 5.30 0.03 0.01 0.70 99.99 DS012-‐3 0.51 45.62 12.61 1.48 14.70 8.70 5.03 0.25 9.20 11.21 2.63 0.89 0.08 0.03 1.21 99.90 Orthopyroxenite EA08-‐6 0.83 52.52 3.09 0.11 9.47 6.36 2.41 0.17 30.06 1.35 0.16 0.04 0.00 0.03 1.32 98.31 Eclogitic rock EA08-‐1 0.59 42.78 13.56 1.46 13.06 9.24 2.79 0.21 13.45 10.83 1.30 0.21 0.18 0.13 2.93 100.1 DS012-‐5 0.43 42.05 12.42 2.79 18.01 11.32 5.43 0.18 8.64 11.82 1.36 0.17 0.07 0.29 1.15 98.95 Mafic Gneiss RT-‐CAL 2X1 0.74 49.75 10.85 0.14 10.12 6.57 2.82 0.18 18.74 8.05 0.72 0.14 0.04 0.06 1.01 99.80 RT-‐CAL 2XL10 0.54 53.42 17.35 0.45 8.62 3.90 4.29 0.05 4.63 1.81 3.70 5.82 0.07 0.09 2.31 98.30 EA08-‐9 0.52 50.78 19.19 0.97 7.15 4.32 2.35 0.05 4.65 3.42 4.72 3.58 0.08 0.20 3.57 98.36 Amphibole Eclogite PIT-‐M10 -‐ 51.27 21.49 0.31 5.30 -‐ -‐ 0.08 5.00 9.65 3.78 1.45 0.06 0.10 0.44 98.92 PIT-‐M22 0.49 49.53 11.50 1.24 12.93 11.18 0.51 0.20 10.85 11.45 1.37 0.47 0.14 0.02 0.47 100.1 Amphibole granulite JS KIM PITR 0.44 48.14 16.50 1.52 11.76 8.22 2.63 0.13 6.43 10.14 3.37 0.63 0.07 0.24 0.83 99.76 PIT-‐M26 0.46 48.98 13.97 1.65 13.45 9.41 3.00 0.19 8.04 10.96 1.99 0.72 0.18 0.02 0.60 100.7 DS012-‐4 0.39 37.21 11.91 5.42 17.49 12.75 3.32 0.19 8.31 12.02 2.09 0.53 3.11 0.11 0.85 99.24

Table 2 continued Mg SiO2 Al2O3 TiO Fe O T FeO Fe O MnO MgO CaO Na O K O P O SO LOI Total Sample 2 2 3 2 3 2 2 2 5 3 # % % % % % % % % % % % % % % % Fd rich Granulite DS012-‐1 0.81 49.39 11.89 1.21 12.63 2.43 9.93 0.20 10.64 11.69 1.54 0.50 0.14 0.03 0.90 100.7 DS012-‐2 -‐ 45.47 16.68 0.79 10.41 -‐ -‐ 0.15 9.41 12.05 2.38 0.20 0.10 0.47 1.20 99.32 DS012-‐6 0.61 46.77 13.81 1.41 10.27 6.63 2.91 0.17 10.49 12.38 2.61 0.50 0.24 0.03 1.37 100.0 DS012-‐7 0.48 44.99 13.88 1.63 14.66 9.51 4.09 0.22 8.93 13.09 2.04 0.17 0.08 0.12 0.58 100.3 EA08-‐3 0.63 42.99 13.35 1.40 12.76 7.94 3.93 0.21 13.31 10.60 1.56 0.23 0.16 0.12 3.01 99.71 EA08-‐5 0.60 42.70 13.75 1.43 13.06 8.61 3.49 0.21 13.02 10.83 1.46 0.19 0.14 0.14 2.70 99.64 EA08-‐8 0.58 42.81 13.74 1.44 13.17 9.53 2.58 0.21 13.30 10.61 1.42 0.19 0.14 0.15 2.75 99.94 PIT-‐M9 0.69 48.73 17.79 0.84 8.31 3.27 4.68 0.12 7.13 10.36 3.33 0.71 0.10 0.32 1.13 98.86 PIT-‐M20 0.60 49.31 14.61 0.48 9.06 6.74 1.57 0.16 10.20 13.46 1.75 0.46 0.10 0.05 0.71 100.3 PIT-‐M21 0.53 50.10 14.39 0.17 10.75 8.33 1.49 0.19 9.50 11.90 1.65 0.34 0.06 0.26 0.29 99.59 PIT-‐M23 0.51 43.71 23.53 0.86 7.29 5.98 0.64 0.07 6.32 10.61 2.87 0.82 0.11 0.19 1.20 97.58 PIT-‐M24 0.61 49.97 16.34 0.33 8.01 5.56 1.83 0.12 8.65 9.43 3.28 1.29 0.06 0.25 0.88 98.61 PIT-‐M25 0.57 51.00 21.19 0.31 5.21 3.80 0.99 0.08 5.01 9.99 3.79 1.35 0.06 0.09 1.01 99.10 Kimberlite ANGAS KIM 0.94 17.30 3.09 1.51 5.08 0.66 4.34 0.08 10.60 30.59 0.37 0.95 0.63 0.09 17.3 87.61 EA08-‐2 0.78 20.43 4.38 3.20 11.90 6.05 5.17 0.20 21.53 13.66 0.19 0.31 0.20 0.21 19.9 96.14 EA08-‐4 0.79 26.75 6.53 1.54 12.70 6.10 5.92 0.20 22.89 9.60 0.18 0.23 0.19 0.03 17.3 98.18 EA08-‐7 0.71 28.86 8.41 1.71 13.98 8.67 4.35 0.23 20.88 9.36 0.15 0.23 0.21 0.03 15.3 99.35

Table 3. Whole rock trace element geochemistry collected using XRF

Xenolith Psamo Psamo-‐ Eclogitic Eclogitic Amph Amph Amph Amph Amph OPXenite Kimberlite Kimberlite Type pelite pelite rock rock Eclogite Granulite Granulite Granulite Eclogite El El Location El Alamein Pitcairn Angaston Angaston Pitcairn Pitcairn Angaston Pitcairn Pitcairn El Alamein Alamein Alamein JS KIM PIT-‐ Sample EA08-‐6 CAX-‐M10 DS012-‐3 DS012-‐5 EA08-‐1 PIT-‐M22 PIT-‐M26 DS012-‐4 EA08-‐4 EA08-‐7 PIT M10 Zr 3.7 192.8 52.4 30.3 84.6 81.9 100.3 43.7 33.5 71.1 86.9 92.0 Nb 0.5 16.4 45.9 2 12.1 4.7 7.3 4.4 22.1 5.4 31.4 23.7 Y 0.8 29.3 28.3 18.9 24.2 24.4 27.4 53.6 17.7 21.9 23.1 26.1 Sr 20.2 175.8 197.6 381.8 140.8 103.2 188.8 527.0 508.5 144.9 376.7 284.8 Rb 3.3 172.4 16.3 12.7 15.1 9.3 14.8 16.2 9.8 11.1 12.8 11.8 U 0.1 1.0 1.6 -‐0.7 -‐1.3 0.5 -‐0.5 0.2 2.3 -‐0.6 1.4 -‐0.2 Th -‐0.2 6.8 0.8 -‐3.1 1.0 -‐0.7 2.3 -‐1.1 -‐0.8 2.5 4.8 2.9 Pb 2.1 75.2 -‐0.9 -‐8.3 -‐3.7 2.7 3.2 0.4 -‐0.6 1.5 2.6 3.2 Ga 4.7 26.1 17.5 12.3 16.4 21.4 21.1 15.6 18.3 17.7 4.9 7.9 Zn 49 62 81 92 100 84 92 89 45 74 61 72 Ni 802 68 347 430 392 216 133 161 89 152 362 419 Cu 87 57 35 220 169 62 96 19 55 36 220 205 Ba 533 1171 502 9492 2469 128 1131 2281 3344 227 389 497 Sc 33.5 9.9 60.9 59.7 40.1 44.9 41.5 39.9 33.1 42.8 53.3 49.8 Co 81 95 105 108 57 152 69 91 64 142 54 61 V 138 84 507 894 376 361 359 577 342 339 513 490 Ce -‐10 48 43 22 39 21 24 80 17 23 58 63 Nd 8 16 27 14 23 17 14 70 8 18 24 28 La -‐1 24 26 10 17 8 5 31 3 8 31 36 Cr 5602 73 17 77 325 434 244 -‐18 117 405 252 217

Table 3 continued Xenolith Fd Rich Fd Rich Fd Rich Fd Rich Fd Rich Fd Rich Fd Rich Fd Rich Fd Rich Fd Rich Kimberlite Kimberlite Type Granulite Granulite Granulite Granulite Granulite Granulite Granulite Granulite Granulite Granulite El El El El El Location Angaston Pitcairn Pitcairn Pitcairn Angaston Angaston Angaston Alamein Alamein Alamein Alamein Alamein Sample Angas Kim EA08-‐2 EA08-‐5 EA08-‐8 EA08-‐9 EA08-‐3 PIT-‐M9 PIT-‐M20 PIT-‐M21 DS012-‐6 DS012-‐7 DS012-‐1 Zr 161.6 47.2 79.4 79.5 224.0 82.0 21.1 25.2 2.8 54.7 25.0 33.2 Nb 109.7 18 7 7.6 16.9 15.5 0.1 1.9 1 8.4 2.8 6.1 Y 40.1 17.9 22.6 23.1 20.0 24.2 5.4 12.5 5.6 22.6 27.4 17.5 Sr 1016.7 476.3 159.7 328.2 674.6 146.5 624.7 130.3 181.7 188.5 269.6 758.0 Rb 73.7 15.9 11.9 12.2 45.0 15.6 18.2 5.1 4.3 12.5 8.3 10.2 U 4.0 2.2 0.6 0.9 0.8 2.2 -‐1.0 0.3 0.8 0.3 0.8 1.3 Th 16.5 -‐1.1 -‐0.5 -‐0.1 -‐0.3 -‐1.3 -‐3.2 1.6 -‐5.2 -‐0.2 -‐2.6 -‐2.8 Pb 4.7 -‐0.4 0.1 2.4 5.9 -‐0.9 -‐4.0 2.6 -‐4.2 -‐0.5 -‐4.7 -‐4.4 Ga 3.8 5.5 17.0 13.7 22.7 13.2 17.3 12.8 13.1 15.9 16.7 15.8 Zn 42 44 94 94 30 89 29 40 43 70 86 65 Ni 288 394 327 473 58 369 99 150 164 298 122 159 Cu 34 22 166 160 84 187 7 35 2 34 85 10 Ba 1901 3466 2155 1876 3350 2229 4947 1220 5573 630 3518 4693 Sc 9.1 38.8 42.0 44.7 22.9 41.9 17.5 45.5 49.9 40.4 57.0 33.8 Co 35 40 100 98 53 81 59 88 105 120 96 91 V 112 345 391 390 179 390 90 229 252 335 529 244 Ce 130 44 27 25 105 44 10 11 3 29 10 21 Nd 59 17 17 18 29 24 2 6 2 19 9 11 La 107 34 10 8 70 24 -‐1 1 0 11 1 7 Cr 317 38 248 521 140 239 164 437 247 531 239 324

Table 3 conitinued Xenolith Fd Rich Fd Rich Fd Rich Fd Rich Fd Rich Fd Rich type Granulite Granulite Granulite Granulite Granulite Granulite Location Angaston Pitcairn Pitcairn Pitcairn Pitcairn Pitcairn Sample DS012-‐2 PIT-‐M23 PIT-‐M24 PIT-‐M25 RT-‐CAL 2X1 RT-‐CAL 2XL10

Zr 34.7 28.4 11.5 19.6 4.6 303.8 Nb -‐0.2 4.1 1.5 1 0.5 6.7 Y 13.3 14.1 9.2 5.7 3.8 10.2 Sr 1122.2 572.2 364.6 616.7 50.2 656.1 Rb 16.9 10.7 19.8 14.9 3.5 121.0 U 0.8 0.8 -‐0.1 -‐1.0 -‐1.1 0.6 Th 0.8 -‐3.0 -‐2.3 -‐3.6 1.7 1.9 Pb -‐3.2 -‐5.0 -‐1.1 0.0 -‐2.5 4.7 Ga 17.5 14.5 12.6 16.7 9.9 22.8 Zn 39 16 53 24 72 29 Ni 101 163 145 89 358 31 Cu 78 6 93 14 156 21 Ba 3517 9691 6751 3867 558 4579 Sc 25.5 16.2 28.9 17.9 41.2 12.9 Co 87 53 55 46 119 21 V 177 172 136 87 146 166 Ce 26 18 13 10 -‐1 57 Nd 11 4 5 2 7 16 La 7 2 2 1 -‐2 32 Cr 175 316 400 189 1174 95

The bulk of the samples, the main subject of this study, are mafic rocks with SiO2 in the range of 40 – 53%. They plot in the “basalt” and “picritic basalt” fields on the Total

Figure. 11Alkalis (Na2O + K2O) vs SiO2 whole rock geochemistry for the xenoliths plotted using IgPet (Carr 2002). Rock type boundaries described by Cox et al (1979). The South Australian xenoliths plot within the Basaltic region. This shows Angaston (red circles and blue squares) (Segui 2010), El Alamein (yellow crosses) and Pitcairn (green triangles)

Alkalis v SiO2 plot (Figure 11). The suites from the three localities are geochemically similar. They have high Mg#, mostly >0.6. They are mostly critically undersaturated and some are Ol-Hy normative (Figure 12). They show positive correlations of MgO with CaO, FeO (T), Ni and Cr, and show negative correlations of MgO with SiO2 with

TiO2. They have high Ni, Cr and Sc, and relatively low Zr (mostly between 50 and 100 ppm). On a MORB-normalised incompatible trace element diagram (“spider plot”), they have show flat middle to heavy REE patterns, with associated elements including the

HFSE (Zr, Nb), these elements are MORB-like in relative concentration. They have somewhat elevated LREE, U, Th and alkalis. Their most distinctive feature is the presence of very significant Ba enrichments and somewhat lesser Sr.

Figure. 12 (A) Calculated CIPW Norm for the South Australian xenoliths, the proposed classification by Thompson (1984) for basalt based on their normative proportions of nepheline (Ne), olivene (Ov), albite (Ab), hypersthenes (Hy) and quartz (Qt). Red circles represent South Australian xenoliths (Segui 2010) which plot within the silica saturated and silica undersaturated portions. Green circles represent MORB (Jenner & O'Neill 2012) which plot in the silica oversaturated and silica saturated parts of the diagram. (B) Mole percent diagram (petrogenetic grid) relevant to variable precent melting (5% to the point where clinopyroxene disappears from the residue) of lherzolite over a pressure range of 0.5 to 3GPa (i.e., about 15-90km depth; pressure shown in bold). Each dashed line at a given pressure represents loci of melt compositions (molar normative) generated by progressive partial melting of lherzolite assemblage (ol + opx + cpx + melt) at that pressure (melt % increasing from left to right on each dashed curve). Each continuous line represents a fixed %melting curve. Aldo shown is the cpx out line. A lherzolitic source rock will lose cpx to the melt beyond this line. Sources of data: Takahashi and Kushiro (1983), Hirose and Kushiro (1993), and Baker and Stopler (1995). Note that it is mainly schematic and does not take into account the changing source composition that must happen as the melt in removed from the source.

In order to demonstrate that the mafic xenoliths do indeed have igneous geochemical trends, Figure 13 shows the variation of these samples compared with a large global data set of MORB compositions (Jenner & O'Neill 2012). The Figure 13 plots show

MgO plotted against SiO2, CaO, TiO2 and Al2O3. In these Figures the igneous variation trend of the MORB suite is indicated with an arrow. The direction towards ‘M’ is that of melt differentiation, that towards ‘C’ is cumulates or crystal extracts that must drive this magmatic trend. As can be seen, the xenolith suite shows significant overlap with the

MORB field, leading us to conclude that: 1) these are indeed metamorphosed

Figure 13 Plate of whole rock geochemical graphs of South Australian xenoliths (Segui 2010) with MORB (Jenner & O'Neill 2012) for comparison. Graphs A, B, C and D are MgO vs SiO2, CaO, TiO2 and Al2O3 respectively. Diamonds on Graph A and B show mineral compositions plagioclase (PLAG), clinopyroxene (CPX), orthopyroxene (OPX) and the mid ocean ridge basalt (MORB) melt composition, with two distinct trends; 1) a trend towards orthopyroxene showing orthopyroxene crystallisation driving the melt and 2) a trend clinopyroxene + plagioclase showing clinopyroxene + plagioclase driving crystalisation. Black arrow shows igneous variation trends, “M” is the direction towards melt differentiation and “C” is towards the cumulates or crystal extracts that must drive the magmatic trend. mafic igneous rocks, and 2) that their parent magmas were MORB-like. It is also obvious that many of the xenolith samples are scattered outside the MORB field, generally towards higher MgO and lower SiO2, in the ‘C’ direction of the indicated trend. This is most likely because the xenoliths have experienced some crystal – melt sorting, many being melt-depleted cumulate-enriched samples (originally gabbros). The polygons on Figures 13 A and B illustrate the compositional space created by the mixture of melt and the probable primary igneous phases (orthopyroxene, clinopyroxene, plagioclase ± spinel). Using the compositional space there appears to be

37 no apparent control on garnet; inferring it was not crystallised as a primary phase but rather metamorphic.

Figure 14 Graph of barium (Ba) vs wt% MgO for the South Australian xenoliths (Segui 2010) (red circles) with MORB (Jenner & O'Neill 2012) (blue circle). South Australian xenoliths show a several order magnitude higher amounts.

As we mentioned earlier, one very strikingly ubiquitous feature of these rocks’ trace elements is their extraordinary Ba content. Figure 14 illustrates that these have Ba several orders of magnitude higher than MORB. We attribute this feature to contamination by the kimberlite that transported the xenoliths to the surface.

Interestingly, this is a very selective contamination because other trace elements (e.g.

Nb, HREE and Zr) are not affected.

Radiogenic Isotopes

The Finigan MAT 262 TIMS at the University of Adelaide was used to obtain

Samarium-Neodymium radiogenic isotopic data. These analyses were carried out to aid in identifying the xenoliths’ protoliths and their age, and to compare with the

Neoproterozoic-Cambrian basalt data (Foden et al. 2002) (John Foden per Comms,

2012). Seven samples were selected to best represent the three xenolith suites. Three samples were chosen from each El Alamein (EA08 #) and Pitcairn (Pit M#), and represent the granulites and eclogites, and one was chosen from Angaston (DS012 #) to add to Segui’s (2010) isotope data. All data is recorded in Table 2. These data were plotted using isoplot (Ludwig 2003) with those of Segui (2010), and for comparison data, Cambrian-Neoproterozoic basalts from S.E. Australia (Foden et al. 2002) (John

Foden per Comms, 2012). The xenoliths isotopic data shows initial εNd0 between -

22.51 (EA08 9) and +8.09 (34.3.2) and Neoproterozoic data εNd700 between -12.02

(EA08 9) and +7.32 (34.4.9).

Table 4 Radiogenic Isotope data

147 144 144 143 Sample Sm(ppm) Nd(ppm) Sm/ Nd 5% error Nd/ Nd 2 σ εNd0 εNd700 EA08 3 4.87 21.83 0.1349456 6.75E-‐04 0.512624 8.20E-‐06 0.282851 5.2595917 EA08 5 4.64 17.26 0.1626150 8.13E-‐04 0.512608 1.28E-‐05 0.593011 2.4536666 EA08 9 3.97 30.31 0.0792297 3.96E-‐04 0.511484 8.40E-‐06 22.51296 12.024218 Pit M25 0.66 2.49 0.1603349 8.02E-‐04 0.512565 1.08E-‐05 1.433760 1.7837394 Pit M24 1.14 4.57 0.1508940 7.54E-‐04 0.512249 2.87E-‐05 7.588201 3.4835258 Pit M22 2.22 14.2 0.0945688 4.73E-‐04 0.512481 1.33E-‐05 3.064541 6.0865036 DS012 #1 3.81 8.97 0.2569307 1.28E-‐03 0.512566 1.46E-‐05 1.408401 6.8313195

The Nd-Sm isotopic ratios have been compiled with Segui’s (2010) isotope values for whole rock samples (Figure 15A). An isochron calculated using the whole rock data from Pitcairn, Angaston and El Alamein gives an age of 739±680Ma (Figure 15A). This age is believed to be approximated to the age of the protoliths of the metamorphosed xenoliths. It is possible that the hint of a steeper trend in the 143/144Nd vs 147Sm/144Nd isochron diagram is due to inclusion of sample EA08 9, which have some crustal contamination of the original magmatic protolith by entrained crustal material. This process has been documented and studied by Rudnick et al (1986)

Figure 15. Isochrons calculated using IsoPlot (Ludwig 2003) graphs show 143Nd/144Nd vs 147Sm/144Nd (A) represents whole rock isotope data for the South Australian xenoliths from Angaston (Segui 2010), El Alamein and Pitcairn and gives an age 739±680Ma. (B) South Australian xenoliths (Segui 2010) (green triangles) and Neoproterozoic Cambrian and South Australian Adelaidean basalts (John Foden, per comms) (Blue diamond’s) and gives an age of 656 ± 92Ma.

The Late Neoproterozoic age of the mantle xenoliths indicate they probably correlate well with the suites of Neoproterozoic to Early Cambrian mafic magmas that were intruded into the Australian passive margin during Rodinia breakup and Gondwana assembly. These suites include Cambrian and South Australian Adelaidean basalts, such as the Wooltana and Depot creek basalts and the Gairdner and Broken Hill dykes and equivalent aged suites on King Island and in Western Tasmania (Foden et al. 2006).

The Nd isotopic composition of these suites show broad correlation with those of the xenoliths studied (Figure 15B). The El Alamein, Pitcairn, Angaston, the Cambrian and

South Australian Adelaidean data shows positive εNd value at 700Ma but not the contaminated (EA08 9). When the Cambrian and South Australian Adelaidean basalts and the El Alamein, Pitcairn and Angaston data is collated the isochron gives the age

656±92Ma, which indicates they both originated in the Late Proterozoic.

Segui (2010) recorded Early Jurassic ages for the Angaston garnet and clinopyroxene separates. His conclusion was that this age represents the closure temperature (Tc) of the

Sm-Nd system for garnet and clinopyroxene. The clolsure temperature is debated to be between 600-800oC (Mezger et al. 1992) and the associated age is likely to rep[resent the timing of the emplacement by the kimberlite, when the minerals (clinopyroxene and garnet) cooled below their Tc.

Pseudosection and Geothermobarometry P–T pseudosections were calculated for sample Pit –M22 (Amphibole eclogite) (Fig

16,Table 2) and Pit-M25 (Fd rich- eclogite) (Fig 17, Table 2) using the THERIAK-

DOMINO software program (De Capitani & Petrakakis 2010), for the geologically realistic chemical system SiO2–Al2O3–FeO–Fe2O3–MgO–CaO–Na2O–K2O–H2O–TiO2

(NCKFMASHTO). The dataset used compiles the follwing a–x models, which incorporate Fe3+ end-member minerals: garnet, biotite and melt (White et al. 2007), orthopyroxene and magnetite (White et al. 2002), amphibole (Diener et al. 2007), cordierite (Holland & Powell 1998), Clinopyroxene (Green et al. 2007), K-feldspar and plagioclase (Holland & Powell 2003) and ilmenite (White et al. 2000). Mn is not considered for the reasons given by White et al. (2007). Mineral abbreviations are as follows: opx – orthopyroxene; g – garnet; sp – spinel; bi – biotite; ksp – K-feldspar;

ANAB – plagioclase; ilm– ilmenite; mt – magnetite; q – quartz; liq – silicate liquid ⁄ melt. The THERIAK–DOMINO software calculates equilibrium mineral assemblages for specific bulk-rock compositions that minimises Gibbs-free energy at a given point in

P-T space. Sample Pit M22 (Table 2, Figure 16) petrography defines a peak assemblage of garnet + clinopyroxene + amphibole. Sample Pit M25 (Table 2, Figure 17) petrography defines a peak assemblage of garnet + clinopyroxene + plagioclase ± amphibole

Table 5 Equations used for Geothermobarometry

Thermometer Equation →⅓

3 2 2 12 2 6 (Ellis & Green 1979, ⅓ Mg Al Si O (pyrope) + CaFeSi O (hedenbergite) ↔

3 2 3 12 2 6 Krogh 1988) Fe Al Si O (almandine) + CaMgSi O (diopsode)

Barometer Equation

2 6 6 (Nimis & Taylor 2000) CaMgSi O (diopside) + CaCrAlSiO (Ca Cr tschermak’s) ↔

2 2 3 12 ½(Ca Mg)Cr Si O (uvarovite and knorringite) +

2 2 3 12 ½(Ca Mg)Al Si O (grossular and pyrope)

The xenoliths thermobarometry calculations have been compared to a number of different data sets to better understand the geotherm under South Australia (Pearson &

O'reilly 1991, Pearson et al. 1991, Pearson et al. 1995, Segui 2010, Tappert et al. 2011).

Individual spot Temperature estimations were produced using the Ellis and Green

(1979) and Krogh’s (1998) Fe2+-Mg garnet-clinopyroxene exchange thermometers.

These estimations can be seen in Table 5, pressure estimations were calculated with

Nimmis and Taylor (2000) CPX barometer. In addition, these pressures were used for the temperature calculations. Fe microprobe data used in the geothermobarometry calculations has been assumed as Fe2+ as the microprobe does not distinguish between ferric (Fe3+) and ferrous (Fe2+) iron. This assumption of all ferrous iron gives a minimum temperature for both thermometers. Averaged microprobe data of garnets and single values of adjacent clinopyroxene spot values were used to create temperature estimations. The garnet values were averaged to give more confidence they were in equilibrium with the clinopyroxene. The Ellis and Green (1979) thermometer showed slightly higher temperatures than Krogh (1988) throughout the slides. Except for rocks with high pressures (≈ >15kbar) and higher Temperatures (≈ >1035oC), Krogh’s (1988) thermometer estimated higher temperatures (Table 5).

Figure 16. Pseudosection calculated for Pit M22 (see table 2) using THERIAK-DOMINO program (De Capitani & Petrakakis 2010), for the geologically realistic chemical system SiO2-Al2O3-FeO- Fe2O3-MgO-CaO-Na2O-K2O-H2O-TiO2 (NCKFMASHTO). The dataset used compiles the following a-x models which incorporate Fe3+ end-member minerals: garnet, biotite and melt (White et al. 2007), orthopyroxene and magnetite (White et al. 2002), amphibole (Diener et al. 2007), clinopyroxene (Green et al. 2007), K-feldspar and plagioclase (Holland & Powell 2003) and ilmenite (White et al. 2000). Mn is not considered for the reasons given by White et al (White et al. 2007). Blue lines represent major introduction of a mineral to the assemblage (amphibole, garnet and plagioclase), arrow represent direction on pseudosection the mineral labled is introduced. The introduction of garnet to the assemblage turns to Gabbroic rock to granulite and the loss of plagioclase turns granulite to eclogite. Blue shaded polygon represents the mineral assemblage seen for Pit M22 and the blue star represents the pressure and temperature estimations for the sample (see table 6).

Table 6 Presure and temperature estimates where TEG79 (Ellis & Green 1979), T K88(Krogh 1988) and PNT95(Nimis & Taylor ) 2000

Sample TEG79 TK88 PNT95 Min Max Min Max Min Max Fd rich Granulite Pit M9 933 972 925 971 14.7 15.3 Pit M20 857 895 836 879 13.1 14.1 Pit M23 1035 1144 1031 1164 23.4 24.8 Pit M24 783 851 715 790 12.4 14.5 Pit M25 893 969 878 967 14.8 15.5 PA 7x2 737 889 659 823 7.1 9.4 PA 78x 733 871 630 818 6.5 8.8 PA7x1 751 896 705 877 6.3 9.6 Eclogitic Rock PA 5x1 946 1054 931 1060 13 14 PA 5x2 941 977 930 971 29.1 29.8 PA 6x2 857 903 832 883 21 22 PA 6x12 955 1048 946 1056 21.8 28.1 Amphibolite Granulite Pit M26 812 840 779 810 5.9 7.2 JS Kim 897 944 864 922 15.4 15.9 Amphibolite Eclogite Pit M10 785 825 724 768 9.1 9.5 Pit M22 724 799 629 739 8.9 11.5

The P- T estimations for the El Alamein xenoliths show a minimum temperature range between 620°C-1200°C and pressures between 5 and 30kbar (Figure 18). This equates to a geotherm. Pitcairn xenoliths show a minimum temperature range between 620-1120°C and pressures between 6-24kbar. The Angaston xenoliths (Segui, 2010) displayed very similar temperature but slightly more xenoliths with an overall range between 11-

30kbar and between 800-1130°C. The Monk Hill estimated Geotherm (Tappert et al.

2011) will be referred to as the Jurassic paleo-geotherm as it represents a steady state, whereas the xenoliths of Angaston, Pitcairn, Angaston, EMAC (Pearson & O'REILLY

1991) and SEA (O'Relly & Griffin 1985) show variable equilibration towards this geotherm. The Monk Hill geotherm is calculated to 40mW/m2

Figure 17 Pseudosection calculated for Pit M25 (see table 2) using THERIAK-DOMINO program (De Capitani & Petrakakis 2010), for the geologically realistic chemical system SiO2-Al2O3-FeO- Fe2O3-MgO-CaO-Na2O-K2O-H2O-TiO2 (NCKFMASHTO). The Dataused compiles the following a-x models which incorporate Fe3+ end-member minerals: garnet, biotite and melt (White et al. 2007), orthopyroxene and magnetite (White et al. 2002), amphibole (Diener et al. 2007), clinopyroxene (Green et al. 2007), K-feldspar and plagioclase (Holland & Powell 2003) and ilmenite (White et al. 2000). Mn is not considered for the reasons given by white et al (2007). Red lines represents major introductions of mineral to an assemblage (amphibole, garnet and plagioclase), arrows represent direction on pseudosection the mineral in labled is introduced. The Introduction of garnet to the assemblage turns Gabbroic rock to granulite and the loss of plagioclase turns granulite to eclogite. Red shaded polygon represents the mineral assemblage seen for Pit M25 and the red star represents the pressure and temperature estimations for the sample (see table 6).

Figure 18 Pressure and temperature plot of geothermobarometry estimations for the SEA (O'Relly & Griffin 1985), EMAC (Pearson & O'REILLY 1991), Monk Hill (Tappert et al. 2011), Angaston (Segui 2010) and Pitcairn and El Alamein. Pressure and temperature estimations using garnet- clinopyroxene Fe-Mg thermometer (Ellis & Green 1979, Krogh 1988) and clinopyroxene barometer (Nimis & Taylor 2000). Data for UHP metamorphic rocks Refrence) schematic subduction metamorphic path taken from Agard (2009) and subduction data points taken from numerous sources(Gao 1999, Dale 2003, Janak 2004). Arrows right of Monk Hill Geotherm (Tappert et al. 2011) show the metamorphic path for the South Australian xenoliths.

and is equivalent to a steady-state continental geotherm (Tappert et al. 2011). Pressure temperature data for all three regions Pitcairn, El Alamein and Angaston plot at significantly higher T-values than the subduction P-T related eclogites (Gao 1999, Dale

& Holland 2003, Janak 2004) (Figure 18). This emphasises that the eclogite and granulite were probably unrelated to subduction. The El Alamein sample derived P-T array geotherm plot as two distinct groups: 1) a shallow group that plot a wide range of temperatures for pressures, and ;2) a deep group that plot on the Jurassic paleogeotherm

(Tappert et al. 2011). The Pitcairn geotherm plots very similar to the EMAC (Pearson et al. 1991) pressure and temperature data.

DISCUSSION

The aim for this study was to better understand the protoliths and metamorphic history of these unique and distinct upper mantle rocks from the eastern margin of the

Australian Craton, close to the Tasman Line (Veevers & Conaghan 1984). This knowledge has helped to tell us about paleo tectonics and geothermal dynamics near the eastern margin of the Australian Craton before the Jurassic (~180ma), the emplacement age of the xenoliths from kimberlite intrusions (Stracke et al. 1979, Tappert et al. 2011).

The core to this study is the interpretation of the origin of the mafic granulite and eclogite xenoliths transported from the mantle by Jurassic kimberlite dykes that intrude

Adelaidean rocks in the Adelaide Fold Belt. The Adelaide Fold Belt is a composed of rocks from the Neoproterozoic to Early Cambrian passive margin/rift sequences that were deformed and metamorphosed during the Mid– to Late Cambrian Delamerian

Orogeny. This orogeny resulted from the onset of subduction in this part of the west

Pacific Margin of Gondwana (Foden et al. 2002, 2006). These mafic xenoliths are, therefore, potentially very important as they may present us with a unique sample set from the mantle beneath this rifted-orogen.

These are clearly metamorphic rocks, with strong indications that metamorphism occurred at upper mantle depths (i.e. within the sub-continental lithospheric mantle).

Their equant and well-equilibrated textures indicate passive metamorphism, unconnected with strain. As we will discuss, their garnet-cpx-rich metamorphic assemblages in some samples clearly replace prior plagioclase bearing igneous assemblages and textures. All the indications are that they have undergone metamorphism during cooling at depth.

Based on their major element geochemical characteristics (see section Whole rock geochemistry), there are good grounds for concluding that the origins of the mafic xenoliths are an igneous suite with geochemical affiliations to rift –related parent magmas of generally MORB –like geochemical character. This is also the conclusion if their HFSEs (Nb, Zr and Ti) and HREE and Y concentrations and ratios are considered.

However, they are systematically more silica undersaturated then MORB (Figure 12) and it is clear that many have bulk compositions that fall outside the field of mafic igneous melts (Figure 13). These samples may result from crystal-liquid sorting (i.e. the

49 bulk compositions of some of the xenoliths is biased towards their crystallizing minerals, specifically pyroxenes and plagioclase ± spinel). Some preferential contamination of the xenoliths has been observed and is likely a result of being transported by kimberlites, particularly affecting Ba and perhaps other LIL and LREE elements.

It seems increasingly likely that these eclogites and mafic granulites are mafic magmas emplaced in the upper mantle below the moho. Their Nd-isotope compositions make them like some of the Late Neoproterozoic rift tholeiites emplaced during the passive margin stage in this part of S.E. Gondwana in Adelaidean sequences in Tasmania, South

Australia, W. New South Wales and W. Victoria, (Foden et al., 2002). This origin is similar to that proposed for some petrologically similar suites of xenoliths transported by Cenozoic alkali basalts in eastern Australia (O'Relly & Griffin 1985, Rudnick et al.

1986). However, it is supposed that the eastern Australian xenolith suite represents mafic sub-crustal underplating of Cenozoic age (Rudnick et al. 1986) whereas these

South Australian xenoliths probably preserve Late Neoproterozoic to Early Cambrian mantle events.

If the xenoliths represent magmas that crystallized at high pressures, then they may have distinctive characteristics that distinguish them from erupted or shallowly intruded mafic magmas, such as MORB. We have already observed that though there are suggestions that the suite may have a MORB-like mantle source (based on HFSE and

HREE geochemistry), they are systematically more silica undersaturated than MORB

(Figure 12A). It is a systematic feature that melts derived from increasingly high

50 pressure partial melting of mantle peridotite are increasingly more silica undersaturated

(Takahashi 1983, Hirose 1993, Baker 1995) (Figure 12B). The liquidus phase of mafic melts typically shifts from being olivine (± plagioclase) at low pressures (< 5 kbar) to pyroxene (CPX and/ or OPX) + olivine at pressures > 5 kbar, to be joined by garnet above ~ 11-12 kbar (see fig 2 in Rudnick et al. 1986).

Under these circumstances, the fractionation trends of mafic melts crystallizing at >

Moho depths should be dominated much more by pyroxene than those of shallowly crystallizing mafic magmas, where early olivine will dominate. As pyroxene has a crystal-melt distribution Cr >> Ni (but both > 1) , whereas olivine has Ni>>Cr (Ni >>1), this should mean that high pressure fractionation should lead to more rapid Cr depletion than in lower pressure fractionation. Figure 19 shows the Ni-Cr variation of the South

Australian mafic xenoliths and the field of MORB melts. This shows that the most melt- like xenoliths have relatively lower Cr/Ni ratios than MORB. Figure 19 shows melt fractionation curves for high pyroxene/olivine (high pressure) and lower pyroxene/olivine trends and indicate that the cumulate compliment to the high pressure trend falls across the more cumulative xenolith compositions.

Figure 19 Ni-Cr (ppm) variation of the South Australian mafic xenoliths (Segui 2010) (red circles) and MORB data (Jenner & O'Neill 2012) (green circles). Trends on this Figure show melt fractionation curves for high pyroxene/olivene (high pressure) (blue line) and lower pyroxene/olivene trends (black line with yellow triangles) and the complimentary cumulate trend for a high pressure (black line with orange circles). Trends created using MELTS (Ghiorso & Sack 1995). The specific chosen starting basalt used was an olivene tholeiite from the Adelaidean Smithon basin in N.W. Tasmania. This was chosen as it clearly had experienced no crustal contamination (John Foden, per comms)

Another piece of very good evidence for high pressure crystallization of the xenolith pre-cursor magmas is provided by the orthopyroxenite xenolith from El Alamein (EA

08 6). This plots as a relatively high MgO, low CaO point on the MgO-CaO variation diagram (Figure 13) and aligns with some other samples at higher Cao and lower MgO, inferring a phase of orthopyroxene crystallization. To produce a mono-mineralic

52 cumulate figure 13 shows that the P-T conditions must be on the mafic melt liquidus and implies high-pressure crystallization.

To test if the compositions of the xenoliths can be modelled by high pressure crystallization of an olivine tholeiite using one of the specific Neoproterozoic basalts from this part of S.E Gondwana, calculations were made using the MELTS2 software.

The specific chosen starting basalt used was an olivine tholeiite from the Adelaidean

Smithton basin in N.W. Tasmania. This was chosen as it had clearly experienced no crustal contamination.

This composition was run with low water content and an oxygen fugacity of QFM +1.

Figure 20 plots the temperature versus melt percentage for the most favourable run made at a pressure of 8.5 kbar, and indicates that this composition has orthopyroxene on its liquidus at this pressure. At pressures less than 5kbar it does, indeed, have olivine on its liquids, while at pressures > 10 kbar it crystallizes significant amounts of garnet later in its cooling history (note that there is no geochemical evidence that the xenoliths had a magmatic history of garnet crystallization and accumulation).

2 MELTS is a software package designed to facilitate thermodynamic modeling of phase equilibria in magmatic systems. It provides the ability to compute equilibrium phase relations for igneous systems over the temperature range 500-2000 °C and the pressure range 0-2 GPa.

Ghiorso, Mark S., and Sack, Richard O. (1995) Chemical Mass Transfer in Magmatic Processes. IV. A Revised and Internally Consistent Thermodynamic Model for the Interpolation and Extrapolation of Liquid-Solid Equilibria in Magmatic Systems at Elevated Temperatures and Pressures. Contributions to Mineralogy and Petrology, 119, 197- 212 Gualda G.A.R., Ghiorso M.S., Lemons R.V., Carley T.L. (submitted) Rhyolite-MELTS: A modified calibration of MELTS optimized

Figure 20. percentage of melt remaining vs Temperature showing melt evolution path (red crossed) and the complimentary solid cumulate path (black dashes) created from the results of MELTS (Ghiorso & Sack 1995) modelling on the specific chosen starting basalt, an olivene tholeiite from the Adelaidean smithton basin in N.W. Tasmania. This was chosen as it clearly had experienced no crustal contamination (John Foden, per comms). The most favourable run made at pressure 8.5 kbar, low water content and oxygen fugacity of QFM + 1as seen in the MELTS list. Minerals crystallised orthopyroxene (OPX), clinopyroxene (CPX), spinel (SP) and plagioclase (PLAG)

The results of the MELTS modelling showing the melt evolution path (blue crosses) and the complimentary solid cumulate path (black dashes), is shown for MgO v CaO and

SiO2 v MgO on Figure 21A and B. The model maps the early OPX-driven trend of the melt with its prominent inflection in the MgO-CaO variation brought about by the onset of CPX and plagioclase crystallization. It also predicts an initial liquidus OPX that is virtually identical to that in El Alamein xenolith EA 08 6.

In summary, there seems excellent evidence that the mafic xenolith suite formed as a sub-Moho depth, mafic underplate during Neoproterozoic rifting.

A B

Figure 21 MELTS (Ghiorso & Sack 1995) modelling of the south Australian xenoliths on Wt% MgO vs Wt% CaO (A) and SiO2 (B). Melt evolution path (blue crosses) and the complimentary solid cumulate path (black dashes) are shown on the diagram. Starting compostion is shown to be the orthopyroxenite (sample EA08 6).

The Sm-Nd isochron calculated from whole rock geochemistry gives the protoliths for the xenoliths an age of 656±92Ma (Figure 15B). This age corresponds to the

Neoproterozoic to Early Cambrian passive margin/rift sequences found at the south eastern margin of Gondwana. Magmatic underplating has been explained as the plausible origin for these rocks, this crystallisation saw the magmatic melts rise through the mantle and then along the adiabat (Figure 18) to crystallise at high pressures. The rocks then proceeded to be metamorphosed and now show re-equilibration textures, as noted in the “Petrology” section before.

Metamorphism of the xenoliths saw them evolve from plagioclase + pyroxene ± olivine cumulates/melts to the garnet granulites and eclogites that make up the samples (Figure

3A). As observed in the “whole rock geochemistry” section and above in Figure 20, the starting rock assemblage is assumed to be an igneous plagioclase + olivine + pyroxene cumulate, possibly similar to the gabbroic rock seen in Figure 3C. These samples showed no primary garnet crystallisation. I suggest that these rock cooled near isobarically as the EMAC xenoliths did (Pearson & O'reilly 1991), to temperatures of

620-1200°C from ~1300°C at pressures between 5-30kbar (geothermobarometry estimations). Once cooling crystallised the xenoliths, they continued to cool to the geothermal gradient. This initiated the metamorphism and activated the plagioclase pyroxene reaction to form garnet + quartz carona rims (Equations 1 and 2). The

Angaston xenoliths experienced a very similar event except these xenoliths recrystallised Kyanite in their metamorphic reactions much like the EMAC suite

(Pearson & O'reilly 1991, Segui 2010). These reactions went on the colder the rocks became, until the plagioclase was removed from the assemblage to create eclogites or they reached the geotherm.

Figure 18 shows the pressure and temperature estimations for the mafic eclogites and granulites along with the adiabat and subduction metamorphic paths. Rocks that have metamorphosed through subduction are characterised by ultra high pressures and low temperature gradient. They also display a clockwise metamorphic path due to thermal lag. If the xenoliths were metamorphosed due to subduction you would expect there to be some evidence of this within the rocks, such as up temperature and up pressure metamorphic textures. However I believe these rocks however I believe have evidence

56 for a metamorphic path that reflects isobaric cooling from the adiabat towards the stable cratonic geotherm gradient, which in the Jurassic was defined by the Monk Hill

Geotherm (Tappert et al. 2011) as mentioned above.

Two groups of pressure and temperature estimations were noted in the xenoliths data; a low pressure group with varied temperatures and a high pressure group (Figure 18). The high pressure group has estimations that reach the Jurassic geotherm (Monk Hill geotherm) (Tappert et al. 2011), while the low pressure group is much more diverse in temperature and no samples have reached the geotherm. A simple answer for this difference in location due to depth (30-90km) is the amount of cooling needed to reach the geotherm and to equilibrate according to pressure and temperature conditions.

Pseudosections created using the THERIAK-DOMINO program (De Capitani &

Petrakakis 2010) for samples Pit M22 (Amphibole Eclogite) (Figure 16) and Pit M25

(Fd-rich Granulite) (Figure 17) give further evidence to isobarically cooling metamorphic reactions that were observed in the “mineral relationship” section by

Equation 1 and 2 and Figure 3 A, B and C. Tracing metamorphic paths under isobaric cooling, the pseudosections of Pit M22 and Pit M25 (Figure 16 and 17) show that the xenoliths, depending on their original pressure will produce the assemblages and rock types we have sampled from Angaston (Segui 2010), El Alamein and Pitcairn. Segui

(2010) created a pseudosection for a granulite xenolith from Angaston and found similar mineral relationships, mainly that an isobarically cooled magma will form granulite and eclogite rock types.

The comparison of the two pseudosections (Figure 16 and 17) gives evidence for the transition of granulite to eclogite, to not just represent differences in pressure and therefore depth, but also differences in bulk composition. Wood (1987) showed that a quartz-tholeiite composition, which experienced Isobaric cooling (IBC) at lower crustal pressures, would not produce eclogites; even on a steady state geotherm (40mW/m2), but would remain a granulite. The rock type transition zones, granulite → eclogite (loss of plagioclase from the assemblage) and gabbroic rock → granulite (introduction of metamorphic garnet) depicted by blue lines in Pit M22 and red lines in Pit M25 are at much lower temperatures for Pit M22. For a given temperature of 600oC the granulite to eclogite transition (loss of plagioclase from the mineral assemblage) is at 14.7kbars for

Pit M25 and 11.6kbars for Pit M22 this shows that it is more difficult for Pit M25 to reach the eclogite field (no Plagioclase). This difference in transition temperatures at the same pressures, is possibly due to the high amount of aluminium needed to form

Plagioclase. Once in the eclogite P-T field, the granulites are at a much higher temperature; thus a lot more energy, in the form of heat or pressure, is required to from the cpx and garnet mineralogy of eclogites.

The geochemistry section describes that garnet was not a primary mineral in crystallisation from the original melt. The MELTS software was used to calculate the melt and cumulate trends associated with these xenoliths (Figure 20 and 21) and it illustrated that garnet was a part of the primary mineral trends. Therefore, I suggest the original emplacement onto the bottom of the Moho was no deeper than 9kbar or 30km.

Using the geothermobarometry estimations we see that some of the estimates reach pressures of 25-30kbar, which represents depths of 80 to 90km (Table 6, Figure 18).

The cessation of the Delamerian Orogeny has been inferred to have occurred due to a buoyancy control (i.e. delamination) (Foden et al. 2006). Modelled delamination of eclogite has shown that some of the delaminated material can be left behind (Percival &

Pysklywec 2007) and not fully delaminated into the mantle. This delamination is inferred to take ~12myr but the pressure increase is instantaneous and may result in the higher pressure rocks observed in the suite (Figure 18).

In conclusion these xenoliths show metamorphic signatures indicative of near isobaric cooling towards the stable geotherm and converted gabbroic rocks to granulites and eclogites due to their original emplacement depth (30km) and their original bulk composition higher pressures were then reached by some xenoliths possibly due to delamination. There is also evidence that the metamorphic paths were not controlled by subduction.

CONCLUSIONS

The major aim of this thesis was to further constrain the origin and metamorphic processes under the eastern margin of the Australian craton. Kimberlitic xenoliths from

Pitcairn, Angaston and El Alamein suites are dominated by mafic granulite and eclogite xenoliths. Modal proportions of the minerals garnet, clinopyroxene and plagioclase were used, along with Al(6)/Al(4) ratios of clinopyroxenes, to distinguish between the different rock types. Geochemically all three regions of xenoliths were very similar.

However, modally the Pitcairn xenoliths showed a larger percent of feldspar and a more varied composition of feldspar. Whole rock geochemistry gave evidence that the mafic xenolith suite formed as a sub-Moho depth, mafic underplate during Neoproterozoic rifting with a more than likely MORB style melt high pressure cumulates and melts

Geothermobarometry estimates were varied but all fell between the EMAC geotherm

(Pearson et al. 1991) and the Monk Hill garnet peridotite geotherm (Tappert et al.

2011). This has been identified as the signature of the sub lithospheric mantle cooling from underplating mafic intrusions from the adiabat towards the stable geotherm (Monk

Hill geotherm) and not subduction related.

The end of the Delamerian Orogeny has been suggested to have occurred due to a delamination event around the middle Ordovician under the Adelaidean Fold Belt

(Foden et al. 2006). The xenoliths of this study may, therefore, represent the delaminated remains of the eclogite that caused the cessation of the Delamerian

Orogeny. Further work could be done to justify this hypothesis through dating the metamorphic age of these rocks to further constrain the process.

Acknowledgments.

I would like to thank Kevin Wills for his extensive knowledge of the kimberlites located in South Australia and for his help while conducting the field work. Thanks must go to

Phd student, Alec Walsh for helping me to make my two pseudosections, which would not have been completed without his help. I would also like to thank David Bruce, John

Stanley and Katie Howard for introductions on the sample handling and preparing equipment in the Mawson Laboratories. I would also like to thank Angus Netting, Ben

Wad and Adelaide microscopy for the use and help with their instruments. But my

60 biggest thanks must go to my supervisor John Foden for his countless talks and hours he put into to help me understand and finish this thesis.

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APPENDIX : A METHODS

Sample Preparation Whole rock and mineral separate preparation for radiogenic isotope and XRF work was carried out in the Mawson Laboratories at Adelaide University. Sample preparation involved the removal of weathered surfaces from samples using a diamond saw to produce 5-7 cm3 blocks to be crushed. The crushing was completed in a stainless steel jaw crusher which was cleaned in- between each sample. The fine and coarse material produced from crushing was then divided into thirds with care taken to ensure each fraction contained representative amounts. Two of these fractions were further processes for whole rock analysis and isotope work while the other fraction was set aside for future work. Cleaning was very extensive using all machines and implements between samples.

Samples that were selected for whole rock XRF work were then milled down to a fine powder in a tungsten carbide mill which ran for between 2 to 3 minutes.

Major Element Geochemistry Major and minor element analysis was undertaken in situ on individual mineral grains in thin section. The Cameca SX51 microprobe located at Adelaide University was used to collect major and minor element results. It produced these results using a focused beam produced by a 15kV accelerating voltage and a 20nA beam current. Calibration of the machine was carried out during and before analysis of samples.

Whole rock major element analysis involved the production of fused glass disks for XRF work. To remove the water from the sample 6g of the sample powder was heated at 130oC for 4 hours. Samples were then put into ceramic crucibles and weighed in a Toledo balance. The loss of ignition was calculated once the sample was ignited at 960oC for 3 hours.1g of this powder was then mixed with 4 g of lithium borate flux and fused in Pt/Au crucibles and moulds producing fused discs.

Trace Element Geochemistry Whole rock trace element geochemistry was acquired by XRF analyses carried out on pressed pellets created from milled sample using the same procedure as the major elements. Pressed pellets were created by mixing 0.8mL of EtOH/PVA binder with 6g of whole rock powder and then put into the hydraulic press found in the Mawson Laboratories.

Radiogenic Isotope work Radiogenic isotope work was carried to obtain Nd-Sm values of samples so they could be radiometrically dated. It was undertaken for 7 samples. The standard used was a weighed and spiked into cleaned 15mL Teflonware PFA Vials using a Mettler Toledo AT201 balance. The samples were spiked using Nd-Sm spike F (calculated at the additions of 0.2 Sm-Nd spike F per 1µg Nd) at estimations of 4 ppm for the whole rocks and 10ppm for the mineral separates with the standard known to be 25ppm spiked accordingly. The samples are dissolved through a process involving 2 lots of HF, and a final dissolution in

HCL with 7M HNO3 being added at crucial stages to retard the formation of insoluble fluorides. Samples are then centrifuged and loaded onto a Biorad Poly Prep separating columns (2mL AG50W X8 200-400 mesh Biorad cation exchange resin) for initial REE separation and then loaded onto the Sm-Nd separating columns (2mL Teflon powder impregnated with HDEHP) separating the Nd and Sm. Second dissolution involved the addition of 15M HNO3 along with 2mL

.01 µg/g H3BO3 in 6M HCL with the samples being capped and boiled for 3 days after no aqua regia was observed. Ultra sounding was also undertaken in an attempt to ensure complete dissolution of samples. Nd and Sm were subsequently dried and located onto double Re filaments for Thermal Ionisation Mass Spectrometer (TIMS) analysis. Nd and Sm analysis was carried out on a Finigan Mat 262 TIMS at Adelaide University using dynamic measurement for 143Nd/144Nd and static measurement for 150Nd/144Nd, 147Sm/149Sm and 152Sm/149Sm. The blank failed contained <200pg 150Nd/144Nd and <150pg Sm. The international standard JNDi-1 produced 144Nd/ 143Nd measurements of .512074 ± 27 (n=2) and the BCR2 basalt standard produced results of 144Nd/ 143Nd .512662 ± 41 (n=1). 143Nd/144Nd and 147Sm/144Nd values were calculated using depleted mantle values taken from Goldstein et al (1984).

APPENDIX AVERAGE B GARNET AND CLINOPYROXENE DATA (SEE EXTENDED APPENDIX FOR ALL DATA) Garnet

Sample Rock Type SiO 2 TiO 2 Al 2O3 Cr 2O3 ∑ FeO MnO MgO CaO Na 2O K 2O Sum PA 5x1 ER 38.6922 0.1099 21.8583 0.0072 20.3850 0.8484 9.1744 8.3938 0.0426 0.0083 99.52 PA 5x2 ER 38.7040 0.0696 21.1053 0.0101 21.6789 0.4797 6.7896 9.5448 0.0384 0.0103 98.43 PA 6x2 ER 38.2422 0.0353 21.6609 0.0212 0.4386 22.7472 7.0507 9.2672 0.0208 0.0060 99.49 PA 6x12 ER 37.5902 0.1116 21.8501 0.0221 19.5057 0.4637 8.9194 9.4045 0.0450 0.0065 97.92 PA 78x Fd 38.5500 0.0423 21.0820 0.0605 22.2608 0.3594 11.3838 5.7355 0.1990 0.2742 99.95 PA 7x1 Fd 38.0804 0.0318 21.1569 0.0105 24.4398 0.6274 8.1536 8.4626 0.0207 0.0323 101.02 PA 7x2 Fd 38.8425 0.0255 20.9259 0.0189 18.9980 0.3404 11.6534 5.7642 0.3288 0.6839 97.58 Pit M9 Fd 38.8691 0.0605 22.4463 0.0226 17.1976 0.3970 9.7796 11.1657 0.0166 0.0085 99.96 Pit M20 Fd 38.8420 0.0443 22.6527 0.0199 16.5478 0.3961 10.7405 10.2007 0.0165 0.0063 99.47 Pit M23 Fd 38.2208 0.1030 23.5829 0.0203 14.6148 0.1915 9.0226 13.4335 0.0344 0.0174 99.24 Pit m25 Fd 39.6510 0.0485 22.3432 0.0164 16.9428 0.4451 9.2149 11.4013 0.0810 0.0230 100.17 Pit M24 Fd 40.2964 0.0222 22.2574 0.0387 17.6654 0.4461 12.2032 5.8706 0.0656 0.2464 99.11 JS Kim AM G 37.8135 0.0478 21.8043 0.0115 22.5739 0.4605 8.5213 7.8107 0.0184 0.0075 99.07 Pit M26 AM G 37.6813 0.2297 21.5027 0.0270 23.2270 0.4806 7.4231 8.5601 0.0064 0.0212 99.16 Pit M10 AM E 39.8328 0.0000 22.3251 0.0207 21.5280 0.5797 10.0807 6.4044 0.0185 0.0116 100.80 Pit M22 AM E 39.1188 0.0344 22.2700 0.0275 21.5163 0.5668 10.1163 6.3541 0.0344 0.0142 100.05

CPX

Sample Rock Type SiO 2 TiO 2 Al 2O3 Cr 2O3 ∑FeO MnO MgO CaO Na 2O K 2O Sum PA7x2 Fd 52.7823 0.1949 3.4947 0.0472 7.3557 0.0539 17.2495 15.9123 1.5538 0.0071 98.6513 PA78x Fd 51.4913 0.2102 4.1645 0.0666 6.2070 0.0446 13.5394 20.0805 2.0399 0.4344 98.2785 PA7x1 Fd 50.2455 0.3142 5.0639 0.0141 8.1499 0.0510 11.5260 19.3984 2.4359 0.0391 97.2380 PA6x2 ER 52.5858 0.2801 8.0752 0.0356 6.4136 0.0228 10.0207 17.0738 4.2285 0.0060 98.7421 PA5x2 ER 52.9142 0.2887 9.8585 0.0061 6.1128 0.0510 8.7463 14.9760 5.0787 0.0123 98.0445 PA5x1 ER 52.5080 0.3849 5.4640 0.0124 7.6880 0.0944 11.5366 18.1390 3.4283 0.0060 99.2615 PA6x12 ER 51.5812 0.5177 8.8141 0.0257 5.8899 0.0514 10.4128 16.1474 4.6852 0.0145 98.1399

Pit M9 Fd 50.1396 0.5055 8.6426 0.0400 4.8288 0.0397 11.8841 20.5608 2.2584 0.0118 98.9113 Pit M20 Fd 50.7554 0.4262 7.6067 0.0452 4.0693 0.0402 12.7513 20.9767 2.0893 0.0086 98.7689 Pit M23 Fd 45.3256 1.1680 13.3129 0.1294 4.1291 0.0293 9.6284 18.3168 2.9883 0.0695 95.0972 Pit M24 Fd 52.9777 0.2728 5.6205 0.0405 4.6481 0.0417 13.3488 19.7133 2.2784 0.0186 98.9603 Pit M25 Fd 51.2061 0.5082 8.6218 0.0386 4.8902 0.0398 11.7049 20.5890 2.2109 0.0062 99.8158 JS Kim AMG 50.8395 0.3951 7.0936 0.0217 7.5194 0.0468 10.7914 18.2690 3.2661 0.0092 98.2517 Pit M26 AM G 50.9573 0.3424 5.2170 0.0222 7.6806 0.0418 11.8716 20.1112 0.0042 2.2741 98.5224 Pit M10 AM E 53.3985 0.3110 4.8223 0.0304 6.1969 0.0601 13.0694 20.3726 2.1216 0.0081 ####### Pit M22 AM E 52.1200 0.3218 4.8368 0.0850 6.0273 0.0616 12.9073 20.0830 2.0993 0.0079 98.5501

APPENDIX C HAND SAMPLE DESCRIPTIONS

Lithology Mineralogy Sample names Shape and Size Surface Textures DS012-‐1, DS012-‐2, DS012-‐ coarse grained light blue green in 6, DS012-‐7, EA08-‐3, EA08-‐ small (3cm) to medium colour with red orange garnets, black Fd rich garnet + CPX + OPX +plag 5, EA08-‐8, PIT-‐M9, PIT-‐ (8cm) and larger (up to brown Opx and green le CPX, possib Granulite +quartz M20, PIT-‐M21, PIT-‐M23, fabric.weathered plagioclase. Some PIT-‐M24, PIT-‐M25, PA 7x2, 12cm) with well defined fabrics PA 78x, PA 7x1 coarse grained smooth light in garnet + qtz + plagioclase + large(10cm) well colour exterios with some Metapelite CAX-‐M10, DS012-‐3 biotite ± CPX rounded xenoliths kimberlite still attached. Dark red large (1-‐3cm) garnets very visible 5cm rounded very dark OPX and green cpx Pyroxenite OPX + CPX ± Qt DS012-‐4, EA08 6 xenotliths possible foliations very small (1cm) and DS012-‐5, EA08-‐1, PIT-‐ mineralogy dominater by red small (3cm) well Eclogitic Rock garnet + CPX ± Amph ± Qt M10, Pit M22 PA 5x1, garnet and dark CPX. Well rounded spheroidal PA5x2, PA 6x1, PA 6x12 weathered outside surface elipse shaped xenolith small (6cm) angular strong fabric defined by OPX Mafic Gneiss Opx + Calcite + Plagioclase EA08-‐9, RT-‐CAL 2XL10 xenoliths minerals. small to large boulder characterised by red garnets, Amph Eclogite garnet + CPX + Plag + Amph Qt Pit M26, JS Kim size and sub-‐rounded green cpx and Dark amphibole. nodules Some plagioclase also seen. small to large boulder phlogopite + calcite + glass ± AngasKim, EA02-‐2, rough green/white well weathered Kimberlite size and sub-‐rounded garnet ± serpentine EA02-‐4, EA02-‐7 exterior, visible brecciated clasts nodules of kimberlite

APPENDIX THINSECTION D DESCRIPTIONS

Major Minor lithology Thin Section Mineralogy Mineralogy Textures PA5x1, PA5x2, PA6x2, Triple point equi- to sub granular euhedral texture with coarse grained Eclogite Rock Grt, Cpx, Am, Rt, Qt, llm PA6x12 rutile PA7x1, PA78x, PA7x2,Pit Cpx, Opx, Grt, Diverse stages of exsolution textures, rutile inclusions within garnet Fd rich Granulite M9, Pit M20, Pit M23, Pit Rt, llm, Am M24, Pit M25 Pla and or clinopyroxene Cpx, Opx, Grt, Diverse stages of exsolution textures, rutile inclusions within garnet Amphibole Granulite Pit M26, JS Kim Rt, llm, Pla, Am and or clinopyroxene Triple point equi- to sub granular euhedral texture with coarse grained Amphibole Eclogite Pit M10, Pit M22 Grt, Cpx, Am Rt, Qt, llm rutile Doleritic microstructure, lath shaped plagioclase, clinopyroxenes Gabbroic Rock Pit 5x9 Pl, Cpx, Opx, Am llm, Rt showing an intergrowth with amphibole and minor ilmenite