Structural History of the Batholith Paul Lennox1, Robert Trzebski2 & Ian Williams3 1. School of BEES, UNSW, 2052, [email protected] 2. Australian Business Ltd., 140 Walker Street, North Sydney 2060, [email protected] 3. RSES, ANU, Canberra, ACT 0200, [email protected]

SUMMARY FAULT MOVEMENT CONSTRAINTS (continued) The Late Silurian(?), usually foliated Wyangala Batholith consists of 30 mainly S- & I- type plutons which intruded deformed Ordovician metasediments and Thrust volcaniclastics passively along pre-existing faults. Some plutons are displaced by The Reid Flat Granite post-dates the thrust faulting and D1 deformation in the faults, other granites have metamorphic aureoles which overprint faults and others Warbisco Shale and Adaminaby Group country rocks. Thus D1 would be Late post-date thrust faulting and S1 development in country rocks. U-Pb (SHRIMP) Benambran given the Late Ordovician age of the Warbisco Shale. dating of zircons from these key plutons yields emplacement ages around 424 Ma. This indicates that some key faults were active prior to 424 Ma and others post 424 Summary of thrust movements Ma consistent with movement occurring from the Ordovician to the Carboniferous as The Reids Flat Thrust and the northern end of the Frogmore Fault System on the demonstrated from fault map patterns. western side of the newly defined Hill End Trough (Scott 2004) in the middle of the Wyangala Batholith was active prior to the 424 Ma. In contrast the Blackmans Creek a) Scheibner & Basden 1996 Thrust was active after 424Ma. This indicates significant fault movement at discrete intervals from the Late Ordovician to the Early Carboniferous. Figure 1 Locality maps: a) Lachlan Fold Belt in SE Australia, b) Hill End Zone in the Eastern Lachlan Fold Belt (ELFB) and c) Wyangala Batholith in the Hill End Zone. IMPLICATIONS

c) Macquarie Arc The 422Ma Roseburg Granite truncates folds within the Warbisco Shale-Adaminaby Group sequence which are believed to be F2 (Glen & Wyborn 1997). This constrains the F2 event to be pre-422Ma in this area. That is it would be Late Benambran (435- 425Ma). Scott et al. (2000) considered the Granite intruded during D2 of a

Hill progressive three phase deformation. The 423 Ma date of the crystallisation of the End Trough Binda Granite indicates that D may be Late Benambran in this area rather than b) 2 New England Tabberabberan as proposed by Scott et al. (2000). The Ar-Ar dating of biotite from S Eastern Lachlan Fold Belt Orogen foliation in the Reids Flat granite yielded an average age for a discordant spectrum of Hill End Yass Zone Trough 381 Ma, which is thought to represent the age of ductile thrust deformation and S2 Western Newbridge TN development within the Adaminaby Group in this area (Glen et al. 1999). This Lachlan Sydney Adaminaby Wyangala Orogen Gp Batholith Delamerian 081624 corresponds to the Tabberabberan event. Fold Belt 200 Kilometers Central 0 Gravity transects Lachlan km Orogen Base map courttesy GSNSW Thus it appear that despite some anomalies D1 is usually either Early or Late Benambran in age and D2 is either Late Benambran to Tabberabberan (Fig. 3)

A. Early Benambran: Back Arc Setting A N Ordovician back-arc setting D.Shear -Bindian zone - Tabberabberan: development, Shear Zone DevelopmentWyangala in the Wyangala Granite Granite

V

FAULT MOVEMENT CONSTRAINTS o N l

c

a 5km n N D i s 1 c ’ All granites other than the Carcoar, Barry and Sunset Hills granites (427- Z ’s S Z

I

s S S L S l 5km a H n E

434Ma) crystallised around 424Ma. d

A 5km

r

c

S-C Mylonites & Grain Size Blackmans Creek Thrust Reduction The Mulgowrie Granite is truncated by the Blackmans Creek Thrust which is LateB. Late Benambran: BenambranBenambran Folding and deformationFaulting of Ordovician Rocks overlain by the Miocene Wheeo basalt (Fig. 2). This fault must have moved post- N 424Ma and pre-Miocene. Strain Decreasing

D1-2 E.Tabberabberan-Kanimblan Tabberabberan - Kanimblan: Folding of the Wyangala Deformation Granite Copperhannia Thrust and/or Anastoming Foliations Relatively poorly constrained Ar/Ar studies on sericite from the Copperhannia N o N Thrust (CT) indicates possible closure below 350-400 C at ~ 386 and ~ 352 Ma D consistent with sericite formation in the Tabberabberan and Kanimblan events 2-3 during movement on this fault (Fig. 2; Glen et al. 1999).

Folded Granite Anastomosing Foliations Late Frogmore Fault System C. Late Benambran: BenambranGranite Emplacement The Ballyhooley Granite aureole overprints this fault system (Fig. 2). This indicates that some of the faults in this system finished moving before 424Ma. Figure 3: Schematic model of deformation of the Adaminaby Group prior to granite intrusion and then once or twice since granite intrusion. See TN Carcoar G’de. Granite intrusion White et al. 2006 & White (2005) for Roseb erg Granite along pre-existing Barry Granite further details. Copperhannia faults Thrust Figure 2: Wyangala Batholith Kempfield Granite with key dated granites and key faults. Current dating is Reids Flat Sunset Hills aimed at constraining the Granite References: Thrust deformation history of these faults. Glen R.A., Lennox P.G. & Foster D.A. 1999 40Ar-39Ar dating of deformations Blackmans west of the Hill End Trough, Lachlan Orogen, . Quarterly Notes Reids Flat Grani te Creek Thrust of the Geological Survey of New South Wales 110, 13-22. Ballyhooley Granite Lennox P.G., Trzebski R., Armstrong R. & Siebel W. 2005 Structural evolution Binda Granite and granite chronology of the central Molong Zone, Eastern Lachlan Fold Belt, Australia. Australian Journal of Earth Sciences 52, 79-99. 020Frogmore Fault White L. 2005 The Geology and Structure of the Maryamma District. BSc(Hons), System Mulgowrie Km Granite (unpubl.) UNSW, Sydney. White L., Lennox P., Czarnota K. & Crump J. 2006 Shear zones and possible folding, Wyangala Granite, NSW. Australian Earth Science Convention. SHRIMP dated granites GS NSW UN SW Acknowledgments: The UNSW Faculty Research Grants Program for 2004-2006 is thanked for funding this work. Mr Lloyd White, 2005 Honours student & University Medallist collaborated on development of the tectonic model for the more deformed parts of the Wyangala Batholith.