The Lachlan Orogen of New South Wales,Victoria and eastern Tasmania is the best understood element of the eastern Australian Tasmanides.The Tasmanides encompass continental growth in a Neoproterozoic passive margin se...The Lachlan Orogen of New South Wales,Victoria and eastern Tasmania is the best understood element of the eastern Australian Tasmanides.The Tasmanides encompass continental growth in a Neoproterozoic passive margin setting and a Paleozoic–Mesozoic active margin in east Gondwana,bounded to the east by the Pacific Ocean.In the Ordovician,the supra-subduction zone element in the Lachlan Orogen is the Macquarie Arc.This comprises one minor and three major belts of mafic to intermediate volcanic and volcaniclastic rocks,limestones and intrusions that,with two hiatuses in magmatism,span the Ordovician and extend into the Early Silurian.The three major belts in central New South Wales are separated by Silurian–Devonian rift basins and are therefore,inferred to have been rifted apart during crustal extension.Chemical and isotopic data suggest the Macquarie Arc is intraoceanic,developed on primitive oceanic crust.Despite this,key features such as its longevity,stacked magmatic phases,little deformation and flanking coeval craton-derived turbidites and black shales with no provenance mixing indicate differences from modern intraoceanic arcs.Paleogeographic setting and magmatic evolution of the Macquarie Arc provided perfect conditions for mainly porphyry-related,rich Au-Cu deposits,in the Ordovician,and especially in the Early Silurian after amalgamation of the arc with its flanking terranes.展开更多
The Narooma-Batemans Bay(NBB)area along the southeast coast of Australia is a part of the eastern zone of the Early Paleozoic Lachlan Orogen.In the NBB,a set of rock association consisting of turbidites,siliceous rock...The Narooma-Batemans Bay(NBB)area along the southeast coast of Australia is a part of the eastern zone of the Early Paleozoic Lachlan Orogen.In the NBB,a set of rock association consisting of turbidites,siliceous rock,basic lava,and argillaceous melange zone is mainly developed.According to systematic field geological survey,the deformation of 3 stages(D1,D2,and D3)was identified in the NBB.At stage D1,with the original bedding S0 in a nearly east-west trending as the deformation plane,tight folds,isoclinal folds,and other structures formed in the NBB accompanied by structural transposition.As a result,crenulation cleavage developed along the axial plane of the folds and schistosity S1 formed.At stage D2,with north-south-trending schistosity S1 as the deformation plane,a large number of asymmetrical folds and rotated porphyroclasts formed owing to thrusting and shear.At stage D3,leftlateral strike-slip occurred along the main north-south-trending schistosity.Based on the analysis of the characteristics of tectonic deformation in the NBB and summary of previous research results,it is determined that the early-stage(D1)deformation is related to Ordovician Macquarie arc-continent collision and the deformation at stages D2 and D3 is the result of the westward subduction of Paleo-Pacific Plate.That is,it is not the continuous westward subduction of the Paleo-Pacific Plate that constitutes the evolution model of the NBB as previously considered.展开更多
文摘The Lachlan Orogen of New South Wales,Victoria and eastern Tasmania is the best understood element of the eastern Australian Tasmanides.The Tasmanides encompass continental growth in a Neoproterozoic passive margin setting and a Paleozoic–Mesozoic active margin in east Gondwana,bounded to the east by the Pacific Ocean.In the Ordovician,the supra-subduction zone element in the Lachlan Orogen is the Macquarie Arc.This comprises one minor and three major belts of mafic to intermediate volcanic and volcaniclastic rocks,limestones and intrusions that,with two hiatuses in magmatism,span the Ordovician and extend into the Early Silurian.The three major belts in central New South Wales are separated by Silurian–Devonian rift basins and are therefore,inferred to have been rifted apart during crustal extension.Chemical and isotopic data suggest the Macquarie Arc is intraoceanic,developed on primitive oceanic crust.Despite this,key features such as its longevity,stacked magmatic phases,little deformation and flanking coeval craton-derived turbidites and black shales with no provenance mixing indicate differences from modern intraoceanic arcs.Paleogeographic setting and magmatic evolution of the Macquarie Arc provided perfect conditions for mainly porphyry-related,rich Au-Cu deposits,in the Ordovician,and especially in the Early Silurian after amalgamation of the arc with its flanking terranes.
基金This research was supported financially by the National Natural Science(41702213)Fundamental Research Funds of the Chinese Academy of Geological Sciences(K1614,YYWF201709).
文摘The Narooma-Batemans Bay(NBB)area along the southeast coast of Australia is a part of the eastern zone of the Early Paleozoic Lachlan Orogen.In the NBB,a set of rock association consisting of turbidites,siliceous rock,basic lava,and argillaceous melange zone is mainly developed.According to systematic field geological survey,the deformation of 3 stages(D1,D2,and D3)was identified in the NBB.At stage D1,with the original bedding S0 in a nearly east-west trending as the deformation plane,tight folds,isoclinal folds,and other structures formed in the NBB accompanied by structural transposition.As a result,crenulation cleavage developed along the axial plane of the folds and schistosity S1 formed.At stage D2,with north-south-trending schistosity S1 as the deformation plane,a large number of asymmetrical folds and rotated porphyroclasts formed owing to thrusting and shear.At stage D3,leftlateral strike-slip occurred along the main north-south-trending schistosity.Based on the analysis of the characteristics of tectonic deformation in the NBB and summary of previous research results,it is determined that the early-stage(D1)deformation is related to Ordovician Macquarie arc-continent collision and the deformation at stages D2 and D3 is the result of the westward subduction of Paleo-Pacific Plate.That is,it is not the continuous westward subduction of the Paleo-Pacific Plate that constitutes the evolution model of the NBB as previously considered.
