Detrital zircon U-Pb geochronology has become the gold standard in evaluating source to sink relationships in sedimentary basins. However, the physical and chemical robustness of zircon, which make it such a useful mi...Detrital zircon U-Pb geochronology has become the gold standard in evaluating source to sink relationships in sedimentary basins. However, the physical and chemical robustness of zircon, which make it such a useful mineral for provenance studies, is also a hindrance as zircon can be recycled through numerous sedimentary basins, thus obscuring the first cycle source to sink relationship. An elegant approach to addressing this potential issue is to compare the Pb isotope composition of detrital K-feldspar, a mineral which is unlikely to survive more than one erosion-transport-deposition cycle, with that of magmatic K-feldspar from potential basement source terranes. Here we present new in situ Pb isotope data on detrital K-feldspar from two Proterozoic arkosic sandstones from Western Australia, and magmatic K-feldspar grains from potential igneous source rocks, as inferred by the age and Hf isotope composition of detrital zircon grains. The data indicate that the detrital zircon and K-feldspar grains could not have been liberated from the same source rocks, and that the zircon has most likely been recycled through older sedimentary basins. These results provide a more complete understanding of apparently simple source to sink relationships in this part of Proterozoic Western Australia.展开更多
The post-Mesoproterozoic tectonometamorphic history of the Musgrave Province, central Australia, has previously been solely attributed to intracontinental compressional deformation during the 580 -520 Ma Petermann Oro...The post-Mesoproterozoic tectonometamorphic history of the Musgrave Province, central Australia, has previously been solely attributed to intracontinental compressional deformation during the 580 -520 Ma Petermann Orogeny. However, our new structurally controlled multi-mineral geochronology results,from two north-trending transects, indicate protracted reactivation of the Australian continental interior over ca. 715 million years. The earliest events are identified in the hinterland of the orogen along the western transect. The first tectonothermal event, at ca. 715 Ma, is indicated by40 Ar/39 Ar muscovite and U e Pb titanite ages. Another previously unrecognised tectonometamorphic event is dated at ca. 630 Ma by Ue Pb analyses of metamorphic zircon rims. This event was followed by continuous cooling and exhumation of the hinterland and core of the orogen along numerous faults, including the Woodroffe Thrust,from ca. 625 Ma to 565 Ma as indicated by muscovite, biotite, and hornblende40 Ar/39 Ar cooling ages. We therefore propose that the Petermann Orogeny commenced as early as ca. 630 Ma. Along the eastern transect,40 Ar/39 Ar muscovite and zircon(Ue Th)/He data indicate exhumation of the foreland fold and thrust system to shallow crustal levels between ca. 550 Ma and 520 Ma, while the core of the orogen was undergoing exhumation to mid-crustal levels and cooling below 600-660℃. Subsequent cooling to 150 -220℃ of the core of the orogen occurred between ca. 480 Ma and 400 Ma(zircon [Ue Th]/He data)during reactivation of the Woodroffe Thrust, coincident with the 450 -300 Ma Alice Springs Orogeny.Exhumation of the footwall of the Woodroffe Thrust to shallow depths occurred at ca. 200 Ma. More recent tectonic activity is also evident as on the 21 May, 2016(Sydney date), a magnitude 6.1 earthquake occurred, and the resolved focal mechanism indicates that compressive stress and exhumation along the Woodroffe Thrust is continuing to the present day. Overall, these results demonstrate repeated amagmatic reactivation of the continental interior of Australia for ca. 715 million years, including at least 600 million years of reactivation along the Woodroffe Thrust alone. Estimated cooling rates agree with previously reported rates and suggest slow cooling of 0.9 -7.0℃/Ma in the core of the Petermann Orogen between ca. 570 Ma and 400 Ma. The long-lived, amagmatic, intracontinental reactivation of central Australia is a remarkable example of stress transmission, strain localization and cratonization-hindering processes that highlights the complexity of Continental Tectonics with regards to the rigid-plate paradigm of Plate Tectonics.展开更多
Recent studies have shown that Cu-rich sulfide accumulates in the lower continental crust and serves as a critical reservoir to balance Cu depletion in the upper crust.Recycling of Cu in the lower crust is also assume...Recent studies have shown that Cu-rich sulfide accumulates in the lower continental crust and serves as a critical reservoir to balance Cu depletion in the upper crust.Recycling of Cu in the lower crust is also assumed to be a major metal source for non-arc setting porphyry Cu deposits.To test this hypothesis and further explore the behavior of Cu in the lower crust,we analyzed the elemental and Cu isotopic compositions of lower crustal rocks from different geological domains.The collected samples include hornblendites from the Kohistan arc,granulite xenoliths and hornblendites from the Gangdese arc,hornblendites and gabbros from the Laiyuan complex in the North China Craton,and hornblendite xenoliths from the western margin of the Yangtze Craton.These lower crustal rocks have experienced varying degrees of primary or secondary sulfide accumulation,with significantly varied Cu contents(11.2 to 145 ppm)andδδ^(65)(1.05‰to 1.40‰).Petrography and geochemistry reveal varying degrees of metasomatism and fluid interaction in these rocks,and based on this,they can be further divided into three groups:Group I includes the Gangdese granulites and Yunnan hornblendites,which perhaps experienced significant metasomatism.This suite of rocks shows enrichment ofδ^(65)(dδ^(65)=0.01‰to 1.40‰),positively correlated with metasomatism(dδ^(65)vs.Ce/Pb).We suggest the secondary sulfides which transformed from sulfates during the interaction between lower crust and arc magma are dominant in these rocks,so the feature of heavy isotope enrichment is inherited.Group II includes Laiyuan hornblendites and gabbros,derived from the same parental magma and emplaced at different depths(hornblendites,23.3–28.1 km;gabbros 8.4–11.1 km).The Cu isotopic compositions are strongly fractionated between these two kinds of rocks,with low dδ^(65)in the hornblendites(0.00‰to 0.28‰)and highly polarized dδ^(65)in the gabbros(1.05‰to 0.81‰).Geochemical indicators and mineral assemblages reveal that fluid interaction is most likely responsible for this feature.Primary sulfides were decomposed by fluids and reprecipitated at shallower depths.Since this process involves multiple redox reactions,the Cu isotopic composition in the shallowed emplaced gabbros was large fractionated.Group III includes the Gangdese hornblendites and Kohistan hornblendites which show negligible impacts of subduction-like metasomatism and fluid interaction.The Gangdese hornblendites show a homogeneous and unfractionated Cu isotopic composition(-0.09‰to 0.18‰)and Cu content(83.4 to 128 ppm),suggesting insignificant Cu migration and isotope fractionation.In contrast,the Cu isotopic composition of the Kohistan hornblendites is strongly fractionated(-0.36‰to 1.27‰).Geochemistry and modeling results suggest partial melting plays a role in the Cu isotope fractionation.The light Cu isotopes are preferentially distributed into sulfide melts and removed from the source region during partial melting of the lower crust,resulting in a decrease in Cu content and enrichment of heavy Cu isotopes in residues.Results suggest that partial melting and fluid interaction are two efficient mechanisms that encourage Cu migration in the lower crust.展开更多
基金funded via an Australian Geophysical Observing System grant provided to Au Scope Pty Ltd.the AQ44 Australian Education Investment Fund programpartly funded by the Western Australian Exploration Incentive Scheme
文摘Detrital zircon U-Pb geochronology has become the gold standard in evaluating source to sink relationships in sedimentary basins. However, the physical and chemical robustness of zircon, which make it such a useful mineral for provenance studies, is also a hindrance as zircon can be recycled through numerous sedimentary basins, thus obscuring the first cycle source to sink relationship. An elegant approach to addressing this potential issue is to compare the Pb isotope composition of detrital K-feldspar, a mineral which is unlikely to survive more than one erosion-transport-deposition cycle, with that of magmatic K-feldspar from potential basement source terranes. Here we present new in situ Pb isotope data on detrital K-feldspar from two Proterozoic arkosic sandstones from Western Australia, and magmatic K-feldspar grains from potential igneous source rocks, as inferred by the age and Hf isotope composition of detrital zircon grains. The data indicate that the detrital zircon and K-feldspar grains could not have been liberated from the same source rocks, and that the zircon has most likely been recycled through older sedimentary basins. These results provide a more complete understanding of apparently simple source to sink relationships in this part of Proterozoic Western Australia.
基金M.D. was supported by the AuScope NCRIS2 program,Australian Scientific Instruments Pty Ltd., Australian ResearchCouncil (ARC) Discovery funding scheme (DP160102427)Cur-tin Research Fellowship
文摘The post-Mesoproterozoic tectonometamorphic history of the Musgrave Province, central Australia, has previously been solely attributed to intracontinental compressional deformation during the 580 -520 Ma Petermann Orogeny. However, our new structurally controlled multi-mineral geochronology results,from two north-trending transects, indicate protracted reactivation of the Australian continental interior over ca. 715 million years. The earliest events are identified in the hinterland of the orogen along the western transect. The first tectonothermal event, at ca. 715 Ma, is indicated by40 Ar/39 Ar muscovite and U e Pb titanite ages. Another previously unrecognised tectonometamorphic event is dated at ca. 630 Ma by Ue Pb analyses of metamorphic zircon rims. This event was followed by continuous cooling and exhumation of the hinterland and core of the orogen along numerous faults, including the Woodroffe Thrust,from ca. 625 Ma to 565 Ma as indicated by muscovite, biotite, and hornblende40 Ar/39 Ar cooling ages. We therefore propose that the Petermann Orogeny commenced as early as ca. 630 Ma. Along the eastern transect,40 Ar/39 Ar muscovite and zircon(Ue Th)/He data indicate exhumation of the foreland fold and thrust system to shallow crustal levels between ca. 550 Ma and 520 Ma, while the core of the orogen was undergoing exhumation to mid-crustal levels and cooling below 600-660℃. Subsequent cooling to 150 -220℃ of the core of the orogen occurred between ca. 480 Ma and 400 Ma(zircon [Ue Th]/He data)during reactivation of the Woodroffe Thrust, coincident with the 450 -300 Ma Alice Springs Orogeny.Exhumation of the footwall of the Woodroffe Thrust to shallow depths occurred at ca. 200 Ma. More recent tectonic activity is also evident as on the 21 May, 2016(Sydney date), a magnitude 6.1 earthquake occurred, and the resolved focal mechanism indicates that compressive stress and exhumation along the Woodroffe Thrust is continuing to the present day. Overall, these results demonstrate repeated amagmatic reactivation of the continental interior of Australia for ca. 715 million years, including at least 600 million years of reactivation along the Woodroffe Thrust alone. Estimated cooling rates agree with previously reported rates and suggest slow cooling of 0.9 -7.0℃/Ma in the core of the Petermann Orogen between ca. 570 Ma and 400 Ma. The long-lived, amagmatic, intracontinental reactivation of central Australia is a remarkable example of stress transmission, strain localization and cratonization-hindering processes that highlights the complexity of Continental Tectonics with regards to the rigid-plate paradigm of Plate Tectonics.
基金supported by National Key R&D Program of China(2022YFF0800902)National Natural Science Foundation of China(No.42121002)+3 种基金the Open Research Project from the State Key Laboratory for Mineral Deposits Research,Nanjing University(2022-LAMD-K11)SinoProbe Lab 202204,State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(GPMR202110)the 111 Project(B18048)the Fundamental Research Funds for the Central Universities(2-9-2019-034).
文摘Recent studies have shown that Cu-rich sulfide accumulates in the lower continental crust and serves as a critical reservoir to balance Cu depletion in the upper crust.Recycling of Cu in the lower crust is also assumed to be a major metal source for non-arc setting porphyry Cu deposits.To test this hypothesis and further explore the behavior of Cu in the lower crust,we analyzed the elemental and Cu isotopic compositions of lower crustal rocks from different geological domains.The collected samples include hornblendites from the Kohistan arc,granulite xenoliths and hornblendites from the Gangdese arc,hornblendites and gabbros from the Laiyuan complex in the North China Craton,and hornblendite xenoliths from the western margin of the Yangtze Craton.These lower crustal rocks have experienced varying degrees of primary or secondary sulfide accumulation,with significantly varied Cu contents(11.2 to 145 ppm)andδδ^(65)(1.05‰to 1.40‰).Petrography and geochemistry reveal varying degrees of metasomatism and fluid interaction in these rocks,and based on this,they can be further divided into three groups:Group I includes the Gangdese granulites and Yunnan hornblendites,which perhaps experienced significant metasomatism.This suite of rocks shows enrichment ofδ^(65)(dδ^(65)=0.01‰to 1.40‰),positively correlated with metasomatism(dδ^(65)vs.Ce/Pb).We suggest the secondary sulfides which transformed from sulfates during the interaction between lower crust and arc magma are dominant in these rocks,so the feature of heavy isotope enrichment is inherited.Group II includes Laiyuan hornblendites and gabbros,derived from the same parental magma and emplaced at different depths(hornblendites,23.3–28.1 km;gabbros 8.4–11.1 km).The Cu isotopic compositions are strongly fractionated between these two kinds of rocks,with low dδ^(65)in the hornblendites(0.00‰to 0.28‰)and highly polarized dδ^(65)in the gabbros(1.05‰to 0.81‰).Geochemical indicators and mineral assemblages reveal that fluid interaction is most likely responsible for this feature.Primary sulfides were decomposed by fluids and reprecipitated at shallower depths.Since this process involves multiple redox reactions,the Cu isotopic composition in the shallowed emplaced gabbros was large fractionated.Group III includes the Gangdese hornblendites and Kohistan hornblendites which show negligible impacts of subduction-like metasomatism and fluid interaction.The Gangdese hornblendites show a homogeneous and unfractionated Cu isotopic composition(-0.09‰to 0.18‰)and Cu content(83.4 to 128 ppm),suggesting insignificant Cu migration and isotope fractionation.In contrast,the Cu isotopic composition of the Kohistan hornblendites is strongly fractionated(-0.36‰to 1.27‰).Geochemistry and modeling results suggest partial melting plays a role in the Cu isotope fractionation.The light Cu isotopes are preferentially distributed into sulfide melts and removed from the source region during partial melting of the lower crust,resulting in a decrease in Cu content and enrichment of heavy Cu isotopes in residues.Results suggest that partial melting and fluid interaction are two efficient mechanisms that encourage Cu migration in the lower crust.
