The Wulungu Depression is the northernmost first-order tectonic unit in the Junggar Basin. It can be divided into three sub-units： the Hongyan step-fault zone, the Suosuoquan sag and the Wulungu south slope. The Ceno...The Wulungu Depression is the northernmost first-order tectonic unit in the Junggar Basin. It can be divided into three sub-units： the Hongyan step-fault zone, the Suosuoquan sag and the Wulungu south slope. The Cenozoic strata in the basin are intact and Mesozoic-Cenozoic deformation can be observed in the Wulungu step-fault zone, so this is an ideal place to study the Mesozoic-Cenozoic deformation. By integration of fault-related folding theories, regional geology and drilling data, the strata of the Cretaceous-Paleogene systems are divided into small layers which are selected as the subjects of this research. The combination of the developing unconformity with existing growth strata makes it conceivable that faults on the step-fault zone have experienced different degrees of reactivation of movement since the Cretaceous. Evolutionary analyses of the small layers using 2D-Move software showed certain differences in the reactivation of different segments of the Wulungu Depression such as the timing of reactivation of thrusting, for which the reactivity time of the eastern segment was late compared with those of the western and middle segments. In addition the resurrection strength was similarly slightly different, with the shortening rate being higher in the western segment than in the other segments. Moreover, the thrust fault mechanism is basement-involved combined with triangle shear fold, for which a forward evolution model was proposed.展开更多
Many orogenic belts in the world exhibit accretionary and collisional orogenic phases to varying extents.How accretion evolves into collision of the Central Asian Orogenic Belt(CAOB),the largest Phanerozoic accretiona...Many orogenic belts in the world exhibit accretionary and collisional orogenic phases to varying extents.How accretion evolves into collision of the Central Asian Orogenic Belt(CAOB),the largest Phanerozoic accretionary orogenic belt,is an intriguing question.In this paper,we present new U-Pb age,geochemical and isotopic data for Permian-Triassic granitoids from middle Inner Mongolia,Northern China in the southeastern CAOB,and delineate the magmatic transition from subduction to(soft)collision.The magmatic record of soft collision is identified and characterized by thickened lower crust-derived high Sr/Y granitoids with a sub-linear distribution along the Solonker suture zone.Granitoids from Early Permian to Late Permian became more enriched in whole-rock Nd and zircon Hf isotopic compositions(εNd(t)values from 2.4 to-19.5,εHf(t)values from 11.6 to-33.7),indicating increasing incorporation of old crust.The change in peak timing of magmatism from west(ca.264 Ma)to east(ca.251 Ma)along the Solonker suture zone implies"scissor-like"closure of the Paleo-Asian Ocean.Integrated with previous studies,a three-stage tectonic model from the Permian to Triassic by accretion leading to collision on the south-eastern margin of CAOB is proposed.(1)Early Permian(>ca.285 Ma):Juvenile magmatism on an active continental margin with double-sided subduction of the Paleo-Asian Ocean;(2)Middle Permian to Middle Triassic(ca.285–235 Ma):Magma source transition from juvenile to old crust induced by a tectonic switch from arc to"scissor-like"closure and subsequent intracontinental orogenic contraction;(3)Late Triassic(<ca.235 Ma):A-type and alkaline magmatism in response to post-collisional extension.展开更多
The Central Tianshan Block is one of numerous microcontinental blocks within the Central Asian Orogenic Belt(CAOB)that overlies Precambrian basement rocks.Constraining the evolution of these ancient basement rocks is ...The Central Tianshan Block is one of numerous microcontinental blocks within the Central Asian Orogenic Belt(CAOB)that overlies Precambrian basement rocks.Constraining the evolution of these ancient basement rocks is central to understanding the accretionary and collisional tectonics of the CAOB,and their place within the Rodinia supercontinent.However,to date,the timing and tectonic settings in which the basement rocks in the Central Tianshan Block formed are poorly constrained,with only sparse geochemical and geochronological data from granitic rocks within the northern segment of the block.Here,we present a systematic study combining U-Pb geochronology,whole-rock geochemistry,and the Sr-Nd isotopic compositions of newly-identified granitic gneisses from the Bingdaban area of Central Tianshan Block.The analyzed samples yield a weighted mean Neoproterozoic 206Pb/238U ages of 975-911 Ma.These weakly-peraluminous granitic rocks show a common geochemical I-type granite affinity.The granitic gneisses are calc-alkaline and enriched in large ion lithophile elements(LILEs)and light rare earth elements(LREEs),but they are depleted in high field strength elements(HFSEs);these characteristics are similar to those of typical subduction-related magmatism.All samples show initial(^(87)Sr/^(86)Sr)(t)ratios between 0.705136 and 0.706745.Values forεNd(t)in the granitic gneisses are in the range from-5.7 to-1.2,which correspond to Nd model ages of 2.0-1.7 Ga,indicating a role for Mesoproterozoic to Paleoproterozoic rocks in the generation of the granitic protoliths.The documented geochemical features indicate that the protoliths for the gneisses have a similar petrogenesis and magmatic source,which may reflect partial melting of thickened crust with the addition of small amounts of mantle-derived material.The Central Tianshan Block probably constitute part of an exterior orogen that developed along the margin of the Rodinian supercontinent during the Early Neoproterozoic and underwent a transition from subduction to syn-collision compression at 975-911 Ma.展开更多
Duobaoshan is the largest porphyry-related Cu-Mo-Au orefield in northeastern(NE)Asia,and hosts a number of large-medium porphyry Cu(PCDs),epithermal Au and Fe-Cu skarn deposits.Formation ages of these deposits,from th...Duobaoshan is the largest porphyry-related Cu-Mo-Au orefield in northeastern(NE)Asia,and hosts a number of large-medium porphyry Cu(PCDs),epithermal Au and Fe-Cu skarn deposits.Formation ages of these deposits,from the oldest(Ordovician)to youngest(Jurassic),have spanned across over 300 Ma.No similar orefields of such size and geological complexity are found in NE Asia,which reflects its metallogenic uniqueness in forming and preserving porphyry-related deposits.In this study,we explore the actual number and timing of magmatic/mineralization phases,their respective magma genesis,fertility,and regional tectonic connection,together with the preservation of PCDs.We present new data on the magmatic/mineralization ages(LA-ICP-MS zircon U-Pb,pyrite and molybdenite Re-Os dating),whole-rock geochemistry,and zircon trace element compositions on four representative deposits in the Duobaoshan orefield,i.e.,Duobaoshan PCD,Tongshan PCD,Sankuanggou Fe-Cu skarn,and Zhengguang epithermal Au deposits,and compiled published ones from these and other mineral occurrences in the orefield.In terms of geochronology,we have newly summarized seven magmatic phases in the orefield:(1)Middle-Late Cambrian(506-491 Ma),(2)Early and Middle Ordovician(485-471 Ma and~462 Ma),(3)Late Ordovician(450-447 Ma),(4)Early Carboniferous and Late-Carboniferous to Early Permian(351-345 and 323-291 Ma),(5)Middle-Late Triassic(244-223 Ma),(6)Early-Middle and Late Jurassic(178-168 Ma and~150 Ma),and(7)Early Cretaceous(~112 Ma).Three of these seven major magmatic phases were coeval with ore formation,including(1)Early Ordovician(485-473 Ma)porphyry-type Cu-Mo-(Au),(2)Early-Middle Triassic(246-229 Ma)porphyry-related epithermal Au-(Cu-Mo),and(3)Early Jurassic(177-173 Ma)Fe-Cu skarn mineralization.Some deposits in the orefield,notably Tongshan and Zhengguang,were likely formed by more than one mineralization events.In terms of geochemistry,ore-causative granitoids in the orefield exhibit adakite-like or adakite-normal arc transitional signatures,but those forming the porphyry-/epithermal-type Cu-Mo-Au mineralization are largely confined to the former.The varying but high Sr/Y,Sm/Yb and La/Yb ratios suggest that the ore-forming magmas were mainly crustal sourced and formed at different depths(clinopyroxene-/amphibole-/garnet-stability fields).The adakite-like suites may have formed by partial melting of the thickened lower crust at 35-40 km(for the Early Ordovician arc)and>40 km(for the Middle-Late Triassic arc)depths.The Early Jurassic Fe-Cu skarn orecausative granitoids show an adakitic-normal arc transitional geochemical affinity.These granitoids were likely formed by partial melting of the juvenile lower crust(35-40 km depth),and subsequently modified by assimilation and fractional crystallization(AFC)processes.In light of the geological,geochronological and geochemical information,we proposed the following tectonometallogenic model for the Duobaoshan orefield.The Ordovician Duobaoshan may have been in a continental arc setting during the subduction of the Paleo-Asian Ocean,and formed the porphyry-related deposits at Duobaoshan,Tongshan and Zhengguang.Subduction may have ceased in the latest Ordovician,and the regional tectonics passed into long subsidence and extension till the latest Carboniferous.This extensional tectonic regime and the Silurian terrestrial-shallow marine sedimentation had likely buried and preserved the Ordovician Duobaoshan magmatic-hydrothermal system.The south-dipping Mongol-Okhotsk Ocean subduction from north of the orefield had generated the Middle-Late Triassic continental arc magmatism and the associated Tongshan PCD and Zhengguang epithermal Au mineralization(which superimposed on the Ordovician PCD system).The Middle Jurassic closure of Mongol-Okhotsk Ocean in the northwestern Amuria block(Erguna terrane),and the accompanying Siberia-Amuria collision,may have placed the Paleo-Pacific subduction system in NE China(including the orefield)under compression,and formed the granodiorite-tonalite and Fe-Cu skarn deposits at Sankuanggou and Xiaoduobaoshan.From the Middle Jurassic,the consecutive accretion of Paleo-Pacific arc terranes(e.g.,Sikhote-Alin and Nadanhada)onto the NE Asian continental margin may have gradually distant the Duobaoshan orefield from the subduction front,and consequently arc-type magmatism and the related mineralization faded.The minor Late Jurassic and Cretaceous unmineralized magmatism in the orefield may have triggered mainly by the far-field extension led by the post-collisional(Siberia-Amuria)gravitational collapse and/or Paleo-Pacific backarc-basin opening.展开更多
To constrain the ore-fluid source(s)of the Laoshankou Fe-Cu-Au deposit(Junggar orogen,NW China),we analyzed the fluid inclusion(FI)noble gas(Ar,Kr and Xe)and halogen(Cl,Br and I)compositions in the hydrothermal epidot...To constrain the ore-fluid source(s)of the Laoshankou Fe-Cu-Au deposit(Junggar orogen,NW China),we analyzed the fluid inclusion(FI)noble gas(Ar,Kr and Xe)and halogen(Cl,Br and I)compositions in the hydrothermal epidote and quartz.Four hypogene alteration/mineralization stages,including(I)pre-ore Ca-silicate,(II)early-ore amphibole-epidote-magnetite,(III)late-ore pyrite-chalcopyrite,and(IV)post-ore hydrothermal veining,have been identified at Laoshankou.Stage II FIs have salinity of 15.7 wt.%(NaCl eq.),I/Cl molar ratios of 75×10^(−6)-135×10^(−6),and Br/Cl molar ratios of 1.4×10^(−3)-2.1×10^(−3).The moderately-high seawatercorrected Br*/I ratios(0.5-1.5)and low 40ArE/Cl slope(-10−5)indicate the presence of sedimentary marine pore fluid,which was modified by seawater reacting with the Beitashan Fm.volcanic rocks.Stage III fluid is more saline than their stage II and IV counterparts,reaching up to 23.3 wt.%(NaCl+CaCl2 eq.)close to halite saturation(-26 wt.%).The fluid has I/Cl ratios of 75×10^(−6)-90×10^(−6) and Br/Cl ratios of 1.5×10^(−3)-1.8×10^(−3).Considering the increasing 40ArE/Cl trend toward bittern brine and the higher 36Ar content than air-saturated water(ASW),a bittern fluid source is inferred from seawater evaporation,which was modified by interaction with organic-rich marine sedimentary rocks.Stage IV FIs have lower temperature(110-228°C)and Br/Cl(0.90×10^(−3)-1.2×10^(−3)),but higher 36Ar content than ASW,indicative of dissolved evaporite or halite input.Considering also the lowδDfluid(−114‰to−144‰)andδ18Ofluid(2.1‰-3.5‰)values,meteoric water(with minor dissolved evaporites)likely dominated the stage IV fluid.The evaporites may have formed through continuous evaporation of the stage III surface-derived bittern.Involvement of non-magmatic fluids and different ore-fluid origins in stages II and III suggest that the ore-forming process was different from a typical magmatichydrothermal fluid-dominated skarn mineralization,which was previously proposed for Laoshankou.Our noble gas and halogen study at Laoshankou provide new insights on the fluid sources for the Paleozoic Fe−Cu(−Au)deposits in the Central Asian Orogenic Belt(CAOB),and our non-magmatic fluid source interpretation is consistent with the basin inversion setting for the mineralization.展开更多
基金financially supported by the National Science and Technology Major Project (No.2011ZX05008-001)the Natural Science Foundation of China (No.40739906)the Chinese State 973 Project(No. 2011CB201100)
文摘The Wulungu Depression is the northernmost first-order tectonic unit in the Junggar Basin. It can be divided into three sub-units： the Hongyan step-fault zone, the Suosuoquan sag and the Wulungu south slope. The Cenozoic strata in the basin are intact and Mesozoic-Cenozoic deformation can be observed in the Wulungu step-fault zone, so this is an ideal place to study the Mesozoic-Cenozoic deformation. By integration of fault-related folding theories, regional geology and drilling data, the strata of the Cretaceous-Paleogene systems are divided into small layers which are selected as the subjects of this research. The combination of the developing unconformity with existing growth strata makes it conceivable that faults on the step-fault zone have experienced different degrees of reactivation of movement since the Cretaceous. Evolutionary analyses of the small layers using 2D-Move software showed certain differences in the reactivation of different segments of the Wulungu Depression such as the timing of reactivation of thrusting, for which the reactivity time of the eastern segment was late compared with those of the western and middle segments. In addition the resurrection strength was similarly slightly different, with the shortening rate being higher in the western segment than in the other segments. Moreover, the thrust fault mechanism is basement-involved combined with triangle shear fold, for which a forward evolution model was proposed.
基金supported by the National Key Research and Development Program of China from the Ministry of Science and Technology of China(Grant No.2017YFC0601301)the National Natural Science Foundation of China(Grant Nos.41772232 and 41830216)the Projects of the China Geological Survey(Grant Nos.DD20190358 and DD20190001)。
文摘Many orogenic belts in the world exhibit accretionary and collisional orogenic phases to varying extents.How accretion evolves into collision of the Central Asian Orogenic Belt(CAOB),the largest Phanerozoic accretionary orogenic belt,is an intriguing question.In this paper,we present new U-Pb age,geochemical and isotopic data for Permian-Triassic granitoids from middle Inner Mongolia,Northern China in the southeastern CAOB,and delineate the magmatic transition from subduction to(soft)collision.The magmatic record of soft collision is identified and characterized by thickened lower crust-derived high Sr/Y granitoids with a sub-linear distribution along the Solonker suture zone.Granitoids from Early Permian to Late Permian became more enriched in whole-rock Nd and zircon Hf isotopic compositions(εNd(t)values from 2.4 to-19.5,εHf(t)values from 11.6 to-33.7),indicating increasing incorporation of old crust.The change in peak timing of magmatism from west(ca.264 Ma)to east(ca.251 Ma)along the Solonker suture zone implies"scissor-like"closure of the Paleo-Asian Ocean.Integrated with previous studies,a three-stage tectonic model from the Permian to Triassic by accretion leading to collision on the south-eastern margin of CAOB is proposed.(1)Early Permian(>ca.285 Ma):Juvenile magmatism on an active continental margin with double-sided subduction of the Paleo-Asian Ocean;(2)Middle Permian to Middle Triassic(ca.285–235 Ma):Magma source transition from juvenile to old crust induced by a tectonic switch from arc to"scissor-like"closure and subsequent intracontinental orogenic contraction;(3)Late Triassic(<ca.235 Ma):A-type and alkaline magmatism in response to post-collisional extension.
基金supported by the National Natural Science Foundation of China(92055208,41772059,42174080)the CAS"Light of West China"Program(2018-XBYJRC-003)+3 种基金the Guangxi Natural Science Foundation for Distinguished Young Scholars,China(2018GXNSFFA281009)the Guangxi Science Innovation Base Construction Foundation(GuikeZY21195031)the Guangxi Natural Science Foundation for Innovation Research Team Program(GXNSFGA380004)the Fifth Bagui Scholar Innovation Project of Guangxi Zhuang Autonomous Region,China。
文摘The Central Tianshan Block is one of numerous microcontinental blocks within the Central Asian Orogenic Belt(CAOB)that overlies Precambrian basement rocks.Constraining the evolution of these ancient basement rocks is central to understanding the accretionary and collisional tectonics of the CAOB,and their place within the Rodinia supercontinent.However,to date,the timing and tectonic settings in which the basement rocks in the Central Tianshan Block formed are poorly constrained,with only sparse geochemical and geochronological data from granitic rocks within the northern segment of the block.Here,we present a systematic study combining U-Pb geochronology,whole-rock geochemistry,and the Sr-Nd isotopic compositions of newly-identified granitic gneisses from the Bingdaban area of Central Tianshan Block.The analyzed samples yield a weighted mean Neoproterozoic 206Pb/238U ages of 975-911 Ma.These weakly-peraluminous granitic rocks show a common geochemical I-type granite affinity.The granitic gneisses are calc-alkaline and enriched in large ion lithophile elements(LILEs)and light rare earth elements(LREEs),but they are depleted in high field strength elements(HFSEs);these characteristics are similar to those of typical subduction-related magmatism.All samples show initial(^(87)Sr/^(86)Sr)(t)ratios between 0.705136 and 0.706745.Values forεNd(t)in the granitic gneisses are in the range from-5.7 to-1.2,which correspond to Nd model ages of 2.0-1.7 Ga,indicating a role for Mesoproterozoic to Paleoproterozoic rocks in the generation of the granitic protoliths.The documented geochemical features indicate that the protoliths for the gneisses have a similar petrogenesis and magmatic source,which may reflect partial melting of thickened crust with the addition of small amounts of mantle-derived material.The Central Tianshan Block probably constitute part of an exterior orogen that developed along the margin of the Rodinian supercontinent during the Early Neoproterozoic and underwent a transition from subduction to syn-collision compression at 975-911 Ma.
基金funded by the China Geological Survey,the Chinese Ministry of Science and Technology(2017YFC0601304)the Cu-Mo-Au-Ag Metallogenic Regularity in Duobaoshan-Sankuanggou Belt Project(DT-2017-SJC-12)。
文摘Duobaoshan is the largest porphyry-related Cu-Mo-Au orefield in northeastern(NE)Asia,and hosts a number of large-medium porphyry Cu(PCDs),epithermal Au and Fe-Cu skarn deposits.Formation ages of these deposits,from the oldest(Ordovician)to youngest(Jurassic),have spanned across over 300 Ma.No similar orefields of such size and geological complexity are found in NE Asia,which reflects its metallogenic uniqueness in forming and preserving porphyry-related deposits.In this study,we explore the actual number and timing of magmatic/mineralization phases,their respective magma genesis,fertility,and regional tectonic connection,together with the preservation of PCDs.We present new data on the magmatic/mineralization ages(LA-ICP-MS zircon U-Pb,pyrite and molybdenite Re-Os dating),whole-rock geochemistry,and zircon trace element compositions on four representative deposits in the Duobaoshan orefield,i.e.,Duobaoshan PCD,Tongshan PCD,Sankuanggou Fe-Cu skarn,and Zhengguang epithermal Au deposits,and compiled published ones from these and other mineral occurrences in the orefield.In terms of geochronology,we have newly summarized seven magmatic phases in the orefield:(1)Middle-Late Cambrian(506-491 Ma),(2)Early and Middle Ordovician(485-471 Ma and~462 Ma),(3)Late Ordovician(450-447 Ma),(4)Early Carboniferous and Late-Carboniferous to Early Permian(351-345 and 323-291 Ma),(5)Middle-Late Triassic(244-223 Ma),(6)Early-Middle and Late Jurassic(178-168 Ma and~150 Ma),and(7)Early Cretaceous(~112 Ma).Three of these seven major magmatic phases were coeval with ore formation,including(1)Early Ordovician(485-473 Ma)porphyry-type Cu-Mo-(Au),(2)Early-Middle Triassic(246-229 Ma)porphyry-related epithermal Au-(Cu-Mo),and(3)Early Jurassic(177-173 Ma)Fe-Cu skarn mineralization.Some deposits in the orefield,notably Tongshan and Zhengguang,were likely formed by more than one mineralization events.In terms of geochemistry,ore-causative granitoids in the orefield exhibit adakite-like or adakite-normal arc transitional signatures,but those forming the porphyry-/epithermal-type Cu-Mo-Au mineralization are largely confined to the former.The varying but high Sr/Y,Sm/Yb and La/Yb ratios suggest that the ore-forming magmas were mainly crustal sourced and formed at different depths(clinopyroxene-/amphibole-/garnet-stability fields).The adakite-like suites may have formed by partial melting of the thickened lower crust at 35-40 km(for the Early Ordovician arc)and>40 km(for the Middle-Late Triassic arc)depths.The Early Jurassic Fe-Cu skarn orecausative granitoids show an adakitic-normal arc transitional geochemical affinity.These granitoids were likely formed by partial melting of the juvenile lower crust(35-40 km depth),and subsequently modified by assimilation and fractional crystallization(AFC)processes.In light of the geological,geochronological and geochemical information,we proposed the following tectonometallogenic model for the Duobaoshan orefield.The Ordovician Duobaoshan may have been in a continental arc setting during the subduction of the Paleo-Asian Ocean,and formed the porphyry-related deposits at Duobaoshan,Tongshan and Zhengguang.Subduction may have ceased in the latest Ordovician,and the regional tectonics passed into long subsidence and extension till the latest Carboniferous.This extensional tectonic regime and the Silurian terrestrial-shallow marine sedimentation had likely buried and preserved the Ordovician Duobaoshan magmatic-hydrothermal system.The south-dipping Mongol-Okhotsk Ocean subduction from north of the orefield had generated the Middle-Late Triassic continental arc magmatism and the associated Tongshan PCD and Zhengguang epithermal Au mineralization(which superimposed on the Ordovician PCD system).The Middle Jurassic closure of Mongol-Okhotsk Ocean in the northwestern Amuria block(Erguna terrane),and the accompanying Siberia-Amuria collision,may have placed the Paleo-Pacific subduction system in NE China(including the orefield)under compression,and formed the granodiorite-tonalite and Fe-Cu skarn deposits at Sankuanggou and Xiaoduobaoshan.From the Middle Jurassic,the consecutive accretion of Paleo-Pacific arc terranes(e.g.,Sikhote-Alin and Nadanhada)onto the NE Asian continental margin may have gradually distant the Duobaoshan orefield from the subduction front,and consequently arc-type magmatism and the related mineralization faded.The minor Late Jurassic and Cretaceous unmineralized magmatism in the orefield may have triggered mainly by the far-field extension led by the post-collisional(Siberia-Amuria)gravitational collapse and/or Paleo-Pacific backarc-basin opening.
基金supported by the Fundamental Research Funds for the Central Universities(FRF-TP-18-080A1)the National Natural Science Foundation of China(Grant Nos.42002076,41930427,41725009,U1603244)the Science and Technology Planning of Guangdong Province,China(2020B1212060055)。
文摘To constrain the ore-fluid source(s)of the Laoshankou Fe-Cu-Au deposit(Junggar orogen,NW China),we analyzed the fluid inclusion(FI)noble gas(Ar,Kr and Xe)and halogen(Cl,Br and I)compositions in the hydrothermal epidote and quartz.Four hypogene alteration/mineralization stages,including(I)pre-ore Ca-silicate,(II)early-ore amphibole-epidote-magnetite,(III)late-ore pyrite-chalcopyrite,and(IV)post-ore hydrothermal veining,have been identified at Laoshankou.Stage II FIs have salinity of 15.7 wt.%(NaCl eq.),I/Cl molar ratios of 75×10^(−6)-135×10^(−6),and Br/Cl molar ratios of 1.4×10^(−3)-2.1×10^(−3).The moderately-high seawatercorrected Br*/I ratios(0.5-1.5)and low 40ArE/Cl slope(-10−5)indicate the presence of sedimentary marine pore fluid,which was modified by seawater reacting with the Beitashan Fm.volcanic rocks.Stage III fluid is more saline than their stage II and IV counterparts,reaching up to 23.3 wt.%(NaCl+CaCl2 eq.)close to halite saturation(-26 wt.%).The fluid has I/Cl ratios of 75×10^(−6)-90×10^(−6) and Br/Cl ratios of 1.5×10^(−3)-1.8×10^(−3).Considering the increasing 40ArE/Cl trend toward bittern brine and the higher 36Ar content than air-saturated water(ASW),a bittern fluid source is inferred from seawater evaporation,which was modified by interaction with organic-rich marine sedimentary rocks.Stage IV FIs have lower temperature(110-228°C)and Br/Cl(0.90×10^(−3)-1.2×10^(−3)),but higher 36Ar content than ASW,indicative of dissolved evaporite or halite input.Considering also the lowδDfluid(−114‰to−144‰)andδ18Ofluid(2.1‰-3.5‰)values,meteoric water(with minor dissolved evaporites)likely dominated the stage IV fluid.The evaporites may have formed through continuous evaporation of the stage III surface-derived bittern.Involvement of non-magmatic fluids and different ore-fluid origins in stages II and III suggest that the ore-forming process was different from a typical magmatichydrothermal fluid-dominated skarn mineralization,which was previously proposed for Laoshankou.Our noble gas and halogen study at Laoshankou provide new insights on the fluid sources for the Paleozoic Fe−Cu(−Au)deposits in the Central Asian Orogenic Belt(CAOB),and our non-magmatic fluid source interpretation is consistent with the basin inversion setting for the mineralization.
