蚀变岩帽在地表一般表现为陡倾的正地形,是高温、高氧逸度流体对围岩进行酸性淋滤,形成的一系列高级泥化和泥化等蚀变矿物组合。这种蚀变是浅成低温热液蚀变系统的一部分,其深部可能具有寻找斑岩型矿化的潜力。浙东南陆相火山岩地区普...蚀变岩帽在地表一般表现为陡倾的正地形,是高温、高氧逸度流体对围岩进行酸性淋滤,形成的一系列高级泥化和泥化等蚀变矿物组合。这种蚀变是浅成低温热液蚀变系统的一部分,其深部可能具有寻找斑岩型矿化的潜力。浙东南陆相火山岩地区普遍发育此种蚀变岩帽,但该类型蚀变常被前人定义为"次生石英岩"。本文选择其中典型的后坑蚀变岩帽,通过大比例尺蚀变填图、岩心编录,利用短波红外(ASD)、电子探针(EPMA)、扫描电镜(SEM)、能谱仪(EDS)等分析技术手段,发现蚀变岩帽具有垂直方向和水平方向的蚀变矿物分带。垂直方向由深到浅依次发育刚玉-绢云母,绢云母-叶蜡石,明矾石-高岭石-地开石具分带特征;水平方向上从核部到边部依次发育多孔状石英-金红石、高级泥化带(明矾石-叶蜡石-高岭石-地开石-水铝石-Aluminum Phosphate and sulphates矿物)、泥化带(高岭石-伊利石-蒙脱石)。并得出以下几点认识:①后坑蚀变岩帽中明矾石短波红外特征吸收峰在1480~1491nm之间,以岩浆-热液成因的钾明矾石为主,含少量钠明矾石;②叶蜡石短波红外特征吸收峰在2167nm左右,分为两种成因:早期高级泥化阶段的绢云母经后期热液退变质蚀变而成以及早期高岭石经后期热液进变质作用形成;③蚀变岩帽根部的刚玉被后期热液蚀变形成绢云母,刚玉-绢云母蚀变带之下可能是黄铁绢英岩化带;④早期水铝石被后期热液蚀变形成地开石,代表了热液的多期次性;通过对比后坑蚀变岩帽与其他斑岩-浅成低温热液矿床(如Horse-Ivaal和Vuda等矿床)的蚀变矿物分带后,发现后坑蚀变岩帽蚀变矿物分带与这些典型矿床相似。本文认为后坑蚀变岩帽属于该成矿系统上部的浅成低温热液蚀变部分,其深部具有寻找斑岩矿床的潜力,同时提出浙东南其他发育在陆相火山岩中的蚀变岩帽也属于该蚀变系统,具有寻找斑岩型铜金矿床的较大潜力。展开更多
Granitic gneiss(orthogneiss)and Himalayan leucogranite are widely distributed in the Himalayan orogen,but whether or not the granitic gneiss made a contribution to the Himalayan leucogranite remains unclear.In this st...Granitic gneiss(orthogneiss)and Himalayan leucogranite are widely distributed in the Himalayan orogen,but whether or not the granitic gneiss made a contribution to the Himalayan leucogranite remains unclear.In this study,we present the petrological,geochronological and geochemical results for orthogneisses and leucogranites from the Zhada area,Western Himalayas.Zhada orthogneiss is composed mainly of quartz,plagioclase,K-feldspar,biotite and muscovite,with accessory zircon and apatite.Orthogneiss zircon cathodoluminescence(CL)images show that most grains contain a core with oscillatory zoning,which indicates an igneous origin.Sensitive high-resolution ion microprobe(SHRIMP)U-Pb dating of the zircon cores in the orthogneiss shows a weighted ^(206)Pb/^(238)U age of 515±4 Ma(early Paleozoic),with sponge-like zircon rims of 17.9±0.5 Ma(Miocene).Zhada leucogranite shows^(206)Pb/^(238)U ages ranging from 19.0±0.4 Ma to 12.4±0.2 Ma,the weighted average age being 16.2±0.4 Ma.The leucogranites have a low Ca content(<1 wt%),FeOt content(<1 wt%),Rb content(67.0-402 ppm),Sr content(<56.6 ppm),Ba content(3.35-238 ppm)and Rb/Sr ratio(0.5-14.7),which are similar to the geochemical characteristics of the Himalayan leucogranite derived from muscovite dehydration partial melting of metasediments and representative of most Himalayan leucogranites.The highly variable Na_(2)O+K_(2)O(4.33 wt%-9.13 wt%),Al_(2)O_(3)(8.44 wt%-13.51 wt%),ΣREE(40.2-191.0 ppm),Rb(67.0-402 ppm)and Nb(8.23-26.4 ppm)contents,^(87)Sr/^(86)Sr(t)ratios(0.7445-0.8605)andεNd(t)values(−3.6 to−8.2)indicate that the leucogranite is derived from a heterogenetic source.The nonradiogenic Nd isotope values of the studied Zhada leucogranite and orthogneiss range from−8.2 to−3.6 and from−8.7 to−4.1,respectively.Therefore,the general mixing equation was used to perform the Sr and Nd isotope mixing calculations.The results indicate that the heterogenetic source was the Tethyan Himalayan Sequence(THS)/Higher Himalayan Crystalline(HHC)metasediments and Zhada orthogneiss.The Zhada area experienced crustal anatexis during the Miocene and the heterogenetic source of the orthogneiss and metasediment may have experienced crustal anatexis controlled by muscovite dehydration.The Zhada leucogranite inherited not only the geochemical characteristics of the Himalayan metasediment(muscovite dehydration melting),but also the trace elements and Sr-Nd isotopic characteristics of the Zhada orthogneiss.These results indicate that the Paleozoic Zhada orthogneiss was involved in crustal anatexis at 17.9±0.5 Ma(Miocene)and that the muscovite dehydration of the metasediments in the heterogenetic source produced fluid,which may have caused the orthogneiss solidus lines to decline,triggering a partial melting of the Zhada orthogneiss.It is therefore proposed that Himalayan leucogranite is a crust-derived granite rather than a S-type granite,as previously hypothesized.展开更多
ObjectiveThe Himalaya terrain together with the ribbon terrains （e.g., Lhasa, Qiangtang, and Sibumasu blocks） of the Gondwana supercontinent has experienced episodic tectonic events since the Neoproterozoic. However...ObjectiveThe Himalaya terrain together with the ribbon terrains （e.g., Lhasa, Qiangtang, and Sibumasu blocks） of the Gondwana supercontinent has experienced episodic tectonic events since the Neoproterozoic. However, almost not any documentation with regard to the tectonic processes links the peri-Gondwana subduction between 510-480 Ma with the Carboniferous-Permian （-360-260 Ma） continental rifting event. This possible link is important for testing and formulating the tectonic model for the evolution of the present-day Himalayan orogenic belt, if we consider this belt has also experienced typical Wilson cycle plate tectonics. Recently, we have found several lines of evidence which imply that the Himalayan terrain and possibly other ribbon terrains of the eastern Gondwana have experienced unrecognized tectonic processes during the Late Ordovician to Early Silurian.展开更多
Objective“Orogenic gold deposits,”which account for 30%of global gold resources(Frimmel and Hennigh,2015),is one of the most important types of gold deposits in the world.This kind of gold deposit is supposed to hav...Objective“Orogenic gold deposits,”which account for 30%of global gold resources(Frimmel and Hennigh,2015),is one of the most important types of gold deposits in the world.This kind of gold deposit is supposed to have spatial and temporal distribution association with the accretionary orogenic belt.The Ailaoshan Gold Belt,where there are many large orogenic gold deposits including Jinchang,Daping,Laowangzhai,Donggualing,and Changan,contribute substantially to Chinese gold resources.The Himalayan orogen and Ailaoshan Orogen,both have experienced the early accretionary orogenesis and the subsequent collisional orogenesis are one of the biggest orogenic belts on the earth.Gold mineralization can be divided into that the earlier Yarlung Zangbo suture zone(59–44 Ma)and the later Ailaoshan Orogen(35–26 Ma)(Li et al.,2017),based on previous geochronological studies.In order to find out if there are any connections between these two gold events,we present 40Ar/39Ar data of hydrothermal sericite collected from the Xiachahe gold deposit in the northwest of the Ailaoshan Gold Belt.However,our new geochronology data regards this as a continuous gold mineralization event resulting from the India–Eurasia collision.展开更多
Tourmaline geochemical and boron(B)isotopic compositions in two-mica granites(TMG),tourmaline-bearing leucogranites(Tou-LG),tourmalites and metapelites from the Gyirong-Malashan areas of the Himalayan orogen provide e...Tourmaline geochemical and boron(B)isotopic compositions in two-mica granites(TMG),tourmaline-bearing leucogranites(Tou-LG),tourmalites and metapelites from the Gyirong-Malashan areas of the Himalayan orogen provide evidence for country rock assimilation during the intrusion of Himalayan leucogranite.The schorls in Gyirong leucogranitic plutons show low contents of MgO(0.238%-1.160%)and δ^(11)B values(-12.1‰--11.2‰),while dravites gathered in the contact zone between the leucogranitic veins and metapelites show high contents of MgO(4.815%-6.755%)and δ^(11)B values(-10.7‰--9.3‰).This geochemical and isotopic variation of tourmalines can also be identified in the Malashan gneiss dome.As a result,three types of tourmaline were identified in the Himalayan orogen:(1)Tou-Ⅰ in the TMG and Tou-LG,which is the most common tourmaline type of schorl;(2)Tou-Ⅱ(dravite and high-Mg schorl)in the Tou-LG and tourmalite at the margins of the leucogranite;and(3)Tou-Ⅲ(mainly dravite,with minor high-Mg schorl)in metapelites of the High Himalayan Crystalline Sequence.The lenses and veins of Tou-LG may have experienced metasomatism and assimilation as a result of interaction with the High Himalayan Crystalline Sequence metasedimentary country rocks,which can be traced by the geochemical and isotopic characteristics of the tourmaline therein.展开更多
The Paiku composite leucogranitic pluton in the Malashan gneiss dome within the Tethyan Himalaya consists of tourmaline leucogranite,two-mica granite and garnet-bearing leucogranite.Zircon U-Pb dating yields that(1)to...The Paiku composite leucogranitic pluton in the Malashan gneiss dome within the Tethyan Himalaya consists of tourmaline leucogranite,two-mica granite and garnet-bearing leucogranite.Zircon U-Pb dating yields that(1)tourmaline leucogranite formed at28.2±0.5 Ma and its source rock experienced simultaneous metamorphism and anatexis at 33.6±0.6 Ma;(2)two-mica granite formed at 19.8±0.5 Ma;(3)both types of leucogranite contain inherited zircon grains with an age peak at^480 Ma.These leucogranites show distinct geochemistry in major and trace elements as well as in Sr-Nd-Hf isotope compositions.As compared to the two-mica granites,the tourmaline ones have higher initial Sr and zircon Hf isotope compositions,indicating that they were derived from different source rocks combined with different melting reactions.Combined with available literature data,it is suggested that anatexis at^35 Ma along the Himalayan orogenic belt might have triggered the initial movement of the Southern Tibetan Detachment System(STDS),and led to the tectonic transition from compressive shortening to extension.Such a tectonic transition could be a dominant factor that initiates large scale decompressional melting of fertile high-grade metapelites along the Himalayan orogenic belt.Crustal anatexis at^28 Ma and^20 Ma represent large-scale melting reactions associated with the movement of the STDS.展开更多
文摘蚀变岩帽在地表一般表现为陡倾的正地形,是高温、高氧逸度流体对围岩进行酸性淋滤,形成的一系列高级泥化和泥化等蚀变矿物组合。这种蚀变是浅成低温热液蚀变系统的一部分,其深部可能具有寻找斑岩型矿化的潜力。浙东南陆相火山岩地区普遍发育此种蚀变岩帽,但该类型蚀变常被前人定义为"次生石英岩"。本文选择其中典型的后坑蚀变岩帽,通过大比例尺蚀变填图、岩心编录,利用短波红外(ASD)、电子探针(EPMA)、扫描电镜(SEM)、能谱仪(EDS)等分析技术手段,发现蚀变岩帽具有垂直方向和水平方向的蚀变矿物分带。垂直方向由深到浅依次发育刚玉-绢云母,绢云母-叶蜡石,明矾石-高岭石-地开石具分带特征;水平方向上从核部到边部依次发育多孔状石英-金红石、高级泥化带(明矾石-叶蜡石-高岭石-地开石-水铝石-Aluminum Phosphate and sulphates矿物)、泥化带(高岭石-伊利石-蒙脱石)。并得出以下几点认识:①后坑蚀变岩帽中明矾石短波红外特征吸收峰在1480~1491nm之间,以岩浆-热液成因的钾明矾石为主,含少量钠明矾石;②叶蜡石短波红外特征吸收峰在2167nm左右,分为两种成因:早期高级泥化阶段的绢云母经后期热液退变质蚀变而成以及早期高岭石经后期热液进变质作用形成;③蚀变岩帽根部的刚玉被后期热液蚀变形成绢云母,刚玉-绢云母蚀变带之下可能是黄铁绢英岩化带;④早期水铝石被后期热液蚀变形成地开石,代表了热液的多期次性;通过对比后坑蚀变岩帽与其他斑岩-浅成低温热液矿床(如Horse-Ivaal和Vuda等矿床)的蚀变矿物分带后,发现后坑蚀变岩帽蚀变矿物分带与这些典型矿床相似。本文认为后坑蚀变岩帽属于该成矿系统上部的浅成低温热液蚀变部分,其深部具有寻找斑岩矿床的潜力,同时提出浙东南其他发育在陆相火山岩中的蚀变岩帽也属于该蚀变系统,具有寻找斑岩型铜金矿床的较大潜力。
基金This work was supported by the National Natural Science Foundation of China(Grant Nos.42072114,41503006)the Deep Resources Exploration and Mining,the National Key R&D Program of China(Grant No.2018YFC0604106)+1 种基金the Chinese Geological Survey(Grant No.DD20190167)the China Scholarship Council(Grant No.201808110080).
文摘Granitic gneiss(orthogneiss)and Himalayan leucogranite are widely distributed in the Himalayan orogen,but whether or not the granitic gneiss made a contribution to the Himalayan leucogranite remains unclear.In this study,we present the petrological,geochronological and geochemical results for orthogneisses and leucogranites from the Zhada area,Western Himalayas.Zhada orthogneiss is composed mainly of quartz,plagioclase,K-feldspar,biotite and muscovite,with accessory zircon and apatite.Orthogneiss zircon cathodoluminescence(CL)images show that most grains contain a core with oscillatory zoning,which indicates an igneous origin.Sensitive high-resolution ion microprobe(SHRIMP)U-Pb dating of the zircon cores in the orthogneiss shows a weighted ^(206)Pb/^(238)U age of 515±4 Ma(early Paleozoic),with sponge-like zircon rims of 17.9±0.5 Ma(Miocene).Zhada leucogranite shows^(206)Pb/^(238)U ages ranging from 19.0±0.4 Ma to 12.4±0.2 Ma,the weighted average age being 16.2±0.4 Ma.The leucogranites have a low Ca content(<1 wt%),FeOt content(<1 wt%),Rb content(67.0-402 ppm),Sr content(<56.6 ppm),Ba content(3.35-238 ppm)and Rb/Sr ratio(0.5-14.7),which are similar to the geochemical characteristics of the Himalayan leucogranite derived from muscovite dehydration partial melting of metasediments and representative of most Himalayan leucogranites.The highly variable Na_(2)O+K_(2)O(4.33 wt%-9.13 wt%),Al_(2)O_(3)(8.44 wt%-13.51 wt%),ΣREE(40.2-191.0 ppm),Rb(67.0-402 ppm)and Nb(8.23-26.4 ppm)contents,^(87)Sr/^(86)Sr(t)ratios(0.7445-0.8605)andεNd(t)values(−3.6 to−8.2)indicate that the leucogranite is derived from a heterogenetic source.The nonradiogenic Nd isotope values of the studied Zhada leucogranite and orthogneiss range from−8.2 to−3.6 and from−8.7 to−4.1,respectively.Therefore,the general mixing equation was used to perform the Sr and Nd isotope mixing calculations.The results indicate that the heterogenetic source was the Tethyan Himalayan Sequence(THS)/Higher Himalayan Crystalline(HHC)metasediments and Zhada orthogneiss.The Zhada area experienced crustal anatexis during the Miocene and the heterogenetic source of the orthogneiss and metasediment may have experienced crustal anatexis controlled by muscovite dehydration.The Zhada leucogranite inherited not only the geochemical characteristics of the Himalayan metasediment(muscovite dehydration melting),but also the trace elements and Sr-Nd isotopic characteristics of the Zhada orthogneiss.These results indicate that the Paleozoic Zhada orthogneiss was involved in crustal anatexis at 17.9±0.5 Ma(Miocene)and that the muscovite dehydration of the metasediments in the heterogenetic source produced fluid,which may have caused the orthogneiss solidus lines to decline,triggering a partial melting of the Zhada orthogneiss.It is therefore proposed that Himalayan leucogranite is a crust-derived granite rather than a S-type granite,as previously hypothesized.
基金supported by the National Science Foundation of China(grants No.41425010,41503023 and 41273034)China Geological Survey(grant No.12120115027101)+1 种基金Special Fund for Scientific Research in the Public Welfare(grant No.201511022)the Outlay Research Fund of Institute of Geology(grant No.J1516)
文摘ObjectiveThe Himalaya terrain together with the ribbon terrains （e.g., Lhasa, Qiangtang, and Sibumasu blocks） of the Gondwana supercontinent has experienced episodic tectonic events since the Neoproterozoic. However, almost not any documentation with regard to the tectonic processes links the peri-Gondwana subduction between 510-480 Ma with the Carboniferous-Permian （-360-260 Ma） continental rifting event. This possible link is important for testing and formulating the tectonic model for the evolution of the present-day Himalayan orogenic belt, if we consider this belt has also experienced typical Wilson cycle plate tectonics. Recently, we have found several lines of evidence which imply that the Himalayan terrain and possibly other ribbon terrains of the eastern Gondwana have experienced unrecognized tectonic processes during the Late Ordovician to Early Silurian.
基金supported by the National Science Foundation of China(grant No.41772075)the National Key R&D Program of China,Deep Resources Exploration and Mining(grant No.2018YFC0604105).
文摘Objective“Orogenic gold deposits,”which account for 30%of global gold resources(Frimmel and Hennigh,2015),is one of the most important types of gold deposits in the world.This kind of gold deposit is supposed to have spatial and temporal distribution association with the accretionary orogenic belt.The Ailaoshan Gold Belt,where there are many large orogenic gold deposits including Jinchang,Daping,Laowangzhai,Donggualing,and Changan,contribute substantially to Chinese gold resources.The Himalayan orogen and Ailaoshan Orogen,both have experienced the early accretionary orogenesis and the subsequent collisional orogenesis are one of the biggest orogenic belts on the earth.Gold mineralization can be divided into that the earlier Yarlung Zangbo suture zone(59–44 Ma)and the later Ailaoshan Orogen(35–26 Ma)(Li et al.,2017),based on previous geochronological studies.In order to find out if there are any connections between these two gold events,we present 40Ar/39Ar data of hydrothermal sericite collected from the Xiachahe gold deposit in the northwest of the Ailaoshan Gold Belt.However,our new geochronology data regards this as a continuous gold mineralization event resulting from the India–Eurasia collision.
基金supported by the National Natural Science Foundation of China(42072114 and 41503006)。
文摘Tourmaline geochemical and boron(B)isotopic compositions in two-mica granites(TMG),tourmaline-bearing leucogranites(Tou-LG),tourmalites and metapelites from the Gyirong-Malashan areas of the Himalayan orogen provide evidence for country rock assimilation during the intrusion of Himalayan leucogranite.The schorls in Gyirong leucogranitic plutons show low contents of MgO(0.238%-1.160%)and δ^(11)B values(-12.1‰--11.2‰),while dravites gathered in the contact zone between the leucogranitic veins and metapelites show high contents of MgO(4.815%-6.755%)and δ^(11)B values(-10.7‰--9.3‰).This geochemical and isotopic variation of tourmalines can also be identified in the Malashan gneiss dome.As a result,three types of tourmaline were identified in the Himalayan orogen:(1)Tou-Ⅰ in the TMG and Tou-LG,which is the most common tourmaline type of schorl;(2)Tou-Ⅱ(dravite and high-Mg schorl)in the Tou-LG and tourmalite at the margins of the leucogranite;and(3)Tou-Ⅲ(mainly dravite,with minor high-Mg schorl)in metapelites of the High Himalayan Crystalline Sequence.The lenses and veins of Tou-LG may have experienced metasomatism and assimilation as a result of interaction with the High Himalayan Crystalline Sequence metasedimentary country rocks,which can be traced by the geochemical and isotopic characteristics of the tourmaline therein.
基金supported by the National Basic Research Program of China(2011CB403102)the National Natural Science Foundation of China(41073024 and 41273034)
文摘The Paiku composite leucogranitic pluton in the Malashan gneiss dome within the Tethyan Himalaya consists of tourmaline leucogranite,two-mica granite and garnet-bearing leucogranite.Zircon U-Pb dating yields that(1)tourmaline leucogranite formed at28.2±0.5 Ma and its source rock experienced simultaneous metamorphism and anatexis at 33.6±0.6 Ma;(2)two-mica granite formed at 19.8±0.5 Ma;(3)both types of leucogranite contain inherited zircon grains with an age peak at^480 Ma.These leucogranites show distinct geochemistry in major and trace elements as well as in Sr-Nd-Hf isotope compositions.As compared to the two-mica granites,the tourmaline ones have higher initial Sr and zircon Hf isotope compositions,indicating that they were derived from different source rocks combined with different melting reactions.Combined with available literature data,it is suggested that anatexis at^35 Ma along the Himalayan orogenic belt might have triggered the initial movement of the Southern Tibetan Detachment System(STDS),and led to the tectonic transition from compressive shortening to extension.Such a tectonic transition could be a dominant factor that initiates large scale decompressional melting of fertile high-grade metapelites along the Himalayan orogenic belt.Crustal anatexis at^28 Ma and^20 Ma represent large-scale melting reactions associated with the movement of the STDS.
