Basalts from the Late Carboniferous to Early Permian are extensively developed in the central Lhasa subterrane, southern Tibet. Studying the petrogenesis of these rocks may have implications for the late Paleozoic arc...Basalts from the Late Carboniferous to Early Permian are extensively developed in the central Lhasa subterrane, southern Tibet. Studying the petrogenesis of these rocks may have implications for the late Paleozoic arc magmatism along the central Lhasa subterrane uncovering more of the evolution of the Sumdo Paleo-Tethys Ocean and its dynamic mechanism. Basalt samples from the Luobadui Formation in the Leqingla area, NW of Linzhou City in the central Lhasa subterrane, southern Tibet exhibit arc-like geochemical signatures in a subduction-zone tectonic setting characterized by high Al_(2)O_(3) and low TiO_(2) contents, fractionated REE patterns with low Nb/La ratios and high LREE concentrations, and negative HFSE anomalies. Based on their higher Th/Ce, Nb/Zr, and lower Ba/Th, Pb/Nd ratios, slightly negative to positive ε_(Nd)(t) values, and the relatively high Sr-Pb isotopic compositions, these samples were probably derived from partial melting of a depleted mantle source of garnet + spinel lherzolite, metasomatized by subducted sediments around 297 Ma. Modeling of the trace elements indicates that these basalts experienced fractional crystallization of olivine, clinopyroxene and minor plagioclase during magma ascent and eruption. It is proposed that these Late Carboniferous–Early Permian basalts are associated with the northward subduction of the Sumdo Paleo-Tethys Ocean seafloor along the southern margin of the central Lhasa subterrane.展开更多
Muscovite 40 Ar-39 Ar dating of muscovite-quartz schist, eclogite and retrograde eclogite indicates an Indosinian orogenesis occurred at 220-240 Ma in the Lhasa terrane, which is caused by the closure of Paleo-Tethyan...Muscovite 40 Ar-39 Ar dating of muscovite-quartz schist, eclogite and retrograde eclogite indicates an Indosinian orogenesis occurred at 220-240 Ma in the Lhasa terrane, which is caused by the closure of Paleo-Tethyan ocean basin and the following collision of the northern Lhasa terrane and southern Gondwana land. This Indosinian orogenesis is further confirmed by the regional sedimentary characteristics, magmatic activity and ophiolite mélange. This evidence suggests that the Indosinian orogenic belt in the Lhasa terrane is widely distributed from the Coqen county in the west, and then extends eastward through the Ningzhong and Sumdo area, finally turning around the eastern Himalayan syntaxis into the Bomi county. Based on the evolutionary process, the geological development of Lhasa terrane from early Paleozoic to early Mesozoic can be divided into seven stages. All of the seven stages make up a whole Wilson circle and reveal a perfect evolutionary process of the Paleo-Tethys ocean between the northern Lhasa terrane and southern Gondwana land. The Indosinian orogenisis is a significant event for the evolution of the Lhasa terrane as well as the Tibetan Plateau.展开更多
The southern Lhasa Terrane is famous for its huge magmatic belt which records the magmatism during Mesozoic and Cenozoic. Although the Mesozoic continental-margin setting in the southern Lhasa Terrane has been identif...The southern Lhasa Terrane is famous for its huge magmatic belt which records the magmatism during Mesozoic and Cenozoic. Although the Mesozoic continental-margin setting in the southern Lhasa Terrane has been identified, details of this tectonic setting and the evolution history during the Late Cretaceous remain unclear. To further constrain these issues, we present zircon LA-ICP-MS U-Pb, Hf isotopic and geochemical data of the Gongbari dacites （of the Sangri Group） which intruded by Paleocene granodiorites from the eastern part of the southern Lhasa Terrane, Tibet. New age data indicate that the dacites were generated at -95.4 Ma, which suggests the Sangri Group volcanism may last to Late Cretaceous. The Gongbari dacites are characterized by high Sr （428-758 ppm） contents, low concentration of heavy rare earth elements and Y （e.g. Yb=0.78-1.14 ppm; Y=8.85-11.4 ppm） with high Sr/Y （41.91-67.59） and La/Yb （22.64-30.64） ratios, similar to those of adakite. The rocks are calc-alkaline, metaluminous, enriched in LILEs, depleted in HFSEs, and have positive tar（t） values （＋7.7 to ＋11.6）. The Gongbari dacites were probably produced by partial melting of young and hot subducted Neo- Tethyan oceanic crust under amphibolite to garnet amphibolite-facies conditions. Though the Gangdese Mountains may have formed before Indo-Asian collision, the southern margin of Lhasa Terrane might not go through obviously crustal thickening during the northward subduction of Neo-Tethyan oceanic lithosphere.展开更多
the India and Eurasia plates. Knowledge of the stress state is critical to evaluate the crustal stability and the design of underground excavations. Because of the limitations imposed by natural conditions, little res...the India and Eurasia plates. Knowledge of the stress state is critical to evaluate the crustal stability and the design of underground excavations. Because of the limitations imposed by natural conditions, little research has been performed on the present crustal in situ stress in the Tibetan Plateau, and further study is imperative. In this study, hydraulic fracturing measurements were conducted in Nyching County （LZX） and Lang County （LX）, Lhasa terrane to characterize the shallow crustal stress state. The results indicate that the stress state in the LZX borehole is markedly different from that in the LX borehole, in both magnitude and orientation. At the same measurement depths, the magnitudes of horizontal principal stresses in the LX borehole are 1.5–3.0 times larger than those in the LZX borehole. The stress regime in the LX borehole favors reverse faulting characterized by SH〉Sh〉Sv, where SH, Sh, and Sv are maximum horizontal, minimum horizontal, and vertical principal stresses, respectively. The SH and Sh values are approximately three and two times greater than Sv. Fracture impression results reveal that SH in the LX borehole are predominantly N–S, while in the LZX borehole the maximum horizontal principal stress is mainly in the NNE-direction. The heterogeneity of the regional stress state might be a result of the population and distribution of local structures and seismic activities. The stress state in the LX borehole has exceeded the critical state of failure equilibrium, and there is an optimally orientated pre-existing fault near the borehole. It can be concluded that the optimally orientated fault is likely to be active when the stress has built up sufficiently to destroy the frictional equilibrium; it is suggested that research focus should be placed on this in future. The stress states in boreholes LZX and LX indicate uniformity of the regional stress field and diversity of the local stress fields resulting from the interactions among regional dynamic forces, tectonic stress field, and geological structures.展开更多
The history and geodynamic mechanisms of Cenozoic exhumation and denudation of the Lhasa terrane(LT),southern Tibetan Plateau, remain poorly constrained. Most previous studies investigating the exhumation of the LT ha...The history and geodynamic mechanisms of Cenozoic exhumation and denudation of the Lhasa terrane(LT),southern Tibetan Plateau, remain poorly constrained. Most previous studies investigating the exhumation of the LT have relied on extrapolating interpretations based on a few well-studied but small areas, which inevitably introduce bias. Here,our compilation of new and published thermochronologic ages are plotted against latitude, longitude, and elevation, to illustrate the distribution of cooling ages across broad regions of the LT. Primary results reveal that(1) the north LT experienced significant exhumation during 80–40 Ma;(2) compared with north LT, exhumation and erosion in the south LT continued after ~40 Ma;and(3) N–S striking rifting, E–W striking river incision, and thrusts led to continued local denudation of the south LT between 20–5 Ma.展开更多
The Himalayan-Tibetan orogen is the youngest and arguably most spectacular of all the continent-continent collisional belts on the Earth. There are not only north-south extrusions but also east-west extensions in the ...The Himalayan-Tibetan orogen is the youngest and arguably most spectacular of all the continent-continent collisional belts on the Earth. There are not only north-south extrusions but also east-west extensions in the Tibetan Plateau. All these phenomena are the results of the Indian plate subducting into the Eurasia plate about 70 Ma ago （Yin and Harrison, 2000）, but the deep dynamics mechanism is still an enigma. Exploring the crust and upper mantle structure of Tibetan plateau and revealing the process and the effect of collision are crucial for solving the puzzle of the Tibet uplift and the continent-continent collision. This research is based on the data from the 360km-long Dagze-Deqen-Domar profile, which can be divided into two sections. The Dagze-Deqen section traverses the Nyainqntanglha Mountains and the Yadong-Gulu rift, the biggest rift in the Tibet. The Deqen-Domar section crosses Lhasa terrane and Qiangtang terrane. We study the transverse density structure of the crust and mantle beneath the Dagze-Deqen-Domar profile using a joint gravity-seismic inversion technique in order to obtain the Moho and the asthenospheric configuration beneath the profile and understand the deep dynamics mechanism of the Yadong-Gulu rift.展开更多
Bangong-Nujiang collisional zone(BNCZ)is an older one in Qinghai-Tibet Plateau and resulted in the famous Bangong-Nujiang metallogenic belt,which plays an important role in evaluating the formation and uplift mechanis...Bangong-Nujiang collisional zone(BNCZ)is an older one in Qinghai-Tibet Plateau and resulted in the famous Bangong-Nujiang metallogenic belt,which plays an important role in evaluating the formation and uplift mechanism of plateau.The northern and central Lhasa Terrane composed the southern part of the BNCZ.Since ore deposits can be used as markers of geodynamic evolution,the authors carried 1∶50000 stream sedimental geochemical exploration in the Xiongmei area in the Northern Lhasa Terrane to manifest the mineralization,and based on this mineralization with geochemical and chronological characteristics of related magmatic rocks to constrain their geodynamics and connection with the evolution of the Lhasa Terrane.The authors find Early Cretaceous magma mainly resulted in Cu,Mo mineralization,Late Cretaceous magma mainly resulted in Cu,Mo,and W mineralization in the studying area.The results suggest a southward subduction,slab rolling back and break-off,and thickened lithosphere delamination successively occurred within the Northern Lhasa Terrane.展开更多
Asthemaintectoniccomponentofthe Himalayan–Tibetan orogen,the Lhasa terrane has received much attention as it records the entire history of the orogeny.The occurrence of high pressure eclogite in the Sumdo complex in ...Asthemaintectoniccomponentofthe Himalayan–Tibetan orogen,the Lhasa terrane has received much attention as it records the entire history of the orogeny.The occurrence of high pressure eclogite in the Sumdo complex in central Lhasa terrane has a significant importance on the understanding of the Paleo-Tethys subduction and plate itineration processes in this area.The petrological,geochemical and geochronological data of eclogite and associated blueschist and garnet-bearing mica schist from Sumdo,Jilang and Bailang area have been briefly reviewed to explore the origin and metamorphic evolution of this suture.Eclogites from the Sumdo complex have experienced low temperature,high pressure to ultrahigh pressure metamorphism,revealing a fastsubduction and exhumation process in a typical oceanic subduction zone.The large P-T range between different eclogites in the literature may be affected by the big error of unappropriated using geothermobarometry and may also because of slices of subducted blocks derived from different depths juxtapose together during exhumation.By summarizing the U-Pb,Lu-Hf and Sm-Nd ages of eclogites,the eclogite facies metamorphism is likely to occur in early Triassic during 245-225 Ma,but not the previously accepted late Permian at ca.260 Ma by the reinterpretation of the former geochronological data from literature.The opening of Paleo-Tethys Ocean between the Lhasa terrane initiate prior to ca.280 Ma and ultimate closure to integrate the Lhasa terrane was no earlier than225 Ma and may triggered by the initial subduction of Bangong-Nujiang Tethys Ocean in the north.展开更多
Objective The potassic and ultrapotassic rocks relating to the India-Eurasia collision and continual plate convergence are widely distributed in the Lhasa terrane. These rocks are very important to understand the dee...Objective The potassic and ultrapotassic rocks relating to the India-Eurasia collision and continual plate convergence are widely distributed in the Lhasa terrane. These rocks are very important to understand the deep processes of the India-Eurasia collision and the uplift and evolution of the Tibetan Plateau. Although high-potassic volcanic rocks are also exposed in the western Lhasa terrane, their formation time is still uncertain for the lack of reliable dating. We carried out zircon U-Pb geochronological study on the Langjiu Formation volcanic rocks, which are part of the Early Cretaceous Zenong group volcanic rocks based on 1：250000 scale Shiquanhe regional geological survey report, in the Shiquanhe area of the western Lhasa terrane. These new age data not only offer chronological basis for the regional stratigraphic correlation and classification, but also provide an essential opportunity for revealing signatures of magmatic pulses hidden in the deep crust of the Lhasa terrane.展开更多
The Tibetan Plateau geographically contains internal and external drainage areas based on the distributions of river flows and catchments.The internal and external drainage areas display similar highelevations,while t...The Tibetan Plateau geographically contains internal and external drainage areas based on the distributions of river flows and catchments.The internal and external drainage areas display similar highelevations,while their topographic reliefs are not comparable;the former shows a large low-relief surface,whereas the latter is characterized by relatively high relief.The eastern Lhasa terrane is a key tectonic component of the Tibetan Plateau.It is characterized by high topography and relief,but the thermal history of its basement remains relatively poorly constrained.In this study we report new apatite fission track data from the eastern part of the central Lhasa terrane to constrain the thermo-tectonic evolution of the external drainage area in the southern Tibetan Plateau.Twenty-one new AFT ages and associated thermal history models reveal that the basement underlying the external drainage area in southern Tibet experienced three main phases of rapid cooling in the Cenozoic.The Paleocene-early Eocene(-60–48 Ma)cooling was likely induced by crustal shortening and associated rock exhumation,due to accelerated northward subduction of the NeoTethys oceanic lithosphere.A subsequent cooling pulse lasted from the late Eocene to early Oligocene(-40–28 Ma),possibly due to the thickening and consequential erosion of the Lhasa lithosphere resulted from the continuous northward indentation of the India plate into Eurasia.The most recent rapid cooling event occurred in the middle Miocene-early Pliocene(-16–4 Ma),likely induced by accelerated incision of the Lhasa River and local thrust faulting.Our AFT ages and published low-temperature thermochronological data reveal that the external drainage area experienced younger cooling events compared with the internal drainage area,and that the associated differentiated topographic evolution initiated at ca.30 Ma.The contributing factors for the formation of the high-relief topography mainly contain active surface uplift,fault activity,and the enhanced incision of the Yarlung River.展开更多
Helium isotopic compositions are considered to be ideal tracers to identify whether mantle materials have been added to crustal rocks or fluids.In this paper,we present the helium isotopic compositions of the Songduo ...Helium isotopic compositions are considered to be ideal tracers to identify whether mantle materials have been added to crustal rocks or fluids.In this paper,we present the helium isotopic compositions of the Songduo eclogites in the Lhasa terrane,Tibet.We found that garnet and omphacite in the eclogites have different helium retention characteristics.The 4He content of most omphacite grains are about 10–20 times of that of garnet,suggesting that omphacite has a higher ability to capture 4He than garnet.Similarly,there is about 10–20 times difference in 3He content between omphacite and garnet in the same eclogite samples.The 3He/4He ratios of garnet and omphacite in these rocks range from 0.27 to 0.60 Ra(relative to the modern air 3He/4He ratio,1.4×10^-6).These ratios are within the range of both mantle-and crust-derived helium,suggesting mixed sources.The Songduo eclogites have much higher3He/4He ratios than those observed in the Dabie eclogites of eastern China.Such high ratios are typically thought to be associated with deep mantle sources.We cautiously conclude that deep mantle materials might have been involved during the formation of the Songduo eclogites.展开更多
基金the National Key Research and Development Program of China (Grant No. 2022YFF0800903)the National Natural Science Foundation of China (Grant Nos. 42302107, 92162322, 42261144669, 41922022, 42003036)+4 种基金the China Geological Survey (Grant Nos. DD20243512, DD20230008)the National Postdoctoral Research Program of China (Grant No. GZC20232489)the Second Tibetan Plateau Scientific Expedition and Research (Grant No. 2021QZKK0304)Xing Dian Youth Talent Plan of Yunnan Province (Grant No. XDYC-QNRC-2022-0136)the UNESCO: IUGS IGCP-662 Program。
文摘Basalts from the Late Carboniferous to Early Permian are extensively developed in the central Lhasa subterrane, southern Tibet. Studying the petrogenesis of these rocks may have implications for the late Paleozoic arc magmatism along the central Lhasa subterrane uncovering more of the evolution of the Sumdo Paleo-Tethys Ocean and its dynamic mechanism. Basalt samples from the Luobadui Formation in the Leqingla area, NW of Linzhou City in the central Lhasa subterrane, southern Tibet exhibit arc-like geochemical signatures in a subduction-zone tectonic setting characterized by high Al_(2)O_(3) and low TiO_(2) contents, fractionated REE patterns with low Nb/La ratios and high LREE concentrations, and negative HFSE anomalies. Based on their higher Th/Ce, Nb/Zr, and lower Ba/Th, Pb/Nd ratios, slightly negative to positive ε_(Nd)(t) values, and the relatively high Sr-Pb isotopic compositions, these samples were probably derived from partial melting of a depleted mantle source of garnet + spinel lherzolite, metasomatized by subducted sediments around 297 Ma. Modeling of the trace elements indicates that these basalts experienced fractional crystallization of olivine, clinopyroxene and minor plagioclase during magma ascent and eruption. It is proposed that these Late Carboniferous–Early Permian basalts are associated with the northward subduction of the Sumdo Paleo-Tethys Ocean seafloor along the southern margin of the central Lhasa subterrane.
基金Financial support was provided by Geological Survey Program of China Geological Survey (Grant No. 1212010610105)the Basic Foundation of Institute of Geology, Chinese Academy of Geological Sciences (Grant No. J0918)
文摘Muscovite 40 Ar-39 Ar dating of muscovite-quartz schist, eclogite and retrograde eclogite indicates an Indosinian orogenesis occurred at 220-240 Ma in the Lhasa terrane, which is caused by the closure of Paleo-Tethyan ocean basin and the following collision of the northern Lhasa terrane and southern Gondwana land. This Indosinian orogenesis is further confirmed by the regional sedimentary characteristics, magmatic activity and ophiolite mélange. This evidence suggests that the Indosinian orogenic belt in the Lhasa terrane is widely distributed from the Coqen county in the west, and then extends eastward through the Ningzhong and Sumdo area, finally turning around the eastern Himalayan syntaxis into the Bomi county. Based on the evolutionary process, the geological development of Lhasa terrane from early Paleozoic to early Mesozoic can be divided into seven stages. All of the seven stages make up a whole Wilson circle and reveal a perfect evolutionary process of the Paleo-Tethys ocean between the northern Lhasa terrane and southern Gondwana land. The Indosinian orogenisis is a significant event for the evolution of the Lhasa terrane as well as the Tibetan Plateau.
基金funded by grants from the National Natural Science Foundation of China (No.40930313)the China Geological Survey (No.12120114057701,No.12120114061801 and No.12120114061501)
文摘The southern Lhasa Terrane is famous for its huge magmatic belt which records the magmatism during Mesozoic and Cenozoic. Although the Mesozoic continental-margin setting in the southern Lhasa Terrane has been identified, details of this tectonic setting and the evolution history during the Late Cretaceous remain unclear. To further constrain these issues, we present zircon LA-ICP-MS U-Pb, Hf isotopic and geochemical data of the Gongbari dacites （of the Sangri Group） which intruded by Paleocene granodiorites from the eastern part of the southern Lhasa Terrane, Tibet. New age data indicate that the dacites were generated at -95.4 Ma, which suggests the Sangri Group volcanism may last to Late Cretaceous. The Gongbari dacites are characterized by high Sr （428-758 ppm） contents, low concentration of heavy rare earth elements and Y （e.g. Yb=0.78-1.14 ppm; Y=8.85-11.4 ppm） with high Sr/Y （41.91-67.59） and La/Yb （22.64-30.64） ratios, similar to those of adakite. The rocks are calc-alkaline, metaluminous, enriched in LILEs, depleted in HFSEs, and have positive tar（t） values （＋7.7 to ＋11.6）. The Gongbari dacites were probably produced by partial melting of young and hot subducted Neo- Tethyan oceanic crust under amphibolite to garnet amphibolite-facies conditions. Though the Gangdese Mountains may have formed before Indo-Asian collision, the southern margin of Lhasa Terrane might not go through obviously crustal thickening during the northward subduction of Neo-Tethyan oceanic lithosphere.
基金supported by the China Geological Survey Project(No.12120113038000)the National Science and Technology Major Project(2016ZX05034-003-2)the scientific research plan of the China Railway Eryuan Engineering Group CO.LTD(No.13164007)
文摘the India and Eurasia plates. Knowledge of the stress state is critical to evaluate the crustal stability and the design of underground excavations. Because of the limitations imposed by natural conditions, little research has been performed on the present crustal in situ stress in the Tibetan Plateau, and further study is imperative. In this study, hydraulic fracturing measurements were conducted in Nyching County （LZX） and Lang County （LX）, Lhasa terrane to characterize the shallow crustal stress state. The results indicate that the stress state in the LZX borehole is markedly different from that in the LX borehole, in both magnitude and orientation. At the same measurement depths, the magnitudes of horizontal principal stresses in the LX borehole are 1.5–3.0 times larger than those in the LZX borehole. The stress regime in the LX borehole favors reverse faulting characterized by SH〉Sh〉Sv, where SH, Sh, and Sv are maximum horizontal, minimum horizontal, and vertical principal stresses, respectively. The SH and Sh values are approximately three and two times greater than Sv. Fracture impression results reveal that SH in the LX borehole are predominantly N–S, while in the LZX borehole the maximum horizontal principal stress is mainly in the NNE-direction. The heterogeneity of the regional stress state might be a result of the population and distribution of local structures and seismic activities. The stress state in the LX borehole has exceeded the critical state of failure equilibrium, and there is an optimally orientated pre-existing fault near the borehole. It can be concluded that the optimally orientated fault is likely to be active when the stress has built up sufficiently to destroy the frictional equilibrium; it is suggested that research focus should be placed on this in future. The stress states in boreholes LZX and LX indicate uniformity of the regional stress field and diversity of the local stress fields resulting from the interactions among regional dynamic forces, tectonic stress field, and geological structures.
基金co-funded by the National Key Research and Development Project 'Key scientific issues of transformative technology' (Grant No. 2019YFA0708601)the second Tibetan Plateau Scientific Expedition and Research Program (STEP) Grant (Grant No. 2019QZKK0802)+3 种基金the Key Special Project for Introduced Talents Team of Southern Marine Science and Engineering Guangdong Laboratory (Guangzhou) (Grant No. GML2019ZD0201)National Natural Science Foundation of China (Grant Nos. 41502198, 40921001, 41672223)Research Grant of Chinese Academy of Geological Sciences (Grant No. J2024)Geological Survey of China (Grant Nos. DD20190057, DD20190060)。
文摘The history and geodynamic mechanisms of Cenozoic exhumation and denudation of the Lhasa terrane(LT),southern Tibetan Plateau, remain poorly constrained. Most previous studies investigating the exhumation of the LT have relied on extrapolating interpretations based on a few well-studied but small areas, which inevitably introduce bias. Here,our compilation of new and published thermochronologic ages are plotted against latitude, longitude, and elevation, to illustrate the distribution of cooling ages across broad regions of the LT. Primary results reveal that(1) the north LT experienced significant exhumation during 80–40 Ma;(2) compared with north LT, exhumation and erosion in the south LT continued after ~40 Ma;and(3) N–S striking rifting, E–W striking river incision, and thrusts led to continued local denudation of the south LT between 20–5 Ma.
基金supported by National Natural Science Foundation of China (Nos.40404011 and 40774051)National Probing Project (SinoProbe-02)the Basic outlay of scientific research work from the Ministry of Science and Technology of the People’s Republic of China in 2007, 2008, 2009
文摘The Himalayan-Tibetan orogen is the youngest and arguably most spectacular of all the continent-continent collisional belts on the Earth. There are not only north-south extrusions but also east-west extensions in the Tibetan Plateau. All these phenomena are the results of the Indian plate subducting into the Eurasia plate about 70 Ma ago （Yin and Harrison, 2000）, but the deep dynamics mechanism is still an enigma. Exploring the crust and upper mantle structure of Tibetan plateau and revealing the process and the effect of collision are crucial for solving the puzzle of the Tibet uplift and the continent-continent collision. This research is based on the data from the 360km-long Dagze-Deqen-Domar profile, which can be divided into two sections. The Dagze-Deqen section traverses the Nyainqntanglha Mountains and the Yadong-Gulu rift, the biggest rift in the Tibet. The Deqen-Domar section crosses Lhasa terrane and Qiangtang terrane. We study the transverse density structure of the crust and mantle beneath the Dagze-Deqen-Domar profile using a joint gravity-seismic inversion technique in order to obtain the Moho and the asthenospheric configuration beneath the profile and understand the deep dynamics mechanism of the Yadong-Gulu rift.
基金Financial support was provided by the program of China Geological Survey(DD20190167)National Natural Science Foundation of China(41902099)。
文摘Bangong-Nujiang collisional zone(BNCZ)is an older one in Qinghai-Tibet Plateau and resulted in the famous Bangong-Nujiang metallogenic belt,which plays an important role in evaluating the formation and uplift mechanism of plateau.The northern and central Lhasa Terrane composed the southern part of the BNCZ.Since ore deposits can be used as markers of geodynamic evolution,the authors carried 1∶50000 stream sedimental geochemical exploration in the Xiongmei area in the Northern Lhasa Terrane to manifest the mineralization,and based on this mineralization with geochemical and chronological characteristics of related magmatic rocks to constrain their geodynamics and connection with the evolution of the Lhasa Terrane.The authors find Early Cretaceous magma mainly resulted in Cu,Mo mineralization,Late Cretaceous magma mainly resulted in Cu,Mo,and W mineralization in the studying area.The results suggest a southward subduction,slab rolling back and break-off,and thickened lithosphere delamination successively occurred within the Northern Lhasa Terrane.
文摘Asthemaintectoniccomponentofthe Himalayan–Tibetan orogen,the Lhasa terrane has received much attention as it records the entire history of the orogeny.The occurrence of high pressure eclogite in the Sumdo complex in central Lhasa terrane has a significant importance on the understanding of the Paleo-Tethys subduction and plate itineration processes in this area.The petrological,geochemical and geochronological data of eclogite and associated blueschist and garnet-bearing mica schist from Sumdo,Jilang and Bailang area have been briefly reviewed to explore the origin and metamorphic evolution of this suture.Eclogites from the Sumdo complex have experienced low temperature,high pressure to ultrahigh pressure metamorphism,revealing a fastsubduction and exhumation process in a typical oceanic subduction zone.The large P-T range between different eclogites in the literature may be affected by the big error of unappropriated using geothermobarometry and may also because of slices of subducted blocks derived from different depths juxtapose together during exhumation.By summarizing the U-Pb,Lu-Hf and Sm-Nd ages of eclogites,the eclogite facies metamorphism is likely to occur in early Triassic during 245-225 Ma,but not the previously accepted late Permian at ca.260 Ma by the reinterpretation of the former geochronological data from literature.The opening of Paleo-Tethys Ocean between the Lhasa terrane initiate prior to ca.280 Ma and ultimate closure to integrate the Lhasa terrane was no earlier than225 Ma and may triggered by the initial subduction of Bangong-Nujiang Tethys Ocean in the north.
基金granted by the National Natural Science Foundation of China (Grant No.41572205)
文摘Objective The potassic and ultrapotassic rocks relating to the India-Eurasia collision and continual plate convergence are widely distributed in the Lhasa terrane. These rocks are very important to understand the deep processes of the India-Eurasia collision and the uplift and evolution of the Tibetan Plateau. Although high-potassic volcanic rocks are also exposed in the western Lhasa terrane, their formation time is still uncertain for the lack of reliable dating. We carried out zircon U-Pb geochronological study on the Langjiu Formation volcanic rocks, which are part of the Early Cretaceous Zenong group volcanic rocks based on 1：250000 scale Shiquanhe regional geological survey report, in the Shiquanhe area of the western Lhasa terrane. These new age data not only offer chronological basis for the regional stratigraphic correlation and classification, but also provide an essential opportunity for revealing signatures of magmatic pulses hidden in the deep crust of the Lhasa terrane.
基金supported by National Key Research and Development Program of China(2022YFC2905001,2018YFC0604105)the Opening Foundation of Ministry of Natural Resources Key Laboratory for Mineral Deposits Research,Chengdu University of Technology(grant number:gzck202104)+2 种基金the Fund for Scientific Research-Flanders(FWO,Bilateral Project VS06520N)China Scholarship Council(201908320260,201806190214)support for W.Su and Z.He for their research stay in Belgium.S.Glorie is supported by an Australian Research Council Future Fellowship(FT210100906)。
文摘The Tibetan Plateau geographically contains internal and external drainage areas based on the distributions of river flows and catchments.The internal and external drainage areas display similar highelevations,while their topographic reliefs are not comparable;the former shows a large low-relief surface,whereas the latter is characterized by relatively high relief.The eastern Lhasa terrane is a key tectonic component of the Tibetan Plateau.It is characterized by high topography and relief,but the thermal history of its basement remains relatively poorly constrained.In this study we report new apatite fission track data from the eastern part of the central Lhasa terrane to constrain the thermo-tectonic evolution of the external drainage area in the southern Tibetan Plateau.Twenty-one new AFT ages and associated thermal history models reveal that the basement underlying the external drainage area in southern Tibet experienced three main phases of rapid cooling in the Cenozoic.The Paleocene-early Eocene(-60–48 Ma)cooling was likely induced by crustal shortening and associated rock exhumation,due to accelerated northward subduction of the NeoTethys oceanic lithosphere.A subsequent cooling pulse lasted from the late Eocene to early Oligocene(-40–28 Ma),possibly due to the thickening and consequential erosion of the Lhasa lithosphere resulted from the continuous northward indentation of the India plate into Eurasia.The most recent rapid cooling event occurred in the middle Miocene-early Pliocene(-16–4 Ma),likely induced by accelerated incision of the Lhasa River and local thrust faulting.Our AFT ages and published low-temperature thermochronological data reveal that the external drainage area experienced younger cooling events compared with the internal drainage area,and that the associated differentiated topographic evolution initiated at ca.30 Ma.The contributing factors for the formation of the high-relief topography mainly contain active surface uplift,fault activity,and the enhanced incision of the Yarlung River.
基金supported jointly by the National Natural Science Foundation of China (Nos. 41373029, 41773029)the China Geological Survey (Nos.DD20190060, 12120114061501)
文摘Helium isotopic compositions are considered to be ideal tracers to identify whether mantle materials have been added to crustal rocks or fluids.In this paper,we present the helium isotopic compositions of the Songduo eclogites in the Lhasa terrane,Tibet.We found that garnet and omphacite in the eclogites have different helium retention characteristics.The 4He content of most omphacite grains are about 10–20 times of that of garnet,suggesting that omphacite has a higher ability to capture 4He than garnet.Similarly,there is about 10–20 times difference in 3He content between omphacite and garnet in the same eclogite samples.The 3He/4He ratios of garnet and omphacite in these rocks range from 0.27 to 0.60 Ra(relative to the modern air 3He/4He ratio,1.4×10^-6).These ratios are within the range of both mantle-and crust-derived helium,suggesting mixed sources.The Songduo eclogites have much higher3He/4He ratios than those observed in the Dabie eclogites of eastern China.Such high ratios are typically thought to be associated with deep mantle sources.We cautiously conclude that deep mantle materials might have been involved during the formation of the Songduo eclogites.
