The Pamir plateau may have been a westward continuation of Tibet plateau.Meanwhile,the Rushan-Pshart suture is correlative to the Bangong-Nujiang suture of Tibet,and the Central Pamir is the lateral equivalent of the ...The Pamir plateau may have been a westward continuation of Tibet plateau.Meanwhile,the Rushan-Pshart suture is correlative to the Bangong-Nujiang suture of Tibet,and the Central Pamir is the lateral equivalent of the Qiangtang Block.We present the first detailed LA-ICPMS zircon U-Pb chronology,major and trace element,and Lu-Hf isotope geochemistry of Taxkorgan two-mica monzogranite to illuminate the Tethys evolution in central Pamir.LA-ICPMS zircon U-Pb dating shows that two-mica monzogranite is emplaced in the Cretaceous(118 Ma).Its geochemical features are similar to S-type granite,with enrichment in LREEs and negative Ba,Sr,Zr and Ti anomalies.All the samples show negative zirconεHf(t)values ranging from 17.0 to 12.5(mean 14.5),corresponding to crustal Hf model(TDM2)ages of 1906 to 2169 Ma.It is inferred that these granitoids are derived from partial melting of peliticmetasedimentary rocks analogous to the Paleoproterozoic Bulunkuole Group,predominantly with muscovite schists component.Based on the petrological and geochemical data presented above,together with the regional geology,this work provides new insights that Bangong Nujiang Ocean closed in Early Cretaceous(120114 Ma).展开更多
The Ceno\|Tethys is a southern branch of the Tethyan ocean and existed in the Mesozoic and early Cenozoic times. The evolution of the Ceno\|Tethys has been discussed based mainly on geological and paleontological data...The Ceno\|Tethys is a southern branch of the Tethyan ocean and existed in the Mesozoic and early Cenozoic times. The evolution of the Ceno\|Tethys has been discussed based mainly on geological and paleontological data obtained from shallow marine sediments on the both sides of the ocean. Pelagic sediments deposited in a deep ocean basin of the Ceno\|Tethys are often incorporated in suture zones. However, geological and paleontological data from the pelagic sediments, which enable us to elucidate the paleoceanography and tectonic evolution of the Ceno\|Tethys, are still limited. The Xialu chert crops out about 30 km south of Xigaze and occupies the southern marginal part of the E—W trending Yarlung Zangbo Suture zone. As a result of radiolarian biostratigraphic research along two continuous sections, we identified seven different aged radiolarian assemblages from pelagic and hemipelagic sediments ranging early Middle Jurassic (Aalenian) to Early Cretaceous. The Aalenian radiolarian fauna is the oldest known record so far for the Xialu chert. It is noteworthy to point out that the fauna came from a chert sample which contains no terrigenous elements other than clay minerals. There is a possibility that radiolarian faunas older than Aalenian age will be discovered from the Xialu chert in the future.展开更多
The formation of the Tibetan Plateau is closely related to the evolution of Tethys. There have been many researchers and articles concerning the Tethys since E.Suess proposed the concept in 1893. It means a large ocea...The formation of the Tibetan Plateau is closely related to the evolution of Tethys. There have been many researchers and articles concerning the Tethys since E.Suess proposed the concept in 1893. It means a large ocean which lies between Eurasia and Gondwanaland. With the development of Tethyan research, some new terms, appeared such as Neo\|Tethys, Paleo\|Tethys, and Proto\|Tethys, representing the Tethys in Mesozoic—Cenozoic, late Paleozoic and early Paleozoic respectively. The trace of an ocean from Sinian to Ordovician was discovered during the scientific expedition and Proto\|Tethys was proposed to name the ocean. Therefore, the Tibetan Plateau is the main scope of the Eastern Tethys. It can be divided c losely related into three zones which represent the main oceanic locations in th ree different stages.The Northern Tethyan Region lies in the Kunlun and Qilian Mountains, its remnant is the Fifth Suture Zone. It is also the northern boundary of the Tibetan Plateau The rift initiated after the continental basement had been formed in Sinian and gradually developed into an ocean, which was named Proto\|Tethys, the earliest Tethyan ocean known up to now. The petrochemical compositions of pillow lava in this zone show the characteristics of mid\|ocean ridge tholeiite basalt and the pelagic ophiolitic flysch were well developed, indicating a matured ocean. It was closed in Ordovician and Silurian.展开更多
There has been a long\|term debate about the Paleo\|Tethyan Ocean in South China continent. Based on the geological and geochemical studies, it is suggested that there exist two tectonic belts in SE Yunnan, SW China c...There has been a long\|term debate about the Paleo\|Tethyan Ocean in South China continent. Based on the geological and geochemical studies, it is suggested that there exist two tectonic belts in SE Yunnan, SW China called Ailao Shan zone and Shizong—Mile zone, which separate Yangtze Block, Cathysian Block and Indo\|China Block from each other. The evolutionary history and its geodynamics of these suture zones are correlated with the Paleo\|Tethyan Ocean. Both of the zones are keys to understanding whether the Paleo\|Tethyan Ocean extended from Western Yunnan area to east of the South China continent. The Ailao Shan belt consists of Red River fault, Ailao Shan fault, Shuanggou fault and Huashan—Yayi fault, which are the boundaries of the Ailao Shan basement metamorphic belt, ophiolitic melange belt and Island\|arc volcanic\|sediments belt, respectively.The ophiolitic melange belt is characterized by the existence of the ophiolite in Shuanggou area, which represents the relicts of the oceanic crust of the Ailao Shan Ocean. In addition, there exist volcanic rocks in west of the ophiolitic melange belt in Jingdong area. The geochemical characteristics of basalts in Jingdong are similar to that of the E\|MORB. Synthesized studies on geochemistry and tectonics suggest that the basalts in Jingdong area were formed in an extensional rift setting in Devonian.展开更多
The Kunlun Mountains is situated in the north margin of the Tibetan plateau and is one of crucial areas for unraveling the tectonic evolutionary history of the plateau and Eurasia. However, there is no widely accepted...The Kunlun Mountains is situated in the north margin of the Tibetan plateau and is one of crucial areas for unraveling the tectonic evolutionary history of the plateau and Eurasia. However, there is no widely accepted model for this area. One of the reasons is that some basic issues for the tectonic reconstruction have not been well settled, they are: (1) Is the Kunlun Mountains an ancient accretion prism, or a mini continent with old basement?(2) What is the age of the Kudi ophiolite, early Paleozoic or late Paleozoic?(3) When did the South Kunlun Block accrete to the Tarim Block?(4) Do the fifth and the forth sutures represent different oceans, or they are just the chronologically different relics of the same ocean?(5) Did the Kunlun Mountains experience continuous subduction since Neoproterozoic?(6) When did the Paleo\|Tethys closed in the West Kunlun range?展开更多
There are abundant Bajocian—Tithonian bivalves in the main ridge of the Tanggula Mountains of northern Qinghai—Xizang Plateau, China. After figuring the common and coeval species between Tanggula and other areas (Fi...There are abundant Bajocian—Tithonian bivalves in the main ridge of the Tanggula Mountains of northern Qinghai—Xizang Plateau, China. After figuring the common and coeval species between Tanggula and other areas (Fig. 1), and tracing the temporal and spacial historical distribution of the bivalves very capable of dispersion, some Jurassic bivalve biogeographic items, particularly the biogeographic relations, have been lit up. In the known 21 taxa of the Jurassic Pectinoida and Ostreoida from the main ridge of the Tanggula Mountains, there are 12 (57%) common and coeval species in northern Tethys, 13 (62%) common and coeval species in southern Tethys and 12 (57%) in Kachchh—southern Xizang area. It has demonstrated that there existed intermigration of bivalves between Tanggula and various parts of Tethys. Although there is no coeval species between Tanggula and western Australia, in these two areas there exist 6 (29%) close range common species of which 4 (19%) coevaity existed in western Australia and India Plate. Tanggula fauna is, therefore, still very close to that of western Australia. However, there are 15 (71%) common and 14 (67%) coevality species between the main ridge of the Tanggula Mountains and northwestern Europe, among the common species, 8 (38%) ones have lower limitation (first occurrence) in northwestern Europe but only 2 (10%) taxa are older in the main ridge of the Tanggula Mountains. It is very clear that pectinite and ostrea fauna of Tethys, particularly the main ridge of the Tanggula Mountains and Europe had very close relation and most Tanggula’s or northern Tethyan taxa migrated from northwestern Europe.展开更多
Whilst the topographic relief of the Tibetan Plateau’s northeast margin reflects recent Himalayan Orogenesis, its position and geometry reflect much older structures that developed during the Indosinian Orogeny c.200...Whilst the topographic relief of the Tibetan Plateau’s northeast margin reflects recent Himalayan Orogenesis, its position and geometry reflect much older structures that developed during the Indosinian Orogeny c.200Ma. The Indosinian Orogeny was responsible for closure and shortening of the Songpan Garzê Basin, a Palaeo\|Tethyan relict, during accretion of the Cimmerian Continental Chain to the southern margin of Laurasia. Sandwiched between Laurasia and the Cimmerian fragments of the Qangtang (North Tibet) and Yangtze (South China) blocks, this basin evolved into the Songpan Garzê Fold Belt—a major accretionary prism which now forms the northeast portion of the Tibetan Plateau.展开更多
In carboniferous and triassic metacarbonates (anchizone to lower greenschist facies) of the Tethyan Himalayas the characteristic remanent magnetisations are carried by magnetite (ChRM\-1) and pyrrhotite (ChRM\-2;Kloot...In carboniferous and triassic metacarbonates (anchizone to lower greenschist facies) of the Tethyan Himalayas the characteristic remanent magnetisations are carried by magnetite (ChRM\-1) and pyrrhotite (ChRM\-2;Klootwijk & Bingham,1980;Appel et al.,1991 & 1995;Schill et al.,1999).Magnetite may carry a primary remanent magnetisation whereas the pyrrhotite component is secondary and related to the last cooling event below 300℃. Pyrrhotite is formed in marly carbonates during low\|grade metamorphism.In Spiti the last cooling is represented by an 40 Ar/ 39 Ar age of 42～45Ma (Wiesmayr & Grasemann,1999).Five locations were sampled in the Spiti valley (Fig.1).Besides a present earth field direction,both remanent components (ChRM 1+2 ) are present in single specimens.The contribution to the total NRM is around 30% for the ChRM\-2 (coercivity of 20～100mT) and only around 8% for the ChRM\-2 (unblocking temperature of 250～330℃).Despite of the contribution stable remanence directions could be obtained for the ChRM\-2.For all sampling locations well grouping overall mean directions were obtained (Table 1,Fig.1).Results from Losar and the lower Pin valley are preliminary.They were estimated by great circle analyses or by taking the residual component after AF\|demagnetisation. Clockwise block rotations of around 10～40° in respect to stable India since 42 Ma are calculated by using the apparent polar wander path of Besse & Courtillot (1991).The α 95 \|angles show no overlapping (Fig.1 small figure).Therefore local rotations are not negligible.展开更多
The isotopic signature of mid\|ocean ridge basalts (MORB) from the Indian Ocean is different from that of MORB from the Pacific and North\|Atlantic oceans.. The Indian MORB is characterized by lower 206 Pb/ 204 Pb, hi...The isotopic signature of mid\|ocean ridge basalts (MORB) from the Indian Ocean is different from that of MORB from the Pacific and North\|Atlantic oceans.. The Indian MORB is characterized by lower 206 Pb/ 204 Pb, hi gher 87 Sr/ 86 Sr, and lower 206 Pb/ 204 Pb for given 143 Nd/ 144 Nd than the latter (Hart, 1984; Castillo, 1988; Mahoney et al., 1998). Why the Indian Ocean mantle domain is different from the Pacific and North\|Atlantic ocean mantle domain is still unclear. Two general classes of hypotheses have been proposed to explain the origin of Indian mantle (Mahoney et al., 1998). The first one is that the components of the Indian Ocean mantle domain are a fairly young mantle end\|member created during the processes of breakup of the Gondwana continent to form the Indian Ocean. The second hypothesis posits that the Indian MORB\|type isotopic signature is a long\|lived mantle domain that existed prior to the formation of the present Indian Ocean. Thus it appears that one of the keys to a better understanding of origin of the Indian Ocean\|type isotopic signature depends on its age. Although some studies (Mahoney et al., 1998; Weis and Frey, 1997) showed that the isotopic signature was as old as the Indian ocean crust (140Ma), basalts investigated in the Indian Ocean region do not prove or disprove the existence of the Indian MORB\|type isotopic signature prior to the Indian Ocean because they were taken from the Indian ocean basin itself.展开更多
基金Project(41802103)supported by the National Natural Science Foundation of ChinaProject(2017YFC0601403)supported by the National Key R&D Program of China
文摘The Pamir plateau may have been a westward continuation of Tibet plateau.Meanwhile,the Rushan-Pshart suture is correlative to the Bangong-Nujiang suture of Tibet,and the Central Pamir is the lateral equivalent of the Qiangtang Block.We present the first detailed LA-ICPMS zircon U-Pb chronology,major and trace element,and Lu-Hf isotope geochemistry of Taxkorgan two-mica monzogranite to illuminate the Tethys evolution in central Pamir.LA-ICPMS zircon U-Pb dating shows that two-mica monzogranite is emplaced in the Cretaceous(118 Ma).Its geochemical features are similar to S-type granite,with enrichment in LREEs and negative Ba,Sr,Zr and Ti anomalies.All the samples show negative zirconεHf(t)values ranging from 17.0 to 12.5(mean 14.5),corresponding to crustal Hf model(TDM2)ages of 1906 to 2169 Ma.It is inferred that these granitoids are derived from partial melting of peliticmetasedimentary rocks analogous to the Paleoproterozoic Bulunkuole Group,predominantly with muscovite schists component.Based on the petrological and geochemical data presented above,together with the regional geology,this work provides new insights that Bangong Nujiang Ocean closed in Early Cretaceous(120114 Ma).
文摘The Ceno\|Tethys is a southern branch of the Tethyan ocean and existed in the Mesozoic and early Cenozoic times. The evolution of the Ceno\|Tethys has been discussed based mainly on geological and paleontological data obtained from shallow marine sediments on the both sides of the ocean. Pelagic sediments deposited in a deep ocean basin of the Ceno\|Tethys are often incorporated in suture zones. However, geological and paleontological data from the pelagic sediments, which enable us to elucidate the paleoceanography and tectonic evolution of the Ceno\|Tethys, are still limited. The Xialu chert crops out about 30 km south of Xigaze and occupies the southern marginal part of the E—W trending Yarlung Zangbo Suture zone. As a result of radiolarian biostratigraphic research along two continuous sections, we identified seven different aged radiolarian assemblages from pelagic and hemipelagic sediments ranging early Middle Jurassic (Aalenian) to Early Cretaceous. The Aalenian radiolarian fauna is the oldest known record so far for the Xialu chert. It is noteworthy to point out that the fauna came from a chert sample which contains no terrigenous elements other than clay minerals. There is a possibility that radiolarian faunas older than Aalenian age will be discovered from the Xialu chert in the future.
文摘The formation of the Tibetan Plateau is closely related to the evolution of Tethys. There have been many researchers and articles concerning the Tethys since E.Suess proposed the concept in 1893. It means a large ocean which lies between Eurasia and Gondwanaland. With the development of Tethyan research, some new terms, appeared such as Neo\|Tethys, Paleo\|Tethys, and Proto\|Tethys, representing the Tethys in Mesozoic—Cenozoic, late Paleozoic and early Paleozoic respectively. The trace of an ocean from Sinian to Ordovician was discovered during the scientific expedition and Proto\|Tethys was proposed to name the ocean. Therefore, the Tibetan Plateau is the main scope of the Eastern Tethys. It can be divided c losely related into three zones which represent the main oceanic locations in th ree different stages.The Northern Tethyan Region lies in the Kunlun and Qilian Mountains, its remnant is the Fifth Suture Zone. It is also the northern boundary of the Tibetan Plateau The rift initiated after the continental basement had been formed in Sinian and gradually developed into an ocean, which was named Proto\|Tethys, the earliest Tethyan ocean known up to now. The petrochemical compositions of pillow lava in this zone show the characteristics of mid\|ocean ridge tholeiite basalt and the pelagic ophiolitic flysch were well developed, indicating a matured ocean. It was closed in Ordovician and Silurian.
文摘There has been a long\|term debate about the Paleo\|Tethyan Ocean in South China continent. Based on the geological and geochemical studies, it is suggested that there exist two tectonic belts in SE Yunnan, SW China called Ailao Shan zone and Shizong—Mile zone, which separate Yangtze Block, Cathysian Block and Indo\|China Block from each other. The evolutionary history and its geodynamics of these suture zones are correlated with the Paleo\|Tethyan Ocean. Both of the zones are keys to understanding whether the Paleo\|Tethyan Ocean extended from Western Yunnan area to east of the South China continent. The Ailao Shan belt consists of Red River fault, Ailao Shan fault, Shuanggou fault and Huashan—Yayi fault, which are the boundaries of the Ailao Shan basement metamorphic belt, ophiolitic melange belt and Island\|arc volcanic\|sediments belt, respectively.The ophiolitic melange belt is characterized by the existence of the ophiolite in Shuanggou area, which represents the relicts of the oceanic crust of the Ailao Shan Ocean. In addition, there exist volcanic rocks in west of the ophiolitic melange belt in Jingdong area. The geochemical characteristics of basalts in Jingdong are similar to that of the E\|MORB. Synthesized studies on geochemistry and tectonics suggest that the basalts in Jingdong area were formed in an extensional rift setting in Devonian.
文摘The Kunlun Mountains is situated in the north margin of the Tibetan plateau and is one of crucial areas for unraveling the tectonic evolutionary history of the plateau and Eurasia. However, there is no widely accepted model for this area. One of the reasons is that some basic issues for the tectonic reconstruction have not been well settled, they are: (1) Is the Kunlun Mountains an ancient accretion prism, or a mini continent with old basement?(2) What is the age of the Kudi ophiolite, early Paleozoic or late Paleozoic?(3) When did the South Kunlun Block accrete to the Tarim Block?(4) Do the fifth and the forth sutures represent different oceans, or they are just the chronologically different relics of the same ocean?(5) Did the Kunlun Mountains experience continuous subduction since Neoproterozoic?(6) When did the Paleo\|Tethys closed in the West Kunlun range?
文摘There are abundant Bajocian—Tithonian bivalves in the main ridge of the Tanggula Mountains of northern Qinghai—Xizang Plateau, China. After figuring the common and coeval species between Tanggula and other areas (Fig. 1), and tracing the temporal and spacial historical distribution of the bivalves very capable of dispersion, some Jurassic bivalve biogeographic items, particularly the biogeographic relations, have been lit up. In the known 21 taxa of the Jurassic Pectinoida and Ostreoida from the main ridge of the Tanggula Mountains, there are 12 (57%) common and coeval species in northern Tethys, 13 (62%) common and coeval species in southern Tethys and 12 (57%) in Kachchh—southern Xizang area. It has demonstrated that there existed intermigration of bivalves between Tanggula and various parts of Tethys. Although there is no coeval species between Tanggula and western Australia, in these two areas there exist 6 (29%) close range common species of which 4 (19%) coevaity existed in western Australia and India Plate. Tanggula fauna is, therefore, still very close to that of western Australia. However, there are 15 (71%) common and 14 (67%) coevality species between the main ridge of the Tanggula Mountains and northwestern Europe, among the common species, 8 (38%) ones have lower limitation (first occurrence) in northwestern Europe but only 2 (10%) taxa are older in the main ridge of the Tanggula Mountains. It is very clear that pectinite and ostrea fauna of Tethys, particularly the main ridge of the Tanggula Mountains and Europe had very close relation and most Tanggula’s or northern Tethyan taxa migrated from northwestern Europe.
文摘Whilst the topographic relief of the Tibetan Plateau’s northeast margin reflects recent Himalayan Orogenesis, its position and geometry reflect much older structures that developed during the Indosinian Orogeny c.200Ma. The Indosinian Orogeny was responsible for closure and shortening of the Songpan Garzê Basin, a Palaeo\|Tethyan relict, during accretion of the Cimmerian Continental Chain to the southern margin of Laurasia. Sandwiched between Laurasia and the Cimmerian fragments of the Qangtang (North Tibet) and Yangtze (South China) blocks, this basin evolved into the Songpan Garzê Fold Belt—a major accretionary prism which now forms the northeast portion of the Tibetan Plateau.
文摘In carboniferous and triassic metacarbonates (anchizone to lower greenschist facies) of the Tethyan Himalayas the characteristic remanent magnetisations are carried by magnetite (ChRM\-1) and pyrrhotite (ChRM\-2;Klootwijk & Bingham,1980;Appel et al.,1991 & 1995;Schill et al.,1999).Magnetite may carry a primary remanent magnetisation whereas the pyrrhotite component is secondary and related to the last cooling event below 300℃. Pyrrhotite is formed in marly carbonates during low\|grade metamorphism.In Spiti the last cooling is represented by an 40 Ar/ 39 Ar age of 42～45Ma (Wiesmayr & Grasemann,1999).Five locations were sampled in the Spiti valley (Fig.1).Besides a present earth field direction,both remanent components (ChRM 1+2 ) are present in single specimens.The contribution to the total NRM is around 30% for the ChRM\-2 (coercivity of 20～100mT) and only around 8% for the ChRM\-2 (unblocking temperature of 250～330℃).Despite of the contribution stable remanence directions could be obtained for the ChRM\-2.For all sampling locations well grouping overall mean directions were obtained (Table 1,Fig.1).Results from Losar and the lower Pin valley are preliminary.They were estimated by great circle analyses or by taking the residual component after AF\|demagnetisation. Clockwise block rotations of around 10～40° in respect to stable India since 42 Ma are calculated by using the apparent polar wander path of Besse & Courtillot (1991).The α 95 \|angles show no overlapping (Fig.1 small figure).Therefore local rotations are not negligible.
文摘The isotopic signature of mid\|ocean ridge basalts (MORB) from the Indian Ocean is different from that of MORB from the Pacific and North\|Atlantic oceans.. The Indian MORB is characterized by lower 206 Pb/ 204 Pb, hi gher 87 Sr/ 86 Sr, and lower 206 Pb/ 204 Pb for given 143 Nd/ 144 Nd than the latter (Hart, 1984; Castillo, 1988; Mahoney et al., 1998). Why the Indian Ocean mantle domain is different from the Pacific and North\|Atlantic ocean mantle domain is still unclear. Two general classes of hypotheses have been proposed to explain the origin of Indian mantle (Mahoney et al., 1998). The first one is that the components of the Indian Ocean mantle domain are a fairly young mantle end\|member created during the processes of breakup of the Gondwana continent to form the Indian Ocean. The second hypothesis posits that the Indian MORB\|type isotopic signature is a long\|lived mantle domain that existed prior to the formation of the present Indian Ocean. Thus it appears that one of the keys to a better understanding of origin of the Indian Ocean\|type isotopic signature depends on its age. Although some studies (Mahoney et al., 1998; Weis and Frey, 1997) showed that the isotopic signature was as old as the Indian ocean crust (140Ma), basalts investigated in the Indian Ocean region do not prove or disprove the existence of the Indian MORB\|type isotopic signature prior to the Indian Ocean because they were taken from the Indian ocean basin itself.
