The Xialu chert, which contains abundant biological information, were investigated by major element analysis, micro-Raman, SEM and EPMA. The results show that SiO2 content of chert is 84.12%-93.08%, averaging 89.84%. ...The Xialu chert, which contains abundant biological information, were investigated by major element analysis, micro-Raman, SEM and EPMA. The results show that SiO2 content of chert is 84.12%-93.08%, averaging 89.84%. The close packed structures of low degree crystallinity of quartz indicate the hydrothermal origin. SiO2 of modern hot springs exhibit loose silica pellets and nodular, beaded structures. Under polarization microscope, the presence of biological skeleton structures indicate that biological activities are involved in the hydrothermal deposition, which correspond to the geochemical characteristics: w(SiO2)/ w(K2O+Na2O), w(SiO2)/w(Al2O3) and w(SiO2)/w(MgO), with average values of 295.29, 68.88 and 284.45, respectively. SiO2 is enriched in the organism(radiolarian) centers, the degree order of SiO2 within the biologic structures is much higher than that of outside. The impurity minerals albites are formed earlier than the original deposition. Kaolinites, feldspars and mixture of organic materials display lower degree of crystallinities and accumulate as vermicular aggregates.展开更多
Marine uppermost Cretaceous to lowermost Tertiary sequence occurs in the Gamba and Tingri regions of southern Tibet. In previous work, the sequences in both regions were divided into the Zongshan, Jidula and Zhepure F...Marine uppermost Cretaceous to lowermost Tertiary sequence occurs in the Gamba and Tingri regions of southern Tibet. In previous work, the sequences in both regions were divided into the Zongshan, Jidula and Zhepure Formations (Wan, 1985; Hao and Wan, 1985; Xu, Wan, et al. 1990). The K/T boundary in Gamba was studied by Wan Xiaoqiao (1988). This paper deals with the boundary in the Tingri region. Willems (1993) discussed the Cretaceous to Tertiary sequence in the Tingri region. In his work, the Upper Cretaceous to Lower Tertiary passage beds involved the Zongshan, Zhepure Shanpo, Jidula and Zhepure Shan Formations. The lithologies in the Tingri and Gamba regions are generally comparable, and we describe the boundary sequence in the Tingri region as follows:1\ Zongshan Formation (Campanian—Middle Maastrichtian) Hao and Wan (1985) first described this formation in Tingri. It consists of limestones equivalent to the strata in Gamba. The nomination of the Zongshan formation has been used in both regions. The Formation in Gamba ranges from Campanian to Late Maastrichtian age. In Tingri, however, the upper beds were referred to the Zhepure Shanpo Formation because they are clastic sediments (Willems, 1993). Planktonic foraminifera are abundant, such as Globotruncana spp. and Omphalocyclus sp.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 marine early\|middle Early Paleogene in the northern Tethys Himalayas was found in southern Tibet in mid 1980s (Hao and Wan, 1985), and the bio\|, litho\|, and chrono\| stratigraphy were patterned by then (Hao and...The marine early\|middle Early Paleogene in the northern Tethys Himalayas was found in southern Tibet in mid 1980s (Hao and Wan, 1985), and the bio\|, litho\|, and chrono\| stratigraphy were patterned by then (Hao and Wan, 1985; Willems et al., 1993, 1996). It seems that there is not an abrupt boundary between the Paleocene and Eocene (P/E) because they are composed of carbonate rocks. This similarity is widespread in the world. They are well examined in many ocean DSDP and ODP logs in similar continuous sediments. But in fact, it is sure that there is a geologic event between the Paleocene and Eocene around the world. Foraminifer extinction, stable isotope record, clay mineral changes, etc. verify the geologic event existence at the latest Paleocene. Unlike the K/T boundary, there is at present little direct or indirect evidence of such catastrophes coincident with the transition (Zachos et al., 1993). This work first shows that there could be also a geologic event across the boundary of latest Paleocene to earliest Eocene exposed on land, certainly in China territory.The P/E transitional sediment is exposed and remeasured at Gongzha, northwestern flank of the Zhepure Shan Syncline, west to Tingri. Here the P/E transitional stratum is approximately equivalent to the upper Member IV and the entire Member V (Willems et al., 1993, 1996). The exact boundary between the Paleocene and Eocene, i.e. between the Unit 16 and Unit 17, is determined by benthic foraminiferal zonations. The fossil zone Alveolina beginning at Unit 17 is just above the boundary that is partly different from Willems et al (1993, 1996).展开更多
The Damxung—Jiali shear zone is a shear zone in Southern Tibet that trends W—E for>180km.It appears to have a varied history of both displacement sense and deformation conditions.We have examined microscopic and ...The Damxung—Jiali shear zone is a shear zone in Southern Tibet that trends W—E for>180km.It appears to have a varied history of both displacement sense and deformation conditions.We have examined microscopic and field data (including fault plane populations) in the westernmost 40km of the shear zone (on the northern margin of the Damxung graben near to the route of the INDEPTH II deep seismic line). The shear zone outcrops along the southern flank of an W—E trending chain of hills in which all valleys run N—S, providing a series of sections of exposure through the shear zone. The shear zone is 3～5km wide and has varying degrees of deformation. It cuts across the main trends of, and does not seem to be restricted to any particular lithology. The principal fabric in the shear zone is steeply to moderately south dipping. The bulk of the shear zone is phyllite and lower grade schist with a consistent degree of both ductile and brittle strain. A mylonitized carbonate unit that is sometimes present within the phyllites may have locally provided a mechanical instability as indicated by the higher strain. Elsewhere a conglomerate unit contains carbonate clasts that are stretched (prolate) up to 30∶1.The most spectacular unit forms lozenges of quartzifeldspathic rich rock (several 100m wide & 2～5km long) whose microfabric indicates deformation mechanisms (e.g., wholesale grainsize reduction) that operated around 400～500℃; the highest grade of the deformation fabrics. The lozenges are remnant evidence of higher temperature strain (at higher strain rate?) that is preserved only in the quartzifeldspathic rock. They are interpreted to be mega\|scale boudins resulting from their strength contrast with the weaker phyllites and schists during later lower temperature deformation. All the presently preserved sense of shear indicators are observed to be left\|lateral, and bulk shortening directions resolved using slip data from fault plane populations are consistent with this sinistral displacement.展开更多
The marine non\|carbonate sediment is exposed at the southwestern flank of the Zhepure Syncline where it lies about 4 km east to the typical cross\|section, Gongzha cross\|section (Hao and Wan, 1985; Willems et al., 1...The marine non\|carbonate sediment is exposed at the southwestern flank of the Zhepure Syncline where it lies about 4 km east to the typical cross\|section, Gongzha cross\|section (Hao and Wan, 1985; Willems et al., 1993, 1996) and ca.75km north to the Qomolangma. There are few people who can approach the place of the cross\|section, even so are endemic Tibetan. The cross\|section is named of the Qumiba cross\|section in this abstract. The new discovery, conformed on the massive Zhepure Formation limestone, here is named of Qumiba Formation. It is composed of two series of terrigenous sediments: Enba Member—lower gray shales intercalating with sandstones, and Zhaguo Member—upper reddish shales interbedding with sandstones. Abundant nannofossils with chronological meanings are first found out.Enba Member Common calcareous nannofossils in the Lutetian such as Chiastozygus barbatus, Chiasmolithus sp., Discoaster barbadiensis, Helicosphaera compacta, Reticulofenstra bisecta, Sphenolithus radians are processed in sample S12W1\|S17W1, in which the Helicosphaera compacta and Sphenolithus radians are part of the indicators of the nannofossil zone NP15. So it is proposed that Units S12\|17, 110 m in thickness, could have been deposited during Middle\|Late Lutetian.展开更多
Geoelectrical investigations in Tibetan Plateau show that there are two high conductivity layers (HCLs) in the crust of southern Tibetan Plateau. The first HCL is at a depth of 15～20km, and the second at 45～60km. In...Geoelectrical investigations in Tibetan Plateau show that there are two high conductivity layers (HCLs) in the crust of southern Tibetan Plateau. The first HCL is at a depth of 15～20km, and the second at 45～60km. In the central region of the Plateau, such as north Qiangtang and Bayan Har, there is only one HCL in crust at the depth about 15～20km.The origin of HCL in upper crust of southern Tibet is mainly caused by free saline aqueous fluids. The seismic investigation by project INDEPTH in southern Tibet demonstrates that the bright spot reflection at about 15km depth is caused by 10% volume of free aqueous fluids (Makovsky and Klemperer, 1999). Seismic and heat flow research indicates the temperature in 15km depth of Tibet is from 400℃ to 650℃. The high concentration of Cl - in water of geothermal spring in southern Tibet means that the aqueous fluid in crust is saline water. The experiment on conductivity of NaCl solution shows that the conductivity is more than 4.5 S·m -1 under 400MPa and 300～650℃ condition (Quist and Marshall, 1968). This p\|T condition corresponds to the pressure and temperature range at 15～20km depth of Tibet.展开更多
Based on the study of the location of extensional action in the tectonic background and the state of regional tectonic stress, the extensional action can be distinguished into active and passive types. The active exte...Based on the study of the location of extensional action in the tectonic background and the state of regional tectonic stress, the extensional action can be distinguished into active and passive types. The active extensional movement is mainly composed of a set of deposition formed under extensional stress and syntectonic and syndepositional deformational structure. The passive extentional movement is expressed as regional extensional action induced under the compressional elevation. Extensional movement and action are well\|developed in the Tibet\|Tethys domain. By the analysis of tectonic deformation, extensional unconformity, depositional facies and paleogeographical rebuilding in the South Tibet, it is recognized that the extensional movement consists of active extension of Hercynian, Indo\|China and Early Yanshan epochs, and the passive extension of Late Yanshan and Himalayan epochs. Some of the characteristics of extensional movement and structures are discussed in this paper(Table.1).展开更多
藏南地区中生代硅质岩包括蛇绿岩套硅质岩(与蛇绿岩共生)和非蛇绿岩套硅质岩两大类。本文重点分析日喀则地区彭错林、夏鲁以及泽当地区的罗布莎、江孜盆地宗卓组及四个剖面的硅质岩。其中,彭错林、夏鲁和罗布莎硅质岩与蛇绿岩共生,江孜...藏南地区中生代硅质岩包括蛇绿岩套硅质岩(与蛇绿岩共生)和非蛇绿岩套硅质岩两大类。本文重点分析日喀则地区彭错林、夏鲁以及泽当地区的罗布莎、江孜盆地宗卓组及四个剖面的硅质岩。其中,彭错林、夏鲁和罗布莎硅质岩与蛇绿岩共生,江孜盆地宗卓组为非蛇绿岩套硅质岩。分析表明:(1)藏南地区硅质岩剖面地球化学特征鲜明,具有一致性和多样性特点;(2)与蛇绿岩共生的彭错林、夏鲁、罗布莎硅质岩普遍具有高 Si、高 Fe、低 Al 特征,大部分微量元素相对于克拉克值亏损,稀土元素总量低,经北美页岩标准化后,Ce 异常明显或不明显,重稀土相对轻稀土富集。硅质泥岩的∑REE要明显高于硅质岩;(3)非蛇绿岩套宗卓组硅质岩SiO_2含量稍低,Al_2O_3.TiO_2则相反。V、Th、Hf、Ta 等不相容元素上亏损程度较小,部分样品含量可接近克拉克值。稀土总量相对较高,页岩标准化配分模式上体现为弱 Ce 正异常,负 Eu 异常,轻重稀土分异不明显的平坦型曲线图;(4)地球化学特征指示了,藏南地区硅质岩多数具有明显的热水沉积成因属性,同时有正常陆源组分的加入。其中,夏鲁硅质岩的热水沉积地球化学特征较为典型,而宗卓组硅质岩则表现出受陆源物质加入的影响显著的地球化学特点。展开更多
基金Projects(41273040,41303025)supported by the National Natural Science Foundation of China
文摘The Xialu chert, which contains abundant biological information, were investigated by major element analysis, micro-Raman, SEM and EPMA. The results show that SiO2 content of chert is 84.12%-93.08%, averaging 89.84%. The close packed structures of low degree crystallinity of quartz indicate the hydrothermal origin. SiO2 of modern hot springs exhibit loose silica pellets and nodular, beaded structures. Under polarization microscope, the presence of biological skeleton structures indicate that biological activities are involved in the hydrothermal deposition, which correspond to the geochemical characteristics: w(SiO2)/ w(K2O+Na2O), w(SiO2)/w(Al2O3) and w(SiO2)/w(MgO), with average values of 295.29, 68.88 and 284.45, respectively. SiO2 is enriched in the organism(radiolarian) centers, the degree order of SiO2 within the biologic structures is much higher than that of outside. The impurity minerals albites are formed earlier than the original deposition. Kaolinites, feldspars and mixture of organic materials display lower degree of crystallinities and accumulate as vermicular aggregates.
文摘Marine uppermost Cretaceous to lowermost Tertiary sequence occurs in the Gamba and Tingri regions of southern Tibet. In previous work, the sequences in both regions were divided into the Zongshan, Jidula and Zhepure Formations (Wan, 1985; Hao and Wan, 1985; Xu, Wan, et al. 1990). The K/T boundary in Gamba was studied by Wan Xiaoqiao (1988). This paper deals with the boundary in the Tingri region. Willems (1993) discussed the Cretaceous to Tertiary sequence in the Tingri region. In his work, the Upper Cretaceous to Lower Tertiary passage beds involved the Zongshan, Zhepure Shanpo, Jidula and Zhepure Shan Formations. The lithologies in the Tingri and Gamba regions are generally comparable, and we describe the boundary sequence in the Tingri region as follows:1\ Zongshan Formation (Campanian—Middle Maastrichtian) Hao and Wan (1985) first described this formation in Tingri. It consists of limestones equivalent to the strata in Gamba. The nomination of the Zongshan formation has been used in both regions. The Formation in Gamba ranges from Campanian to Late Maastrichtian age. In Tingri, however, the upper beds were referred to the Zhepure Shanpo Formation because they are clastic sediments (Willems, 1993). Planktonic foraminifera are abundant, such as Globotruncana spp. and Omphalocyclus sp.
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 marine early\|middle Early Paleogene in the northern Tethys Himalayas was found in southern Tibet in mid 1980s (Hao and Wan, 1985), and the bio\|, litho\|, and chrono\| stratigraphy were patterned by then (Hao and Wan, 1985; Willems et al., 1993, 1996). It seems that there is not an abrupt boundary between the Paleocene and Eocene (P/E) because they are composed of carbonate rocks. This similarity is widespread in the world. They are well examined in many ocean DSDP and ODP logs in similar continuous sediments. But in fact, it is sure that there is a geologic event between the Paleocene and Eocene around the world. Foraminifer extinction, stable isotope record, clay mineral changes, etc. verify the geologic event existence at the latest Paleocene. Unlike the K/T boundary, there is at present little direct or indirect evidence of such catastrophes coincident with the transition (Zachos et al., 1993). This work first shows that there could be also a geologic event across the boundary of latest Paleocene to earliest Eocene exposed on land, certainly in China territory.The P/E transitional sediment is exposed and remeasured at Gongzha, northwestern flank of the Zhepure Shan Syncline, west to Tingri. Here the P/E transitional stratum is approximately equivalent to the upper Member IV and the entire Member V (Willems et al., 1993, 1996). The exact boundary between the Paleocene and Eocene, i.e. between the Unit 16 and Unit 17, is determined by benthic foraminiferal zonations. The fossil zone Alveolina beginning at Unit 17 is just above the boundary that is partly different from Willems et al (1993, 1996).
文摘The Damxung—Jiali shear zone is a shear zone in Southern Tibet that trends W—E for>180km.It appears to have a varied history of both displacement sense and deformation conditions.We have examined microscopic and field data (including fault plane populations) in the westernmost 40km of the shear zone (on the northern margin of the Damxung graben near to the route of the INDEPTH II deep seismic line). The shear zone outcrops along the southern flank of an W—E trending chain of hills in which all valleys run N—S, providing a series of sections of exposure through the shear zone. The shear zone is 3～5km wide and has varying degrees of deformation. It cuts across the main trends of, and does not seem to be restricted to any particular lithology. The principal fabric in the shear zone is steeply to moderately south dipping. The bulk of the shear zone is phyllite and lower grade schist with a consistent degree of both ductile and brittle strain. A mylonitized carbonate unit that is sometimes present within the phyllites may have locally provided a mechanical instability as indicated by the higher strain. Elsewhere a conglomerate unit contains carbonate clasts that are stretched (prolate) up to 30∶1.The most spectacular unit forms lozenges of quartzifeldspathic rich rock (several 100m wide & 2～5km long) whose microfabric indicates deformation mechanisms (e.g., wholesale grainsize reduction) that operated around 400～500℃; the highest grade of the deformation fabrics. The lozenges are remnant evidence of higher temperature strain (at higher strain rate?) that is preserved only in the quartzifeldspathic rock. They are interpreted to be mega\|scale boudins resulting from their strength contrast with the weaker phyllites and schists during later lower temperature deformation. All the presently preserved sense of shear indicators are observed to be left\|lateral, and bulk shortening directions resolved using slip data from fault plane populations are consistent with this sinistral displacement.
文摘The marine non\|carbonate sediment is exposed at the southwestern flank of the Zhepure Syncline where it lies about 4 km east to the typical cross\|section, Gongzha cross\|section (Hao and Wan, 1985; Willems et al., 1993, 1996) and ca.75km north to the Qomolangma. There are few people who can approach the place of the cross\|section, even so are endemic Tibetan. The cross\|section is named of the Qumiba cross\|section in this abstract. The new discovery, conformed on the massive Zhepure Formation limestone, here is named of Qumiba Formation. It is composed of two series of terrigenous sediments: Enba Member—lower gray shales intercalating with sandstones, and Zhaguo Member—upper reddish shales interbedding with sandstones. Abundant nannofossils with chronological meanings are first found out.Enba Member Common calcareous nannofossils in the Lutetian such as Chiastozygus barbatus, Chiasmolithus sp., Discoaster barbadiensis, Helicosphaera compacta, Reticulofenstra bisecta, Sphenolithus radians are processed in sample S12W1\|S17W1, in which the Helicosphaera compacta and Sphenolithus radians are part of the indicators of the nannofossil zone NP15. So it is proposed that Units S12\|17, 110 m in thickness, could have been deposited during Middle\|Late Lutetian.
文摘Geoelectrical investigations in Tibetan Plateau show that there are two high conductivity layers (HCLs) in the crust of southern Tibetan Plateau. The first HCL is at a depth of 15～20km, and the second at 45～60km. In the central region of the Plateau, such as north Qiangtang and Bayan Har, there is only one HCL in crust at the depth about 15～20km.The origin of HCL in upper crust of southern Tibet is mainly caused by free saline aqueous fluids. The seismic investigation by project INDEPTH in southern Tibet demonstrates that the bright spot reflection at about 15km depth is caused by 10% volume of free aqueous fluids (Makovsky and Klemperer, 1999). Seismic and heat flow research indicates the temperature in 15km depth of Tibet is from 400℃ to 650℃. The high concentration of Cl - in water of geothermal spring in southern Tibet means that the aqueous fluid in crust is saline water. The experiment on conductivity of NaCl solution shows that the conductivity is more than 4.5 S·m -1 under 400MPa and 300～650℃ condition (Quist and Marshall, 1968). This p\|T condition corresponds to the pressure and temperature range at 15～20km depth of Tibet.
文摘Based on the study of the location of extensional action in the tectonic background and the state of regional tectonic stress, the extensional action can be distinguished into active and passive types. The active extensional movement is mainly composed of a set of deposition formed under extensional stress and syntectonic and syndepositional deformational structure. The passive extentional movement is expressed as regional extensional action induced under the compressional elevation. Extensional movement and action are well\|developed in the Tibet\|Tethys domain. By the analysis of tectonic deformation, extensional unconformity, depositional facies and paleogeographical rebuilding in the South Tibet, it is recognized that the extensional movement consists of active extension of Hercynian, Indo\|China and Early Yanshan epochs, and the passive extension of Late Yanshan and Himalayan epochs. Some of the characteristics of extensional movement and structures are discussed in this paper(Table.1).
文摘藏南地区中生代硅质岩包括蛇绿岩套硅质岩(与蛇绿岩共生)和非蛇绿岩套硅质岩两大类。本文重点分析日喀则地区彭错林、夏鲁以及泽当地区的罗布莎、江孜盆地宗卓组及四个剖面的硅质岩。其中,彭错林、夏鲁和罗布莎硅质岩与蛇绿岩共生,江孜盆地宗卓组为非蛇绿岩套硅质岩。分析表明:(1)藏南地区硅质岩剖面地球化学特征鲜明,具有一致性和多样性特点;(2)与蛇绿岩共生的彭错林、夏鲁、罗布莎硅质岩普遍具有高 Si、高 Fe、低 Al 特征,大部分微量元素相对于克拉克值亏损,稀土元素总量低,经北美页岩标准化后,Ce 异常明显或不明显,重稀土相对轻稀土富集。硅质泥岩的∑REE要明显高于硅质岩;(3)非蛇绿岩套宗卓组硅质岩SiO_2含量稍低,Al_2O_3.TiO_2则相反。V、Th、Hf、Ta 等不相容元素上亏损程度较小,部分样品含量可接近克拉克值。稀土总量相对较高,页岩标准化配分模式上体现为弱 Ce 正异常,负 Eu 异常,轻重稀土分异不明显的平坦型曲线图;(4)地球化学特征指示了,藏南地区硅质岩多数具有明显的热水沉积成因属性,同时有正常陆源组分的加入。其中,夏鲁硅质岩的热水沉积地球化学特征较为典型,而宗卓组硅质岩则表现出受陆源物质加入的影响显著的地球化学特点。
