The Yarlung Zangbo Suture Zone (YZSZ), a major lineament in Tibet geological framework, which is accepted as the collision site between India and Asia (Allègre et al., 1984; Coulon et al., 1986; Dewey et al., 199...The Yarlung Zangbo Suture Zone (YZSZ), a major lineament in Tibet geological framework, which is accepted as the collision site between India and Asia (Allègre et al., 1984; Coulon et al., 1986; Dewey et al., 1990; Yin et al., 1994), is an extremely complicated tectonic zone. It includes seven different tectonic\|sedimentary units from north to south as follows: Gangdese arc complex keeping the Sangri Group inside, the Qiuwu Formation, the Giabulin Formation, the Xigaze Group, ophiolitic massifs, the Liuqu Group, and melange zones (Wang et al., 1999). Current models, which mainly focus on researches at the unit of ophiolitic massifs, propose that most of the Tethyan oceanic lithosphere was subducted into one single subduction zone active during the Middle Cretaceous or the Late Cretaceous, and closed during the Paleogene India\|Asia collision. In this report, we present latest research results on units in the Xigaze forearc basin and others in YZSZ after 6\|year\|period of comprehensive investigations. Chronostratigraphy framework, sedimentology, and evolution of the Xigaze forearc basin are discussed in details. Four thrust systems in YZSZ are named. Dynamic evolution of the YZSZ including two subductions of Tethys is presented.展开更多
Basic features Bangonghu—Dingqing Suture is the medial and western segment of the Bangonghu—Nujiang Suture which many researchers called as ,and it is often regarded as the Qiangtang Massif boundary line in the nort...Basic features Bangonghu—Dingqing Suture is the medial and western segment of the Bangonghu—Nujiang Suture which many researchers called as ,and it is often regarded as the Qiangtang Massif boundary line in the northern side and the Lasa (Gangdisi) Massif in the souther. The era of the ophiolites spreading along the Bangonghu\|Dingqing suture include every period of the whole Jurassic, and the spreading of the ophiolites has distinct segmentation. From west to east there are Ritu segment,Gaize segment,Dongqiao segment and Dingqing segment.Between the Gaize segment and Dongqiao one ,that is ,between the E89°and E86°40′,no ophiolites are discovered in the surface.Aeromagnetic data shows that the magnetic field of this segment is quite gentle,there are no difference from its adjacent northern and southern sides. When its east adjacent segment extends into this segment, the high areomagnetic anomaly belt corresponding to of the Dongqiao ophiolite disappear abruptly. Apparently,it is impossible for the ophiolites to develop in such a deep crust of the same segment.展开更多
A discontinuous line of ophiolitic bodies occurs along the Yarlung Zangbo Suture Zone (YTSZ), which stretches across southern Tibet and beyond. This zone marks the locus of collision between Eurasia and India in the E...A discontinuous line of ophiolitic bodies occurs along the Yarlung Zangbo Suture Zone (YTSZ), which stretches across southern Tibet and beyond. This zone marks the locus of collision between Eurasia and India in the Early Cenozoic. Should we assume that the entire Tethyan Ocean basin that lay between these two continental blocks was oceanic or might it have been more complex? Fragments of any terranes that developed within this once extensive ocean potentially lie within the YTSZ. Detailed investigations over the past three field seasons reveal the presence of several terranes distributed along this zone. Work is currently underway to analyze the nature of individual terranes and the timing of any inter\|relationships.展开更多
The Yarlung—Tsangpo Suture Zone, the youngest in Tibet, marks a site of collision of the Eurasia continent and Indian subcontinent. It is characterised by a discontinuous line of ophiolitic bodies in southern Tibet a...The Yarlung—Tsangpo Suture Zone, the youngest in Tibet, marks a site of collision of the Eurasia continent and Indian subcontinent. It is characterised by a discontinuous line of ophiolitic bodies in southern Tibet and beyond. Fragments of Tethyan oceanic pelagic and hemipelagic deposits are distributed along the suture. These oceanic deposits occur in two distinctive tectonic settings: (1) above the ophiolite and (2) in fragments of an accretionary wedge that lies to the south of the ophiolite.Supra\|ophiolite sequences, examined at several localities, are mostly made up of chert and siliceous mudstones and display varied lithostratigraphy. Sections are thin, have different degrees of completeness and are truncated at their tops. Most of them are in undisturbed stratigraphic contact with underlying pillow lava or pillow breccia. Previously the cherts above the ophiolite in this area were dated as late Albian\|possibly early Cenomanian (Marcoux et al., 1982) or early Cenomanian (Wu, 1986). Our investigation reveals Aptian radiolarian fossils in the cherts and siliceous mudstones. The oldest radiolarians, late Barremian, occur in chert at the base of the Qunrang section. This allows reassessment of the timing of eruption of Xigaze ophiolite basalts to during, or before, the late Barremian—early Aptian.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
Platinum\|Group Elements (PGE) along with other highly siderophile elements (HSE) are quantitatively fractionated into the core and mantle,leaving the crust strongly depleted during the formation of the earth.However,...Platinum\|Group Elements (PGE) along with other highly siderophile elements (HSE) are quantitatively fractionated into the core and mantle,leaving the crust strongly depleted during the formation of the earth.However,the transfer of PGE and other HSE from the mantle may occur by tectonic emplacement of mantle material into the crust or by crystallization of the mantle derived magma in the crust.The formation and emplacement of ophiolites,is therefore,a suitable transfer mechanism in the enrichment of PGE and other metallic mineral deposits.Because of this,in recent years,a great deal of attention is being paid in studying the ophiolites in order to better understand the core\|mantle interaction,chemical evolution of the upper mantle and to explore their noble metal potential.The ophiolites along the Indus Suture Zone (ISZ) in the Himalayas are tectonically related to India\|Eurasia collision.But their detailed geochemical evolution history and economic potentiality (chromite,PGE,gold and Ni\|sulfides) is not evaluated so far.Nidar ophiolite of the eastern Ladakh is one of the ophiolitic suites along the ISZ.The general geology of the area was presented in several research papers.This paper presents the geology,mineralogy and geochemistry of the chromitites and reports on the first platinum\|group elements mineralization to have been discovered.展开更多
The detailed geochemical research indicates that the tholeiitic basalts from Ganlongtang-Longba ophiolitic m（?）lange exhibit distinctive geochemical characteristics of high TiO<sub>2</sub> and low K<s...The detailed geochemical research indicates that the tholeiitic basalts from Ganlongtang-Longba ophiolitic m（?）lange exhibit distinctive geochemical characteristics of high TiO<sub>2</sub> and low K<sub>2</sub>O,and depletion of light rare earth elements.They should be originated from a depleted asthenosphere mantle, belonging to ancient oceanic crust ophiolitic volcanic rock association.Compared with the Longba tholeiitic basalt,the Ganlongtang tholeiitic basalt shows展开更多
Ophiolites, which have been tectonically emplaced along continental margins and island arcs, are significant to the understanding of mountain belt evolution. In the Himalayas, the ophiolitic suite of rocks occur along...Ophiolites, which have been tectonically emplaced along continental margins and island arcs, are significant to the understanding of mountain belt evolution. In the Himalayas, the ophiolitic suite of rocks occur along the Indussuture zone from Hanle in the southeast to Dras\|Kargil sector in the northwest and it represents the remnant of the compressed uplifted wedge of the oceanic crust between the two colliding continental masses, the Indian and the Asian plates.. These ophiolites are temporally and spatially correlated with the culminating phase of the Himalayan orogeny. The Indus River flows to its north separating the ophiolite from the Trans Himalayan litho\|units. Geological mapping in the hostile and inaccessible mountainous terrains of the Himalaya has always posed a great challenge to geologists. Nevertheless, a number of geologists have undertaken such arduous mapping expeditions in the past and prepared fairly good geological maps of these terrains .However there always existed disputes on the accuracy of lithological boundaries and structural details in these maps because many of these boundaries and structural features were completed through extrapolations and/or interpolations as the ruggedness and inaccessibility of a large part of the terrain forbid physical examination of every outcrop. It is in this context the potential of remote sensing, especially of satellite images, is to be appreciated.展开更多
The Yarlung Zangpo Suture Zone(YZSZ) is believed to be composed of material largely derived from the destruction of the Neo-Tethys ocean.We report here geochronological and petrological data obtained for newly discove...The Yarlung Zangpo Suture Zone(YZSZ) is believed to be composed of material largely derived from the destruction of the Neo-Tethys ocean.We report here geochronological and petrological data obtained for newly discovered alkaline gabbro blocks embedded in a m(?)lange zone of the YZSZ,in Zhongba area, southwestern Tibet.The gabbros are Late Devonian in age and of intra-oceanic Ocean Island Basalt(OIB) affinity.Single-zircon U-Pb analyses from one representative gabbro sample by SIMS(Secondary展开更多
Introduction\;A suture zone in an orogenic belt marks the paleo\|plate boundaries with its characteristic ocean floor assemblages. In Himalayas, the best and most spectacular example of the continent\|continent collis...Introduction\;A suture zone in an orogenic belt marks the paleo\|plate boundaries with its characteristic ocean floor assemblages. In Himalayas, the best and most spectacular example of the continent\|continent collision orogeny, the suture zone can be traced all along the 2500km long mountain chain and marks the boundary between the Indian and Asian plates. Ladakh region of North\|West Himalaya probably presents the best preserved history of pre\|, syn\|, and post\|collision signatures. It has rocks ranging from Precambrian passive margin sediments to the post collision molasses. The suture zone in Ladakh, referred to as the Indus Suture Zone (ISZ), is characterized by the several occurrences of ophiolitic melange. (M.P. Searle et al, 1987) .Apart from these, various linear belts of the volcanic rocks have been found in the Indus Suture Zone, though their inter relationship is not very clear (K.K.Sharma 1990).展开更多
Meso\| and microstructural characteristics of cataclastic fault rocks developed in the Xialu chert are described. The Xialu chert represents pelagic and deep marine sediments (Middle Jurassic—Lower Cretaceous), and o...Meso\| and microstructural characteristics of cataclastic fault rocks developed in the Xialu chert are described. The Xialu chert represents pelagic and deep marine sediments (Middle Jurassic—Lower Cretaceous), and occupies the southern marginal part of the E—W trending Yarlung Zangbo suture zone. The apparent total thickness of siliceous deposits exceeds 1km. The current study is concentrated along the two measured sections, Xialu\|E and Xialu\|W. The Xialu\|E section is composed mainly of red chert associated with reddish purple siliceous mudstone and greenish gray mudstone. The beds steeply dip north or south. The 45m section studied is divided into three units (chert unit, chert\|siliceous mudstone unit, and melange unit from north to south). They are in fault contact with each other. In the southern half of the chert unit and the northernmost of the chert\|siliceous mudstone unit, a 15m thick cohesive cataclasite zone can be defined. The cataclasites are composed of chert fragments in a fine grained matrix, and deformed with jigsaw puzzle structures. The chert\|siliceous mudstone unit is made up of four slabs of chert\|siliceous mudstone sequence. Mesoscopic duplex zones in thickness from 1 to 3m are recognized at slab boundaries. Flat and ramp structure and associated P foliations, R1 shears, Y surfaces are developed. Shear spacing range from 1 to 10cm. The slip senses are dextral strike\|slip movement along these duplex zones. The cataclasite zone is cut by the duplex zone along the southern boundary.展开更多
The collision between and Indian and Asian plate has not only give rise to some of the highest mountains of the world but also is responsible for the various global phenomena associated with paleoclimate and paleo\|oc...The collision between and Indian and Asian plate has not only give rise to some of the highest mountains of the world but also is responsible for the various global phenomena associated with paleoclimate and paleo\|oceanography.Various indirect approaches have been employed in order to constrain the age of initiation of this collision (Beck et al 1995,D.B.Rowley 1996,Dewey 1989).Still it is being quoted anywhere between ca.60 to 40Ma in the literature.The main reason for the poor constraints on the age of the initiation of the collision is unavailability of a direct method to date this.In this paper we present the Ar\|Ar ages of the ophiolites from the Indus Suture,Ladakh and discuss the scope of this approach in constraining the age of the collision more narrowly.1\ Samples and methodology\;Several ophiolitic melange occurrences have been reported belonging to the Indus Suture in the Ladakh sector.These are characterized by the typical oceanic floor assemblages like chert,limestone etc mixed with the peridotites,serpentinites,dolerites,basalts,and pillow lavas (K.K.Sharma 1990).We present here the 40 Ar\| 39 Ar age spectra of two volcanics from the Sumdo Nala section of central Ladakh and one pillow lava from Chiktan,which is about 100km west of the Sumdo Nala.These samples were analysed using Ar\|Ar step heating method following the procedures described by Venketesan et al.1993.展开更多
An earthquake of 6.8 magnitude struck the eastern Shan State in Myanmar at 20:29:30 Myanmar Standard Time(01:55:12 PM UTC) on 24 March 2011.It is one of the earthquakes in plate-interior setting.Six after-shocks occur...An earthquake of 6.8 magnitude struck the eastern Shan State in Myanmar at 20:29:30 Myanmar Standard Time(01:55:12 PM UTC) on 24 March 2011.It is one of the earthquakes in plate-interior setting.Six after-shocks occurred the same year.The nucleation point of this earthquake was defined by an epicenter at 20 km west of Tarlay(20.705°N,99.949°E) at a depth of 10 km and its magnitude was 6.8.The earthquake damage was disastrous.The geological disasters were linearly distributed along the surface rupture zone.The earthquake produced cracks,arch bend,erupting sand,gush water,etc.in many places.As a result of this strong earthquake,224-305 houses were seriously damaged,74 people were killed,124 injured.The event was named after the nearest village Tarlay and the NE-or ENE-striking Nan Ma fault was responsible for it.A detailed morphotectonic study was carried out in the area using satellite image 1:24,000 scale aerial photographs and 1:63360 scale topographic maps,to correlate the seismicity with tectonics.It is found that there are two prominent lineaments striking in NE-or ENE-and N-S or NNE-SSW direction.The present-day deformation of the Than Lwin suture zone is consistent with roughly NW-SE extension and NE-SW striking compression,but with more conjugate strike-slip faulting and only minor normal faulting.展开更多
To extend our successful Magnetotelluric(MT) experiments in the area from Yadong to Bamocuo in 1995 (Chen et al., 1996), two new Magnetotelluric(MT)experiments have been carried out along two main profiles in the cent...To extend our successful Magnetotelluric(MT) experiments in the area from Yadong to Bamocuo in 1995 (Chen et al., 1996), two new Magnetotelluric(MT)experiments have been carried out along two main profiles in the central and Northern Tibetan Plateau in the summer of 1998 and 1999. While the 1995 MT work mainly focused on the study of the electrical structure of the Yarlung\|Zangbo River Suture , the 1998 and 1999 experiments have been designed with following purpose:(1) Study whether partially molten layer widely exists in the crust of the central and northern Tibet.(2) Study the electrical structures of crust and upper mantle in central and northern Tibet which may relate to the attenuated Shear Seismic waves.(3) Study the detail electrical structures of Bangong\|Nujiang Suture and Jinsha Suture.In 1998, the MT team (China University of Geosciences, University of Washington and Geological Survey of Canada) recorded MT data along the Tibet 500 Line which extends about three hundred and eighty kilometers from Deqing to Longweicuo. We used LIMS system to record the long period(20～20000s) MT data at twenty\|six sites and used MT24 to record broadband(320Hz,2000s) MT data at fifty\|eight sites.展开更多
The Qinghai—Xizang (Tibet) Plateau was assembled by the successive accretion of continental and arc terranes to Asia during the Palaeozoic, Mesozoic and early Tertiary. From north to south, the Plateau was divided in...The Qinghai—Xizang (Tibet) Plateau was assembled by the successive accretion of continental and arc terranes to Asia during the Palaeozoic, Mesozoic and early Tertiary. From north to south, the Plateau was divided into four terranes (from north to south): Songpan\|Garze, Qingtang, Lhasa and India terranes. The Qiangtang terrane was divided into two parts by Chabu\|Shuanghu suture: Northern Qiangtang and Southern Qiangtang blocks. It was believed that there is a suture as Palaeotethyan suture between the two blocks from Lungmu lake to Chabu, to Shuanghu, to Langcangjiang, but some geologists opposited this opinion, such as Wang Chengshan et al.(1987) and Deng Wanming et al.(1996). The blueschists that bear the typical glaucophane were found in the Gangmar Area in summer of 1997. The blueschists consist of glaucophane, crossite, phengite, actinolite, epidote, sphene ,rutile, and so on. Blueschists show nappe structures in enclosing rocks, and thrust over Tertiary from north to south.The age of blueschist is 275～285Ma which stand for the metamorphic age of blueschist. The geochemical contents of blueschists are the following: SiO\-2 is 45 37%～53 82%, Na 2O>K 2O, K 2O+Na 2O are 3 72%～7 61%, Na 2O/K 2O is 1 70～19 67, MnO is 0 16%～0 22%, FeO+Fe 2O 3 are 11 12%～14 27%, TiO 2 is 2 34%～4 28%, P 2O 5 is 0 34%～1 03%. From the contents, SiO 2 is inverse relation with K 2O+Na 2O, K 2O and FeO+Fe 2O 3. In the SiO 2\|K 2O+Na 2O diagram, the blueschists fall in the field of Alkali basalt; in the TiO 2\|MnO(10\|P 2O 5×10 triangular diagram, these plot within the Ocean Island Basalts(OIB) field. The whole REE content is (117 03～390 97)×10 -6 , LREE/HREE is 5 05～9 80, the REE diagram shows the feature that LREE is rich and HREE is depleted, this is similar to the OIB. In the spidergram of trace elements show the same characterristics as the OIB. Meanwhile, the trace elements ratios, such as Ba/Nb, La/Nb, Nb/Th, Nb/Y, Zr/Y, Zr/Nb, Hf/Sm, Ta/Hf, Nb/Ta, Nb/U, suggest the tectonic setting is OIB. On the basis of these materials, the blueschists are akin to within\|plate ocean island basalts. This shows that there is a ocean or oceanic basin in the Chabu\|Shuanghu belts and the formation of blueschists is the quicky subduction of the Ocean Island Basalts in Early Permian between the Gondwana and Eurasia continents. It demonstrated, therefore, that the Chabu\|Suanghu suture exists and may extend to the east to Lnagchangjiang, and may extend into Thailand\|Malaysia Peninsula.展开更多
文摘The Yarlung Zangbo Suture Zone (YZSZ), a major lineament in Tibet geological framework, which is accepted as the collision site between India and Asia (Allègre et al., 1984; Coulon et al., 1986; Dewey et al., 1990; Yin et al., 1994), is an extremely complicated tectonic zone. It includes seven different tectonic\|sedimentary units from north to south as follows: Gangdese arc complex keeping the Sangri Group inside, the Qiuwu Formation, the Giabulin Formation, the Xigaze Group, ophiolitic massifs, the Liuqu Group, and melange zones (Wang et al., 1999). Current models, which mainly focus on researches at the unit of ophiolitic massifs, propose that most of the Tethyan oceanic lithosphere was subducted into one single subduction zone active during the Middle Cretaceous or the Late Cretaceous, and closed during the Paleogene India\|Asia collision. In this report, we present latest research results on units in the Xigaze forearc basin and others in YZSZ after 6\|year\|period of comprehensive investigations. Chronostratigraphy framework, sedimentology, and evolution of the Xigaze forearc basin are discussed in details. Four thrust systems in YZSZ are named. Dynamic evolution of the YZSZ including two subductions of Tethys is presented.
文摘Basic features Bangonghu—Dingqing Suture is the medial and western segment of the Bangonghu—Nujiang Suture which many researchers called as ,and it is often regarded as the Qiangtang Massif boundary line in the northern side and the Lasa (Gangdisi) Massif in the souther. The era of the ophiolites spreading along the Bangonghu\|Dingqing suture include every period of the whole Jurassic, and the spreading of the ophiolites has distinct segmentation. From west to east there are Ritu segment,Gaize segment,Dongqiao segment and Dingqing segment.Between the Gaize segment and Dongqiao one ,that is ,between the E89°and E86°40′,no ophiolites are discovered in the surface.Aeromagnetic data shows that the magnetic field of this segment is quite gentle,there are no difference from its adjacent northern and southern sides. When its east adjacent segment extends into this segment, the high areomagnetic anomaly belt corresponding to of the Dongqiao ophiolite disappear abruptly. Apparently,it is impossible for the ophiolites to develop in such a deep crust of the same segment.
文摘A discontinuous line of ophiolitic bodies occurs along the Yarlung Zangbo Suture Zone (YTSZ), which stretches across southern Tibet and beyond. This zone marks the locus of collision between Eurasia and India in the Early Cenozoic. Should we assume that the entire Tethyan Ocean basin that lay between these two continental blocks was oceanic or might it have been more complex? Fragments of any terranes that developed within this once extensive ocean potentially lie within the YTSZ. Detailed investigations over the past three field seasons reveal the presence of several terranes distributed along this zone. Work is currently underway to analyze the nature of individual terranes and the timing of any inter\|relationships.
文摘The Yarlung—Tsangpo Suture Zone, the youngest in Tibet, marks a site of collision of the Eurasia continent and Indian subcontinent. It is characterised by a discontinuous line of ophiolitic bodies in southern Tibet and beyond. Fragments of Tethyan oceanic pelagic and hemipelagic deposits are distributed along the suture. These oceanic deposits occur in two distinctive tectonic settings: (1) above the ophiolite and (2) in fragments of an accretionary wedge that lies to the south of the ophiolite.Supra\|ophiolite sequences, examined at several localities, are mostly made up of chert and siliceous mudstones and display varied lithostratigraphy. Sections are thin, have different degrees of completeness and are truncated at their tops. Most of them are in undisturbed stratigraphic contact with underlying pillow lava or pillow breccia. Previously the cherts above the ophiolite in this area were dated as late Albian\|possibly early Cenomanian (Marcoux et al., 1982) or early Cenomanian (Wu, 1986). Our investigation reveals Aptian radiolarian fossils in the cherts and siliceous mudstones. The oldest radiolarians, late Barremian, occur in chert at the base of the Qunrang section. This allows reassessment of the timing of eruption of Xigaze ophiolite basalts to during, or before, the late Barremian—early Aptian.
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Platinum\|Group Elements (PGE) along with other highly siderophile elements (HSE) are quantitatively fractionated into the core and mantle,leaving the crust strongly depleted during the formation of the earth.However,the transfer of PGE and other HSE from the mantle may occur by tectonic emplacement of mantle material into the crust or by crystallization of the mantle derived magma in the crust.The formation and emplacement of ophiolites,is therefore,a suitable transfer mechanism in the enrichment of PGE and other metallic mineral deposits.Because of this,in recent years,a great deal of attention is being paid in studying the ophiolites in order to better understand the core\|mantle interaction,chemical evolution of the upper mantle and to explore their noble metal potential.The ophiolites along the Indus Suture Zone (ISZ) in the Himalayas are tectonically related to India\|Eurasia collision.But their detailed geochemical evolution history and economic potentiality (chromite,PGE,gold and Ni\|sulfides) is not evaluated so far.Nidar ophiolite of the eastern Ladakh is one of the ophiolitic suites along the ISZ.The general geology of the area was presented in several research papers.This paper presents the geology,mineralogy and geochemistry of the chromitites and reports on the first platinum\|group elements mineralization to have been discovered.
文摘The detailed geochemical research indicates that the tholeiitic basalts from Ganlongtang-Longba ophiolitic m（?）lange exhibit distinctive geochemical characteristics of high TiO<sub>2</sub> and low K<sub>2</sub>O,and depletion of light rare earth elements.They should be originated from a depleted asthenosphere mantle, belonging to ancient oceanic crust ophiolitic volcanic rock association.Compared with the Longba tholeiitic basalt,the Ganlongtang tholeiitic basalt shows
文摘Ophiolites, which have been tectonically emplaced along continental margins and island arcs, are significant to the understanding of mountain belt evolution. In the Himalayas, the ophiolitic suite of rocks occur along the Indussuture zone from Hanle in the southeast to Dras\|Kargil sector in the northwest and it represents the remnant of the compressed uplifted wedge of the oceanic crust between the two colliding continental masses, the Indian and the Asian plates.. These ophiolites are temporally and spatially correlated with the culminating phase of the Himalayan orogeny. The Indus River flows to its north separating the ophiolite from the Trans Himalayan litho\|units. Geological mapping in the hostile and inaccessible mountainous terrains of the Himalaya has always posed a great challenge to geologists. Nevertheless, a number of geologists have undertaken such arduous mapping expeditions in the past and prepared fairly good geological maps of these terrains .However there always existed disputes on the accuracy of lithological boundaries and structural details in these maps because many of these boundaries and structural features were completed through extrapolations and/or interpolations as the ruggedness and inaccessibility of a large part of the terrain forbid physical examination of every outcrop. It is in this context the potential of remote sensing, especially of satellite images, is to be appreciated.
文摘The Yarlung Zangpo Suture Zone(YZSZ) is believed to be composed of material largely derived from the destruction of the Neo-Tethys ocean.We report here geochronological and petrological data obtained for newly discovered alkaline gabbro blocks embedded in a m(?)lange zone of the YZSZ,in Zhongba area, southwestern Tibet.The gabbros are Late Devonian in age and of intra-oceanic Ocean Island Basalt(OIB) affinity.Single-zircon U-Pb analyses from one representative gabbro sample by SIMS(Secondary
文摘Introduction\;A suture zone in an orogenic belt marks the paleo\|plate boundaries with its characteristic ocean floor assemblages. In Himalayas, the best and most spectacular example of the continent\|continent collision orogeny, the suture zone can be traced all along the 2500km long mountain chain and marks the boundary between the Indian and Asian plates. Ladakh region of North\|West Himalaya probably presents the best preserved history of pre\|, syn\|, and post\|collision signatures. It has rocks ranging from Precambrian passive margin sediments to the post collision molasses. The suture zone in Ladakh, referred to as the Indus Suture Zone (ISZ), is characterized by the several occurrences of ophiolitic melange. (M.P. Searle et al, 1987) .Apart from these, various linear belts of the volcanic rocks have been found in the Indus Suture Zone, though their inter relationship is not very clear (K.K.Sharma 1990).
文摘Meso\| and microstructural characteristics of cataclastic fault rocks developed in the Xialu chert are described. The Xialu chert represents pelagic and deep marine sediments (Middle Jurassic—Lower Cretaceous), and occupies the southern marginal part of the E—W trending Yarlung Zangbo suture zone. The apparent total thickness of siliceous deposits exceeds 1km. The current study is concentrated along the two measured sections, Xialu\|E and Xialu\|W. The Xialu\|E section is composed mainly of red chert associated with reddish purple siliceous mudstone and greenish gray mudstone. The beds steeply dip north or south. The 45m section studied is divided into three units (chert unit, chert\|siliceous mudstone unit, and melange unit from north to south). They are in fault contact with each other. In the southern half of the chert unit and the northernmost of the chert\|siliceous mudstone unit, a 15m thick cohesive cataclasite zone can be defined. The cataclasites are composed of chert fragments in a fine grained matrix, and deformed with jigsaw puzzle structures. The chert\|siliceous mudstone unit is made up of four slabs of chert\|siliceous mudstone sequence. Mesoscopic duplex zones in thickness from 1 to 3m are recognized at slab boundaries. Flat and ramp structure and associated P foliations, R1 shears, Y surfaces are developed. Shear spacing range from 1 to 10cm. The slip senses are dextral strike\|slip movement along these duplex zones. The cataclasite zone is cut by the duplex zone along the southern boundary.
文摘The collision between and Indian and Asian plate has not only give rise to some of the highest mountains of the world but also is responsible for the various global phenomena associated with paleoclimate and paleo\|oceanography.Various indirect approaches have been employed in order to constrain the age of initiation of this collision (Beck et al 1995,D.B.Rowley 1996,Dewey 1989).Still it is being quoted anywhere between ca.60 to 40Ma in the literature.The main reason for the poor constraints on the age of the initiation of the collision is unavailability of a direct method to date this.In this paper we present the Ar\|Ar ages of the ophiolites from the Indus Suture,Ladakh and discuss the scope of this approach in constraining the age of the collision more narrowly.1\ Samples and methodology\;Several ophiolitic melange occurrences have been reported belonging to the Indus Suture in the Ladakh sector.These are characterized by the typical oceanic floor assemblages like chert,limestone etc mixed with the peridotites,serpentinites,dolerites,basalts,and pillow lavas (K.K.Sharma 1990).We present here the 40 Ar\| 39 Ar age spectra of two volcanics from the Sumdo Nala section of central Ladakh and one pillow lava from Chiktan,which is about 100km west of the Sumdo Nala.These samples were analysed using Ar\|Ar step heating method following the procedures described by Venketesan et al.1993.
文摘An earthquake of 6.8 magnitude struck the eastern Shan State in Myanmar at 20:29:30 Myanmar Standard Time(01:55:12 PM UTC) on 24 March 2011.It is one of the earthquakes in plate-interior setting.Six after-shocks occurred the same year.The nucleation point of this earthquake was defined by an epicenter at 20 km west of Tarlay(20.705°N,99.949°E) at a depth of 10 km and its magnitude was 6.8.The earthquake damage was disastrous.The geological disasters were linearly distributed along the surface rupture zone.The earthquake produced cracks,arch bend,erupting sand,gush water,etc.in many places.As a result of this strong earthquake,224-305 houses were seriously damaged,74 people were killed,124 injured.The event was named after the nearest village Tarlay and the NE-or ENE-striking Nan Ma fault was responsible for it.A detailed morphotectonic study was carried out in the area using satellite image 1:24,000 scale aerial photographs and 1:63360 scale topographic maps,to correlate the seismicity with tectonics.It is found that there are two prominent lineaments striking in NE-or ENE-and N-S or NNE-SSW direction.The present-day deformation of the Than Lwin suture zone is consistent with roughly NW-SE extension and NE-SW striking compression,but with more conjugate strike-slip faulting and only minor normal faulting.
文摘To extend our successful Magnetotelluric(MT) experiments in the area from Yadong to Bamocuo in 1995 (Chen et al., 1996), two new Magnetotelluric(MT)experiments have been carried out along two main profiles in the central and Northern Tibetan Plateau in the summer of 1998 and 1999. While the 1995 MT work mainly focused on the study of the electrical structure of the Yarlung\|Zangbo River Suture , the 1998 and 1999 experiments have been designed with following purpose:(1) Study whether partially molten layer widely exists in the crust of the central and northern Tibet.(2) Study the electrical structures of crust and upper mantle in central and northern Tibet which may relate to the attenuated Shear Seismic waves.(3) Study the detail electrical structures of Bangong\|Nujiang Suture and Jinsha Suture.In 1998, the MT team (China University of Geosciences, University of Washington and Geological Survey of Canada) recorded MT data along the Tibet 500 Line which extends about three hundred and eighty kilometers from Deqing to Longweicuo. We used LIMS system to record the long period(20～20000s) MT data at twenty\|six sites and used MT24 to record broadband(320Hz,2000s) MT data at fifty\|eight sites.
文摘The Qinghai—Xizang (Tibet) Plateau was assembled by the successive accretion of continental and arc terranes to Asia during the Palaeozoic, Mesozoic and early Tertiary. From north to south, the Plateau was divided into four terranes (from north to south): Songpan\|Garze, Qingtang, Lhasa and India terranes. The Qiangtang terrane was divided into two parts by Chabu\|Shuanghu suture: Northern Qiangtang and Southern Qiangtang blocks. It was believed that there is a suture as Palaeotethyan suture between the two blocks from Lungmu lake to Chabu, to Shuanghu, to Langcangjiang, but some geologists opposited this opinion, such as Wang Chengshan et al.(1987) and Deng Wanming et al.(1996). The blueschists that bear the typical glaucophane were found in the Gangmar Area in summer of 1997. The blueschists consist of glaucophane, crossite, phengite, actinolite, epidote, sphene ,rutile, and so on. Blueschists show nappe structures in enclosing rocks, and thrust over Tertiary from north to south.The age of blueschist is 275～285Ma which stand for the metamorphic age of blueschist. The geochemical contents of blueschists are the following: SiO\-2 is 45 37%～53 82%, Na 2O>K 2O, K 2O+Na 2O are 3 72%～7 61%, Na 2O/K 2O is 1 70～19 67, MnO is 0 16%～0 22%, FeO+Fe 2O 3 are 11 12%～14 27%, TiO 2 is 2 34%～4 28%, P 2O 5 is 0 34%～1 03%. From the contents, SiO 2 is inverse relation with K 2O+Na 2O, K 2O and FeO+Fe 2O 3. In the SiO 2\|K 2O+Na 2O diagram, the blueschists fall in the field of Alkali basalt; in the TiO 2\|MnO(10\|P 2O 5×10 triangular diagram, these plot within the Ocean Island Basalts(OIB) field. The whole REE content is (117 03～390 97)×10 -6 , LREE/HREE is 5 05～9 80, the REE diagram shows the feature that LREE is rich and HREE is depleted, this is similar to the OIB. In the spidergram of trace elements show the same characterristics as the OIB. Meanwhile, the trace elements ratios, such as Ba/Nb, La/Nb, Nb/Th, Nb/Y, Zr/Y, Zr/Nb, Hf/Sm, Ta/Hf, Nb/Ta, Nb/U, suggest the tectonic setting is OIB. On the basis of these materials, the blueschists are akin to within\|plate ocean island basalts. This shows that there is a ocean or oceanic basin in the Chabu\|Shuanghu belts and the formation of blueschists is the quicky subduction of the Ocean Island Basalts in Early Permian between the Gondwana and Eurasia continents. It demonstrated, therefore, that the Chabu\|Suanghu suture exists and may extend to the east to Lnagchangjiang, and may extend into Thailand\|Malaysia Peninsula.
