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
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
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
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
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
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 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
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
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 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.
