The Arun mega\|antiform, a large N—S structure transversal to the tectonic trend of the E Nepal Himalaya, is a tectonic window offering a complete section of the Himalayan nappe pile, from the Lesser Himalayan zone t...The Arun mega\|antiform, a large N—S structure transversal to the tectonic trend of the E Nepal Himalaya, is a tectonic window offering a complete section of the Himalayan nappe pile, from the Lesser Himalayan zone to the Tethyan Himalaya. At the northern end of the Arun tectonic window (ATW), the Ama Drime—Nyonno Ri range of south Tibet exposes a section of that portion of the Main Central Thrust (MCT) zone and Lesser Himalayan Crystallines (LHC) which elsewhere in Nepal is concealed below the overlying Higher Himalayan Crystalline (HHC) nappe (Fig. 1). As throughout the Himalaya at the structural level of the MCT, the ATW is characterized by an inverted metamorphic field gradient characterized by a progression from chlorite to sillimanite grade from low to high structural levels of the nappe pile. Metamorphic peak temperatures rise from circa 400℃ in the pelitic and psammitic Precambrian metasediments of the Lesser Himalayan Tumlingtar Unit, to 550～620℃ in the overlying LHC, to over 700℃ in the muscovite\|free Barun Gneiss, the lowermost HHC unit in the Arun valley.展开更多
Lingtse gneiss (LGn) and Higher Himalayan crystallines (HHC) comprise parts of main central thrust (MCT) in the Darjeeling Sikkim Himalaya. Tourmaline bearing gneiss and quartz tourmaline veins are reported in immedia...Lingtse gneiss (LGn) and Higher Himalayan crystallines (HHC) comprise parts of main central thrust (MCT) in the Darjeeling Sikkim Himalaya. Tourmaline bearing gneiss and quartz tourmaline veins are reported in immediate contact with the LGn and some lesser Himalayan rocks in this study. Their importance is inferred via their comparative occurrence, micro-texture and chemistry. Flow of ductile crust was proposed to expose deep crustal rocks in the Himalayas in form of these gneissic rocks. Generation of paragneissic HHC from the protolith like the lesser Himalayan rocks like biotite-muscovite schist was proposed and documented in previous studies. The main central thrust where the principal motion is reported to date at circa 20 Ma appears in the contact regions of the HHC and lesser Himalayan rocks. Whether the tourmaline bearing gneiss or veins is a product during the episode of generation of the Higher Himalayan crystallines, which is taken as a component of the higher Himalayan crystallines episode remains a question as both concordant and discordant tourmaline bearing gneiss and/or quartzo-feldspahic veins appear respectively. The mm-cm scale tourmaline in the occasionally discordant quartz tourmaline veins shows strong zonation and less effects of shearing. Those are strongly zoned indicating magmatic hydrothermal character. The matrix tourmaline shows a separate composition. However, evidences of a less prominent shearing in them might signify rejuvenation. Lower temperature activity and fluid movement in this thrust zone are signified from the microstructure signifying that the high grade main central thrust was probably rejuvenated during or after the veining.展开更多
The Arun Tectonic Window (ATW) and its inverted metamorphic zonation were first described by Bordet (1961) and Hagen (1969) in their regional surveys of the eastern Nepal Himalaya. The ATW is centred on the Arun antif...The Arun Tectonic Window (ATW) and its inverted metamorphic zonation were first described by Bordet (1961) and Hagen (1969) in their regional surveys of the eastern Nepal Himalaya. The ATW is centred on the Arun antiform (“ trans\|anticlinal de l’Arun”, Bordet, 1961), a major late structure, c. 100km long, which strikes north to north\|northeast, transversely to the E—W tectonic trend of the eastern Himalaya from the lower Arun valley to southern Tibet. From south to north, i.e. from the core of the window upwards in the nappe pile, the tectonic units exposed in the ATW are:(1) The Lesser Himalayan Tumlingtar Unit (Nawakot nappes of Hagen,1969), a thick sequence of greenschist\|facies Upper Precambrian metasediments, bounded to the north by a thrust zone (Main Central Thrust 1 of Maruo & Kizaki, 1983; Main Central Thrust Zone of Meyer & Hiltner, 1993). (2) The Lesser Himalayan Crystalline nappe (LHC), comprised of staurolite to kyanite grade micaschists and granitic orthogneiss (Kathmandu Nappes of Hagen,1969), lying on top of the low\|grade metasediments. (3) The Higher Himalayan Crystalline nappe (Tibetan Slab of Bordet, 1977), bounded on both side of the ATW by thrust sheets defining a major syn\|metamorphic thrust (Main Central Thrust of Bordet,1961; Main Central Thrust 2 of Maruo & Kizaki, 1983).In this contribution some results of geological investigations in the hitherto unrecognized northern part of the ATW (Kharta region of the Arun—Phung Chu valley and Ama Drime—Nyonno Ri range), are presented. The Kharta region is 30km east of the Everest—Makalu massif and sits in the western limb of the Arun antiform, whereas the Ama Drime—Nyonno Ri Range, to the east of Kharta, is right in the core of the Arun antiform. Here the ATW exposes a section of deep tectonic levels of the Lesser Himalayan Crystalline nappe and MCT zone which elsewhere in the Nepal Himalaya are concealed below the overlying Higher Himalayan Crystalline nappe.展开更多
Rishi Khola,a sub-watershed of Teesta river,traverses along the Main Central Thrust(MCT)with a multitude of litho units and structural entities.This study examines the impact of tectonic and lithologic controls in con...Rishi Khola,a sub-watershed of Teesta river,traverses along the Main Central Thrust(MCT)with a multitude of litho units and structural entities.This study examines the impact of tectonic and lithologic controls in configuring the catchment characteristics of Rishi Khola,Sikkim,India.Corrected SRTM 30m DEM and Landsat 8 satellite image have been used for extracting the river network,preparing the sub-catchments,the longitudinal profile and thereby calculating the morphotectonic indices.An aggregated tectonic index(ATI)has been prepared to map the intensity of tectonic perturbations in the fluvial environment using the entropy weightage method(EWM)and Weighted Linear Combination(WLC).The undulating nature of the longitudinal profile with prominent knick points confirms the presence of tectonic disturbances and lithological variations.From all the computed morphotectonic indices and the ATI,it has been evident that the region has experienced surface deformations.When viewed at the entire catchment,the morphotectonic indices suggest ample responses to the tectonic perturbations due to the dominance of lithology-controlled hill slope processes and fluvial erosion.The spatiality of the tectonic sensitiveness is rather concentrated into certain pockets of differential stress field formed due to fault thrusting of the Himalayas.The study chiefly focuses on the peculiarity of the watershed which displays a complex response of tectonic and rock structure;wherein the proposed methodology has been successful in excavating such complex responses around the Himalayan thrusts.展开更多
In the central Himalaya,the Greater and Lesser Himalayan tectonostratigraphic zones can be distinguished from each other by combining detrital zircon U-Pb ages and whole-rock Nd isotopic data.In the Hazara-Kashmir syn...In the central Himalaya,the Greater and Lesser Himalayan tectonostratigraphic zones can be distinguished from each other by combining detrital zircon U-Pb ages and whole-rock Nd isotopic data.In the Hazara-Kashmir syntaxis of northern Pakistan,rock units in the Kaghan valley have been variously assigned to the Tethyan,Greater,and Lesser Himalayan zones.To determine which tectonostratigraphic zones are represented,we sampled across the Batal thrust in the northern Kaghan valley because this structure is identified in some research as the Main Central thrust.Samples from the footwall yield Paleo-to Mesoproterozoic maximum depositional ages(-1.8-1.1 Ga)and an averageεNd(0)value of-14.3.Samples from the hanging wall yield Neoproterozoic maximum depositional ages(~1000-600 Ma)andεNd(0)values of-17.3.The contrasting detrital zircon ages show that the Batal thrust in the Kaghan valley is a major structural division.However,these data lack the characteristic detrital zircon age spectra andεNd(0)values of Greater and Lesser Himalayan rocks north and south of the Main Central thrust in the central Himalaya,respectively.Therefore,either the Batal thrust is not the Main Central thrust,or the Main Central thrust in the Kaghan valley cuts a different structural level and carries rock units not seen outside the Hazara-Kashmir syntaxis.展开更多
基于融合的GPS速度场结果,使用DEFNODE负位错反演程序估算了喜马拉雅主逆冲断层(the main Himalayan thrust,MHT)的闭锁程度和滑动亏损空间分布,并结合剖面结果分析了断层远、近场的运动特征。结果表明,MHT的闭锁深度基本达到18~24km,...基于融合的GPS速度场结果,使用DEFNODE负位错反演程序估算了喜马拉雅主逆冲断层(the main Himalayan thrust,MHT)的闭锁程度和滑动亏损空间分布,并结合剖面结果分析了断层远、近场的运动特征。结果表明,MHT的闭锁深度基本达到18~24km,断层面闭锁宽度达到102~136km,两次历史大地震破裂区域之间的未破裂段落和未发生大地震的段落闭锁深度更深,闭锁断层面更宽,2015年尼泊尔Mw7.8大地震就发生在两次大地震破裂区域之间的段落;MHT总滑动亏损速率和垂直断层挤压滑动亏损速率自东向西逐渐减小,平行断层右旋滑动亏损速率则基本上自东向西逐渐增加;MHT 3条剖面拟合结果也反映出其存在很强的闭锁。根据估算的此次Mw7.8地震的复发周期230年和最近500多年发生的大地震分布,认为MHT整条段落尤其是尼泊尔西部与印度接壤处和可能还没有破裂的不丹地区依然有发生8级大地震的危险。展开更多
文摘The Arun mega\|antiform, a large N—S structure transversal to the tectonic trend of the E Nepal Himalaya, is a tectonic window offering a complete section of the Himalayan nappe pile, from the Lesser Himalayan zone to the Tethyan Himalaya. At the northern end of the Arun tectonic window (ATW), the Ama Drime—Nyonno Ri range of south Tibet exposes a section of that portion of the Main Central Thrust (MCT) zone and Lesser Himalayan Crystallines (LHC) which elsewhere in Nepal is concealed below the overlying Higher Himalayan Crystalline (HHC) nappe (Fig. 1). As throughout the Himalaya at the structural level of the MCT, the ATW is characterized by an inverted metamorphic field gradient characterized by a progression from chlorite to sillimanite grade from low to high structural levels of the nappe pile. Metamorphic peak temperatures rise from circa 400℃ in the pelitic and psammitic Precambrian metasediments of the Lesser Himalayan Tumlingtar Unit, to 550～620℃ in the overlying LHC, to over 700℃ in the muscovite\|free Barun Gneiss, the lowermost HHC unit in the Arun valley.
文摘Lingtse gneiss (LGn) and Higher Himalayan crystallines (HHC) comprise parts of main central thrust (MCT) in the Darjeeling Sikkim Himalaya. Tourmaline bearing gneiss and quartz tourmaline veins are reported in immediate contact with the LGn and some lesser Himalayan rocks in this study. Their importance is inferred via their comparative occurrence, micro-texture and chemistry. Flow of ductile crust was proposed to expose deep crustal rocks in the Himalayas in form of these gneissic rocks. Generation of paragneissic HHC from the protolith like the lesser Himalayan rocks like biotite-muscovite schist was proposed and documented in previous studies. The main central thrust where the principal motion is reported to date at circa 20 Ma appears in the contact regions of the HHC and lesser Himalayan rocks. Whether the tourmaline bearing gneiss or veins is a product during the episode of generation of the Higher Himalayan crystallines, which is taken as a component of the higher Himalayan crystallines episode remains a question as both concordant and discordant tourmaline bearing gneiss and/or quartzo-feldspahic veins appear respectively. The mm-cm scale tourmaline in the occasionally discordant quartz tourmaline veins shows strong zonation and less effects of shearing. Those are strongly zoned indicating magmatic hydrothermal character. The matrix tourmaline shows a separate composition. However, evidences of a less prominent shearing in them might signify rejuvenation. Lower temperature activity and fluid movement in this thrust zone are signified from the microstructure signifying that the high grade main central thrust was probably rejuvenated during or after the veining.
文摘The Arun Tectonic Window (ATW) and its inverted metamorphic zonation were first described by Bordet (1961) and Hagen (1969) in their regional surveys of the eastern Nepal Himalaya. The ATW is centred on the Arun antiform (“ trans\|anticlinal de l’Arun”, Bordet, 1961), a major late structure, c. 100km long, which strikes north to north\|northeast, transversely to the E—W tectonic trend of the eastern Himalaya from the lower Arun valley to southern Tibet. From south to north, i.e. from the core of the window upwards in the nappe pile, the tectonic units exposed in the ATW are:(1) The Lesser Himalayan Tumlingtar Unit (Nawakot nappes of Hagen,1969), a thick sequence of greenschist\|facies Upper Precambrian metasediments, bounded to the north by a thrust zone (Main Central Thrust 1 of Maruo & Kizaki, 1983; Main Central Thrust Zone of Meyer & Hiltner, 1993). (2) The Lesser Himalayan Crystalline nappe (LHC), comprised of staurolite to kyanite grade micaschists and granitic orthogneiss (Kathmandu Nappes of Hagen,1969), lying on top of the low\|grade metasediments. (3) The Higher Himalayan Crystalline nappe (Tibetan Slab of Bordet, 1977), bounded on both side of the ATW by thrust sheets defining a major syn\|metamorphic thrust (Main Central Thrust of Bordet,1961; Main Central Thrust 2 of Maruo & Kizaki, 1983).In this contribution some results of geological investigations in the hitherto unrecognized northern part of the ATW (Kharta region of the Arun—Phung Chu valley and Ama Drime—Nyonno Ri range), are presented. The Kharta region is 30km east of the Everest—Makalu massif and sits in the western limb of the Arun antiform, whereas the Ama Drime—Nyonno Ri Range, to the east of Kharta, is right in the core of the Arun antiform. Here the ATW exposes a section of deep tectonic levels of the Lesser Himalayan Crystalline nappe and MCT zone which elsewhere in the Nepal Himalaya are concealed below the overlying Higher Himalayan Crystalline nappe.
文摘Rishi Khola,a sub-watershed of Teesta river,traverses along the Main Central Thrust(MCT)with a multitude of litho units and structural entities.This study examines the impact of tectonic and lithologic controls in configuring the catchment characteristics of Rishi Khola,Sikkim,India.Corrected SRTM 30m DEM and Landsat 8 satellite image have been used for extracting the river network,preparing the sub-catchments,the longitudinal profile and thereby calculating the morphotectonic indices.An aggregated tectonic index(ATI)has been prepared to map the intensity of tectonic perturbations in the fluvial environment using the entropy weightage method(EWM)and Weighted Linear Combination(WLC).The undulating nature of the longitudinal profile with prominent knick points confirms the presence of tectonic disturbances and lithological variations.From all the computed morphotectonic indices and the ATI,it has been evident that the region has experienced surface deformations.When viewed at the entire catchment,the morphotectonic indices suggest ample responses to the tectonic perturbations due to the dominance of lithology-controlled hill slope processes and fluvial erosion.The spatiality of the tectonic sensitiveness is rather concentrated into certain pockets of differential stress field formed due to fault thrusting of the Himalayas.The study chiefly focuses on the peculiarity of the watershed which displays a complex response of tectonic and rock structure;wherein the proposed methodology has been successful in excavating such complex responses around the Himalayan thrusts.
基金This work was made possible by funding support from National Academy of Sciences Prime Cooperative Agreement No.AID-391-A-17-00001 to Dr.RobinsonPakistan-U.S.Science and Technology Cooperation Program Phase-VII No.HEC/R&D/PAK-US/2017/360 to Dr.Faisal+1 种基金Additional funding was provided by Graduate Student Research Grant 13308-21 from the Geological Society of America to Joel SchifferLogistical support in the field was provided by faculty and students at the National Centre of Excellence in Geology,University of Peshawar,Pakistan.Mineral separations,sample preparation,and analytical services were carried out with the help of GeoSep Services,the Arizona LaserChron Center,and students at the RadIs Laboratory,University of Alabama.
文摘In the central Himalaya,the Greater and Lesser Himalayan tectonostratigraphic zones can be distinguished from each other by combining detrital zircon U-Pb ages and whole-rock Nd isotopic data.In the Hazara-Kashmir syntaxis of northern Pakistan,rock units in the Kaghan valley have been variously assigned to the Tethyan,Greater,and Lesser Himalayan zones.To determine which tectonostratigraphic zones are represented,we sampled across the Batal thrust in the northern Kaghan valley because this structure is identified in some research as the Main Central thrust.Samples from the footwall yield Paleo-to Mesoproterozoic maximum depositional ages(-1.8-1.1 Ga)and an averageεNd(0)value of-14.3.Samples from the hanging wall yield Neoproterozoic maximum depositional ages(~1000-600 Ma)andεNd(0)values of-17.3.The contrasting detrital zircon ages show that the Batal thrust in the Kaghan valley is a major structural division.However,these data lack the characteristic detrital zircon age spectra andεNd(0)values of Greater and Lesser Himalayan rocks north and south of the Main Central thrust in the central Himalaya,respectively.Therefore,either the Batal thrust is not the Main Central thrust,or the Main Central thrust in the Kaghan valley cuts a different structural level and carries rock units not seen outside the Hazara-Kashmir syntaxis.
文摘基于融合的GPS速度场结果,使用DEFNODE负位错反演程序估算了喜马拉雅主逆冲断层(the main Himalayan thrust,MHT)的闭锁程度和滑动亏损空间分布,并结合剖面结果分析了断层远、近场的运动特征。结果表明,MHT的闭锁深度基本达到18~24km,断层面闭锁宽度达到102~136km,两次历史大地震破裂区域之间的未破裂段落和未发生大地震的段落闭锁深度更深,闭锁断层面更宽,2015年尼泊尔Mw7.8大地震就发生在两次大地震破裂区域之间的段落;MHT总滑动亏损速率和垂直断层挤压滑动亏损速率自东向西逐渐减小,平行断层右旋滑动亏损速率则基本上自东向西逐渐增加;MHT 3条剖面拟合结果也反映出其存在很强的闭锁。根据估算的此次Mw7.8地震的复发周期230年和最近500多年发生的大地震分布,认为MHT整条段落尤其是尼泊尔西部与印度接壤处和可能还没有破裂的不丹地区依然有发生8级大地震的危险。
