Our study area covered the Eastern Himalayan Syntaxis (EHS) and its southern extension (Hengduan Mountain or western Sichuan and Yunnan (WSY)) which is located at the orthogonal and oblique collisional front between I...Our study area covered the Eastern Himalayan Syntaxis (EHS) and its southern extension (Hengduan Mountain or western Sichuan and Yunnan (WSY)) which is located at the orthogonal and oblique collisional front between Indian and Asian continents during Cenozoic.Based on geometric and kinematic mapping of the major boundary or regional faults (Dongjug—Mainling(1), Anigiao(2) and Jali(3), Guyu(4) faults in EHS, Ailaoshan—Red River(5), Lancangjiang(6), Gaoligong(7), Binlangjiang(8) and Magok(9) faults in WSY) (see Fig.1), especially on abundant geochronological dating of the mylonitic rocks along these faults, and coupled with magmato\|metamorphic sequences of this region, we try to deal with the temporal and spatial relationships of collisional process to answer questions such as: (1) when did collision start ? (2) is thrusting as a initial and dominant deformation mode to absorb the crustal shortening after suturing, or earlier thrusting usually followed by large\|scale strike\|slip faults? (3) are the two structural patterns coeval at times, or do they occur alternatively during deformation history? (4) are the collisional and associate uplift processes a continuous one or periodic? Insight into such questions is crucial for better understanding of the continental deformation and testing the models available or constraining a new one.展开更多
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
We present a preliminary result of the study carried out in the northern and southern sections of the Taplejung Window and the frontal part of the thrust sheet near The study area comprises of three tectonic units: (1...We present a preliminary result of the study carried out in the northern and southern sections of the Taplejung Window and the frontal part of the thrust sheet near The study area comprises of three tectonic units: (1) The Lesser Himalayan (LH) Unit exposed in the Taplejung Window (Fig. 1a, 1b, Upreti and Le Fort, 1999), (2) The thrust sheet consisting of the Higher Himalayan Crystallines (HHC) and forming the hanging wall of the Main Central Thrust (MCT) exposed around the window, and which has traveled far south reaching very close to the MBT (Fig.1c), and (3) The Lesser Himalayan Unit sandwiched between the MBT and the southern extension of the MCT (Fig.1c).The LH Unit of the window and the sandwiched southern part consist mainly of phyllites, schists, quartzites, gneisses and augen gneiss of granitic origin with minor association of amphibolites, marbles (Fig. 1a, 1c). An foliated granitic rock is found within the phyllites and schists near the Kabeli bridge within the window. The HHC consists mainly of the garnet, kyanite, sillimanite bearing banded gneisses interbedded with quartzites with incipient traces of mobilization. Detailed petrography of all these rocks are described.展开更多
文摘Our study area covered the Eastern Himalayan Syntaxis (EHS) and its southern extension (Hengduan Mountain or western Sichuan and Yunnan (WSY)) which is located at the orthogonal and oblique collisional front between Indian and Asian continents during Cenozoic.Based on geometric and kinematic mapping of the major boundary or regional faults (Dongjug—Mainling(1), Anigiao(2) and Jali(3), Guyu(4) faults in EHS, Ailaoshan—Red River(5), Lancangjiang(6), Gaoligong(7), Binlangjiang(8) and Magok(9) faults in WSY) (see Fig.1), especially on abundant geochronological dating of the mylonitic rocks along these faults, and coupled with magmato\|metamorphic sequences of this region, we try to deal with the temporal and spatial relationships of collisional process to answer questions such as: (1) when did collision start ? (2) is thrusting as a initial and dominant deformation mode to absorb the crustal shortening after suturing, or earlier thrusting usually followed by large\|scale strike\|slip faults? (3) are the two structural patterns coeval at times, or do they occur alternatively during deformation history? (4) are the collisional and associate uplift processes a continuous one or periodic? Insight into such questions is crucial for better understanding of the continental deformation and testing the models available or constraining a new one.
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We present a preliminary result of the study carried out in the northern and southern sections of the Taplejung Window and the frontal part of the thrust sheet near The study area comprises of three tectonic units: (1) The Lesser Himalayan (LH) Unit exposed in the Taplejung Window (Fig. 1a, 1b, Upreti and Le Fort, 1999), (2) The thrust sheet consisting of the Higher Himalayan Crystallines (HHC) and forming the hanging wall of the Main Central Thrust (MCT) exposed around the window, and which has traveled far south reaching very close to the MBT (Fig.1c), and (3) The Lesser Himalayan Unit sandwiched between the MBT and the southern extension of the MCT (Fig.1c).The LH Unit of the window and the sandwiched southern part consist mainly of phyllites, schists, quartzites, gneisses and augen gneiss of granitic origin with minor association of amphibolites, marbles (Fig. 1a, 1c). An foliated granitic rock is found within the phyllites and schists near the Kabeli bridge within the window. The HHC consists mainly of the garnet, kyanite, sillimanite bearing banded gneisses interbedded with quartzites with incipient traces of mobilization. Detailed petrography of all these rocks are described.
