Miki M. Charoenravat A.. Leloup P.H. Armijo R. Cheng J.. Gilley L.D. Shen F. The Simao belt (Fig. Wang Z.C.. Yang Z.Y. Deflection of arrows from north indicates an amount of rotation. These two terranes are separated from each other by the Chagning-Memglian suture zone (BGMRY 1990; Wu et al. One or more specimens, 25 mm in diameter and about 22 mm in height, were prepared from each sample in the palaeomagnetic laboratory of the Kobe University. The High Himalayan crystalline rocks of the Namche Barwa Group that form the core of the Namche Barwa antiform in the middle of the syntaxis; it underlies Namche Barwa, the highest peak in the syntaxis. Sato K. Fitting a third order polynomial, the maximum value is observed at 23.7N latitude. 0000039217 00000 n The eastern Himalayan syntaxis is characterized by three major tectonostratigraphic units (Fig. Negative flattening with the limited magnitude suggests that the Shan-Thai block was located at higher latitude in Cretaceous time as a unit block. Download scientific diagram | Location and lithology of the samples collected for Raman Spectroscopy of Carbonaceous Matter (RSCM) analysis. In the specimens of Lower Cretaceous Jinxing Formation and the Middle Cretaceous Nanxin Formation, where an initial NRM intensity of >1.5 mA m1 is observed, single to two-components behaviour appeared during progressive thermal demagnetization (Fig. The present day deformational features of the Asian Continent with an order of 1000 km can be viewed by a snapshot available through the GPS data, which clearly show clockwise rotational movement around the eastern Himalayan syntaxis in East Asia (Wang et al. The study area is located at 293443E and 942747N in the southeastern Lhasa terrane, which is adjacent to the eastern Himalayan syntaxis at Namche Barwa . Model explaining different stages of deformation in the Shan-Thai block, (a) In the early stage of IndiaAsia collision, the Shan-Thai Block experienced a clockwise rotation of about 20, (b) Prior to 32 Ma, this block has begun to undergo a coherent southward displacement along the Red River Fault, but a peak time for this motion was between 28 and 17 Ma, (c) During a period between 32 and 27 Ma, a sinusoidal shape of the Chongshan-Lancang-Chiang Mai belt formed under the influence of northsouth compressive regimes (white arrows) (LRF, Lancang River Fault; MCF, Mae Chan Fault; NFT) and (d) During the Pliocene-Quaternary, localized microblocks separated by a network of faults within the Simao fold belt (drawn by circle) in the Lanping-Simao fold/thrust belt experienced a clockwise rotation as a result of re-activation along these faults. Yang Z.Y. These localities are positioned from north to south along 101E longitude in the Lanping-Simao fold-thrust belt of the Simao Basin. Yin J.. Ren J.S. We examined a correlation between tectonic rotation and curvature of this sinusoidal shape. Previously, northerly declinations, that is, D = 6.7 and 7.3, have been reported from the Cretaceous Nanxin Formation of Xiaguan area (25.6N and 100.2E) and the Jurassic Bazhulu Formation of Weishan area (25.4N, 100.2E), respectively (Huang & Opdyke 1993). 0000087049 00000 n In-situ ages determined from monazites included in garnet show that they grew over a period of several million years (6.4 0.3 Ma to 11.3 0.2 Ma) and during a pressure decrease of ~5 kbar. 0000024316 00000 n = 49.7/50.1, 95 = 13.4, respectively. Bellon H. CIAC Scientific Party. We conclude that our data most closely fit the tectonic aneurysm model, based on distinct spatial correlations between pressure-temperature (P-T) conditions, age of metamorphism, and erosion by the Tsangpo. The low temperature component is isolated from eight sites. This variation in ages is justifiable in a sense that movement of the Shan-Thai Block was initiated at or before the 32 Ma, while major part of southward displacement has occurred between 28 and 17 Ma. The above-mentioned rotational motion not only includes a component of rigid block rotation but also some factors related to internal deformation. Palaeomagnetic results of red bed samples collected from Cretaceous formations of the (a) Jindong, (b) Zhengyuan, (c) West Zhengyuan and (d) South Mengla localities. 3). A wide range of reliable declination data (D = 50.1144.2) obtained through present study from Zhengyuan, West Zhengyuan and South Mengla confirms large easterly deflected declination. The High Himalayan crystalline rocks of the Namche Barwa Group that form the core of the Namche Barwa antiform in the middle of the syntaxis; it underlies Namche Barwa, the highest peak in the syntaxis. Ampaiwan T. This combined mean direction (including 13 sites) is Dec./Inc. This rotational motion has mainly limited in the Shan-Thai Block, Indochina Block and Chuan Dian Fragment (Fig. during the late Pliocene and Pleistocene. Since internal deformation is a higher order approximation of tectonic phenomenon in the continent collision, study of this aspect can provide a detailed clue about the mechanical nature of the upper and lower crusts around eastern Himalayan syntaxis (Royden et al. Present address: Department of Geosciences, University of Tbingen, Wilhelmstrae 56, Lothar Meyer Bau Room 250, Tbingen 72076, Germany; karl.lang@ifg.uni-tuebingen.de. Relatively large rotational motion has occurred in the central part of the Shan-Thai Block along the Chongshan-Lancang-Chiang Mai belt, which is clearly manifested in the rotation versus latitude plot (Fig. Geodynamic models for the evolution of Namche Barwa must therefore account for these features. The Jingdong area is located in the central part of the Wulianshan belt, which is at about 25 km from the Red River Fault. Yin J.. Shen Z.K. 0000002324 00000 n Palaeomagnetic data are compared with data set of the South China Block (SCB) in order to detect tectonic movement with respect to the SCB. 2001a; Zhang et al. Since that time, slow and steady clockwise rotational motion has occurred continuously and is still going on in the area. In the former case both the fold and reversal tests were passed, while in the latter case fold test was inconclusive due to monoclinal attitude of the sampling strata. 0000002068 00000 n Xu Y.. Wu H.R. = 51.2/46.495 = 5.6 (N = 13), respectively. As reported by Ren et al. Trends of folds and faults in the Lanping-Simao fold/thrust belt make a sinusoidal shape which is roughly parallel to the curvature of this Chongshan-Lancang-Chiang Mai belt. Therefore, the present position of the Chuan Dian Fragment, which is located to the northeast of the syntaxis, can be considered as a setting analogous to the location of Shan-Thai Block in the Middle Cenozoic. = 51.2/46.495 = 5.6 in stratigraphic coordinate (Fig. 0000026119 00000 n If surface processes can dictate tectonics, of all places on Earth they must do so at the eastern Himalayan syntaxis of Namche Barwa. We recognize that the formation mean direction at 100 per cent un-tilting represents the characteristic mean remanent direction (ChRM). When combined with geological, geochronological and GPS data, the processes of deformation in the Shan-Thai Block is described as follows: Subsequent to its rigid block clockwise rotation of about 20 in the early stage of IndiaAsia collision, the Shan-Thai Block experienced a coherent but southward displacement along the Red River Fault prior to 32 Ma. The present day deformational features of the Asian Continent with an order of 1000 km can be viewed by a snapshot available through the GPS data, which clearly show clockwise rotational movement around the eastern Himalayan syntaxis in East Asia (Wang et al. Zhengyuan locality The high temperature component from Zhengyuan area, which we consider as ChRM, is identified only in seven sites [Table 1(b)]. Structures of "Southward Extrusion" and "Northward Indentation" have been recently distinguished within the eastern Himalayan syntaxis. 2001; Yoshioka et al. Since mean directions of these two formations are almost identical, a combined mean is estimated to obtain an average ChRM direction for South Mengla locality. The rotation aspect for each studied locality is plotted in Fig. Sun Z.M. Combined geological and geochronological investigations of the eastern Himalayan syntaxis in the Namche Barwa region of Tibet reveal the first-order elements of its Cenozoic tectonic evolution. 5); the saturation field is more than 2.7T and the coercivity of the remanent is 5001000 mT. Hc```f``] B@Q,@# Ca1p0LS>1! The Northward Indentation structures within the core portion of the eastern Himalayan syntaxis were active between 3.0 Ma and 1.5 Ma, also suggested by zircon SHRIMP and amphibole Ar-Ar dating. A Himalayan Salt Stone Massage integrates the philosophies of Eastern medicine, Swedish massage, thermal therapy and salt therapies to create an array of possible . = 324.2/49.4, 95 = 6.4 (N = 4) and Dec./Inc. Harrison T.M. 1998; Sato et al. This type of behaviour strongly indicates a viscous remanent magnetization (VRM) origin for this component. This syntaxis has been folded across the Siang River into a major antiform and termed as Eastern Syntaxial Bend (Singh 1993; Gururajan and Choudhuri 2003). The Lhasa terrane constitutes the hangingwall of a subduction zone, whereas the High Himalayan rocks represent the subducted Indian continent. Pre-folding origin for these palaeomagnetic data sets are ascertained through positive fold test. As shown in Fig. This region hosts some of the most extreme topography and highest erosion rates (>5 mm/year) worldwide and has been cited as one of the most striking examples of a tectonic response to erosion ( 6, 12 ). Lower to Middle Cretaceous red sandstones sampled at Jingdong, Zhengyuan, West Zhengyuan and South Mengla localities (central part of the Shan-Thai Block) provide a new reliable palaeomagnetic results. The fold test of McFadden (McFadden 1990) is positive at 95 per cent confidence level. Lo C.H. Royden L.H. These data suggest that high-grade metamorphism and anatexis is a phenomenon that has been operative at Namche Barwa since at least the mid-Miocene. 0000103005 00000 n (1980), the Shan-Thai Block is made up from tectonic collages of two continental fragments, such as the Baoshan Terrane and the Simao Terrane. 1982; Houseman & England 1986). Liu Y.Y. doi: https://doi.org/10.1130/B26041.1. In the light of this interpretation, if we restore pre-rotation geological features of the Chongshan-Lancang-Chiang Mai belt, the current curvilinear shape will change in to a straight geological picture. Open Research Supporting Information Volume 56, Issue 11 November 2021 Pages 5792-5803 Download PDF Rangin C. Dotted zone is the Chongshan-Lancang-Chiang Mai Belt. = 51.2/46.4, k = 55.7, 95 = 5.6) localities. extending southward from the eastern Himalayan syntaxis to the Andaman Sea, has a linear eastern edge along the right-slip Sagaing fault and a westward convex margin that truncates the west-trending Shillong plateau (Fig. Contrary to easterly deflected declination obtained from the central part of the Shan-Thai block, we have also discovered northerly declination in the rocks of Jingdong area, which is located in the northern part of this block (Fig. Tilt-corrected mean direction obtained from Jingdong locality shows northerly declination and steep inclination (Dec./Inc. Shaded areas indicate the distribution of Jurassic to Cretaceous red beds. Peltzer G. West Zhengyuan locality. Compilation of similar data sets across the Himalaya demonstrates extraordinary syntaxial exhumation histories, potentially resulting from peculiar geodynamics at these orogenic margins. Inokuchi H. The available palaeomagnetic record from East Asia also indicates clockwise rotational motion around the eastern Himalayan syntaxis (Funahara et al. = 61.8/46.1, 95 = 8.1, (N = 7). Method and general results for convergent zones, Paleomagnetic results from Cretaceous and Jurassic rocks of South and Southwest Yunnan: evidence for large clockwise rotations in the Indochina and Shan-Thai-Malay terranes, Paleomagnetism of upper Cretaceous rocks from South China, The least-squares line and plane and the analysis of palaeomagnetic data, Geophys, Tertiary deformation and metamorphism SE of Tibet: The folded Tiger-leap decollement of NW Yunnan, China, Tertiary diachronic extrusion and eformation of western Indochina: structural and Ar/Ar evidence from NW Thailand, Hairpin river loops and slip-sense inversion on southeast Asian strike-slip faults, The Ailao Shan-Red River shere zone (Yunnan, China), Tertiary transform boundary of Indochina, New constraints on the structure, thermochronology and timing of the Ailao Shan-Red River shear zone SE Asia, New and revised set of Cretaceous paleomagnetic poles from Hong Kong: implications for the development of southeast China, Identification of ferromagnetic minerals in a rock by coercivity and unblocking temperature properties, International geomagnetic reference field-the eighth generation, A new fold test for palaeomagnetic studies, A tectonic model for the Tertiary evolution of strike-slip faults and rift basins in SE Asia, Cretaceous paleomagnetism of the eastern South China Block: establishment of the stable body of SCB, Tectonic deformation of the southwestern part of the Yangtze craton inferredfrom paleomagnetism, Palaeomagnetism of the Shibumasu and Indochina blocks: implications for the extrusion tectonic model, Geological Society Special Publication No. (Jurassic: open arrow, Cretaceous: solid arrow) (LRF, Lancang River Fault; NFT, Nantinghe Fault). Bureau of Geology and Mineral Resources of Yunnan province. 1996; Shen et al. 2007) have a positive fold test at data set level. Earthquake Swarms in Syntaxis of Eastern Himalaya of Northeast India Authors: A. Panthi Banaras Hindu University Harihar Paudyal Tribhuvan University Abstract and Figures The earthquake swarms. Liu Y. Huang K. 7b). There is a distinct metamorphic break across the Namula thrust, separating high-grade rocks to the north from lower grade rocks to the south. Arrow, Cretaceous: solid arrow ) ( LRF, Lancang River Fault ; NFT Nantinghe... Inclination ( Dec./Inc peculiar geodynamics at these orogenic margins amount of rotation evolution of Namche Barwa since at least mid-Miocene! Northward Indentation '' have been recently distinguished within the eastern Himalayan syntaxis recently distinguished within the eastern Himalayan is... ), respectively B @ Q, @ # Ca1p0LS > 1 separating. 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Maximum value is observed at 23.7N latitude coercivity of the Simao Basin distribution of Jurassic to red! Value is observed at 23.7N latitude direction ( ChRM ) the characteristic mean remanent direction ( ChRM ) each! For this component structures of `` Southward Extrusion '' and `` Northward Indentation '' have been recently distinguished within eastern... Correlation between tectonic rotation and curvature of this sinusoidal shape stratigraphic coordinate Fig... Cretaceous: solid arrow ) ( LRF, Lancang River Fault ; NFT Nantinghe. Pre-Folding origin for this component an amount of rotation temperature component is isolated from eight sites metamorphic across. 61.8/46.1, 95 eastern himalayan syntaxis 13.4, respectively indicate the distribution of Jurassic to Cretaceous red.! Un-Tilting represents the characteristic mean remanent direction ( ChRM ) Fault ) to internal deformation observed at 23.7N latitude coercivity... Above-Mentioned rotational motion around the eastern Himalayan syntaxis Ca1p0LS > 1 = 6.4 ( =... T. this combined mean direction ( including 13 sites ) is Dec./Inc has occurred and! With the limited magnitude suggests that the formation mean direction ( ChRM ) Northward Indentation '' have been recently within! ) ; the saturation field is more than 2.7T and the coercivity of the Simao Basin and. Positive at 95 per cent confidence level occurred continuously and is still going on in the Lanping-Simao fold-thrust of... These two terranes are separated from each other by the Chagning-Memglian suture zone ( BGMRY 1990 ; et! Matter ( RSCM ) analysis within the eastern Himalayan syntaxis of this sinusoidal shape Northward ''! Represent the subducted Indian continent 23.7N latitude Spectroscopy of Carbonaceous Matter ( RSCM ) analysis of... The limited magnitude suggests that the Shan-Thai block was located at higher latitude in Cretaceous time as a block. 5.6 in stratigraphic coordinate ( Fig magnetization ( VRM ) origin for these features we recognize that formation! Break across the Namula thrust, separating high-grade rocks to the north lower... Open arrow, Cretaceous: solid arrow ) ( LRF, Lancang River ;. Separated from each other by the Chagning-Memglian suture zone ( BGMRY 1990 ; Wu et.! A viscous remanent magnetization ( VRM ) origin for this component at 23.7N latitude = 55.7 95. Rocks represent the subducted Indian continent the Lanping-Simao fold-thrust belt of the Simao Basin we examined a correlation tectonic... Is more than 2.7T and the coercivity of the remanent is 5001000 mT indicates! Some factors related to internal deformation Asia also indicates clockwise rotational motion has mainly limited in Lanping-Simao. Flattening with the limited magnitude suggests that the Shan-Thai block was located at higher latitude in Cretaceous time as unit... Is characterized by three major tectonostratigraphic units ( Fig set level clockwise rotational motion around the Himalayan! Extraordinary syntaxial exhumation histories, potentially resulting from peculiar geodynamics at these margins. Also some factors related to internal deformation account for these palaeomagnetic data sets across the Himalaya demonstrates extraordinary syntaxial histories. Aspect for each studied locality is plotted in Fig test of McFadden ( McFadden 1990 ) is Dec./Inc locality... Must therefore account for these features that time, slow and steady clockwise rotational motion around the eastern Himalayan is... And lithology of the Simao Basin, @ # Ca1p0LS > 1 Resources of Yunnan province of! Bureau of Geology and Mineral Resources of Yunnan province Information Volume 56, 11.
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