Petrology and Petrographic Delineation of Kamlial Formation Sandstone Mong and Thorar Village, Northern Pakistan

The origin of sandstone in the Rawalpindi group is disputed because of the lesser Himalayas complicated geological structure and ongoing tectonic activity. The goal of the study is to learn more about the petrographic and geological aspects of the Siwalik molasses deposits, which are formations that belong to the same age group. The Early Miocene Kamlial Formation, the Middle to Late Miocene Chinji Formation, and the Late Miocene Nagri Formation are the stratigraphic units revealed in the project area. The texture of the sandstone found in the Rawalpindi Group and Siwalik is fine to medium-grained. The hue ranges from grey to greenish grey. The sandstone displays thin to medium-bedded layers and exhibits thin lamination throughout. The sandstone of the Kamlial Formation contains load casts, potholes, worm burrows, hematite layers, and filled and unfilled mud cracks in basic structures. Model petrographic research reveals that the Murree Formation primarily consists of light minerals like feldspar, quartzite, and felice, whereas the Kamlial Formation is composed of heavy minerals like garnet and tourmaline. Sandstone from the Rawalpindi group undergoes analysis to ascertain its provenance using the quartz feldspar lithic fragments ternary diagram technique. Each plot in the QFL diagram’s recycled orogeny provenance field is plotted.

Structural and Chronological Evidence for the India-Eurasia Collision of the Early Paleocene in the Eastern Himalayan Syntaxis, Namjagbarwa

The eastern Himalayan syntaxis in Namjagbarwa is a high-grade metamorphicterrain formed by the India-Eurasia collision and northward indentation of the Indian continent intoAsia. Right- and left-lateral slip zones were formed by the indentation on the eastern and westernboundaries of the syntaxis respectively. The Dongjug-Mainling fault zone is the main shear zone onthe western boundary. This fault zone is a left-lateral slip belt with a large component ofthrusting. The kinematics of the fault is consistent with the shortening within the syntaxis, andthe slipping history along it represents the indenting process of the syntaxis. The Ar-Archronological study shows that the age of the early deformation in the Dongjug-Mainling fault zoneranges from 62 to 59 Ma. This evidences that the India-Eurasia collision occurred in the earlyPaleocene in the eastern Himalayan syntaxis.

DEFORMATION OF THE EASTERN HIMALAYAN SYNTAXIS: EVIDENCES FROM STRUCTURES AND KINEMATICS OF ITS WESTERN BOUNDARY

The western boundary of the Eastern Himalayan Syntaxis (EHS) is a deformation belt up to 30km wide (Fig.1). Trending ca. N35°E, it separates the Gangdise magmatic belt in the west from the gneiss of EHS in the east. Its rock association, mica\|schist, quartzite, marble, and amphibolite, can be traced to the south to Gangdise belt and they were probably metamorphosed from the sediments along Yarlung Zangbo. This belt consists of several intensive deformation zones, the largest one of which is along the belt’s western margin from Dongjug to Mainling and we called this ca. 10km wide shear zone as the Dongjug\|Mainling shear zone (DMSZ).DMSZ experienced earlier ductile shear and later ductile\|brittle normal faulting. The earlier deformation produced mylonitic rocks. Their foliation trends N30°～40°E and dips northwest with the angle ranging from 55°to 80°, steepening northeastward. The penetrative kinematic lineation in the rocks has a varying attitude along the trend of DMSZ. It dips southwest with an angle of ca.35° in the southwest near Mainling, whereas dips northeast in the northeast. Moreover, the northeast dipping lineation steepens northeastwards, e.g., its angle ranges form 30° to 45° in the segment from Serkyim La to Dongjug but becomes 60～70° in the northeast most in another zone near Parlung. Kinematic indicators show that the motion of DMSZ had a left\|lateral slipping component, but the vertical motion components were different in the southwest from the northeast. From Serkyim La to the northeast, DMSZ had a kinematics of NW plate (Gangdise belt) thrusting over the SE plate (EHS) and its thrusting component increased toward northeast. However, the DMSZ has a vertical motion with the SE plate (EHS) as the uplifting plate.

Earthquake swarms near eastern Himalayan Syntaxis along Jiali Fault in Tibet:A seismotectonic appraisal

The seismotectonic characteristics of ten repeated earthquake swarm sequence within a seismic cluster along Jiali Fault in eastern Himalayan Syntaxis(EHS) have been analysed.The swarms are spatially disposed in and around Yigong Lake(a natural lake formed by blocking of Yigong River by landslide) and are characterized by low magnitude,crustal events with low to moderate b values.Ms:mb discriminant functions though indicate anomalous nature of the earthquakes within swarm but are considered as natural events that occurred under condition of high apparent stress and stress gradients.Composite fault plane solutions of selected swarms indicate strike-slip sense of shear on fault planes;solution parameters show low plunging compression and tensional axes along NW-SE and NE-SW respectively with causative fault plane oriented ENE-WSW.dipping steeply towards south or north.The fault plane is in excellent agreement with the disposition and tectonic movement registered by right lateral Jiali Fault.The process of pore pressure perturbation and resultant ’r—t plot’ with modelled diffusivity(D = 0.12 m^2/s) relates the diffusion of pore pressure to seismic sequence in a fractured poro-elastic fluid saturated medium at average crustal depth of 15-20 km.The low diffusivity depicts a highly fractured interconnected medium that is generated due to high stress activity near the eastern syntaxial bent of Himalaya.It is proposed that hydro fracturing with respect to periodic pore pressure variations is responsible for generation of swarms in the region.The fluid pressure generated due to shearing and infiltrations of surface water within dilated seismogenic fault(Jiali Fault) are causative factors.

Estimation of Seismic Landslide Hazard in the Eastern Himalayan Syntaxis Region of Tibetan Plateau

The eastern Himalayan syntaxis is one of the most tectonically active and earthquake-prone regions on Earth where earthquake-induced geological disasters occur frequently and caused great damages. With the planning and construction of Sichuan-Tibet highway, Sichuan-Tibet railway and hydropower development on the Yarlung Zangbo River etc. in recent years, it is very important to evaluate the seismic landslide hazard of this region. In this paper, a seismic landslide hazard map is produced based on seismic geological background analysis and field investigation using Newmark method with 10% PGA exceedance probabilities in future 50 years by considering the influence of river erosion, active faults and seismic amplification for the first time. The results show that the areas prone to seismic landslides are distributed on steep slopes along the drainages and the glacier horns as well as ridges on the mountains. The seismic landslide hazard map produced in this study not only predicts the most prone seismic landslide areas in the future 50 years but also provides a reference for mitigation strategies to reduce the exposure of the new building and planning projects to seismic landslides.

Tectonic Imprints of the Hazara Kashmir Syntaxis on the Mesozoic Rocks Exposed in Munda, Mohmand Agency, Northwest Pakistan

Two well-developed mesoscopic folds, D_2 and D_3, which postdate the middle amphibolite metamorphism, were recognized in the western hinterland zone of Pakistan. NW–SE trending D_2 folds developed during NE–SW horizontal bulk shortening followed by NE–SW trending D_3 folds, which developed during SE–NW shortening. Micro- to mesoscopically the NW–SE trending S2 crenulation cleavage, boudins and mineral stretching lineations are overprinted by D_3. The newly established NW–SE trending micro- to mesoscopic structures in Munda termed D_2, which postdated F_1/F_2, is synchronously developed with F3 structures in the western hinterland zone of Pakistan. We interpret that D2 and D3 folds are counterclockwise rotated in the tectonic event that has evolved the Hazara Kashmir Syntaxis after the main phase Indian plate and Kohistan Island Arc collision. Chlorite replacement by biotite in the main matrix crenulation cleavages indicates prograde metamorphism related with D2. The inclusion of muscovite and biotite in garnet porphyroblasts and the presence of staurolite in these rocks indicate that the Barrovian metamorphic conditions predate D2 and D3. We interpret that garnet, staurolite and calcite porphyroblasts grew before D2 because the well developed S2 crenulation cleavage wraps around these porphyroblasts.

SYNCONVERGENT, DUCTILE N-DIRECTED SHEARING ON THE WESTERN MARGIN OF THE NANGA PARBAT SYNTAXIS, N. PAKISTAN

A key issue in orogenic research today is the recognition and explanation of normal faulting in the heart of collisional mountain belts. The active Himalayan system remains an ideal locality for studying this phenomenon, both as E—W synconvergent extension of the Tibetan plateau and normal motion on the South Tibetan Detachment System (STDS). However, these processes are difficult to correlate with the evolution of the northwest Himalaya, particularly the Nanga Parbat syntaxis where a Neogene tectono\|thermal overprint partially obscures the early collisional history. An integrated programme of structural mapping, petrography, thermobarometry and isotopic dating is presented that places important constraints on both the early\| and pre\|Himalayan evolution of the syntaxis. These data include evidence for synconvergent, ductile extension predating syntaxis development, and improved isotopic correlation of the tectonic units with the familiar central Himalayan thrust sheets, building on the work of Whittington et al (1999).Recent studies have focused on the rapid exhumation of the Nanga Parbat\|Haramosh Massif (NPHM) during the last 10Ma, and the related Neogene thermal effects dominating the core of the massif (e.g. Zeitler et al. 1982, 1993). However, the degree of both structural and metamorphic Neogene overprinting varies within the massif, becoming weaker away from the summit region. In addition, the considerable variation in rock\|type outside the gneissic core results in both strain partitioning and various degrees of metamorphic reworking. Thus several workers (e.g. Wheeler et al. 1995) could reconstruct elements of the early and pre\|Himalayan history from field relations and mineral assemblages virtually untouched by Neogene processes. The eastern margin of the massif, in contrast to the active western margin, has remained largely unchanged during the Neogene, except for essentially passive rotation on the limb of the major syntaxial antiform. The original, ductile Main Mantle Thrust (MMT), which emplaced the Ladakh Island Arc (LIA) over the Indian margin in the late Cretaceous, is preserved in a steepened orientation. Dextral shear sense indicators in this steep fabric can be clearly related to southward thrusting on the MMT at peak metamorphic conditions during the early Himalayan stage (600～700°C and 900～1200MPa) once the N—S trending syntaxial antiform is unfolded.

GEOTECTONIC OF NAMCHE BARWA SYNTAXIS IN EAST TIBET, CHINA

Eastern Himalayan Syntaxis consists of Namche Barwa and Assam syntaxis. Namche Barwa, located at south east edge Tibet plateau, is the least\|known place for geologist, because there are thick trees and more rains as well as difficult traffic condition, but Namche Barwa syntaxis is very important to Himalayan and Tibet plateau research. A Big Bend of Yalu Tsangpo and the deepest Grand Canyon in the word developed in Namche Barwa region. From core to surrounding Namche Barwa syntaxis may be divided into Himalayan,Yalu Tsangpo as well as Gangdise three tectonic units and three boundary fault zone.The core of syntaxis is Himalayan unit with Zircon U\|Pb age 1312±6Ma which is correlated to High Himalayan unit in central Himalayan, major rocks of core are garnet\|plagioclase gneiss and hornblende\|plagioclase gneiss as well as layered migmatites, some lens or band of high pressure granulite,garnet\|clinopyroxenite(ecologite) and rare marbles also exist in this unit. Research result indicates that rock of core may have experienced poly\|phase metamorphism and deformation, from early granulite or eclogite facies to late amphibole face.

CARBONATITES FROM THE EASTERN HIMALAYAN SYNTAXIS: PETROLOGY AND TECTONIC IMPLICATIONS

Most carbonatites occur in relatively stable, intra\|plate areas but some are found to occur in near to plate margins and may be linked with plate separation (Woolley, 1989). Although many carbonatites have been discovered to occur in the orogenic belts in recent years, most of these rocks are related to post\|orogenic magmatism, that is, the rocks occur in the specially extensional setting. Therefore it is unusual that such magmatic rocks occur in the typical convergent environment. Here we report carbonatites and associated ultramafic and mafic rocks in the core of the eastern Himalayan syntaxis. The eastern Himalayan syntaxis consists of three tectonic units: the Gangdise, the Yarlung Zangbo, and the Himalayan units, each of which is bounded by faults (Liu & Zhong, 1997). The Himalayan unit, the northernmost exposed part of the Indian plate, is divided into two complexes, the amphibolite facies complex in the south and the granulite facies complex in the north. The granulite facies complex in the Himalayan unit have been argued to experience high\|pressure metamorphism and represent materials buried to upper\|mantle depths (Liu & Zhong, 1997). The carbonatites and associated ultramafic and mafic rocks only occur in the granulite facies rocks and are divided into two belts: northern and southern belts.The northern belt extends at least 30km, and is about 20km in width. The southern belt extends several kilometers, and is 3km or so in width. Each belt consists mainly of differently compositional dykes, extending parallel to gneissosity of granulite facies gneiss. Carbonatitic agglomerates are observed in the northern belt. From the center of carbonatite dykes to country rocks, five types of rock are observed: the center parts of carbonatites, the rim parts of carbonatites, ultramafic and mafic rocks, altered rocks and country rocks. The gneissosity of country rock was deformed by intrusion of dykes.

PRELIMINARY STUDY ON THE OPHIOLITIC MELANGE IN THE YALU TSANGPU GRAND CANYON AREA

Since 1980’s Chinese geologists have organized several scientific expeditions with foreign colleagues to enter the Canyon to study its geology and geography.1\ Major petrologic units\;There are three major petrologic units in this region: (1)Namche barwa formation(Pt nj ). It is situated in the center of great bend area ,representing the lower part of Indian plate wedged into Eurasia plate, which is composed of plagioclase gneiss, amphibole\|containing high\|pressure granulite lenses. (2)Gandise formation(Pt gd ).It is exposed in the outside of Namche barwa edge(Pt nj ), and is considered to be the lower part of Eurasia plate which is composed of plagioclase\|gneiss, amphibolite, marble, quartzite, etc., and were intruded by large granite batholiths (γ 2 5 to γ 6). (3)Great bend formation(Mz). It stretches along Yarlung Zangbo river and is constrained between Pt nj and Pt gd . It is composed of metamorphic basic igneous rocks , ultramafic rocks and quartzite. The whole rock assemblage is characterized by ophiolite suite. Nice ophiolitic mélange exposures exist in Pangxin, Jiaresa and between Pailong and Zhaqu.2\ Basic rock assemblage\;The present ophiolitic components are mostly metamorphic rocks after structural movements and metamorphism for long period. (1) Meta\|intermediate rocks. Amphibolite is a dominant component of ophiolitic mélange in this region . Chemical analysis and protolith recognition shows that amphibolite originated from basalt, diabase and gabbro. (2) Ultramafic rocks. This kind of rocks distributes along the northeast edge of the wedge from Pangxin to Jiaresa. Original pyroxene\|olivinite and serpentine exposures have been found . Electronic\|probe and bulk\|rock analysis suggest that original olivinite is strongly MgO\|enriched and can be named magnesian olivinite. (3) Quartzite. It is exposed along the northeast and southeast margin of the wedge forming steep cliffs and high peaks . In some places it consists of pure fine\|grained quartz and may contain muscovite, biotite, plagioclase or epidote grains in different amount, which suggest that quartzite in this area was formed in small sea basin and not deep oceanic environment as traditionally considered for standard ophiolite suite. (4) Marble blocks. Pure white marble blocks have been found near the village of Bayu and Daduka which were surrounded by amphibolite , quartzite (Mz) or plagioclase\|gneiss(Pt nj ).

CENOZOIC COLLISIONAL DEFORMATION AND LITHOSPHERE TECTONIC EVOLUTION OF THE EASTERN HIMALAYAN SYNTAXIS

The Eastern Himalayan Syntaxis (EHS) is one of the strongest deformation area along the Himalayan belt resulted from the collision between Indian plate and the Eurasian plate since 50～60Ma, and has sensitivity tracked and preserved the whole collisional processes. It should depend on the detail geological investigations to establish the deformational accommodate mode, and the uplift history, to elucidate the deep structure and the crust\|mantle interaction of the EHS. The Namjabarwa metamorphic complex indented into the Gangdise arc along the sinistral Pai shear fault and the dextral Aniqiao shear fault on the both sides of the Great Canyon of Yalung Zangbo river since the collision of the NE corner of the Indian plate and the Eurasian Plate at 60～70Ma [1] . The distance between Yarlung Zangbo suture and Bangong—Nujiang suture is shortened more 120km in the EHS area than that of the Lhasa block.

PALEOCENE—MIDDLE EOCENE DEXTRAL STRIKE-SLIP DEFORMATION AND ITS TECTONIC IMPLICATION IN THE WESTERN YUNNAN, CHINA

The Western Yunnan located at the southeast margin of east Himalaya\|Burman syntaxis. A great number of small basins filled with lacustrine developed in the Indochina block during the Paleocene\|middle Eocene. Occurrence of basins as en chelon arrangement suggests that they were formed under tectonic setting of right\|lateral strike\|slip. The north termination of main faults controlling basins deposition and evolution, meet the Red River fault as an acute angle. The Lanping basin, one representative of all basins, is chosen to study its formation mechanism. Facts of rapid lateral phase change, sediment offset from their source and lateral migration of alluvial fan, indicate that the Lanping basin is a strike\|slip basin and its boundary main fault is syndepositional left\|lateral strike\|slip normal fault. Basin formation was controlled by mechanism of strike\|slip and pull\|apart, the Lanping basin belongs to extension strike\|slip basin. The nature of the Lanping basin and infill suggest that the boundary fault controlling basin deposit was formed during right\|lateral strike\|slip deformation of the Red River fault. Whether formation mechanism of single basin or occurrence of basins supported that the Red River fault was a right\|lateral strike\|slip fault during the Paleocene\|middle Eocene.

Field investigations and numerical modeling of a giant landslide in the region of Eastern Himalayan Syntaxis:Jiaobunong landslide

Eastern Himalayan Syntaxis(EHS)is a tectonically active region that undergoes continuous geomorphic changes.Large landslides are predominant in this region.A giant landslide called Jiaobunong landslide on the northwestern flank of the EHS were studied and simulated to investigate the formation mechanism,evolutionary process,and failure mechanism of the landside,so that we could better understand the large complex ancient landslides in this region.Field investigation,geological background analyses,and numerical modeling were conducted to reveal the natural and seismic characteristics,as well as dynamic process of the landslide.The results show that the Jiaobunong landslide was the result of long-term geological and geomorphic evolution.Uplift,river incision,weathering,fault creep,glaciation,and earthquakes play key roles in the formation of landslides.Given the huge landslide volume,strong seismicity of the study area,proximity to an active fault,and the need for extra forces to induce landsliding,the Jiaobunong landslide was triggered by a paleo-earthquake.Using numerical simulation based on the discrete element method,the slope dynamic response of the earthquake as well as the mass movement and accumulation process was reproduced.Simulation results showed that the landslide movement experienced four stages:initiation phase(0-5 s),acceleration phase(5-35 s),deceleration phase(35-95 s),and the compaction and self-stabilization stage(after 95 s).The rock mass was disintegrated and experienced strong collisions during the movement.The dammed lake gradually disappeared because of long-term river incision by the overtopping river water.These processes play a vital role in the evolution of landforms in the region of EHS.

Pressure-temperature Evolution of the Metapelites in the Motuo Area, the Eastern Himalayan Syntaxis

The Motuo area is located in the east of the Eastern Himalayan Syntaxis.There outcrops a sequence of high-grade metamorphic rocks,such as metapelites.Petrology and mineralogy data suggest that these rocks have experienced three stages of metamorphism.The prograde metamorphic mineral assemblages （M1） are mineral inclusions （biotite ＋ plagioclase ＋ quartz ± sillimanite ± Fe-Ti oxides） preserved in garnet porphyroblasts,and the peak metamorphic assemblages （M2） are represented by garnet with the lowest Xsps values and the lowest XFe# ratios and the matrix minerals （plagioclase ＋ quartz ± K-feldspar ＋ biotite ＋ muscovite ＋ kyanite ± siilimanite）,whereas the retrograde assemblages （M3） are composed of biotite ＋ plagioclase ＋ quartz symplectites rimming the garnet porphyroblasts.Thermobarometric computation shows that the metamorphic conditions are 562-714℃ at 7.3-7.4 kbar for the M1 stage,661-800℃ at 9.4-11.6 kbar for the M2 stage,and 579-713℃ at 5.5-6.6 kbar for the M3 stage.These rocks are deciphered to have undergone metamorphism characterized by clockwise P-T paths involving nearly isothermal decompression （ITD） segments,which is inferred to be related to the collision of the India and Eurasia plates.

The migration of the crustal deformation peak area in the eastern Himalayan Syntaxis inferred from present-day crustal deformation and morpho-tectonic markers

The present-day Global Positioning System(GPS)velocity field shows that the Indian Plate is not a complete rigid block,as its northeastern corner has been torn off and clockwise rotating relative to the main part.With the updated GPS velocity data,the Euler vector of the northeastern corner of the Indian Plate relative to the stable main plate is deduced as(89.566±0.06°E,26.131±0.05°N,1.34±0.11°/Myr).The peak area of the present-day crustal deformation is located in the Chayu deformation belt with the compressional dilation strain rate over 160 nanostrain/yr.However,the Namche-Barwa Syntaxis with the massive crustal thickening and intense surface erosion is generally considered to be the previous locus of the strongest compressional stress in the Eastern Himalayan Syntaxis over long geological timescales.Thus,there is a discrepancy between the previous and present-day crustal deformation peak areas.We argue the migration of the crustal deformation peak area with a total distance of about 120 km and ascribe it to the variation of stress conditions caused by northeast India’s clockwise rotation.

A Reappraisal of the 2005 Kashmir Earthquake in the Northwestern Himalaya Syntaxis

The collision of the Indian and Eurasian plates caused a massive surface uplift and formed the Himalayas.Throughout the 2500-km long Himalaya mountain range,significant earthquake hazards have occurred either on the interface between the plates,above the interface at the Himalayan wedge.

The Interrelationship of Micro-Meso and Macroscopic Structures on the Western Limb of the Hazara Kashmir Syntaxis, Pakistan

Detailed micro-meso to macroscopic structural analyses reveal two deformation phases in the western limb of the Hazara-Kashmir Syntaxis（HKS）. Bulk top to NW shearing transformed initially symmetrical NNE-SSW trending meso to macroscopic folds from asymmetric to overturned ones without changing their trend. Sigmoidal en-echelon tension gashes developed during this deformation,that were oblique to bedding parallel worm burrows and bedding planes themselves. Strain analyses of deformed elliptical ooids using the Rf/Ф method constrain the internal strain patterns of the NNE-SSW structures. The principal stretching axis（S3） defined by deformed elliptical ooids is oriented N27°E at right angles to WNW-ESE shortening. The deformed elliptical ooids in sub-vertical bedding vertical planes contain ooids that plunge -70° SE due to NW-directed tectonic transport. Finite strain ratios are1.45（Rxy） parallel to bedding plane and 1.46（Ryz） for the vertical plane. From these 2D strain values, we derive an oblate strain ellipsoidal in 3D using the Flinn and Hsu/Nadai techniques. Strains calculated from deformed elliptical ooids average-18.10% parallel to bedding and-18.47% in the vertical plane.However, a balanced cross-section through the study area indicates a minimum of--28% shortening.Consequently, regional shortening was only partially accommodated by internal deformation.

Active Deformation Measurements at Mishmi Complex of Eastern Himalayan Syntaxis

We focus the geodynamic status of Eastern Himalayan Syntaxis with reference to Tibetan Plateau,Chinaand Burmese Arc using the crustal deformation constraints with GPS observation. We have used the GPS data, surface geomorphic constraints and compared the existing Pn velocity and Anisotropy [1], determined the crustal velocity of Tibetan Block and North andEast Chinablock as 2 - 8 mm/yr and 6 - 11 mm/yr considering the EHS as stable block. The lack of crustal deformation studies in EHS poses a gap in its geodynamic setup. The present attempt is first time in EHS to estimate crustal deformation by GPS. We presented GPS results from 10 stations along with one permanent station covering the EHS 2 - 3 mm/yr with an azimuth of N460. It reveals that the EHS is moving very slow rates, which accommodates the maximum strain (after Great Earthquake of8.7 M, Arunachal China Border 1950). The neotectonic activities are recorded along the major rivers traversing EHS follow the major thrusts and faults.

New occurrence of Ba-REE fluorcarbonate minerals at Bayan Obo,Inner Mongolia,North China,and their mineralogical features

Ba-REE fluorcarbonate minerals from a carbonatite dyke at Bayan Obo, Inner Mongolia, North China, are first reported in this contribution, in which chemical composition, rare earth element (REE) patterns, and intergrowth relationships for these minerals have been investigated. Syntactic intergrowth or syntaxy between cebaite and cordylite, as well as cordylite and huanghoite were observed. This syntactic texture resulted from the variation of chemical composition of crystallizing agents for those minerals that crystallized directly from carbonatite magmas. It is worth noting that REE patterns of the Ba-REE fluorcarbonate minerals in the dyke are similar to those of the corresponding minerals from the ore hosted dolomite marble of the Bayan Obo giant REE-Nb-Fe mineral deposit, which implies their relation in origin.

Structural pattern of eastern Himalayan syntaxis in Namjagbarwa and its formation process

The structural pattern of the eastern Himalayan syntaxis in Namjagbarwa consists of two series of structures with different styles. One series compiles the earlier ductile contractional and lateral-slip deformation system, formed by nearly north-south shortening within the syntaxis, left-lateral and right-lateral slipping along its western and eastern boundaries respectively. They were possibly produced by the indentation of the Indian continent into Asian continent after India-Asia collision. The peak deformation-metamorphic ages in these structures are 62-60 Ma, ～23 Ma and ～13 Ma. The other series is composed of ductile-brittle normal faults distributing concentrically and dipping toward the outsides of Namjagbarwa Peak. They were probably the collapse structures caused by rapid uplift in a later time and the beginning ages for the normal faulting are about 7.3-6.3 Ma.