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1.
Despite similar geological and tectonic setting along the Himalayan orogen, distinct thermochronological/exhumational and seismicity variability exists between the Kumaun and the Garhwal regions of the NW‐ Himalaya. The processes responsible for such variability are still debated. To understand this, published thermochronological ages from several traverses across the Higher Himalayan Crystalline (HHC) and Lesser Himalayan Crystalline (LHC) have been correlated with the seismicity pattern in both Garhwal and Kumaun segments. The seismicity pattern coincides with the zone of rapid uplift and exhumation. The profiles of seismicity across the Kumaun and the Garhwal regions agree with the existence of the Main Himalayan Thrust (MHT) underlying the regions and reflect its geometry and architecture. Slip along the MHT is responsible for occurrence of seismicity on decade time‐scale and exhumation pattern on Myr time‐scale of the Himalaya.  相似文献   

2.
The series of four different, steeply inclined thrusts which sharply sever the youthful autochthonous Cenozoic sedimentary zone, including the Siwalik, from the mature old Lesser Himalayan subprovince is collectively known as the Main Boundary Thrust (MBT). In the proximity of this trust in northwestern and eastern sectors, the parautochtonous Lesser Himalayan sedimentary formations are pushed up and their narrow frontal parts split into imbricate sheets with attendant repetition and inversion of lithostratigraphic units. The superficially steeper thrust plane seems to flatten out at depth. The MBT is tectonically and seismically very active at the present time.The Main Central Thrust (MCT), inclined 30° to 45° northwards, constitutes the real boundary between the Lesser and Great Himalaya. Marking an abrubt change in the style and orientation of structures and in the grade of metamorphism from lower amphibolitefacies of the Lesser Himalayan to higher metamorphic facies of the Great Himalayan, the redefined Main Central Thrust lies at a higher level as that originally recognized by A. Heim and A. Gansser. They had recognized this thrust as the contact of the mesozonal metamorphics against the underlying sedimentaries or epimetamorphics. It has now been redesignated as the Munsiari Thrust in Kumaun. It extends northwest in Himachal as the Jutogh Thrust and farther in Kashmir as the Panjal Thrust. In the eastern Himalaya the equivalents of the Munsiari Thrust are known as the Paro Thrust and the Bomdila Thrust. The upper thrust surface in Nepal is recognized as the Main Central Thrust by French and Japanese workers. The easterly extension of the MCT is known as the Khumbu Thrust in eastern Nepal, the Darjeeling Thrust in the Darjeeling-Sikkim region, the Thimpu Thrust in Bhutan and the Sela Thrust in western Arunachal. Significantly, hot springs occur in close proximity to this thrust in Kumaun, Nepal and Bhutan. There are reasons to believe that movement is taking place along the MCT, although seismically it is less active than the MBT.  相似文献   

3.
The Lesser Himalaya in central Nepal consists of Precambrian to early Paleozoic, low- to medium-grade metamorphic rocks of the Nawakot Complex, unconformably overlain by the Upper Carboniferous to Lower Miocene Tansen Group. It is divided tectonically into a Parautochthon, two thrust sheets (Thrust sheets I and II), and a wide shear zone (Main Central Thrust zone) from south to north by the Bari Gad–Kali Gandaki Fault, the Phalebas Thrust and the Lower Main Central Thrust, respectively. The Lesser Himalaya is overthrust by the Higher Himalaya along the Upper Main Central Thrust (UMCT). The Lesser Himalaya forms a foreland-propagating duplex structure, each tectonic unit being a horse bounded by imbricate faults. The UMCT and the Main Boundary Thrust are the roof and floor thrusts, respectively. The duplex is cut-off by an out-of-sequence fault. At least five phases of deformation (D1–D5) are recognized in the Lesser Himalaya, two of which (D1 and D2) belong to the pre-Himalayan (pre-Tertiary) orogeny. Petrographic, microprobe and illite crystallinity data show polymetamorphic evolution of the Lesser and Higher Himalayas in central Nepal. The Lesser Himalaya suffered a pre-Himalayan (probably early Paleozoic) anchizonal prograde metamorphism (M0) and a Neohimalayan (syn- to post-UMCT) diagenetic to garnet grade prograde inverted metamorphism (M2). The Higher Himalaya suffered an Eohimalayan (pre or early-UMCT) kyanite-grade prograde metamorphism (M1) which was, in turn, overprinted by Neohimalayan (syn-UMCT) retrograde metamorphism (M2). The isograd inversion from garnet zone in the Lesser Himalaya to kyanite zone in the Higher Himalaya is only apparent due to post-metamorphic thrusting along the UMCT. Both the Lesser and Higher Himalayas have undergone late-stage retrogression (M3) during exhumation.  相似文献   

4.
Along the North Almora Thrust (NAT) in the Kumaun Lesser Himalaya, a zone of mylonitic rocks has developed due to strain localization during the tectonic emplacement of the Almora Nappe over the Lesser Himalayan Sequence. This zone is referred here as the NAT zone (NATZ) that is dissected by faults, which are transverse to the Himalayan orographic trend and are known as seismically active structures. Trending NNW-SSE these are the Chaukhutiya and Raintoli faults. Two E-W oriented subsidiary brittle faults across the Chaukhutiya Fault are also recognized. Based on the field study and magnetic fabric analysis an attempt has been made to evaluate the deformation and kinematic history of northeastern margin of the Almora Nappe superposed by the Chaukhutiya faulting that coincides with northeastern margin of the NAT. Field study reveals brittle-ductile and brittle regimes of deformation along the Chaukhutiya Fault. Away from the NAT variable attitudes (E-W or ENE-WSW with gentle dip) of field foliation and axial planes of folds are observed, whereas at and near the NAT the attitudes of beds, including curved lithounits, are steeply dipping and are oriented parallel with the NNW-SSE trending NAT. Curvature in fold hinge line and discontinuous occurrence of lithounits are observed along the fault.  相似文献   

5.
The crystalline sheet of the Higher Himalaya, referred to as the Central Crystallines, is a continuous lithotectonic unit which can be traced from the River Kali of eastern Kumaun in the east to Sankoo in the Suru River valley of Kashmir in the west. The principal lithostratigraphic units of this zone are pelites, psammites, gneisses, amphibolites, migmatites and leucocratic granites. The rocks of this zone show progressive regional metamorphism of normal as well as reverse types, the metamorphic grade ranging from chlorite to sillimanite zone. The Main Central Thrust, which demarcates the southern boundary of the Central Crystallines, has brought the crystalline rocks to rest over the sediments of Deoban Group in Kumaun and Garhwal and over the Outer Crystallines (=Chail-Jutogh Nappe) in Himachal Pradesh. The evidence obtained from metamorphism, deformation and radiometric dating indicate that the Central Crystallines is an old Precambrian basement which has been reactivated during Caledonian and Alpine orogenic movements.  相似文献   

6.
The continuous process of continent–continent collision between the Indian and the Eurasian plates has led to the formation of the Himalayan range and continuously caused earthquakes in the region. Large earthquakes with magnitudes of 8 and above occur in this region infrequently, releasing the elastic strain accumulated over years around the plate boundary. Geodetic measurements can help estimate the strain distribution along the fault system. These measurements provide information on active deformations and associated potential seismic hazards along the Himalayan arc. In order to understand the present deformation around the plate boundary, we collected GPS data during three campaigns in the years of 2005–2007 at 16 sites in the Kumaun region of the Lesser Himalaya. Horizontal velocity vectors estimated in ITRF2000 are found to be in the range of 41–50 mm/yr with an uncertainty level of the order of 1 mm/yr. The velocity field indicates that the present convergence of around 15 mm/yr takes place in the Kumaun Himalaya. Further, we estimate the strain components in the study area for understanding the currently active tectonic process in the region. The estimated dilatational strain indicates that the northern part near the Main Central Thrust (MCT) is more compressional than the southern part. Maximum shear strain is mostly accommodated in the northern part too. The maximum shear and dilatational strain rates are about 1.0 and 0.5 μstrain/yr. It is seen that the distribution of high shear strain spatially correlates with seismicity. The maximum of extensional and compressional strains due to the force acting along the Main Central Thrust (MCT) in the NW–SE direction are found to be 0.4 and 0.1 μstrain/yr, respectively. The maximum shear strain in the northern part of the Himalaya appears to be associated with the convergence of the region proposed by other geophysical studies.  相似文献   

7.
GEOLOGY OF THE NORTHERN ARUN TECTONIC WINDOW1　BordetP .Recherchesg啨ｏｌｏｇｉｑｕｅｓｄａｎｓｌ’ＨｉｍａｌａｙａｄｕＮ啨ｐａｌ,r啨ｇｉｏｎｄｕＭａｋａｌｕ[R].EditionsduCNRS ,Paris ,196 12 75 . 2　BordetP .G啨ｏｌｏｇｉｅｄｅｌａｄａｌｌｅｄｕＴｉｂｅｔ (Himalayacentral) [J].M啨ｍｏｉｒｅｓｈｏｒｓｓ啨ｒｉｅｄｅｌａＳｏｃｉｅｔ啨ｇ啨ｏｌｏｇｉｑｕｅｄｅＦｒａｎｃｅ,1977,8:2 35～ 2 5 0 . 3　BurcfielBC ,ChenZ ,HodgesKV ,etal.TheSouthTibetanDetachmentSystem ,Hima…  相似文献   

8.
The Main Central Thrust (MCT) and the Main Boundary Thrust (MBT) are the two major thrusts in Kumaun, the MCT forming the boundary between highly sheared, deformed and mylonitized rocks of the Great Himalayan Central Crystallines and the Lesser Himalayan metasedimentaries. While in the Central Crystallines four-folding episodes are observed of which two are of the Precambrian age, the Lesser Himalayan rocks show only two phases of folding. MCT has its own distinctive structural history and the crystalline mass comprises an integral part of peninsular India.  相似文献   

9.
MAIN CENTRAL THRUST ZONE IN THE KATHMANDU AREA, CENTRAL NEPAL, AND ITS TECTONIC SIGNIFICANCE1　AritaK ,LallmeyerRD ,TakasuA .TectonothermalevolutionoftheLesserHimalaya ,Nepal:constraintsfrom 4 0 Ar/3 9AragesfromtheKathmandunappe[J].TheIslandArc ,1997,6 :372～ 384. 2　RaiSM ,GuillotS ,LeFortP ,etal.Pressure temperatureevolutionintheKathmanduandGosainkundregions ,CentralNepal[J].JourAsianEarthSci ,1998,16 :2 83～ 2 98. 3　SchellingD ,KArita .…  相似文献   

10.
Nepal can be divided into the following five east–west trending major tectonic zones. (i) The Terai Tectonic Zone which consists of over one km of Recent alluvium concealing the Churia Group (Siwalik equivalents) and underlying rocks of northern Peninsular India. Recently active southward-propagating thrusts and folds beneath the Terai have affected both the underlying Churia and the younger sediments. (ii) The Churia Zone, which consists of Neogene to Quaternary foreland basin deposits and forms the Himalayan mountain front. The Churia Zone represents the most tectonically active part of the Himalaya. Recent sedimentologic, geochronologic and paleomagnetic studies have yielded a much better understanding of the provenance, paleoenvironment of deposition and the ages of these sediments. The Churia Group was deposited between ∼14 Ma and ∼1 Ma. Sedimentary rocks of the Churia Group form an archive of the final drama of Himalayan uplift. Involvement of the underlying northern Peninsular Indian rocks in the active tectonics of the Churia Zone has also been recognised. Unmetamorphosed Phanerozoic rocks of Peninsular India underlying the Churia Zone that are involved in the Himalayan orogeny may represent a transitional environment between the Peninsula and the Tethyan margin of the continent. (iii) The Lesser Himalayan Zone, in which mainly Precambrian rocks are involved, consists of sedimentary rocks that were deposited on the Indian continental margin and represent the southernmost facies of the Tethyan sea. Panafrican diastrophism interrupted the sedimentation in the Lesser Himalayan Zone during terminal Precambrian time causing a widespread unconformity. That unconformity separates over 12 km of unfossiliferous sedimentary rocks in the Lesser Himalaya from overlying fossiliferous rocks which are >3 km thick and range in age from Permo-Carboniferous to Lower to Middle Eocene. The deposition of the Upper Oligocene–Lower Miocene fluvial Dumri Formation records the emergence of the Himalayan mountains from under the sea. The Dumri represents the earliest foreland basin deposit of the Himalayan orogen in Nepal. Lesser Himalayan rocks are less metamorphosed than the rocks of the overlying Bhimphedis nappes and the crystalline rocks of the Higher Himalayan Zone. A broad anticline in the north and a corresponding syncline in the south along the Mahabharat range, as well as a number of thrusts and faults are the major structures of the Lesser Himalayan Zone which is thrust over the Churia Group along the Main Boundary Thrust (MBT). (iv) The crystalline high-grade metamorphic rocks of the Higher Himalayan Zone form the backbone of the Himalaya and give rise to its formidable high ranges. The Main Central Thrust (MCT) marks the base of this zone. Understanding the origin, timing of movement and associated metamorphism along the MCT holds the key to many questions about the evolution of the Himalaya. For example: the question of whether there is only one or whether there are two MCTs has been a subject of prolonged discussion without any conclusion having been reached. The well-known inverted metamorphism of the Himalaya and the late orogenic magmatism are generally attributed to movement along the MCT that brought a hot slab of High Himalayan Zone rocks over the cold Lesser Himalayan sequence. Harrison and his co-workers, as described in a paper in this volume, have lately proposed a detailed model of how this process operated. The rocks of the Higher Himalayan Zone are generally considered to be Middle Cambrian to Late Proterozoic in age. (v) The Tibetan Tethys Zone is represented by Cambrian to Cretaceous-Eocene fossiliferous sedimentary rocks overlying the crystalline rocks of the Higher Himalaya along the Southern Tibetan Detachment Fault System (STDFS) which is a north dipping normal fault system. The fault has dragged down to the north a huge pile of the Tethyan sedimentary rocks forming some of the largest folds on the Earth. Those sediments are generally considered to have been deposited in a more distal part of the Tethys than were the Lesser Himalayan sediments.The present tectonic architecture of the Himalaya is dominated by three master thrusts: the Main Central Thrust (MCT), the Main Boundary Thrust (MBT) and the Main Frontal Thrust (MFT). The age of initiation of these thrusts becomes younger from north to south, with the MCT as the oldest and the MFT as the youngest. All these thrusts are considered to come together at depth in a flat-lying decollement called the Main Himalayan Thrust (MHT). The Mahabharat Thrust (MT), an intermediate thrust between the MCT and the MBT is interpreted as having brought the Bhimphedi Group out over the Lesser Himalayan rocks giving rise to Lesser Himalayan nappes containing crystalline rocks. The position of roots of these nappes is still debated. The Southern Tibetan Detachment Fault System (STDFS) has played an important role in unroofing the higher Himalayan crystalline rocks.  相似文献   

11.
METAMORPHISM IN THE LESSER HIMALAYAN CRYSTALLINES AND MAIN CENTRAL THRUST ZONE IN THE ARUN VALLEY AND AMA DRIME RANGE (EASTERN HIMALAYA)1　BrunelM ,KienastJR . tudep啨ｔｒｏ structuraledeschevauchementsductileshimalayenssurlatrans versaledel’Everest Makalu (N啨ｐａｌｏｒｉｅｎｔａｌ) [J].CanadianJ .EarthSciences,1986 ,2 3:1117～ 1137. 2　LombardoB ,RolfoF .TwocontrastingeclogitetypesintheHimalayas :implicationsfortheHimalayanorogeny…  相似文献   

12.
Abstract The Infra Krol Formation and overlying Krol Group constitute a thick (< 2 km), carbonate-rich succession of terminal Proterozoic age that crops out in a series of doubly plunging synclines in the Lesser Himalaya of northern India. The rocks include 18 carbonate and siliciclastic facies, which are grouped into eight facies associations: (1) deep subtidal; (2) shallow subtidal; (3) sand shoal; (4) peritidal carbonate complex; (5) lagoonal; (6) peritidal siliciclastic–carbonate; (7) incised valley fill; and (8) karstic fill. The stromatolite-rich, peritidal complex appears to have occupied a location seaward of a broad lagoon, an arrangement reminiscent of many Phanerozoic and Proterozoic platforms. Growth of this complex was accretionary to progradational, in response to changes in siliciclastic influx from the south-eastern side of the lagoon. Metre-scale cycles tend to be laterally discontinuous, and are interpreted as mainly autogenic. Variations in the number of both sets of cycles and component metre-scale cycles across the platform may result from differential subsidence of the interpreted passive margin. Apparently non-cyclic intervals with shallow-water features may indicate facies migration that was limited compared with the dimensions of facies belts. Correlation of these facies associations in a sequence stratigraphic framework suggests that the Infra Krol Formation and Krol Group represent a north- to north-west-facing platform with a morphology that evolved from a siliciclastic ramp, to carbonate ramp, to peritidal rimmed shelf and, finally, to open shelf. This interpretation differs significantly from the published scheme of a basin centred on the Lesser Himalaya, with virtually the entire Infra Krol–Krol succession representing sedimentation in a persistent tidal-flat environment. This study provides a detailed Neoproterozoic depositional history of northern India from rift basin to passive margin, and predicts that genetically related Neoproterozoic deposits, if they are present in the High Himalaya, are composed mainly of slope/basinal facies characterized by fine-grained siliciclastic and detrital carbonate rocks, lithologically different from those of the Lesser Himalaya.  相似文献   

13.
The stratigraphic and tectonic setting in the northwest part of Himalayan belt is complex and thrusted due to the collision of Indian plate and the Eurasian plate. During the past, the Himalaya is divided into four parts; these are Outer Himalaya, Lesser Himalaya, Greater or Higher Himalaya and Tethys Himalaya. The appearance of basement rocks played a significant role in the Himalayan periphery for stratigraphic, structural and tectonic movement. The deformation pattern of the crustal rocks causing the rise of basement rocks which constitutes an integral part of crustal configuration during the evolutionary stages of the Himalaya. In this study, an attempt has been made to estimate the basement depth configuration using spectral analysis and Euler deconvolution technique of gravity data in the northwest Himalaya region. The elevation increases continuously from 500 m to 5100 m in SW to NE direction, however, Bouguer gravity anomaly decreases continuously from ?130 mGal to ?390 mGal in SW to NE direction due to the isostaic adjustment. Gravity anomaly is very low near Harsil, Badrinath and Joshimath area and observed higher elevation due to the deep rooted basement. However, there are extrusion of crystalline basement in and around the Badrinath area due to the resettlement of geologic process which are overlaid to the top surface of the sedimentary layers. Euler deconvolution technique has been applied to detect the direct basement depth and results show a good correlation with the average depth of the spectral analysis and other works carried by different authors. Three gravity profiles are selected in appropriate places orienting SW-NE direction with a profile length of 160 km, 150 km and 140 km respectively in the study area for calculating the average depth of the basement rock. The average basement depth calculated is around 11.27 km using the spectral analysis technique and results are well correlated with the results of various workers. Euler deconvolution studies along the three selected profiles have been interpreted. It has been observed that there are more number of cluster points falling between depth ranges of 10 to 15 km, dipping in SW to NE direction. Euler’s study shows deep rooted connection near Main Frontal Thrust (MFT), Main Boundary Thrust (MBT), Main Central Thrust (MCT), Bearing Thrust (BT) and Vaikrita Thrust (VT) locations as per profile study. Based on these studies three geological models have been prepared along the profiles showing different tectonic resettlement and depth of crystalline basement. Crystalline rocks exposed at the surface may be due to uplift along the shear in the MCT zone by kinetic flow basically, Munsiayari Thrust (MT) and VT in the of NW-Himalaya region.  相似文献   

14.
The Main Central Thrust demarcates the boundary between the Lesser Himalaya and the Higher Himalaya in the Himalayan orogen. Several definitions of the Main Central Thrust have been proposed since it was originally described as the southern boundary of the crystalline rocks (the Main Central Thrust mass) in the Kumaun-Garhwal Himalaya. The long-held contention that the Munsiari Thrust represents the Main Central Thrust has been negated by recent isotopic studies. One way to define the Main Central Thrust is that it is a ductile shear zone that is delimited by the Munsiari Thrust (MCT-I) in south and the Vaikrita Thrust (MCT-II) in north. The alternative proposition that the Vaikrita Thrust represents the Main Central Thrust is fraught with practical limitations in many parts of the Himalaya, including the study area. In the metamorphic rocks bounded between the Vaikrita Thrust and the Munsiari Thrust, the isoclinal folds of the earliest phase are routinely ascribed to the pre-Himalayan orogeny, whereas all subsequent folding phases are attributed to the Himalayan orogeny. This article elucidates the structural characteristics of the kilometre-thick Munsiari Thrust Zone and revisits the issue of pre-Himalayan orogenic signatures in the thrust zone. With the help of high-resolution field mapping and the analyses of mesoscopic scale structures, we demonstrate that the Munsiari Thrust is a typical fault zone that is made up of a fault core and two damage zones. The fault core traces the boundary between the quartzite and the biotite-gneiss. The damage zones consist of the low-grade metasedimentary rocks in the footwall and the gneiss-migmatite in the hanging wall. The entire fault zone shares an essentially common history of progressive ductile shearing. Successively developed mesoscopic folds trace various stages of progressive ductile shearing in the damage zones. Two recognizable stages of the shearing are represented by the early isoclinal folds and the late kink folds. As the strain during progressive deformation achieved the levels that were too high for accommodation by ductile flow, it was released by development of a tectonic dislocation along a mechanically weak boundary, the Munsiari Thrust. The isoclinal folds and the Munsiari Thrust were developed at different stages of a common progressive deformation during the Himalayan orogeny. Contrary to the popular notion of consistency with respect to orientation, the stretching lineations show large directional variability due to distortion during the late folding.  相似文献   

15.
The Lesser Himalayan low- to medium-grade metamorphic rocks in central Nepal are rich in K-white micas occurring as porphyroclasts and in matrix defining S1 and S2. Porphyroclasts are usually zoned with celadonite-poor cores and celadonite-rich rims. The cores are the relics of igneous or high grade metamorphic muscovites, and the rims were re-equilibrated or overgrown under lower T metamorphic conditions. The matrix K-white micas defining S1, pre-dating the Main Central Thrust activity, are generally celadonite-rich. They show heterogeneous compositional zoning with celadonite-rich cores and celadonite-poor rims. They were recrystallized at lower T condition prior to the Main Central Thrust activity, most probably prior to the India–Asia collision (pre-Himalayan metamorphism). The matrix K-white micas along S2, synchronous to the Main Central Thrust activity (Neohimalayan metamorphism), are relatively celadonite-poor and were recrystallized under relatively higher T condition. K-white micas defining S1 also were partially re-equilibrated during the Neohimalayan metamorphism. The average compositions of recrystallized K-white micas defining both S1 and S2 become gradually poor in (Fe + Mg)- and Si-contents and rich in Al- and Ti-contents from south to north showing an increase of metamorphic grade from structurally lower to higher parts in the Lesser Himalaya. This shows that the metamorphism is inverted throughout the inner Lesser Himalaya. The tectono-metamorphic significance of the published K–Ar and 40Ar / 39Ar K-white micas ages from the Lesser Himalaya need re-evaluation in the context of observed intrasample compositional variation and zoning, and possible higher closure temperature (500 °C) for K–Ar system.  相似文献   

16.
Causes of large-scale landslides in the Lesser Himalaya of central Nepal   总被引：1，自引：0，他引：1  
Geologically and tectonically active Himalayan Range is characterized by highly elevated mountains and deep river valleys. Because of steep mountain slopes, and dynamic geological conditions, large-scale landslides are very common in Lesser and Higher Himalayan zones of Nepal Himalaya. Slopes along the major highways of central Nepal namely Prithvi Highway, Narayangadh-Mugling Road and Tribhuvan Highway are considered in this study of large-scale landslides. Geologically, the highways in consideration pass through crushed and jointed Kathmandu Nappe affected by numerous faults and folds. The relict large-scale landslides have been contributing to debris flows and slides along the highways. Most of the slope failures are mainly bechanced in geological formations consisting phyllite, schist and gneiss. Laboratory test on the soil samples collected from the failure zones and field investigation suggested significant hydrothermal alteration in the area. The substantial hydrothermal alteration in the Lesser Himalaya during advancement of the Main Central Thrust (MCT) and thereby clay mineralization in sliding zones of large-scale landslide are the main causes of large-scale landslides in the highways of central Nepal. This research also suggests that large-scale landslides are the major cause of slope failure during monsoon in the Lesser Himalaya of Nepal. Similarly, hydrothermal alteration is also significant in failure zone of the large-scale landslides. For the sustainable road maintenance in Nepal, it is of utmost importance to study the nature of sliding zones of large-scale landslides along the highways and their role to cause debris flows and slides during monsoon period.  相似文献   

17.
A large number of fractures, faults and folds trending normal and oblique to the Himalayan tectonic trend have been recognized in recent years. The tear faults of Kumaun and Nepal have caused predominant right-lateral shear movements. There are eloquent indications of tectonic and seismic activities along some of these faults. In Kumaun, some of the NNW—SSE oriented tear faults coincide with the great thrusts that have brought older Precambrian crystallines over the sedimentary rock. This phenomenon has led many workers to interpret the thrusts as high-angled faults. Significantly, these transverse and oblique faults and fractures are parallel to the great faults discovered in the basement of the Ganga Basin and in the South Indian block, implying a certain genetic connection between the two sets.Likewise, the transverse folds of mesoscopic and macroscopic dimensions superposed on earlier folds of normal Himalayan trend are parallel to the great hidden ridges in the base ment of the Ganga Basin, representing undersurface extension of the Peninsular orogenic trends such as the Satpura, Bundelkhand and Aravali.The presence in the Lesser Himalaya of transverse structures having striking parallelism with those of Peninsular India, coupled with the strong lithostratigraphic similarities between the Purana (Riphean) sedimentary formations of the Lesser Himalaya and the greater Vindhyan Basin and the occurrence in many parts of the Himalaya of coalbearing continental Gondwana and marine Permian formations, reminiscent of similar horizons of the Bihar-Madhya Pradesh borders, is a pointer to the tectonic unity of the two provinces and suggests involvement of Peninsular India in the tectonic framework of the Himalaya.  相似文献   

18.
The Siwaliks in the foothills of the Himalayas, containing molasse sediments derived from the rising mountain front, represent a foreland fold-thrust belt which was deformed during the continued northward convergence of the Indian plate following the continent-continent collision. In this contribution we present balanced and restored cross sections along a line from Adampur through Jawalamukhi to Palampur in the foothills of the Punjab and Himachal Himalayas using published surface/subsurface data. The cross section incorporates all the rock units of the Sub-Himalaya Zone as well as that of the northern Lesser Himalaya Zone. The structural geometry of the fold-thrust belt in this section is largely controlled by three buried thrusts within the Sundernagar Formation of the Lesser Himalaya Zone. Two of these buried thrusts splay from the basal detachment and delineate a buried horse. Three thrusts towards foreland, including the Main Frontal Thrust (inferred to be a blind thrust in this sector), splay from these buried thrusts. In the hinterland, an anticlinal fault-bend fold was breached by a sequence of break-back thrusts, one of which is the Main Boundary Thrust. A foreland propagating thrust system is inadequate to explain the evolution of the fold-thrust-belt in this section. We show that a “synchronous thrusting” model in whichin-sequence initiation of thrusts at depth combined with continued motion on all the thrusts leading toout-of-sequence imbrication at the upper structural levels better explains the evolution of the fold-thrust belt in the Jawalamukhi section. The estimated shortening between the two chosen pin lines is about 36% (about 72 km).  相似文献   

19.
DEFORMATIONAL AND METAMORPHIC HISTORY OF THE CENTRAL LONGMEN MOUNTAINS, SICHUAN CHINA1　ArneDC ,WorleyBA ,WilsonCJL ,etal.Differentialexhumationinresponsetoepisodicthrustingalongtheeasternmar ginoftheTibetanPlateau[J] .Tectonophysics,1997,2 80 :2 39～ 2 56 . 2　ChenSF ,WilsonCJL ,WorleyBA .TectonictransitionfromtheSongpan GarzeFoldBelttotheSichuanBasin,south westernChina[J] .BasinResearch ,1995,7:2 35～ 2 53. 3　ChenSF ,WilsonCJL .Emplaceme…  相似文献   

20.
POLYPHASE METAMORPHISM AND INVERTED THERMAL GRADIENT IN THE LESSER HIMALAYA OF CENTRAL NEPAL: CONSTRAINTS FROM WHITE MICA COMPOSITIONS  相似文献   

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