Baddeleyite and zircon U-Pb ages of the ultramafic rocks in Chigu Tso area,Southeastern Tibet and their constraints on the timing of Comei Large Igneous Province     

《China Geology》2020,3(2):262-268

A suite of ultramafic and mafic rocks developed in the Chigu Tso area, eastern Tethyan Himalaya. Baddeleyite and zircon U-Pb ages acquired by SIMS and LA-ICP-MS from olivine pyroxenite rocks in the Chigu Tso area are 138.9±3.0 Ma and 139.0±1.9 Ma, respectively. These two Early Cretaceous ages are similar with the ages of the more abundant mafic rocks in the eastern Tethyan Himalaya, indicating that this suite of ultramafic and mafic rocks in the Chigu Tso area should be included in the outcrop area of the Comei Large Igneous Province (LIP). These ultramafic rocks provide significant evidence that the involvement of mantle plume/hot spot activities in the formation of the Comei LIP. Baddeleyite U-Pb dating by SIMS is one reliable and convenient method to constrain the formation time of ultramafic rocks. The dating results of baddeleyite and zircon from the olivine pyroxenite samples in this paper are consistent with each other within analytical uncertainties, suggesting that baddeleyite and zircon were both formed during the same magmatic process. The consistency of baddeleyite U-Pb ages in the Chigu Tso area with zircon U-Pb ages for a large number of Early Cretaceous mafic rocks in the eastern Tethyan Himalaya further support that zircon grains from such mafic rocks yielding Early Cretaceous ages are also magmatic in origin.  相似文献   

GIS based spatial data analysis for landslide susceptibility mapping   总被引：5，自引：4，他引：1  

S. Sarkar  D. P. Kanungo  A. K. Patra  Pushpendra Kumar 《山地科学学报》2008,5(1):52-62

Landslide susceptibility map delineates the potential zones for landslides occurrence. The paper presents a statistical approach through spatial data analysis in GIS for landslide susceptibility mapping in parts of Sikkim Himalaya. Six important causative factors for landslide occurrences were selected and corresponding thematic data layers were prepared in GIS. Topographic maps,satellite image,field data and published maps constitute the input data for thematic layer preparation. Numerical weights for different categories of these factors were determined based on a statistical approach and the weighted thematic layers were integrated in GIS environment to generate the landslide susceptibility map of the area. The landslide susceptibility map classifies the area into five different landslide susceptible zones i.e.,very high,high,moderate,low and very low. This map was validated using the existing landslide distribution in the area.  相似文献   

Species diversity and population status of threatened plants in different landscape elements of the Rohtang Pass,western Himalaya     

K. N. Singh  Gopichand  Amit Kumar  Brij Lal  N. P. Todaria 《山地科学学报》2008,5(1):73-83

This paper highlights the quantitative estimates of plant species diversity and ecosystems of the Rohtang Pass,which is one of the most preferred visiting spots by tourists in Himachal Pradesh （H.P.）,India. In spite of high pressure of anthropogenic activities,the Rohtang Pass still harbours a variety of flowering plants with economic value,including various medicinal herbs. In order to observe species diversity in different landscape elements （LSEs）,ground surveys were conducted in nine unique LSEs within the elevation range between 3624 m and 4332 m. Plant community structure in each LSE was studied using stratified random sampling where a total 56 quadrats of 1 m^2 in size for herbs and 7 quadrats of 25 m^2 for shrubs were made. Of the total 50 plant species belonging to 15 families recorded in different random quadrats,24 species were found of medicinal value. Maximum species richness （18） and value of Shannon diversity （H＇=2.2648） were observed on northeast-facing slope in Picrorhiza kurrooa dominated LSE in moist area,followed by Rheum emodi LSE （species richness = 17 and H＇ = 2.4141） distributed on south-facing slope. Maximum values of species richness and Shannon diversity in Rheum emodi LSE were observed between 8 ～ 12 and 1.4797 ～ 2.1911,respectively. Rhododendron anthopogon dominated LSE on northwest-facing slope was found least diverse in terms of species richness where the Simpson index of dominance （D） was 0.4205. The species were equal in abundance in P. kurrooa LSE on east-facing slope and Pleurospermum candollii LSE on north-facing slope,showing the maximum similarity in terms of species distribution between the two LSEs. Low turnover of species across common LSEs gives an idea regarding their limited distribution. Five species of threatened category according to the IUCN criteria were observed in seven LSEs. The largest population of threatened medicinal plants was recorded on northeast and northwest-facing slopes where population density of Bergenia stracheyi （  相似文献   

Fluid evolution and thermal structure in the rapidly exhuming gneiss complex of Namche Barwa–Gyala Peri, eastern Himalayan syntaxis     

D. CRAW  P. O. KOONS  P. K. ZEITLER  W. S. F. KIDD 《Journal of Metamorphic Geology》2005,23(9):829-845

High‐grade gneisses (amphibolite–granulite facies) of the Namche Barwa and Gyala Peri massifs, in the eastern Himalayan syntaxis, have been unroofed from metamorphic depths in the late Tertiary–Recent. Rapid exhumation (2–5 mm year^?1) has resulted in a pronounced shallow conductive thermal anomaly beneath the massifs and the intervening Tsangpo gorge. The position of the 300 °C isotherm has been estimated from fluid inclusions using CO₂–H₂O immiscibility phase equilibria to be between 2.5 and 6.2 km depth below surface. Hence, the near‐surface average thermal gradient exceeds 50 °C km^?1 beneath valleys, although the thermal gradient is relatively lower beneath the high mountains. The original metamorphic fluid in the gneisses was >90% CO₂. This fluid was displaced by incursion of brines from overlying marine sedimentary rocks that have since been largely removed by erosion. Brines can exceed 60 wt% dissolved salts, and include Ca, Na, K and Fe chlorides. These brines were remobilized during the earliest stages of uplift at >500 °C. During exhumation, incursion of abundant topography‐driven surface waters resulted in widespread fracture‐controlled hydrothermal activity and brine dilution down to the brittle–ductile transition. Boiling water was particularly common at shallow levels (<2.5 km) beneath the Yarlung Tsangpo valley, and numerous hot springs occur at the surface in this valley. Dry steam is not a major feature of the hydrothermal system in the eastern syntaxis (in contrast to the western syntaxis at Nanga Parbat), but some dry steam fluids may have developed locally.  相似文献   

Palaeomagnetic Results From the Tibetan Sedimentary Series of the Manang Area (North Central Nepal)     

E. Appel  R. Müller  R. W. Widder 《Geophysical Journal International》1991,104(2):255-266

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The Keylong Serai rock avalanche, NW Indian Himalaya: geomorphology and palaeoseismic implications     

W. A. Mitchell  M. J. McSaveney  A. Zondervan  K. Kim  S. A. Dunning  P. J. Taylor 《Landslides》2007,4(3):245-254

This paper describes the geomorphology of rock avalanche deposits that resulted from a major mountain slope failure at Keylong Serai on the north slope of the Indian High Himalaya, an area of high altitude desert. Cosmogenic ¹⁰Be exposure ages of the widespread deposits indicate their formation 7,510 ± 110 years BP. Proxy records for this region of the Himalaya imply a similar dry climatic regime to the present day at this time, suggesting that precipitation was an unlikely trigger for this rock avalanche. An alternative mechanism associated with rock-wall stress relaxation is also unlikely, given the earlier timing of deglaciation in this area. Given the enormous volume of debris generated by this event, the most likely trigger for this mountain collapse and resultant rock avalanche is high ground acceleration during a great earthquake (M > 8). It is proposed that rock avalanches can be used to extend the limited palaeoseismic record and improve information on the recurrence interval of great earthquakes within the Himalaya arc.  相似文献   

Active tectonic influence on the evolution of drainage and landscape: Geomorphic signatures from frontal and hinterland areas along the Northwestern Himalaya, India   总被引：3，自引：0，他引：3  

Javed N. Malik  C. Mohanty 《Journal of Asian Earth Sciences》2007,29(5-6):604-618

The Kangra Re-entrant in the NW Himalaya is one of the most seismically active regions, falling into Seismic Zone V along the Himalaya. In 1905 the area experienced one of the great Himalayan earthquakes with magnitude 7.8. The frontal fault system – the Himalayan Frontal Thrust (HFT) associated with the foreland fold – Janauri Anticline, along with other major as well as secondary hinterland thrust faults, provides an ideal site to study the ongoing tectonic activity which has influenced the evolution of drainage and landscape in the region. The present study suggests that the flat-uplifted surface in the central portion of the Janauri Anticline represents the paleo-exit of the Sutlej River. It is suggested that initially when the tectonic activity propagated southward along the HFT the Janauri Anticline grew along two separate fault segments (north and south faults), the gap between these two fault and the related folds allowed the Sutlej River to flow across this area. Later, the radial propagation of the faults towards each other resulted in an interaction of the fault tips, which caused the rapid uplift of the area. Rapid uplift resulted in the disruption and longitudinal deflection of the Sutlej river channel. Fluvial deposits on the flat surface suggest that an earlier fluvial system flowed across this area in the recent past. Geomorphic signatures, like the sharp mountain fronts along the HFT in some places, as well as along various hinterland subordinate faults like the Nalagarh Thrust (NaT), the Barsar Thrust (BaT) and the Jawalamukhi Thrust (JMT); the change in the channel pattern, marked by a tight incised meander of the Beas channel upstream of the JMT indicate active tectonic movements in the area. The prominent V-shaped valleys of the Beas and Sutlej rivers, flowing across the thrust fronts, with Vf values ranging from <1.0–1.5 are also suggestive of ongoing tectonic activity along major and hinterland faults. This suggests that not only is the HFT system active, but also the other major and secondary hinterland faults, viz. the MBT, MCT, SnT, NaT, BaT, and the JMT can be shown to have undergone recent tectonic displacement.  相似文献   

Discovery of Jurassic ammonoids from the Shyok suture zone to the northeast of Chang La Pass, Ladakh, northwest India and its tectonic significance   总被引：1，自引：0，他引：1  

Masayuki  Ehiro  Satoru  Kojima  Tadashi  Sato  Talat  Ahmad  Tomoyuki  Ohtani 《Island Arc》2007,16(1):124-132

Abstract   Callovian (late Middle Jurassic) ammonoids Macrocephalites and Jeanneticeras were recovered from the Shyok suture zone, northeast of Chang La Pass, Ladakh, northwest India. They are the first reliable Jurassic fossils and the oldest chronologic data from the Shyok suture zone. The ammonoid-bearing Jurassic strata, newly defined as the Tsoltak Formation, consist largely of terrigenous mudstone with thin sandstone beds and were probably a part of the continental basement to the Cretaceous Ladakh Arc.  相似文献   

Seismic microzonation of Dehradun City using geophysical and geotechnical characteristics in the upper 30 m of soil column     

A. K. Mahajan  Siefko Slob  Rajiv Ranjan  Rob Sporry  P. K. Champati ray  Cees J. van Westen 《Journal of Seismology》2007,11(4):355-370

The understanding of geotechnical characteristics of near-surface material is of fundamental interest in seismic microzonation. Shear wave velocity (Vs), one of the most important soil properties for soil response modeling, has been evaluated through seismic profiling using the multichannel analysis of surface waves in the city of Dehradun situated along the foothills of northwest Himalaya. Fifty sites in the city have been investigated with survey lines between 72 and 96 m in length. Multiple 1-D and interpolated 2-D profiles have been generated up to a depth of 30–40 m. The Vs were used in the SHAKE2000 software in combination with seismic input motion of the recent Chamoli earthquake to obtain site response and amplification spectra. The estimated Vs are higher in the northern part of the study area (i.e., 200–700 m/s from the surface to a depth of about 30 m) as compared to the south and southwestern parts of the city (i.e., 180–400 m/s for the same depth range). The response spectra suggest that spectral acceleration values for two-story structures are three to eight times higher than peak ground acceleration at bedrock. The analysis also suggests peak amplification at 3–4, 2–2.5, and 1–1.5 Hz in the northern, central, and south-southwestern parts of the city, respectively. The spatial distributions of Vs and spectral accelerations provide valuable information for the seismic microzonation in different parts of the urban area of Dehradun.  相似文献   

Wintertime Seasonal Scale Simulation over Western Himalaya Using RegCM3     

A. P. Dimri  A. Ganju 《Pure and Applied Geophysics》2007,164(8-9):1733-1746

The Himalayan region of north India is composed of complex mountain ranges with different altitudes and orientations, causing prevailing weather conditions to be complex. Wintertime eastward moving synoptic weather systems `Western Disturbances' (WDs) yield large amounts of precipitation over this region. Numerous micro/mesoscale circulations become generated along with prevailing weather due to surface heterogeneity and land-use variability of the Himalayan region. WDs along with these circulations may give rise to very adverse weather conditions over the region. Intraseasonal variability of surface climate over the Himalayas is studied using regional climate model (RegCM3) with 60 km resolution. A 6-month (Oct. 1999–Mar. 2000) period, as this period has received an enormous amount of precipitation in the form of snow, is considered to study surface climate variability in terms of temperature, precipitation and snow amount. Model simulations show cold bias over the Himalayan region and warm bias over the northwest India. Average monthly distribution of temperature indicates that a controlled experiment could capture the areas of lowest temperature regime. Precipitation fields could be simulated only up to a certain degree of satisfaction and the influence of topographic elevation and valleys needs to be seen. RegCM3 provides a representation of resolvable atmospheric circulations that results in explaining mean variability during winter.  相似文献