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The Thakhola-Mustang Graben of central Nepal represents the Cenozoic extensional tectonic phase of the Tibetan Plateau and the whole Himalaya
. It is located on the northern side of the Dhaulagiri and Annapurna Ranges and south of the Yarlung Tsangpo Suture Zone. The graben is an asymmetrical basin containing thick (more than 850m) continental debris. Stratigraphically, the graben sediments are divided into four formations, namely the Tetang Formation, the Thakkhola Formation, the Sammargaon Formation and the Marpha Formation. The oldest sedimentary units are the Tetang and Thakkhola formations (Miocene) while the Sammargaon and the Marpha formations lying disconformably above these formations represent younger units (Plio-Pleistocene). The Thakkhola and Tetang formations are separated by a lowangled (_
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Reliably relocated earthquake hypocenters in the Pamir-Hindu Kush region for about 1700 earthquakes deeper than 50 km, are examined using 3-D color plots
. The hypocenters define an single contorted “S” shaped seismic zone, 700 km long and no more than 30 km wide and with most activity concentrated in the 100-300 km depth range
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The Main Central Thrust (Mahabharat Thrust of Stöcklin 1980) is one of the key thrusts in central Nepal Himalaya to understand the nappe tectonics because it is considered that MCT acted as a glide plane for the thrust sheets, which traveled more than 100 km towards south over the LHS forming a large folded-thrust sheet called Kathmandu Nappe
. Much of the research has been focused on structural and kinematic analysis of the MCT zone, a root zone of the Kathmandu Nappe. These studies have confirmed a top-to-the south directed sense of shear in the MCT zone, which is associated with the emplacement of Kathmandu Nappe. Although large-scale geometry of the Himalayan thrust sheets and nappes are relatively understood, features of the internal deformation are not well understood in terms of strain geometry. Several studies have shown that the pattern of the internal deformation varies between thrust sheets because it depends on pressure, temperature, and complex tectonic boundary condition. Although strain analysis bears important clues to understand internal deformation, there is still lack of studies across the Himalaya nappes. It is, therefore, necessary to address several problems like (1) three-dimensional strain geometry, (2) relation between inverted metamorphism and strain pattern, (3) precise kinematic model to reveal nature of internal deformation and emplacement mechanism. These issues are certainly useful to decipher tectonics of the Himalayan nappes and thrust sheets. This study, therefore, mainly attempts to discuss above-mentioned issues using structural data, three-dimensional strain geometries, and metamorphism across the MCT and basal part of the Kathmandu Nappe in central Nepal Himalaya
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The South Tibetan Detachment System is characterised by a lower ductile shear zone, an upper low-angle normal fault and high-angle normal faults
. The low-angle normal fault puts in contact the base of the Tibetan Sedimentary Sequence with the high-grade sillimanite-bearing schists and mylonitic leucogranites of the Greater Himlayan Sequence and, in several places, the intervening North Col Formation. In the Rongbuck valley, Sa’er and Nyalam areas (southern Tibet) a sharp contact of the low-angle normal fault is associated to breccias and cataclasites
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In the Arun and Barun valleys the upper portion of the Lesser Himalayan section is made up by the Num orthogneiss
. It is a 3-4 km thick unit of granitic augen gneiss with bands of kyaniteflogopite schists (Lombardo et al. 1993). It records a noncoaxial deformation related to its involvement within the Main Central Thrust zone that produced an heterogeneous mylonitic deformation with rotated feldspar porphyroclasts, bookshelf structures and localized shear bands with a prominent top-to-the SW sense of shear. The base of the Num orthogneiss is the Main Central Thrust I
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Secondary pyrrhotite remanences from the Tethyan Himalaya acquired during Eocene (western Himalaya) and Oligocene to early Miocene (central and eastern Himalaya) were evaluated for block rotations
. Oroclinal bending is well reflected by paleomagnetic data in the western part of the Himalaya also showing a uniform counterclockwise rotation of India versus the Tethyan Himalaya. In contrast, data from the central part and preliminary results from the eastern part indicate an abrupt change to unexpected clockwise rotations versus India where oroclinal bending would predict no rotation or slight counterclockwise rotations. It can be hypothesised that these clockwise rotations are a result of a large dextral shear zone related to lateral extrusion of the Tibetan Plateau, with an onset in central Nepal. However, the existing gap in suitable data from the eastern part of the Himalaya was hindering a closer evaluation of this question. The hypothesis is reconsidered in the light of new findings
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High resolution geochemical data from fossil-poor Blaini-Krol and fossiliferous Lower Tal succession in the Lesser Himalayas closely conform to the geochemical trends demonstrated by the rock sequences at Oman, Newfoundland, South China and Western United States
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The book provides a comprehensive coverage of all the deserts of Arabia largely based on the author's experience in Arabia over the last fifty years
. It deals with every type of desert found there, including those formed by great sand seas, dunefields, evaporites, clay pans, stony plains, volcanic flows, desert plateaux and mountains, deltas, and desert islands. Distinctive landforms of Arabia deserts are described, together with their geological setting and the influence of climates both past and present. The six great sand seas of Arabia are emphasized since Ar Rub' al Khali Desert forms the world’s largest continuous sand desert. Sources, sedimentology, and the mechanisms of formation of these great sand deserts are examined. Distinctive sand dunes and interdunes types found in Arabia are described, classified and explained. Fluvial processes are discussed, as well as the many oases, and lake deposits formed in milder, more humid intervals. Extensive areas of black, basaltic, volcanic desert are described covering three times the area of Belgium. Ecology of Arabia and human influence on desertification are outlined. Climatic changes in the evolution of Arabian deserts during the Quaternary and their causes are explained and a chronology of climatic events during their formation is established.
This book will be of interest to geoscientists, especially Quaternary geologists, geomorphologists, geographers, sedimentologists interested in aeolian and fluvial processes, climatologists, coastal studies groups, desertification interest groups, and ecologists with interest in arid lands
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As part of the Himalayas, Nepal has undergone numerous changes in the past 50 Ma
. Folding was responsible for the creation of the Kathmandu Basin. It is here that the most complete sequence of Pleistocene sediments in Nepal is to be found. In this paper, the palynology and palynofacies of the Gokarna, Thimi and Patan Formations is discussed. It is shown that a scanning electron microscope is essential in order to identify the sporomorphs accurately. Without this detailed information, it would prove impossible to pinpoint the climatic signal. It is also necessary to take the sedimentological regime into consideration before a climatic interpretation can be made. The pollen assemblages show that all three formations were deposited during cool conditions with a mean annual temperature 6–7°C lower that at present. Based on the radiocarbon dates, the Patan Formation would appear to be of Late Glacial age. While the Gokarna and Thimi Formations were deposited during the W.urm, their exact age is still uncertain as some of the radiocarbon dates are at or beyond the limit of this method. It is hoped that optically stimulated luminescence will be able to resolve this problem
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