I determined the source parameters of 53 moderate-sized earthquakes in the region of the Eastern Himalayan Syntaxis through the joint inversion of regional and teleseismic distance long-period body waves. The average rates of deformation are determined by summing the moment tensors from both recent and historic earthquakes. Strike-slip movement on the Sagaing fault terminates in the north (just south of the syntaxis), where thrusting (northeast convergence) and crustal thickening are predominant. Slip vectors for thrust mechanisms in the Eastern Himalaya in general are not orthogonal to the Himalayan mountain front but show an oblique component of slip. A combination of thrust and strike-slip faulting (Molnar and Deng, 1984) for the great 1950 Assam earthquake is consistent with the rates of underthrusting in the entire Himalaya and the rate of spreading in Tibet (assuming that a 1950-type earthquake recurs every 400 years). An estimated 4-21 mm/yr of right-lateral motion between southeast Asia and the Burma subplate is absorbed within the zone of distributed shear between the Sagaing and Red River faults. A component of westward motion (3-7 mm/yr) of the western boundary of the distributed shear zone may cause some of the late Cenozoic compression and folding in the northern Indoburman Ranges. Distributed shear and clockwise rotation of blocks is also occurring in Yunnan north of the Red River Fault. The inversion of 130 regional distancewaveforms for average crustal thickness and upper mantle Pn velocity indicates an increase in Pn velocity, coincident with increase in crustal thickness, of about 0.20 km/s beneath the Tibetan Plateau. Impulsive Pn arrivals from paths that cross the Tibetan Plateau can be modeled with a positive upper mantle velocity gradient, indicating an upper mantle lid approximately 100-km-thick beneath southern Tibet. This "shield-like" structure supports a model in which Indian continental lithosphere has underthrust Tibet. The crustal shortening within Tibet 8 mm/yr is thus viewed as an upper crustal phenomenon in which the faults do not penetrate the deep crust or upper Mantle. The forces generated by the thick crust in Tibet may partly cause the strike-slip faulting and east-west convergence in Sichuan and the movement of upper crustal blocks in Yunnan.

Extensive studies have been undertaking in exploring the tectonic evolution of the Himalayan Orogen. Various tectonic models were developed to explain and constraint spatially and temporally critical events including the collision of Indian Plate with the Eurasia Plate, crustal thickening in association with the indentation, crustal spreading of the Tibetan Plateau. Recent study by King et al., 2011 identified two distinct leucogranite suites which were formed by contrasting tectonic actions at Sakya. They are Equigranular Anastomosing Leucogranite (AEG) formed under prograde fluidpresent condition while the Discrete Porphyritic Pluton Leucogranite (DPP) formed with retro-grade fluid-absent environment. Based on the characteristics of AEG and DPP, this study started with the acquisition of geochemistry data of rock samples collected for researches at various locations of the Himalaya Orogen. The two leucogranite suites were characterized through the study of their geochemistry comprised major elements, trace elements and rare earth elements models. Results of the studies concluded the existence of AEGs and DPPs distributed over the eastern area of the Himalaya Orogen beyond longitude 85 degree East. DPPs are also found at the far West location of the orogen. AEGs are typically formed from around 38Ma to 23Ma, while DPPs are of young age from 23Ma to 15Ma. Based on the observation of missing, or paucity in data for AEG and DPPs available to the west of longitude 85 degree East, it is hypothesized that recent collision of the Arabia plate to the Iran Domain inhibited the northward indentation movement of the Indian plate that not only caused the anticlockwise rotation of the Indian plate but also decreased the rate of tectonic movement of the Indian plate in the West relative to Eurasia plate. The slow rate of tectonic movement may result in insufficient thickening/energy developed within the crustal layer to cause any melting. Further studies to examine and development of the hypothesis is recommended. / published_or_final_version / Applied Geosciences / Master / Master of Science

Mineral textures, preserved in the metamorphosed sedimentary sequences that are exposed in orogenic hinterlands, are crucial to understanding the architecture and evolution of collisional mountain belts. In this thesis the textural record of anatexis and melt transfer in the Himalayan metamorphic core is decoded and the controls that these processes exert on the tectonic evolution of the Himalaya are explored. The problem is divided into two parts, corresponding to variations in protolith lithostratigraphy: melt source - the pelitic region where melt was first generated, and melt sink - the psammitic region where melt accumulated and crystallised. Dehydration melting of muscovite has long been recognized as a critical reaction for the generation of anatectic melt in the Himalaya, but a textural understanding of how this reaction progresses is limited by the inherent difficulties in identifying specific reaction products. Using samples collected from the Langtang area in central Nepal, a mechanistic model for muscovite dehydration melting was constructed, and a set of textural criteria were developed, which were used to distinguish peritectic K-feldspar from K-feldspar grains formed during melt crystallisation. Melt is transferred from the source to the sink in two stages: firstly along a pervasive network of mineral grain boundaries, and secondly via a channelised network of sills and dykes in the melt sink where it solidified as leucogranite. Variation in the primary mineral assemblage and appearance of leucogranite bodies reflect the degree of interaction that occurred between the melt and metasedimentary country rock, rather than a change in primary melt composition. The modal proportion of K-feldspar in the melt source requires vapour-absent conditions during muscovite dehydration melting and leucogranite formation, indicating that the generation of large volumes of granitic melts in orogenic belts is not necessarily contingent on an external source of fluids. The crystallisation of hydrous minerals in leucogranite consumes <15.5 % of water released by the breakdown of muscovite. These results indicate that anatexis efficiently dehydrates the middle crust and suggests that the continents have limited potential to store water over geological time.

Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Science. / Bibliography: leaves 51-56. / by Waris E.K. Warsi. / M.S.

Thesis. 1976. Ph.D.--Massachusetts Institute of Technology. Dept. of Earth and Planetary Sciences. / Microfiche copy available in Archives and Lindgren. / Vita. / Bibliography: leaves 385-402. / Ph.D.