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In the first phase of the International Deep Profiling of Tibet and the Himalaya the INDEPTH project an over 90 km long deep seismic reflection profile was acquired. This was an interdisciplinary program of geophysical and geological studies focus to increase the understanding of the internal architecture and mechanics of the Himalaya-Tibet region. Reprocessing of INDEPTH-I deep seismic reflection image resolves the South Tibetan Detachment System (STDS) as composed by few laterally displaced ramp structures. These can be interpreted to be structurally related to the outcropping gneiss domes. The STDS is recognized as complex extensional shear zone most probably coeval with the emplacement of the leucogranitic bodies. Geologic data indicates that the latter are pre-, syn- and post- kinematic with the deformation and, are generally controlled by the system of detachment faults (including the STDS). The interpreted STDS is broken up, and the individual segments are tilted revealing compressional deformation. Underneath, and down to 42 km depth, two prominent high amplitude, multi cyclic, north dipping events are imaged: the Tethyan Himalayan Sequence (THS) and, the Greater Himalayan Sequence (GHS). Above the GHS the north-dipping reflection fabrics appear imbricate and are seldom interrupted by weak/transparent zones. The existing geological knowledge and, the geometrical relationships (unraveled by the internal architecture constrained by the seismic image suggest that the transparent areas in the GHS could be indicative of leucogranite emplacements. Thus, the latter can be interpreted as the product of rapid exhumation of the upper GHS together with magma along the High Himalayan Thrust (HHT), repeated in-situ remelting due to strain heating by exhumation of the lower GHS and Lesser Himalayan Sequence (LHS), and extension of the South Tibetan Detachment System (STDS). This mechanism is consistent with interpretation of seismically transparent zones as the seismic re

The India-Asia collision is characterized by the widespread occurrence of leucogranites within the Himalaya orogen. Surface outcrops have been studied to constrain: their structural features; their distribution; their volume; their source and emplacement mechanism; among other objectives. However, the latter four targets are still strongly debated and matter of discussion among Earth Scientist working in the Himalaya collisional orogen. To contribute to a better knowledge of the depth distribution and geometry of the leucogranites and associated structures careful reprocessing of the INDEPTH-I deep normal incidence seismic reflection profile was carried out down to a depth of 42 km. The most prominent geologic features as the; Tethyan Himalayan Sequence (THS) and Greater Himalayan Crystalline complex (GHC) are well imaged. In detail the image reveals a multiclyclic relative high amplitude north-dipping event. This is dominated by northward-dipping and imbricate reflections that are laterally interrupted by transparent areas. Reflections in lower GHC display a gentle northward dip. The seismic image integrated with the available geology and other geophysical observation suggests that the GHC has undergone rapid exhumation along the main discontinuity. The geometrical relationships of the overall seismic fabrics, structure and the surface exposures support that the areas lacking reflectivity within the GHC could be consistent with leucogranitic emplaments. These plutons are, most probably, the combined product of: rapid exhumation of the upper GHC, together with, magmatic melts along High Himalayan Thrust (HHT), strain heating induced in-situ melting and, exhumation of lower GHC and Lesser Himalayan Sequence (LHS), and the extension of the South Tibetan Detachment System (STDS). Plain-language Summary This contribution uses deep normal incidence seismic reflection section, the INDEPTH-I to constrain the geometrym and, depth distribution, of possible leucogratite empla

One of the most spectacular characteristics of the India-Asia collision is the widespread occurrence of leucogranites within the Himalaya orogen. There are numerous case studies focusing on the surface exposures of leucogranites, addressing its surface distribution and their associated outcropping structural features. However, the depth extent, volume, the architectural characteristics at depth are topics which are still vague, as well as the emplacement mechanism of such granitic plutons. These are highly debated questions among Earth Scientist working in this collisional orogen. To better characterize leucogranites and associated structural features, here the Indepth-I deep normal incidence seismic reflection profile was reprocessed to image the Tethyan Himalayan Sequence (THS) and Greater Himalayan Crystalline complex (GHC) to a depth of 42 Km. Compared to the previous result, the new images reveal a multiclyclic relative high amplitude north-dipping event. This is dominated by northward-dipping and imbricate reflections that are interrupted by weak/transparent zones. Reflections in lower GHC dip northward at a gentle angle and exhibit relatively homogeneous wave patterns. This seismic signature complemented with other geophysic observations suggest that the upper GHC has undergone rapid exhumation along the main discontinuity. Based on obtained images and the geometrical relationship of the overall structure and the surface exposures of the leucogranites, the seismically transparent areas in GHC could be indicative of leucogranitic emplaments. The Himalaya leucogranites are considered to be the product of rapid exhumation of the upper GHC together with magma along High Himalayan Thrust (HHT), repeated in-situ remelting due to strain heating by exhumation of lower GHC and Lesser Himalayan Sequence (LHS), and the extension of the South Tibetan Detachment System (STDS). This mechanism would be consistent with the proposed interpretation of the seismically transpare

The ongoing India-Asia collision has led to the formation of the northern Himalayan gneiss domes belt in southern Tibet. The domes are the result of the ongoing convergence and were formed by geological processes that may include crustal thickening, metamorphism, partial melting, and exhumation of middle crustal rocks to the surface. A combination of compressional, extensional, and diapiric processes has been invoked to explain the formation and evolution of these domes. Differentiating among these competing hypotheses requires well-defined geophysical images of the internal structure of the domes. The Mabja dome is the largest dome within the northern Himalayan gneiss domes belt. A 70-km long deep seismic reflection profile across Mabja dome was acquired in 2016. The seismic data could provide new information about the structural elements beneath the domes to the depth of 25 Km. We address the structure of the Mabja dome by conducting an integrated analysis of shallow crustal velocity structure and a normal-incidence seismic reflection image of deeper crust. Our work suggests that the Mabja dome is underlain by shear zones at depths of 10–15 km and two high-velocity bodies at depths of 3 km possibly representing the eclogitic-facies rocks or mafic intrusions. We propose that the dome formation may have been controlled by collision-induced north-south shortening expressed by thrust stacking of middle crustal rocks, which led to the doming of the upper-crustal rocks. The proposed mechanism inferred for Mabja dome can be applied to interpret the widespread domes throughout the southern Tibet and other related structures in orogenic mountain belts. © 2021. American Geophysical Union. All Rights Reserved.