Abstract
AbstractThe 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.
Highlights
Crustal shortening and thickening during the India-Asia collision have formed one of the largest active orogenic belts on the Earth, the Himalayan orogen (Aitchison et al, 2007; Dewey & Burke, 1973; Molnar & Tapponnier, 1975; Ni & Barazangi, 1984; Searle, 1986; Yin & Harrison, 2000)
The main structural features of the Himalayan orogen from north to south include: the Tethyan Himalayan Sequence (THS), the Greater Himalayan Crystalline Complex (GHC), the Lesser Himalayan Sequence (LHS), and Sub-Himalayan Sequence (SHS), which area bounded by the South Tibetan Detachment System (STDS), the Main Central Thrust (MCT), the Main Boundary Thrust (MBT), and the Main Frontal Thrust (MFT) (Figures 1a and 1b)
The domes are located between the STDS and Yarlung Tsangpo Suture Zone (YTSZ) (Figure 1a) and have a similar geologic expression characterized by a core of orthogneisses, migmatites, leucogranites, and high-grade metamorphic rocks covered by progressively lower grade to unmetamorphosed strata (Wagner et al, 2010)
Summary
Crustal shortening and thickening during the India-Asia collision have formed one of the largest active orogenic belts on the Earth, the Himalayan orogen (Aitchison et al, 2007; Dewey & Burke, 1973; Molnar & Tapponnier, 1975; Ni & Barazangi, 1984; Searle, 1986; Yin & Harrison, 2000). SG, Siwalik Group; LHS, lesser Himalayan Sequence; GHC, Greater Himalayan Crystalline Complex; THS, Tethyan Himalayan Sequence; GMB, Gangdese magmatic belt; MFT, Main Frontal Thrust; MBT, Main Boundary Thrust; MCT, Main Central Thrust; STDS, South Tibetan Detachment System; NHGD, northern Himalayan gneiss domes; YTSZ, Yarlung Tsangpo suture zone and the location of INDEPTH-I(I) seismic reflection profile. The internal architecture of the Mabja dome is obtained by combining the shallow subsurface velocity structure with the normal incidence seismic reflection image. They provide new details, critical information on the evolution of the domal structures jointly in the southern Tibet
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