Crustal architecture of the Himalayan metamorphic front in eastern Nepal

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doi: 10.1016/j.gr.2006.05.003
Authors:Goscombe, Ben; Gray, David; Hand, Martin
Author Affiliations:Primary:
University of Adelaide, Continental Evolution Research Group, Adelaide, South Aust., Australia
Other:
University of Melbourne, Australia
Volume Title:Gondwana Research
Source:Gondwana Research, 10(3-4), p.232-255. Publisher: Elsevier on behalf of International Association for Gondwana Research, Amsterdam and Kochi, International. ISSN: 1342-937X
Publication Date:2006
Note:In English. Includes appendices. 105 refs.; illus., incl. geol. sketch maps
Summary:The Himalayan Metamorphic Front consists of two basinal sequences deposited on the Indian passive margin, the Mesoproterozoic Lesser Himalayan Sequence and the Neoproterozoic-Cambrian Greater Himalayan Sequence. The current paradigm is that the unconformity between these two basinal sequences coincides with a crustal-scale thrust that has been called the Main Central Thrust, and that this acted as the fundamental structure that controlled the architecture of the Himalayan Metamorphic Front. Geological mapping of eastern Nepal and eight detailed stratigraphic, kinematic, strain and metamorphic profiles through the Himalayan Metamorphic Front define the crustal architecture. In eastern Nepal the unconformity does not coincide with a discrete structural or metamorphic discontinuity and is not a discrete high strain zone. In recognition of this, we introduce the term Himalayan Unconformity to distinguish it from high strain zones in the Himalayan Metamorphic Front. The fundamental structure that controls orogen architecture in eastern Nepal occurs at higher structural levels within the Greater Himalayan Sequence and we suggest the name; High Himal Thrust. This 100-400 m thick mylonite zone marks a sharp deformation discontinuity associated with a steep metamorphic transition, and separates the Upper-Plate from the Lower-Plate in the Himalayan Metamorphic Front. The high-T/moderate-P metamorphism at ∼20-24 Ma in the Upper-Plate reflects extrusion of material between the High Himal Thrust and the South Tibet Detachment System at the top of the section. The Lower-Plate is a broad schistose zone of inverted, diachronous moderate-T/high-P metamorphic rocks formed between ∼18 and 6 Ma. The High Himal Thrust is laterally continuous into Sikkim and Bhutan where it also occurs at higher structural levels than the Himalayan Unconformity and Main Central Thrust (as originally defined). To the west in central Nepal, the Upper-Plate/Lower-Plate boundary has been placed at lower structural levels, coinciding with the Himalayan Unconformity and has been named the Main Central Thrust, above the originally defined Main Central Thrust (or Ramgarh Thrust).
Sections:Petrology
Subsections:General; Metamorphic rocks
Subjects:Basement; Cambrian; Cenozoic; Continental crust; Crust; Eurasian Plate; Faults; Geometry; Granites; Igneous rocks; Indian Plate; Intrusions; Kinematics; Metamorphic rocks; Metamorphism; Miocene; Neogene; Orogenic belts; P-T conditions; Paleozoic; Plate boundaries; Plate tectonics; Plutonic rocks; Precambrian; Proterozoic; Shear zones; Strain; Structural analysis; Tectonics; Tectonostratigraphic units; Tertiary; Thrust faults; Unconformities; Upper Precambrian; Asia; Himalayas; Indian Peninsula; Indus-Yarlung Zangbo suture zone; Main Central Thrust; Nepal; Barun Gneiss; Himalayan Front; Jannu-Kangchenjunga Gneiss; Kathmandu Group; Kushma Formation; Seti Formation; Yangma Paragneiss
Coordinates:N260000 N273000 E0880000 E0860000
Abstract Numbers:06M/4424
Record ID:2007040433
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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