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GEOREF RECORD

Geologic and U-Th-Pb geochronologic evidence for early Paleozoic tectonism in the Kathmandu thrust sheet, central Nepal Himalaya

G. E. Gehrels, P. G. DeCelles, T. P. Ojha and B. N. Upreti
Geologic and U-Th-Pb geochronologic evidence for early Paleozoic tectonism in the Kathmandu thrust sheet, central Nepal Himalaya
Geological Society of America Bulletin (February 2006) 118 (1-2): 185-198

Abstract

The Kathmandu thrust sheet consists of Upper Proterozoic through mid-Paleozoic rocks that were emplaced over Lesser Himalayan strata (part of India's cratonal cover) during middle to late Tertiary time. Primary components of the thrust sheet include Upper Proterozoic metasedimentary rocks of the Bhimphedi Group, Cambrian-Ordovician granite bodies, and Ordovician (through Devonian?) conglomerate, sandstone, shale, and limestone of the Phulchauki Group. Deformation, metamorphism, uplift, and erosion accompanied Tertiary emplacement of the thrust sheet, but there is also evidence of widespread early Paleozoic tectonism, such as: (1) Rocks of the Bhimphedi Group were metamorphosed at ca. 490 Ma, as indicated by Th-Pb ages of monazite inclusions in garnet crystals. (2) Bhimphedi rocks are interpreted to have been imbricated along a south-vergent(?) thrust system during early Paleozoic time, with U-Pb ages recording ductile deformation through ca. 484 Ma but ending (at least locally) by ca. 473 Ma. (3) Cambrian-Ordovician granite bodies may have been generated by crustal melting during thrust loading, and at least some are interpreted to have been emplaced as syntectonic sills along the early Paleozoic thrust faults. (4) Ordovician conglomeratic strata were shed from the uplifted Bhimphedi Group and Cambrian-Ordovician granite bodies and are interpreted to have accumulated in a foreland basin setting with respect to the early Paleozoic thrust system.Our findings, together with evidence for early Paleozoic ductile deformation and metamorphism in adjoining regions, indicate that early Paleozoic tectonism has played an important role in shaping the Himalayan orogen. This early Paleozoic tectonism has been overlooked in most current models for the formation of the Himalayan orogen.


ISSN: 0016-7606
EISSN: 1943-2674
Coden: BUGMAF
Serial Title: Geological Society of America Bulletin
Serial Volume: 118
Serial Issue: 1-2
Title: Geologic and U-Th-Pb geochronologic evidence for early Paleozoic tectonism in the Kathmandu thrust sheet, central Nepal Himalaya
Affiliation: University of Arizona, Department of Geosciences, Tucson, AZ, United States
Pages: 185-198
Published: 200602
Text Language: English
Publisher: Geological Society of America (GSA), Boulder, CO, United States
References: 46
Accession Number: 2006-013202
Categories: Structural geologyGeochronology
Document Type: Serial
Bibliographic Level: Analytic
Annotation: With GSA Data Repository Item 200616
Illustration Description: illus. incl. sects., geol. sketch maps
N27°00'00" - N27°49'60", E84°30'00" - E85°30'00"
Secondary Affiliation: Tribhuvan University, NPL, Nepal
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Reference includes data supplied by the Geological Society of America, Boulder, CO, United States
Update Code: 200605
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