The Open UniversitySkip to content
 

Empirical constraints on extrusion mechanisms from the upper margin of an exhumed high-grade orogenic core, Sutlej valley, NW India

Chambers, Jennifer; Caddick, Mark; Argles, Thomas; Horstwood, Matthew; Sherlock, Sarah; Harris, Nigel; Parrish, Randall and Ahmad, Talat (2009). Empirical constraints on extrusion mechanisms from the upper margin of an exhumed high-grade orogenic core, Sutlej valley, NW India. Tectonophysics, 477(1-2) pp. 77–92.

Full text available as:
[img]
Preview
PDF (Accepted Manuscript) - Requires a PDF viewer such as GSview, Xpdf or Adobe Acrobat Reader
Download (21Mb)
DOI (Digital Object Identifier) Link: http://dx.doi.org/10.1016/j.tecto.2008.10.013
Google Scholar: Look up in Google Scholar

Abstract

The Early–Middle Miocene exhumation of the crystalline core of the Himalaya is a relatively well-understood process compared to the preceding phase of burial and prograde metamorphism in the Eocene–Oligocene. Highly deformed rocks of the Greater Himalayan Sequence (GHS) dominate the crystalline core, and feature a strong metamorphic and structural overprint related to the younger exhumation. The Tethyan Sedimentary Series was tectonically separated from the underlying GHS during the Miocene by the South Tibetan Detachment, and records a protracted and complex history of Cenozoic deformation. Unfortunately these typically low-grade or unmetamorphosed rocks generally yield little quantitative pressure–temperature�time information to accompany this deformation history. In parts of the western Himalaya, however, the basal unit of the Tethyan Sedimentary Series (the Haimanta Group) includes pelites metamorphosed to amphibolite facies. This presents a unique opportunity to explore the tectono-thermal evolution of crystalline rocks which record the early history of the orogen.

Pressure–temperature�time–deformation (P–T�t–d) paths modelled for two Haimanta Group pelitic rocks reveal three distinct stages of metamorphism: (1) prograde Barrovian metamorphism to 610–620 °C at c. 7–8 kbars, with garnet growing over an early tectonic fabric (S1); (2) initial decompression during heating to 640–660 °C at c. 6–7 kbars, with development of a pervasive crenulation cleavage (S2) and staurolite and kyanite porphyroblast growth; (3) further exhumation during cooling, with minor retrograde metamorphism and modification of the pervasive S2 fabric. Monazite growth ages constrain the timing of initial garnet growth (> 34 Ma), the start of D2 and maximum burial (c. 30 Ma), and the termination of garnet growth (c. 28 Ma). Muscovite Ar/Ar ages indicate cooling through c. 300 °C at c. 13 Ma, from which we derive an initial exhumation rate of c. 1.3 mm year? 1 for the Haimanta Group. The underlying GHS was exhumed at a rate of 2.2 to 3 mm year? 1 during this time. The difference in exhumation rate between these two units is considered to reflect Early Miocene displacement on the intervening South Tibetan Detachment. Slower exhumation (c. 0.6 mm year? 1) of both units after c. 13 Ma followed the cessation of major displacement on this structure, after which time the Haimanta Group and the GHS were exhumed as one relatively coherent tectonic block.

Item Type: Journal Article
Copyright Holders: 2008 Elsevier
ISSN: 0040-1951
Academic Unit/Department: Science > Environment, Earth and Ecosystems
Interdisciplinary Research Centre: Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
eSTEeM
Item ID: 18733
Depositing User: Nigel Harris
Date Deposited: 26 Oct 2009 11:47
Last Modified: 05 Mar 2014 22:51
URI: http://oro.open.ac.uk/id/eprint/18733
Share this page:

Altmetrics

Scopus Citations

Actions (login may be required)

View Item
Report issue / request change

Policies | Disclaimer

© The Open University   + 44 (0)870 333 4340   general-enquiries@open.ac.uk