Crustal melting in the Himalayan orogen : field, geochemical and geochronological studies in the Everest region, Nepal

A combination of field studies and geochemical techniques were used to investigate the timing and processes involved in leucogranite generation in the Everest region of the Himalayan orogen. Geochemical investigations focused on samples from three outcrops at different structural levels in the Himalayan metamorphic core where in situ crustal melting and multiple generations of leucogranite intrusions were observed. Accessory phase thermochronological and U-Pb geochronological studies were combined to determine the timing of anatexis in a migmatite at the structurally lowest outcrop. Quantitative measurement of REE and Y in monazites and xenotimes, that were later dissolved and dated by U-Pb IDTIMS, revealed monazite growth at temperatures appropriate for crustal melting (>650⁰C) between 25.4 and 24.8 Ma, suggesting that anatexis was ongoing at that time. Further constraints were placed on the timing of crustal melting, granite crystallization and cooling with a detailed U-Pb IDTIMS and 40Ar/39Ar study of leucogranite dikes, sills, and the metamorphic rocks they intrude. Backscattered electron imaging of accessory minerals provided important insights into the petrogenesis of monazite, xenotime and zircon, and guided efforts to isolate accessory phase growth domains. In two granitic sills, extensive accessory phase crystallization between ca. 26 and ca. 23 Ma was interpreted to be the result of episodic to semi-continuous melt generation and crystallization at least between those times. These melt products were later entrained in melts that crystallized as syntectonic sills at 21-22 Ma. Younger crosscutting dikes crystallized between 17.5 and 18.3 Ma.

Department dc:contributor.department

Massachusetts Institute of Technology. Dept. of Earth, Atmospheric, and Planetary Sciences.

Grantor dc:publisher

Massachusetts Institute of Technology

Year dc:date.issued

2003

Author dc:creator

• Viskupic, Karen M. (Karen Marie), 1975-

Advisor dc:contributor.advisor

• Kip V. Hodges.

• Earth, Atmospheric, and Planetary Sciences.

Statement dc:rights

• M.I.T. theses are protected by copyright. They may be viewed from this source for any purpose, but reproduction or distribution in any format is prohibited without written permission. See provided URL for inquiries about permission.

Licence dc:rights.uri

• http://dspace.mit.edu/handle/1721.1/7582

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/1721.1/59101

OAI identifier oai:identifier

oai:dspace.mit.edu:1721.1/59101