HR: 16:45h
AN: V12I-04 INVITED     [PDF]
TI: The Rates and Timescales of Collisional Orogenesis; Insights From Metamorphic Monazite and the Importance of Garnet
AU: * Foster, G L
EM: g.l.foster@bristol.ac.uk
AF: Department of Earth Sciences, University of Bristol Wills Memorial Building Queens Road, Bristol, BS8 1RJ United Kingdom
AU: * Foster, G L
EM: g.l.foster@bristol.ac.uk
AF: NIGL, British Geological Survey Keyworth, Nottingham, NG12 5GG United Kingdom
AU: Parrish, R
EM: rrp@nigl.nerc.ac.uk
AF: NIGL, British Geological Survey Keyworth, Nottingham, NG12 5GG United Kingdom
AU: Horstwood, M
EM: msah@bgs.ac.uk
AF: NIGL, British Geological Survey Keyworth, Nottingham, NG12 5GG United Kingdom
AB: Much of our understanding of the processes involved in the prograde portion of the orogenic cycle comes from physical and computational models, rather than from geological observation. Although significant progress has been made in the numerical and physical simulation of orogenesis, few constraints exist that permit these models to be rigorously tested. Tools, reliant principally upon metamorphic garnet, that allow the prograde pressure and temperature history to be determined have been applied successfully to a number of orogenic systems. However, it appears the major stumbling block is the necessary time constraints. Traditional methods involve either accessory phase or rock-forming mineral chronometry. Both methods have their drawbacks, for instance, it is difficult to attach an accessory phase age to P-T, and conversely it is notoriously difficult to get precise and accurate ages from rock-forming mineral chronometers (although several new methods have proved successful). To ameliorate this situation, several workers, including ourselves, have been actively seeking methods that allow accessory phase chronometers to be linked to P-T, with particular success being achieved with monazite and xenotime. Fundamentally these methods are of two types: (i) those that are based on detailed textural and chemical studies of the samples in question, or (ii) the empirically or experimentally calibrated accessory phase thermometers. Metamorphic garnet is fundamental to both these methods. Through a combination of these approaches with {\it in situ} accessory mineral dating (SHRIMP, LA-MC-ICPMS) we have been able to constrain the timing of prograde metamorphism, and determine heating and burial rates for several orogenic regions, including the Asian and Indian Himalaya and the Canadian Cordillera.
DE: 1035 Geochronology
DE: 1094 Instruments and techniques
DE: 3620 Crystal chemistry
DE: 3660 Metamorphic petrology
DE: 5475 Tectonics (8149)
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting