HR: 13:40h
AN: V33E-01 INVITED    [Abstracts]
TI: The pace of continental deformation and geochronology
AU: * Parrish, R R
EM: rrp@nigl.nerc.ac.uk
AF: Dept of Geology University of Leicester and NERC Isotope Geosciences Laboratory, British Geological Survey, Keyworth, Nottinghamshire, Nottingham, NG12 5GG, United Kingdom
AB: Continental tectonics and geochronology have had a symbiotic relationship for many decades. A diverse range of chronometers has been applied to tectonic problems and to quantify rates of geological processes. These chronometers include U-Th-Pb, Ar-Ar, ZFTA, U-Th-He, and other systems and fall into geo-chronomters that date geological events (i.e. mineral crystallisation concurre3nt with igneous or metamorphic mineral growth) and thermo-chronometers (dating the time of cooling during exhumation, for example). With advances in linking mineral chemistry of accessory minerals to metamorphic reactions, it goes without saying that careful petrology, petrography, mineral chemistry and imaging are essential to arriving at an appropriate interpretation of U-Th-Pb dates of accessory minerals in metamorphic rocks (e.g. monazite, zircon, titanite). Examples from the Himalaya will be used to illustrate how ID-TIMS and intra-crystal SIMS and LA-ICP-MS U-Th-Pb dating can be used to elucidate P-T-t paths of metamorphic rocks during metamorphism and exhumation. By contrast, an emerging area of study involves using single detrital minerals to reconstruct provenance and patterns of erosion in mountain systems. Because these detrital minerals (mica, monazite, zircon, rutile, allanite, titanite, etc.) have been separated from their petrographic context, interpretations based upon ages of these minerals will be much less constrained and it is all the more important to ask ‘what do the dates mean?'. Further examples will be presented that attempt to explore whether a comprehensive approach to mineral provenance analysis in sedimentary materials (chronology, mineral chemistry, isotopes) can provide an accurate and useful snapshot of the geological characteristics of a portion of a mountain system undergoing erosion and exhumation. What can be reconstructed by this approach and what are its limitations? Of particular interest are monazite, rutile, garnet, and zircon which may provide pivotal information about the metamorphic – orogenic history. The limitations of the use of only zircon in such studies will be discussed.
DE: 1115 Radioisotope geochronology
DE: 1140 Thermochronology
DE: 3652 Pressure-temperature-time paths
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting