Time-scales of crustal anatexis in the Himalaya revealed by petrochronology

Thursday, 18 December 2014
Graham W Lederer, UC Santa Barbara, Santa Barbara, CA, United States and John M Cottle, University of California Santa Barbara, Santa Barbara, CA, United States
Accessory phases, such as monazite, xenotime, and zircon, record a wealth of information regarding the timing, duration, and sources of crustal melting. Combined U-Th/Pb and REE analysis of these petrochronometers by Laser Ablation Split Stream (LASS-) ICPMS reveals complex spatiotemporal relationships on a range of scales, from distinct chemical domains within a single crystal, to cross-cutting dikes within heterogeneous plutons composed of multiple melt batches. The anatectic core of the Himalaya exposes mid-crustal rocks well suited for investigations of the time-scales involved in melt processes, such as generation, segregation, amalgamation, mobilization, and emplacement. Three examples from different settings within the Himalayan orogen, including 1) the Leo Pargil leucogranite injection complex exposed in a gneiss dome in the hinterland, 2) the Manaslu pluton at the interface between the anatectic core and overlying metasediments, and 3) Everest region and Mahabharat granites from the anatectic core to the outermost crystalline thrust sheet of the foreland, illustrate the value of inherited monazite, xenotime, and zircon for deciphering crystallization in the source rock and/or earlier melt batches in addition to determining the age of granite emplacement.