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Time-scales of crustal anatexis: monazite petrochronology of Himalayan granites


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 inductively coupled plasma mass spectrometry (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 crystalline thrust sheet of the foreland, illustrate the value of monazite for deciphering crystallization in source rocks and/or earlier melt batches in addition to determining granite emplacement age.

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