T21 Petrochronology: Advances and Applications to Petrogenesis and Tectonics I

Sunday, 22 October 2017
8:00 AM - 12:00 PM
Skagit 4

RECYCLING OF CONTINENTAL CRUST CAPTURED IN XENOLITHS

Paper number: T21-8
Program: Technical Sessions
Time: 9:35 AM – 9:50 AM

Authors

Abstract

Xenoliths that erupted at 11 Ma in the SE Pamir of Tajikistan illuminate what happens when crust founders into the mantle. U-Pb and trace-element laser-ablation split stream inductively coupled plasma mass spectrometry of zircon shows that the igneous and metasedimentary xenoliths were likely derived from the crustal section into which they were intruded: the Jurassic–Cretaceous Andean-style magmatic arc and its Proterozoic–Mesozoic host rocks along the southern margin of Asia. The xenoliths reached temperatures of 1000–1050°C and depths of 90 km--significantly greater than the 70 km Moho--most probably during foundering of the lower crust and uppermost mantle. Spatially heterogeneous recrystallization of zircons was extensive, yielding a range of dates down to 11 Ma. The zircons show distinct changes in Eu anomaly, Lu/Gd ratio, and Ti concentrations that are interpreted to indicate garnet growth and minimal heating at 22−20 Ma, and then 200–300°C of heating, ~25 km of burial, and alkali−carbonate melt injection at 14−11 Ma. These changes are interpreted to coincide with: i) heat input due to Indian slab breakoff at ~22‒20 Ma; ii) rapid thickening and foundering of the Pamir lithosphere at 14‒11 Ma, prior to and synchronous with collision between deep Indian and Asian lithospheres beneath the Pamir.

Geological Society of America Abstracts with Programs. Vol. 49, No. 6

doi: 10.1130/abs/2017AM-296778

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