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Title: Kinematic Evolution of the Tangra Yumco Rift, South-Central Tibet
We interpret the kinematics of the Tangra Yumco (TYC) rift by evaluating spatiotemporal trends in fault displacement, extension onset, and exhumation rates. We present new geologic mapping, U-Pb geochronology, zircon (U-Th)/He (ZHe) thermochronology, and HeFTy thermal modeling results that are critical to testing dynamic models of extension in Tibet. The TYC rift is bounded by two NNE striking (~N10°E-N35°E) high angle (~45-70°) active normal faults that alternate dominance along strike. Footwall granodiorites show foliation, slip lineation, and fault plane striation measurements indicative of northeast directed oblique sinistral-normal slip. In North and South TYC, hanging wall deposits are cut by a series of active high-angle normal faults which likely sole into a master fault at depth, while in central TYC, hanging wall deposits display synthetic graben structures potentially indicative of low-angle faulting. Analysis of ~50 samples collected across key structural relationships in and around TYC yield 14 mean U-Pb dates between ~59-49 Ma and ~190 single-grain ZHe dates between ~60-4 Ma with spatial trends in ZHe data correlating strongly with latitude. Samples from Gangdese latitudes show a concentration of ~28-15 Ma ages, while those north of ~29.8° latitude yield both younger (~9-4 Ma) and older (~59-45 Ma) ages. We interpret (1) Gangdese Range samples reflect exhumation during contraction and uplift along the GCT peaking at ~21-20 Ma, (2) ~9-4 Ma ages reveal extension timing along fault segments experiencing significant rift-related exhumation, and (3) ~59-45 Ma ages represent un-reset or partially-reset samples from fault segments that have experienced lesser magnitudes of rift exhumation. HeFTy thermal models indicate a two-stage cooling history with initial slow cooling followed by accelerated cooling rates in Late Miocene-Pliocene time (~13-4 Ma) consistent with prior results from TYC and other Tibetan rifts. Our data are consistent with a segment linkage fault evolution model for the TYC rift, with underthrusting of Indian lithosphere likely related to the northward acceleration of rifting. Future work will utilize advanced HeFTy modeling including U-Pb and apatite fission track data to further constrain the exhumation history of TYC and test dynamic models of extension for southern Tibet.  more » « less
Award ID(s):
1917685
NSF-PAR ID:
10485769
Author(s) / Creator(s):
;
Publisher / Repository:
American Geophysical Union
Date Published:
Journal Name:
AGU Fall Meeting 2022, held in Chicago, IL, 12-16 December 2022, id. T25B-06.
Format(s):
Medium: X
Location:
San Francisco, CA
Sponsoring Org:
National Science Foundation
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