SPATIO-TEMPORAL EVOLUTION OF THE TANGRA YUMCO RIFT, SOUTH-CENTRAL TIBET: INSIGHTS FROM ZIRCON (U-TH)/HE THERMOCHRONOMETRY
We present a 1:100,000 scale geologic map of ~2,000 km2 in the southern TYC rift and new ZHe dates across key structural relationships. TYC is bounded by two approximately north striking high angle (~45-70°) active normal faults that alternate dominance along strike. Quaternary alluvial fan deposits in the central rift hanging wall display synthetic graben structures, whereas in northern and southern rift segments, a stepped sequence of high angle normal faults cut Quaternary deposits and likely sole into the rift-bounding faults at depth. Pervasive northeast dipping foliation is observed in the exhumed footwall granodiorite, with slip lineations and fault plane striations suggesting northeast directed oblique sinistral-normal slip. Seventy single-grain ZHe analyses yield dates between 25.72 Ma and 7.58 Ma, with median dates between ~23 Ma and ~8 Ma. Sample transects from the footwall indicate an older in the south (~20 Ma) to younger in the north (~8 Ma) trend in rift age along strike, in agreement with India underthrusting model predictions. This detailed work from the TYC rift may yield insights into fault growth mechanisms and dynamic processes driving changes in crustal thickness and topographic evolution during orogenesis.