HR: 13:45h
AN: T23G-01    [Abstracts]
TI: Mantle Lithosphere Beneath Tibet: A Synthesis With Special References to Results From Project Hi-CLIMB
AU: * Chen, W
EM: wpchen@uiuc.edu
AF: Univ. of Illinois, Dept. of Geology, Urbana, IL 61801, United States
AU: Tseng, T
EM: tseng1@uiuc.edu
AF: Univ. of Illinois, Dept. of Geology, Urbana, IL 61801, United States
AU: Nowack, R L
EM: nowack@purdue.edu
AF: Purdue Univ., Dept. of Earth & Atmos. Sci., W. Lafayette, IN 47907, United States
AU: Hung, S
EM: shung@ntu.edu.tw
AF: Nat. Taiwan Univ., Dept. of Geosci., Taipei, 10617, Taiwan
AU: Chung, S
EM: sunlin@ntu.edu.tw
AF: Nat. Taiwan Univ., Dept. of Geosci., Taipei, 10617, Taiwan
AU: Huang, B
EM: hwbs@earth.sinica.edu.tw
AF: Academia Sinica, Inst. of Earth Sci., Taipei, 115, Taiwan
AB: We present a synthesis regarding the current configuration of Asian and Indian mantle lithosphere beneath the Himalayan-Tibetan collision zone -- the most prominent zone of active continental collision. The following cross- sectional view is achieved by combining new results from complementary approaches, including modeling profiles of triplicate waveforms, migration of scattered wave-fields, patterns in shear-wave birefringence, travel- time tomography, regional gravity anomalies/modeling of plate flexure, and distributions of helium isotopic ratios: The leading edge of the Indian lithospheric mantle (Indian mantle front, IMF) extends about 200 km north of the Bangong-Nujiang suture in the heartland of Tibet while the southern terminus of the Asian counterpart (the mantle suture, MS) is about 100 km to the north of the Indus-Yarlong suture in southern Tibet (see Fig. 1 of the included URL) Furthermore, we carried out a preliminary reconstruction of lithospheric configuration by extrapolating current velocity of ground motions determined from GPS-based geodesy back to 15 Ma ago -- the timing of the last major episode of (potassic) magamtism that mainly occurred in the Qiangtang terrane. The results indicate that a large- scale anomaly of high P-wave speeds (Vp), currently resting just above the 660-km discontinuity under central Tibet, is likely to be associated with a cold remnant of lithospheric mantle that was convectively removed about 15 Ma ago from thickened lithosphere of the Qiangtang terrane. Meanwhile, noticeable lateral (east-west) variations are also recognized. For instance, low Vp in the lower crust/uppermost mantle just north of the Indus-Yarlong suture is not a continuous feature. Intriguingly, the anomaly of low Vp correlates with low amplitudes of P- to S conversions, indicating a gradual crust-mantle transition. These results suggest that currently channel flows in the lower crust, if any, is limited in extent. An anomalous region of null shear-wave birefringence is also apparent in the Lhasa terrane so the MS is not always well-resolved between Hi-CLIMB and Yardong-Golmud profiles.
UR: http://www.uiuc.edu/goto/pubs/63_ChenTsengDetachedLithoTibet.JGR.07.pdf
DE: 1038 Mantle processes (3621)
DE: 7218 Lithosphere (1236)
DE: 8107 Continental neotectonics (8002)
DE: 8108 Continental tectonics: compressional
DE: 8120 Dynamics of lithosphere and mantle: general (1213)
SC: Tectonophysics [T]
MN: 2007 Fall Meeting