HR: 1340h
AN: T33A-1135    [Abstracts]
TI: The Middle AsiaN Active Source (MANAS) Profile: Preliminary Results From A Deep Seismic Transect in the Tien Shan of Kyrgyzstan and China
AU: * Knapp, J H
EM: knapp@geol.sc.edu
AF: Dept. Geological Sciences, Univ. South Carolina, Columbia, SC 29208, United States
AU: Roecker, S W
EM: roecks@rpi.edu
AF: Earth & Environmental Sciences, Rensselaer Polytechnic Institute, Troy, NY 12180, United States
AU: Park, S K
EM: spark@ucr.edu
AF: Dept. Earth Sciences, University of California, Riverside, Riverside, CA 92521, United States
AU: Schelochkov, G
AF: Research Station of the Russian Academy of Sciences, Geodynamic Proving Ground, Bishkek, 720049, Kyrgyzstan
AU: He, R
AF: Chinese Academy of Geological Sciences, No. 26 Bai Wan Zhuang St. Xicheng, Beijing, 100037, China
AB: New near-vertical deep seismic reflection data, acquired during the summer of 2007, constitute an ~350 km lithospheric transect from the northwestern Tarim Basin in China to the central Tien Shan of Kyrgyzstan. Recognized as one of the highest, youngest, and most active orogenic systems on Earth, the Tien Shan are situated internal to the Eurasian continent, removed up to 3000 km from the former plate boundary with the Indian subcontinent. Existing geologic constraints imply that up to 200 km of shortening may have occurred in Late Tertiary to Recent time. Additionally, geologic, topographic, and gravimetric data suggest that continental lithosphere of the Tarim basin may presently be subducting beneath the southern margin of the Tien Shan, in the absence of an oceanic slab. While geodetic measurements document that the Tien Shan currently record about half of the shortening between India and Eurasia, geologic data dictate that active faults are restricted to only several of the individual ranges that make up the mountain belt. Passive-source seismological studies have shown the surprising result that the orogenic crust is thickest (65-70 km) at both the southern and northern margins of the Tien Shan, and thins dramatically to ~35 km within the internal part of the orogen. Key targets of the MANAS (Middle AsiaN Active Source) Profile include (1) the top of the Tarim crust as it descends beneath the southern Tien Shan, (2) an inferred crustal-scale frontal ramp, representing where the continental plate may have broken and is now descending into the upper mantle, (3) the geometry of demonstrably active faults below the shallow depths to which they can be inferred from surface geologic constraints, (4) the topography and seismic reflection signature of the Moho, especially given the unexpected variations in crustal thickness across the orogen, and (5) the significance of both crustal and upper mantle conductivity anomalies previously identified through magnetotelluric studies. The experimental design involved roll-along of stand-alone seismometers (Reftek-125A), allowing essentially continuous CMP coverage along the entire ~350-km transect, despite the challenging terrain. These seismic reflection results will be combined with a coincident broadband array (40 stations at ~10 km spacing for two years) and magnetotelluric measurements along the profile route to provide an integrated geophysical fingerprint of the lithospheric structure of intracontinental mountain building.
DE: 7218 Lithosphere (1236)
DE: 8100 TECTONOPHYSICS
DE: 8108 Continental tectonics: compressional
SC: Tectonophysics [T]
MN: 2007 Fall Meeting