Crustal deformation and crust mantle interaction in active collision zones Cental Tibet and East Anatolia

2004-12-13
Zandt, George
Özacar, Atilla Arda
Beck, Susan L.
A major question in the tectonics of collisional mountain belts concerns the relative coupling or decoupling of the crust and mantle. In this respect, recent IRIS PASSCAL seismic experiments in the Tibetan and East Anatolian plateaus provide an important opportunity to study crustal deformation and crust-mantle interactions in continental collisions. Receiver functions (RF) from the dense INDEPTH III seismic array that was deployed across central Tibet, show a crustal thickness of $\sim65$ km and a very weak Moho beneath the Bangong-Nujiang suture (BNS) that could be due either to a gradational velocity contrast or scattering by topography on the Moho. By using a global minimization technique, we modeled the azimuth dependant variations on RFs recorded at a representative station within the suture and found strong anisotropy near the surface and in the middle crust separated by south dipping ($\sim25\deg$) layer. Mid-crustal anisotropy occurs in a low velocity zone (LVZ) and has a fabric dipping gently ($\sim18\deg$) northward that might be related to a well-developed near-horizontal rock fabric induced by crustal flow. On the other hand, a preliminary analysis of data recorded by the Eastern Turkey Seismic Experiment (ETSE) show a drastic change in crustal structure between the Arabian plate and East Anatolian plateau across the Bitlis suture. RFs show a strong Moho ($\sim40$ km) and a mid-crustal discontinuity ($\sim25$ km) beneath the Arabian plate and a slightly weaker Moho ($\sim45$ km), a mid-crustal LVZ ($\sim25$ km) and a mantle discontinuity ($\sim85$ km) beneath the East Anatolian plateau. Arrival times of multiples also indicate low Vp/Vs ($\sim1.70$) for the Arabian plate and high Vp/Vs ($\sim1.80$) for the plateau. In the central region of the plateau, the fast directions of SKS splitting and Pn anisotropy are parallel to each other but at high angles to the GPS motions suggesting crustal flow within the LVZ that decouples surface deformation from the upper mantle. In contrast, for the Arabian plate, the GPS motions are parallel to the Pn but different from the SKS fast directions and may reflect a coupled crust and upper mantle. In order to test this idea, we will model crustal anisotropy that is characterized by systematic tangential energy and polarity reversals in the existing data and interpret its tectonic significance.

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Citation Formats
G. Zandt, A. A. Özacar, and S. L. Beck, “Crustal deformation and crust mantle interaction in active collision zones Cental Tibet and East Anatolia,” San-Francisco, Kostarika, 2004, vol. 85, Accessed: 00, 2021. [Online]. Available: http://abstractsearch.agu.org/meetings/2004/FM/sections/T/sessions/T51C/abstracts/T51C-0463.html.