Elevation of the 410 km discontinuity beneath the central Tien Shan: Evidence for a detached lithospheric root

Abstract

Abstract. We analyzed P-SV converted phases recorded by the Kyrgyzstan Broadband Network (KNET) to investigate the nature of phase transitions in the upper mantle beneath the central Tien Shan and the Kazakh shield. We find that P-SV phases from the 410 km discontinuity recorded by several stations located along the range front are about 2 s earlier from beneath the Tien Shan than they are from beneath the Kazach shield. Because the delay times at stations located on the Kazakh shield are normal and seismic velocities in the upper mantle beneath this part of the Tien Shan apparently are low (about 4% less than the Kazakh shield to the north), the early arrival of the conversion from 410 km implies that this discontinuity is elevated by about 20 km. Because the 410 km discontinuity can be elevated by the introduction of cold material, our results are consistent with a model in which the lithosphere in this area developed a root during collision that later detached and is now residing near 410 km depth.

Crustal thickness variations across the northern Tien Shan from teleseismic receiver functions

“…They argue that an anomalously buoyant and presumably warm upper mantle makes the Tien Shan easier to deform than the surrounding lithosphere. P-SV conversions from the 410-km discontinuity are found to be 2 s earlier beneath the Tien Shan than beneath the Kazakh Shield [Chen et al, 1997], fact that it is relatively far (approximately 1,500 km) from the suggesting cool material near 410 km depth beneath the Tien active Indo-Eurasian collision zone. Present rates of deformation Shan.…”

Tectonic evolution of the North China Block: from orogen to craton to orogen

“…The formation of China's most important gold vein deposits occurred at the same time along the northern, eastern, and southern margins of the Eastern Block (Mao et al 1999;Zhou et al 2002;Yang, J.-H. et al 2003;Fan et al 2007). Unroofing of many metamorphic core complexes (c. 140-105 Ma), products of SE-NE extension (Niu 2005;Zhang et al 1994;Zheng et al 1998Zheng et al , 2001Zhang, Y. Q. et al 1998;Webb et al 1999;Zhang, Q., et al 2001;Davis et al 2002;Darby et al 2006;, and major animal extinctions were also significant in this period (Chen et al 1997;Wang et al 2001).…”

Analysis of Seismic Activity in the Crust from Earthquake Relocation in the Central Tien Shan

“…6). This suggests that dynamic processes such as the small-scale mantle convection or mantle upwelling, which resulted in the lithospheric thinning or removal (Chen et al, 1997), still occur beneath the central Tien Shan.…”