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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy
(S) - IASPEI - International Association of Seismology and Physics of the Earth's
Interior
JSS014 Poster presentation 2278
Structure of earths crust and upper mantle, inland subduction and its
coupling effects on the Dabie orogenic belt and the Tancheng-lujiang fault
zone
Prof. Jiwen Teng
Institute of Geology and Geophysics Chinese Academy of Sciences IASPEI
Yan Yafen, Wang Guangjie, Xiong Xiong
The Dabieshan Mountains was a nearly EW trending collision orogenic belte under the roughly NS
directed compressive force during the Indo-China and early Yanshan movement periods. It separates
the North China and Yangtze continental blocks, between which exposed broad cores of metamorphic
rocks. Since it lies at the west side of the place where the mountains and the Tanlu fault zone intersect
and converge, the orogenic belte must be constrained by strong translational offset of the Tanlu fault
zone during the late period (late Jurassic-early Cretaceous). This fault zone is an inland giant system of
translational features on the eastern margin of the Chinese mainland, which appeared after the
formation of the Dabieshan orogenic belte. Based on the rock chronology, the metamorphic pressure
difference in the peak period and the discovered coesite in Alpine metamorphic sedimentary rock, the
coesite and eclogite from the Dabie orogenic belt is inferred to be the consequence resulted from their
reentry from mantle around the depth of the 120km to the shallow crust. To provide the quantitative
evidence of the deep structure and dynamic process beneath the Dabie orogenic belt, we attempt to
explore the 3-D velocity structure of S wave beneath this region by using the inversion method with 4 4
network based on the dispersion effect of Rayleigh wave. Our purpose is to reveal the formation
mechanism of the UHPM zone in the Dabieshan, exchange of deep and shallow materials and energy, as
well as deep dynamic processes of intraplate tectonics in terms of block-like features of structure in
crust and upper mantle. Then we would propose new insights and evidence for the strong translational
dislocation of the Dabieshan and the Tanlu fault zone, and the coupling effects of intraplate subduction.
The results show that, there is a high-velocity subduction slab of tongue shape with underthrusting
depth 160km extending from east to west. A low velocity mantle hotspot with a 500km wide head is
found at depth of 70km in the upper mantle beneath the Qingling-Dabie orogenic belt. The outcrop of
coesite and eclogites in the Dabie orogenic belt is the synthetic consequence of the movement and
dynamic effects of deep (upper mantle) material results from the deep substance and energy exchange,
strong strike-slip motion along the Tanlu fault zone and the inland subduction.
Keywords: dabie orogenic, inland subduction, deep process