Composition and tectonic evolution of the Chinese continental crust constrained by Poisson's ratio |
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| Authors: | Shaocheng Ji Qian Wang Matthew H Salisbury |
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| Institution: | 1. Lanzhou Institute of Seismology, China Earthquake Administration, Lanzhou 730000, China;2. Key Lab of Computational Geodynamics, Chinese Academy of Sciences/College of Earth Science, Univeristy of Chinese Academy of Sciences, Beijing 100049, China |
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| Abstract: | We have measured both P- and S-wave velocities (Vp and Vs) and Poisson's ratios (υ) of 60 typical ultrahigh pressure (UHP) metamorphic rock samples from the Chinese Continental Scientific Drilling (CCSD) main and pre-pilot holes and surface outcrops in the Sulu–Dabie orogenic belt at hydrostatic confining pressures up to 850 MPa. The experimental results, together with those compiled in Handbook of Seismic Properties of Minerals, Rocks and Ores Ji, S.C., Wang, Q., Xia, B., 2002. Handbook of Seismic Properties of Minerals, Rocks and Ores. Polytechnic International Press, Montreal, 630 pp.], reveal that except for monomineralic rocks such as quartzite, serpentinite, anorthosite, limestone, and marble the rest of the rock types have Poisson's ratios falling along an upward convex curve determined from the correlations between elastic moduli and density. Poisson's ratios increase with density as the lithology changes from granite, felsic gneiss and schist, through diorite–syenite, intermediate gneiss and metasediment, to gabbro–diabase, amphibolite, and mafic gneiss, and then decrease as the rocks become ultramafic in composition. Eclogite has a higher density but a lower Poisson's ratio than peridotite. The results were applied to constrain the crustal composition and tectonic evolution of the Chinese continental crust based on crustal thickness (H) and Poisson's ratio (υ) from 248 broadband seismic stations, measured using teleseismic receiver function techniques. The North China, Yangtze, South China and Northeast China blocks and Songpan–Ganzi Terrane are dominated by low (υ < 0.26) and moderate (0.26 ≤ υ < 0.28) υ values (> 70%), suggesting the dominance of felsic composition in the crust. The Lhasa terrane, Qiangtang terrane, and Indochina block are characterized by high proportions (33–42%) of measurements with very high υ values (≥ 0.30 and H is found for the South China block, Northeast block, Lhasa block, Qiangtang terrane and Indochina block, indicating either tectonic thickening of the felsic upper and middle crust by folding and thrusting or the removal of mafic layers from the lower crust into the upper mantle by delamination. |
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