Seismic velocities, anisotropy, hysteresis and Poisson's ratio of ultrahigh pressure (UHP) metamorphic rocks

This thesis, entitled "Seismic velocities, anisotropy, hysteresis and Poisson's ratio of ultrahigh pressure (UHP) metamorphic rocks", consists of two parts. The first part presents an introduction to the general background of elasticity and mixture rules and their application to the prediction of physical properties of multiphase solids and rocks (Chapter 1), and an overview of the main scientific results achieved from the CCSD project and the investigations of the Sulu UHP metamorphic terrane (Chapter 2). The second part of the thesis is a collection of 4 research papers published or accepted in international journals (Journal of Geophysical Research and Tectonophysics) (from Chapter 3 to Chapter 6).;The pressure (P) dependence of Poisson's ratios (upsilon) for UHP metamorphic rocks has been studied (Chapter 4). The experimental results display two main types of the upsilon -- P relationships in the range of 40--850 MPa: (1) upsilon shows little variation with P in the range of 40--850 MPa; and (2) with increasing pressure, upsilon increases rapidly below ∼200 MPa and then becomes quasi-constant at higher pressures.;Poisson's ratios of common minerals and rocks have been outlined and the experimental results have been applied to constrain the crustal composition and tectonic evolution of the Chinese continental crust based on crustal thickness (H) and Poisson's ratio (upsilon) data measured from 248 broadband seismic stations using teleseismic receiver function techniques (Chapter 5). It is found that except for monomineralic rocks such as quartzite, serpentinite, anorthosite, limestone and marble, most rock types have Poisson's ratios falling along an upward convex curve determined from the correlations between elastic moduli and density. Poisson's ratios display an 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 teleseismic receiver function data show that the North China, Yangtze, South China and Northeast China blocks and Songpan-Ganzi Terrane of China are dominated by low (upsilon < 0.26) and moderate (0.26 ≤ upsilon < 0.28) upsilon values (>70%), indicating that the crust is predominantly felsic.;We also investigated the correlations between P- and S-wave velocities (Vp and Vs) and corresponding Poisson's ratios (upsilon) for 12 common categories of rocks (amphibolite, anorthosite, basalt, diorite, eclogite, felsic gneiss, gabbro-diabase, granite, intermediate gneiss, limestone, mafic gneiss, and peridotite) and 4 types of massive sulfide ores (chalcopyrite, pyrite, sphalerite and pyrrhotite) (Chapter 6). The linear correlation provides good descriptions for the Vs-Vp, and lnV s-lnVp, relationships. Poisson's ratio is linearly correlated with Vs, Vp, shear modulus (G) and Young's modulus (E) for these rocks and sulfide ores. A decrease in Poisson's ratio is associated with increases in Vs, G and E. However, the variation of Poisson's ratio with Vp depends on the logarithmic ratio Rs/p (i.e., ∂lnVs/∂ln Vp). Poisson's ratio increases or decreases with Vp when Rs/p <1 or >1. Rs/p is found to vary with lithology (0.300 for granite, 0.573 for diorite, 0.602 for felsic gneiss, 0.631 for intermediate gneiss, 0.721 for gabbro-diabase, 0.768 for mafic gneiss, 0.866 for eclogite, 0.890 for amphibolite, and 1.391 for peridotite). Rs/p can be used as a proxy for the composition of the deep continental crust and the upper mantle. This study suggests that the correlations between Vp and Vs, and corresponding Poisson's ratios (upsilon) in should be important in modeling and interpreting seismic data in terms of chemistry and lithology. (Abstract shortened by UMI.);P-wave velocities, anisotropy and hysteresis as a function of confining pressure have been investigated in the UHP-pressure metamorphic rocks (Chapter 3). The comparison between samples collected from surface outcrops and those from the CCSD main borehole cores indicates that the seismic hysteresis is caused by irreversible changes in grain contacts, increases in microcrack aspect ratios and reduction of void space during the pressurization-depressurization cycle. The results suggest that regionally extensive mantle reflectors observed beneath modern and ancient orogenic belts may imply the preservation of rapidly subducted, dry, metastable crustal mafic or felsic material within the lithospheric upper mantle.