| Title | A new calibration of seismic velocities, anisotropy, fabrics, and elastic moduli of amphibole-rich rocks |
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| Author | Ji, S C ; Shao, T
B; Michibayashi, K; Long, C X; Wang, Q; Kondo, Y; Zhao, W H; Wang, H C; Salisbury, M H |
| Source | Journal of Geophysical Research, Solid Earth vol. 118, 9, 2013 p. 4699-4728, https://doi.org/10.1002/jgrb.50352  Open Access |
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| Year | 2013 |
| Alt Series | Natural Resources Canada, Contribution Series 20200239 |
| Publisher | American Geophysical Union |
| Document | serial |
| Lang. | English |
| Media | paper; on-line; digital |
| File format | pdf |
| Subjects | geochemistry; Science and Technology; tectonics; igneous and metamorphic petrology; seismic velocities; anisotropy; fabric analyses; amphibolites; continental crust; oceanic crust |
| Illustrations | tables; distribution diagrams; graphs; equal-area stereonet projections; diagrams; plots |
| Released | 2013 08 29 |
| Abstract | A large portion of the middle to lower crust beneath the continents and oceanic island arcs consists of amphibolites dominated by hornblende and plagioclase. We have measured P and S wave velocities
(V-p and V-s) and anisotropy of 17 amphibole-rich rock samples containing 34-80vol% amphibole at hydrostatic pressures (P) up to 650MPa. Combined petrophysical and geochemical analyses provide a new calibration for mean density, average major element
contents, mean V-p-P and V-s-P coefficients, intrinsic V-p and V-s anisotropy, Poisson's ratios, the logarithmic ratio R-s/p, and elastic moduli of amphibole-rich rocks. The V-p values decrease with increasing SiO2 and Na2O+K2O contents but increase
with increasing MgO and CaO contents. The maximum (0.38-0.40km/s) and minimum S wave birefringence values occur generally in the propagation direction parallel to Y and normal to foliation, respectively. Amphibole plays a critical role in the
formation of seismic anisotropy, whereas the presence of plagioclase, quartz, pyroxene, and garnet diminishes the anisotropy induced by amphibole crystallographic preferred orientations (CPOs). The CPO variations cause different anisotropy patterns
illustrated in the Flinn diagram of V-p(X)/V-p(Y)-V-p(Y)/V-p(Z) plots. The results make it possible to distinguish, in terms of seismic properties, the amphibolites from other categories of lithology such as granite-granodiorite, diorite,
gabbro-diabase, felsic gneiss, mafic gneiss, eclogite, and peridotite within the Earth's crust. Hence, amphibole, aligned by dislocation creep, anisotropic growth, or rigid-body rotation, is the most important contributor to the seismic anisotropy of
the deep crust beneath the continents and oceanic island arcs, which contains rather little phyllosilicates such as mica or chlorite. |
| GEOSCAN ID | 326651 |
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