Publication Date:
2013-03-26
Description:
[1] P wave velocities (Vp) have been measured in the laboratory and calculated using thermodynamic modelling, for 7 representative rock samples from the lower crust to mantle section of the Kohistan paleo-island arc. Lower crustal rocks comprise plagioclase-rich gabbro, garnet-bearing gabbro and hornblendite; mantle rocks comprise garnetite, pyroxenite, websterite and dunite. Measurements were performed at confining pressures up to 0.5 GPa and temperatures up to 1000 °C. Vp were also calculated using rock major element chemistry with the Perple_X software package. Calculated Vp match closely the laboratory measurements. At depths representative for the arc root, Vp of upper mantle rocks vary from 7.7 – 8.1 km/s, whereas the lower crustal rocks have velocities between 6.9 – 7.5 km/s. P wave anisotropy is small, with exceptions of sheared gabbros. Measured and calculated seismic properties are consistent with, and complement a growing database of published seismic properties from the Kohistan arc. In the light of such data, we discuss seismic imaging of present-day island arcs. Intermediate Vp (7.4–7.7 km/s) in arc roots can be explained by pyroxenites and garnet-bearing mafic rocks. Strong seismic reflectors may be related to garnetites (8.0 – 8.2 km/s).
Electronic ISSN:
1525-2027
Topics:
Chemistry and Pharmacology
,
Geosciences
,
Physics
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