Predicted velocity and density structure of the exhuming Papua New Guinea (PNG) ultrahigh-pressure (UHP) terrane
Abstract
The Papua New Guinea (PNG) ultrahigh-pressure (UHP) terrane is the youngest known on Earth, and is actively exhuming, making it the ideal location to study mechanisms of UHP exhumation. Electron backscatter diffraction (EBSD) measurements show that the PNG UHP terrane is dominated by rocks with weakly oriented quartz and feldspar and less abundant strongly oriented hornblende, clinopyroxene, and mica. Acoustic velocities measured at high pressures (600 MPa) show that VP is 5.8-6.3 km/s for gneiss samples, 6.5-7.7 km/s for amphibolite, and 7.7-8.2 km/s for eclogite and VS is 3.4-3.9 km/s for gneiss, 4.0-4.4 km/s for amphibolite, and 4.5-4.6 km/s for eclogite. Velocities and anisotropies calculated from mineral crystal preferred orientations (CPOs) are equivalent to within 5% of the measured values. The highest seismic anisotropy for the PNG terrane is calculated for amphibolite at 8% and 7% for VP and VS, respectively. Calculations of seismic velocities at depth based on predicted mineral assemblages indicate that the exhuming UHP terrane is of dominantly mafic composition below ~20 km depth. Anisotropy in the PNG terrane is expected to be quite low and is controlled by foliation orientation. If observable, changes in seismic anisotropy across the exhuming body may be used to differentiate among the different proposed UHP exhumation mechanisms.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.V51C..01B
- Keywords:
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- 3610 MINERALOGY AND PETROLOGY / Geochemical modeling;
- 3625 MINERALOGY AND PETROLOGY / Petrography;
- microstructures;
- and textures;
- 3654 MINERALOGY AND PETROLOGY / Ultra-high pressure metamorphism;
- 3909 MINERAL PHYSICS / Elasticity and anelasticity