Abstract
Abstract Metamorphic rocks are the records of plate tectonic processes whose reconstruction relies on correct estimates of the pressures and temperatures (P-T) experienced by these rocks through time. Unlike chemical geothermobarometry, elastic geobarometry does not rely on chemical equilibrium between minerals, so it has the potential to provide information on overstepping of reaction boundaries and to identify other examples of non-equilibrium behavior in rocks. Here we introduce a method that exploits the anisotropy in elastic properties of minerals to determine the unique P and T of entrapment from a single inclusion in a mineral host. We apply it to preserved quartz inclusions in garnet from eclogite xenoliths hosted in Yakutian kimberlites (Russia). Our results demonstrate that quartz trapped in garnet can be preserved when the rock reaches the stability field of coesite (the high-pressure and high-temperature polymorph of quartz) at 3 GPa and 850 °C. This supports a metamorphic origin for these xenoliths and sheds light on the mechanisms of craton accretion from a subducted crustal protolith. Furthermore, we show that interpreting P and T conditions reached by a rock from the simple phase identification of key inclusion minerals can be misleading.
Highlights
The mechanisms attending the downward transport of crustal material into the mantle and its return back to Earth’s surface are still a matter of vigorous debate
Elastic geobarometry does not rely on chemical equilibrium between minerals, so it has the potential to provide information on overstepping of reaction boundaries and to identify other examples of non-equilibrium behavior in rocks
We apply it to preserved quartz inclusions in garnet from eclogite xenoliths hosted in Yakutian kimberlites (Russia)
Summary
M. Alvaro1*, M.L. Mazzucchelli1, R.J. Angel1, M. Murri1, N. Campomenosi2, M. Scambelluri2, F. Nestola3, A. Korsakov4, A.A. Tomilenko4, F. Marone5 and M. Morana1 1Department of Earth and Environmental Sciences, University of Pavia, Via A. Ferrata, 1 I-27100 Pavia, Italy 2Department of Earth, Environment and Life Sciences, University of Genoa, Corso Europa 26, 16132 Genoa, Italy 3Department of Geoscience, University of Padua, Via Gradenigo 35, 35131 Padua, Italy 4V.S. Sobolev Institute of Geology and Mineralogy, Siberian Branch of the Russian Academy of Sciences, Koptyug Ave. 3, 90630090 Novosibirsk, Russia 5Swiss Light Source, Paul Scherrer Institut, 5232 Villigen, Switzerland
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