EBSD analysis of eclogitized rocks form the Marun-Keu complex, Polar Urals, Russia
Abstract
The transitions from amphibolite, gabbro, and quartzofeldspathic gneiss to eclogite in the high-pressure Marun-Keu complex in the Polar Urals, Russia, make this complex a good candidate for using mineral chemistries and electron backscatter diffraction (EBSD) to study the interplay between metamorphism and deformation and more broadly understand the orogenic evolution of eclogites in high-pressure subduction zone complexes. The Marun-Keu complex results from the deep crustal processes during the Uralian Orogeny formed by collision of the east European platform with Siberian-Kazakhian terranes in the Devonian to Triassic. Eclogite-facies rocks containing garnet, omphacite, and rutile occur in the central and southern part of the complex and the blueschist-facies and low-T eclogitization are found in the north part of the complex. Based on Glodny et al. (2004), Rb/Sr protolith ages for the gabbros are about 500 Ma which is near the crystallization age from U-Pb zircon data and the eclogite-facies metamorphism was occurred about 355 Ma. Field and microscopic observation of the rocks from the Marun-Keu complex show a sharp contact between the host rocks (gabbro and amphibolite) and the eclogite-facies rocks. This study will mainly focus on the chemistry and different microstructures of the minerals in the samples PU-62, J12, J26 and PU-34 which are showing the transition of the host rocks to the eclogite. Samples PU-62 and J-26 including garnets, omphacite and quartz, show the complete transformation from the gabbro to eclogite and the corona textures and replaced minerals in these two samples indicate incomplete reactions (Molina et al., 2002). Samples J12 and PU-34 - boudins in a quartz/white mica vein- are showing the transitions between the amphibolites and eclogites. There is a sharp contact between the amphibolite core and the eclogite rim in these samples. The major minerals in the eclogite rim are omphacite, garnet, phengite and quartz and the transitional part (amphibolites/eclogite) contains of garnet, omphacite and hornblende and the amphibolite core have the amphibole garnet and quartz. The lattice-preferred orientation (LPO) of all phases, especially garnets in the selected thin sections are being measured by the EBSD method at san Francisco State University and the deformation patterns of the minerals from the host rocks (gabbro/amphibolite) to eclogites will be studied. Understanding the deformation mechanisms related to eclogite-facies metamorphism will provide some information about the deep crust and its activities during the tectonic collision. References: Glodny, J., Pease, V., Montero, P., Austrheim, H., and Rusin, A.I., 2004, Protolith ages of eclogites, Marun-Keu Complex, Polar Urals, Russia: implications for the pre- and early Uralian evolution of the northeastern European continental margin: Geological Society, London, Memoirs, v. 30, p. 87-105. Molina, J.F., Austrheim, H., Glodny, J., and Rusin, A., 2002, The eclogites of the Marun-Keu complex, Polar Urals (Russia): fluid control on reaction kinetics and metasomatism during high P metamorphism: Lithos, v. 61, p. 55-78.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.V33A2344H
- Keywords:
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- 3625 MINERALOGY AND PETROLOGY / Petrography;
- microstructures;
- and textures;
- 3660 MINERALOGY AND PETROLOGY / Metamorphic petrology