Geological Society of America

T56 Metamorphic Petrology Past, Present and Future: Preparing for the Next 100 Years with the Mineralogical Society of America

Sunday, 22 September 2019
1:30 PM - 5:30 PM
Room 126ABC, North Building

ECLOGITES IN MIGMATITES: EVIDENCE FOR EXHUMATION OF LARGE VOLUMES OF DEEP CRUST

Paper number: T56-14
Program: Technical Sessions
Time: 5:00 PM – 5:15 PM

Authors

Donna Whitney Presenting Author
University of Minnesota-Twin Cities, Minneapolis, MN
Christian Teyssier
University of Minnesota, Minneapolis, MN
Clementine Hamelin
University of Minnesota-Twin Cities, Minneapolis, MN
Natalie Raia
University of MinnesotaDept of Earth Sciences, Tate Hall, 150, Minneapolis, MN
Megan Korchinski
University of Minnesota, Minneapolis, MN
Françoise Roger
Montpellier Cedex 05
Patrice Rey
The University of Sydney, Sydney

Abstract

Eclogite lenses and layers in migmatite have been described in many orogens in the past century (e.g. Eskola 1921). The relationship of high-pressure (HP) metamorphism of eclogite inclusions to the moderate/low-P conditions recorded by host gneiss has been discussed and debated for decades (e.g. Coleman et al. 1965) because significant information about metamorphic and tectonic processes can be gleaned from eclogites and host gneiss. Key examples of eclogite-in-migmatite are in the Variscan, Caledonian, and Alpine-Himalayan orogens. Although eclogite may occur as tectonic lenses in gneiss that did not experience HP metamorphism, more commonly, both rock types experienced HP metamorphism but only eclogite preserves an obvious record of it.

In the Variscan Montagne Noire migmatite dome, French Massif Central, eclogite in 2 localities – one in the dome core, one at the margin – had similar gabbro protoliths with the same crystallization age as migmatite protoliths. Both eclogites experienced HP metamorphism that was broadly coeval with crystallization of migmatite. Abundant amphibolite has similar bulk composition as eclogite, indicating that the amphibolites are likely retrogressed eclogite and therefore much of the dome was deeply sourced. However, the 2 eclogites differ in degree of preservation of protolith zircon, record of prograde metamorphism, peak T, and deformation history, providing information about eclogite trajectories from source to emplacement and variation of fluid-rock interaction during metamorphism. Further insights into sources, trajectories, and thermal/melting history of dome rocks is provided by numerical models, including prediction of how the deepest (near-Moho) crust is exhumed to the shallowest levels, inverting crustal structure and emplacing migmatitic sheets above crust that remained below the solidus.

In the Montagne Noire, zircon in dome-core eclogite records an amphibolite facies event that has not been recognized in host migmatite but that is widespread elsewhere in the Massif Central. This may be an indication that domes are the shallowly-emplaced manifestations of vast, connected, deep crustal flow systems that underlie large regions of hot orogens. This hypothesis remains to be tested by integrated petrology/geochemistry and numerical modeling.

Geological Society of America Abstracts with Programs. Vol. 51, No. 5

doi: 10.1130/abs/2019AM-338091

© Copyright 2019 The Geological Society of America (GSA), all rights reserved. Permission is hereby granted to the author(s) of this abstract to reproduce and distribute it freely, for noncommercial purposes. Permission is hereby granted to any individual scientist to download a single copy of this electronic file and reproduce up to 20 paper copies for noncommercial purposes advancing science and education, including classroom use, providing all reproductions include the complete content shown here, including the author information. All other forms of reproduction and/or transmittal are prohibited without written permission from GSA Copyright Permissions.