Precambrian tectonics and the physicochemical evolution of the continental crust; I, The gabbro-eclogite transition revisited

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doi: 10.1016/0301-9268(92)90041-L
Authors:Ellis, D. J.; Maboko, M. A. H.
Author Affiliations:Primary:
Aust. Natl. Univ., Dep. Geol., Canberra, Australia
Other:
Univ. Cape Town, South Africa
Volume Title:Special issue; The Archaean Limpopo granulite belt; tectonics and deep crustal processes
Volume Authors:van Reenen, Dirk D., editor; Roering, Chris; Ashwal, L. D.; de Wit, Maarten J.
Source:Precambrian Research, 55(1-4), p.491-506; Granulites and deep crustal tectonics, June 21-July 1, 1990, edited by Dirk D. van Reenen, Chris Roering, L. D. Ashwal and Maarten J. de Wit. Publisher: Elsevier, Amsterdam, International. ISSN: 0301-9268
Publication Date:1992
Note:In English. 76 refs.; illus. incl. 1 table, sketch map
Summary:The first occurrence from Australia of retrograde eclogite shear zones cutting Proterozoic granulites is reported. The Musgrave range granulites were metamorphosed at approx 12 kbar and 850- 900 degrees C; they then cooled isobarically and developed a variety of lower T mineral reaction coronas typical of garnet granulites. The rocks are cut by a major shear zone, the Davenport shear, in which lower T, fine-grained eclogite developed. It is thus shown that mafic rocks in the deep crust can cool into the thermodynamic stability field of eclogite without undergoing transformation to eclogite. It is proposed that many isobaric, high-P granulites could have cooled into the eclogite field before their later exposure, and did not transform to an eclogite mineralogy. The inability of the lower crust to transform into eclogite by retrograde reaction has important implications for the seismic, petrological and geochemical character of the lower crust. The continental Moho cannot be caused by the gabbro- eclogite transition. Preservation of fairly low density, high-T granulite and gabbroic mineral assemblages in the lower continental crust prohibits major recycling back into the mantle once that crust is removed from active plate boundaries, though in island arcs eclogite could form rapidly and sink back into the mantle. Estimates of the average composition of the continental crust based on a mass balance of plate margin basaltic input from the mantle will not be adequate. [R.E.S.]
Subjects:Continental crust; Crust; Eclogite; Gabbros; Granulites; Igneous rocks; Metamorphic rocks; Metamorphism; Mineral composition; P-T conditions; Plutonic rocks; Precambrian; Retrograde metamorphism; Shear zones; Structural geology; Tectonics; Australasia; Australia; Musgrave Ranges; Evolution
Abstract Numbers:93M/1169
Record ID:1992015377
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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