On the origins and tectonic significance of the charnockite suite of the Archaean Limpopo Belt, northern marginal zone, Zimbabwe

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doi: 10.1016/0301-9268(92)90037-O
Authors:Ridley, John R.
Author Affiliations:Primary:
Univ. West. Aust., Dep. Geol., Nedlands, West. Aust., 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.407-427; 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. 63 refs.; illus. incl. sketch maps
Summary:This zone consists mainly of massive to gneissic charnockites and enderbites. The general textural characteristics and the field relations of the charnockites suggest that they represent plutonic bodies that have undergone relatively little internal tectonic disruption. Mineral textures are more consistent with an origin as direct crystallization products of a felsic magma in granulite- facies conditions than as metamorphosed granites. Available petrological and geochronological evidence suggests that uplift of the charnockites took place fairly rapidly after cessation of granulite-facies metamorphism. Uplift occurred along a diffuse steeply-dipping shear zone that forms the N boundary of the Limpopo belt against the Zimbabwe craton; the steep dip limits the extent of possible underthrusting by the craton as a block beneath the N marginal zone and implies that the charnockites formed within thickened crust, and that movement along the boundary structure is reflecting uplift of this abnormally thick N marginal zone crust. The constraints placed on thermal models by crustal thickness and the P-T conditions of charnockite formation imply development of the N marginal zone in a tectonic regime with low mantle heat flux. This is inconsistent with a model of thickening of the crust through addition of mantle-derived magmas, and suggests thickening involved tectonic processes above a zone of down-welling of mantle convection. [R.E.S.]
Subjects:Archean; Charnockite; Convection; Crystallization; Deformation; Diorites; Enderbite; Facies; Genesis; Gneisses; Granites; Granulite facies; Igneous rocks; Mantle; Metamorphic rocks; Metamorphism; Mineral composition; P-T conditions; Plutonic rocks; Precambrian; Structural geology; Tectonics; Textures; Tonalite; Uplifts; Africa; Limpopo Belt; Southern Africa; Zimbabwe; Zimbabwe Craton
Abstract Numbers:93M/1165
Record ID:1992015373
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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