Precambrian tectonics and the physicochemical evolution of the continental crust; II, Lithosphere delamination and ensialic orogeny

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doi: 10.1016/0301-9268(92)90042-M
Authors:Ellis, D. J.
Author Affiliations:Primary:
Aust. Natl. Univ., Dep. Geol., Canberra, Australia
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.507-524; 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. 102 refs.; illus. incl. 3 tables
Summary:It is considered that Precambrian orogenic events, whether at ancient plate margins or in an ensialic regime, had to be caused by modern-style plate tectonics. Although the process of Wilson- cycle plate tectonics operated throughout the Earth's history, there is evidence tosuggest that the products of this process (plate margin volcanism and metamorphism) have changed significantly through time, due to a secular decrease in heat flow. There is good evidence that some Proterozoic terrains initially developed in an ensialic extensional setting but it is proposed that the cause of later compressive orogenies in these belts must have been transfer of stresses from distant active plate margins and subduction zones. This requires that some Precambrian mobile belts must represent sutures which were formerly ancient active plate margins. There is abundant independent evidence to support subduction in the Precambrian when mantle xenoliths, refractory inclusions in diamonds and the trace element compositions of continental basalts are considered. The occurrence of HFS element depletions in many continental mafic dykes and volcanics ranging back to the Archaean can only be satisfactorily explained by this geochemical signature ultimately being caused by subduction. This is correct irrespective of whether the crustal influence is due to subduction of sediment into the mantle or in situ crustal assimilation by ascending basalts. It is argued that subcontinental lithosphere has remained attached to Precambrian shields as an integral part of moving plates in the Earth's history. Later reactivation of this lithospheric mantle beneath continents may explain the occurrence of HFS element-depleted continental basalts, yet their absence from modern oceanic regions. [R.E.S.]
Subjects:Assimilation; Asthenosphere; Basalts; Compression; Concepts; Continental crust; Crust; Delamination; Density; Dikes; Extension tectonics; Harzburgite; Igneous rocks; Inclusions; Intrusions; Lithosphere; Major elements; Mantle; Orogeny; Peridotites; Plutonic rocks; Precambrian; Structural geology; Subduction; Tectonics; Terranes; Ultramafics; Volcanic rocks; Xenoliths; Evolution
Abstract Numbers:93M/1170
Record ID:1992015378
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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