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Structure and metamorphism of rocks beneath the Semail ophiolite of Oman and their significance in ophiolite obduction

Published online by Cambridge University Press:  03 November 2011

M. P. Searle  and
J. Malpas
M. P. Searle
Affiliation:
Department of Geology, Memorial University of Newfoundland, St John's, Newfoundland, Canada, A1B 3X5.
J. Malpas
Affiliation:
Department of Geology, Memorial University of Newfoundland, St John's, Newfoundland, Canada, A1B 3X5.
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Abstract

Metamorphic rocks showing an inverted metamorphic zonation from upper amphibolite fades immediately beneath the peridotite to greenschist fades at lower levels, crop out discontinuously along the base of the Semail ophiolite thrust sheet in the Oman Mountains of eastern Arabia. These metamorphic rocks show polyphase deformation, mylonitic fabrics, and have been disrupted, folded and imbricated, and in places form tectonic inclusions in a serpentinite melange. In the more intact sequences, garnet-clinopyroxene amphibolites, with rare hornblende-bearing marbles and banded quartzites, occur at the higher levels, whilst a wide range of metasedimentary and metabasaltic rocks occur in the greenschist fades. Low glaucophane content of amphiboles and low jadeite content of clinopyroxenes suggest relatively low pressures of crystallisation. The distribution coefficient KD for co-existing garnet and clinopyroxene suggests a temperature range of 670 to 750°C. Residual heat from the recently formed ophiolite probably provided the dominant heat source for metamorphism, although frictional heating could have supplemented this. The metamorphic rocks were produced during Cenomanian-Turonian (late Cretaceous) times.

The sub-ophiolite metamorphic rocks, together with basal serpentinite, Triassic alkaline and tholeiitic basalts (Haybi volcanic group), mountain-sized ‘exotic’ limestones and an upper Cretaceous sedimentary melange, comprise a distinct thrust slice termed the Haybi complex, which always overlies marine sediments of the allochthonous Hawasina complex and underlies the Semail ophiolite. The rocks of the Haybi complex are bounded by major thrust planes, the Semail thrust above and the Haybi thrust beneath, which truncate all schistosities, fold axes, imbricate thrusts and associated features. A model for ophiolite obducton is presented based on a palinspastic reconstruction of the allochthonous rocks on the Oman continental margin.

Keywords

allochthonousbasaltCenomaniandistribution coefficient KDfoldfrictional heatlimestonemelangeoceanic lithosphereresidual heatserpentinitethrustTuronian24°N56°E
Type
Research Article
Information
Earth and Environmental Science Transactions of The Royal Society of Edinburgh , Volume 71 , Issue 4 , 1980 , pp. 247 - 262
Copyright
Copyright © Royal Society of Edinburgh 1980

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