The gabbroic suite and associated hornfelses of Bukit Kemuning, Trengganu, Peninsular Malaysia

Kumar, S. Chandra (1980) The gabbroic suite and associated hornfelses of Bukit Kemuning, Trengganu, Peninsular Malaysia. Bulletin of the Geological Society of Malaysia, 13. pp. 63-86. ISSN 2637-109X

Abstract

The small body of gabbroic rocks exposed on Bukit Kemuning includes an interesting and highly varied complex of hornfelsed xenoliths and contact rocks. Associated quartz diorite and granophyre are minor occurrences. The Kemuning gabbro is an iron enriched variety which contains high modal proportions of hornblende and biotite. Olivine and orthopyroxene vary in composition from Fo 32 to Fo 14 and En 53 to En 37 respectively while clinopyroxene is augite or ferroaugite. The gabbro texture is typified by reaction rims and intergrowths produced by late magmatic reaction relationships. The hornfelses associated with the gabbro are classified into four major groups: (A) Titaniferous basic granular hornfels; (B) Micro-gabbroid basic granular hornfels; (C) Calc-silicate hornfels and (D) Siliceous hornfels. Some of the hornfelses display strikingly unusual mineralogy and chemistry. All the hornfelses, with one exception, are derived from sedimentary parent material. Basic granular hornfelses are produced by the contact metamorphic action of the gabbroic magma on the original sedimentary material involving a significant metasomatic transfer of Ca, Fe, Mg, Ti and Mn into the sediments. Calc-silicate and siliceous hornfelses have suffered essentially isochemical contact metamorphism. The subalkaline Kemuning gabbroic suite cannot be uniquely identified with either the tholeiite or calc-alkali magma series. The mixed magmatic character of this suite is due to contamination of the gabbroic magma by the hornfelsed xenoliths.

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