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Title: SW Borneo basement : age, origin and character of igneous and metamorphic rocks from the Schwaner mountains
Author: Davies, Lorin Brynmor
Awarding Body: Royal Holloway, University of London
Current Institution: Royal Holloway, University of London
Date of Award: 2013
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Abstract:
SW Borneo is the southeastern promontory of Sundaland the continental core of SE Asia, previously assumed to be the oldest part of Borneo. The rocks in SW Borneo are the Pinoh Metamorphic Group (PMG) and granitoids of the Schwaner batholith . The PMG was undated, but previous authors have interpreted it to be Permo-Carboniferous or older. Previous K-Ar studies of granitoid rocks yielded ages between 112 and 75 Ma. U-Pb zircon dating of two granite samples recorded ages between 86 to 79 Ma, and one xenocryst age of 152 Ma. SW Borneo has been widely assumed to be a crustal fragment which was rifted from the Indochina-China margin and translated to its current location by the Permo-Carboniferous. Recent ly an alternative model has proposed that it was rifted from the NW Australian margin and translated to its current location by the mid-Cretaceous. This study has involved detailed fieldwork, with petrographic, geochemical, metamorphic petrology, U-Pb and Ar-Ar geochronology studies. The aims of the project were to: 1. Determine petrographic and geochemical characteristics of Schwaner granitoids. 2. Constrain age of emplacement.of the Schwaner batholith. 3. Identify protoliths and style of metamorphism of PMG rocks. 4. Date protolit hs and metamorphic history of the PMG. 5. Determine the role of SW Borneo in the tectonic evolution of Sundaland. Granitoids in SW Borneo are I-type. In the Southern Schwaner Mountains (SSZ) they are withinplate granitoids, typically alkali-granites, with U-Pb zircon ages of c. 186 and 76 Ma. In the Northern Schwaner Mountains (NSZ) they are arc-related granitoids, typically tonalites and granodiorites. U-Pb zircon ages show four significant age populations of c. 112, 98, 84, and 76 Ma. The PMG comprises metamorphosed pe lites, quartzites and basalts, which formed a thick volcanic-sediment pile. Metapelites are hornfelses, phyllites and schists. Low pressure regional metamorphism (c. 3-4 kbar, 500-625°C) with localised contact metamorphism resulted from intrusion of granitoid rocks. Later shear zones cut older metamorphic fabrics. U-Pb dating of zircon shows metamorphic protoliths of the PMG are younger than 130 Ma. Ar-Ar geochronology of biotite and white mica indicate that peak regional metamorphism took place at c.110 Ma. Post-metamorphic shearing took place at 25 Ma.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.590823  DOI: Not available
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