I' type features in the so-called 'S' type Western Belt granites, Peninsular Malaysia

Author : Azman A Ghani
Publication : Bulletin of the Geological Society of Malaysia
Page : 133-138
Volume Number : 44
Year : 2000
DOI : https://doi.org/10.7186/bgsm44200017

Geol. Soc. Malaysia, Bulletin 44, July 2000; pp. 133-138

‘I’ type features in the so-called ‘8’ type Western Belt granites, Peninsular Malaysia


Department of Geology
University of Malaya
50603 Kuala Lumpur

Abstract: The Western Belt granites of Peninsular Malaysia have been considered as constituting exclusively ‘S’ type granites. The ‘S’ type features in the granites are, (a) high initial 87Sr/86Sr isotope ratio, > 0.710, (b) low Na20 content, < 3.2% Na2O in rocks with – 5% K2O, (c) narrow range of felsic rock (Si02: 65.95 to 77.4%), (d) high K2O/Na2O ratio, 1.4-2.8 (S type: 0.9-3.2), (e) usually ilmenite-bearing and (f) contain pelitic or quartzose metasedimentary xenoliths. Despite the similarities above, the Western Belt granites also have some characteristics which are more characteristic of ‘I’ type than those of the ‘S’ type granites, namely (a) AI-rich minerals such as sillimanite and cordierite are absent except some andalusite, (b) occurrence of primary wedge sphene and pale green amphibole especially in the northern part of the batholith, (c) pinkish K-feldspar crystals (usually as phenocrysts) present, (d) occurrence of mafic, hornblende-bearing enclaves, (e) increasing ACNK value with Si02, (f) increasing peraluminosity towards the most differentiated rocks (‘S’ type granite: increasing peraluminosity towards the most mafic varieties) and (g) P205 vs Rb trend is similar to the ‘I’ type granite. The aspects of the Western Belt granites highlighted in this paper warrants more serious and in-depth study in order to understand the nature of the granite source rock(s) (cf. Chakraborty, 1994). They are clearly some differences between the Western Belt protolith compared to those of the southern Australian rocks.