Field and petrographic studies of granite from Pulau Jarak and Pulau Sembilan, Peninsular Malaysia

Main Article Content

Azman A. Ghani

Abstract

Jarak and Sembilan islands are the westernmost islands off the mainland of Peninsular Malaysia. Both islands are underlain by granitic rock. Field and textural characteristics of the granites are similar to the tin bearing Main Range granite of Peninsular Malaysia. Structural features such as occurrence of tourmaline pods, accumulation of the large pegmatitic K-feldspar and occurrence of aplopegmatite complex suggest that the granite magma is highly evolved. Both islands are made up of porphyritic to coarse grained biotite granite. The grain size of K-feldspar phenocryst can be up to 4 cm across. The granite is made up of quartz (35%), plagioclase (19%), K-feldspar (43%), biotite (4.5%) and can be classified as monzogranite to syenogranite. Subhedral to anhedral biotite is the main mafic phase. The granitic rocks from Jarak and Sembilan occupy a central area of the QAP diagram. Granites plotting in this area have been regarded as crustal melts and this suggests the importance of crustal material in the source rocks of those plutons. The importance of crustal material in the source rock is supported by the occurrence of metasedimentary enclave. This may suggest that the Jarak and Sembilan magmas are derived from partial melting of the sedimentary rock e.g. pelitic rocks.
Pulau Jarak dan Pulau Sembilan adalah pulau Semenanjung Malaysia yang paling kebarat. Kedua-dua pulau ini dilapisi oleh batuan granit. Ciri-ciri lapangan dan tekstur menunjukkan batuan granit di kedua-dua pulau ini adalah sama dengan batuan granit kaya timah Granit Banjaran Utama. Struktur seperti pod tourmalin, pengumpulan K-feldspar dan aplopegmatit mencadangkan bahawa magma untuk batuan granit Jarak dan Sembilan adalah sangar terevolusi. Kedua dua pulau ini dibentuk oleh batuan granit biotit berbutir kasar ke porfiritik. Saiz butiran fenokris K-fedlspar boleh mencapai sehingga 4 sm. Mineralogi batuan granit ini terdiri dari kuartz (35%), plagioclase (19%), K-feldspar (43%), biotit (4.5%) dan boleh dikelaskan sebagai monzogranit dan syenogranit. Biotit subhedral ke anhedral merupakan fasa mafik yang utama. Batuan granit dari Pulau Jarak dan Sembilan diplotkan dibahagian tengah dalam gambarajah QAP yang mencadangkan magma batuan granit ini berasal dari leburan kerak. Kepentingan bahan kerak di dalam batuan punca disokong oleh kewujudan enklaf metasedimen. Ini mencadangkan magma batuan granit Pulau Jarak dan Sembilan berasal dari leburan separa batuan sediment contohnya batuan pelit.

Downloads

Download data is not yet available.

Article Details

How to Cite
A. Ghani, A. (2008). Field and petrographic studies of granite from Pulau Jarak and Pulau Sembilan, Peninsular Malaysia. Malaysian Journal of Science, 27(3), 7–12. Retrieved from https://ajba.um.edu.my/index.php/MJS/article/view/7703
Section
Original Articles