| Résumé: | The main objective of this study is to investigate the petrology, geochemistry and
petrogenesis of volcanic rocks from southeast Peninsular Malaysia mainly within Teluk
Ramunia. The volcanic rocks from that area are located on the eastern belt magmatism
dominated by I-type rocks. The rocks from study area are dominated by rhyolite,
trachydacite and diorite and they show irregular contact which suggests
contemporaneous crystallization. Petrographically, all rocks shows occurrence of
microgranophyric, interstitial biotite and hornblende which is characteristic of the Atype
rocks and sub-volcanic emplacement. Field and geochemical evidence shows that
the rhyolite is derived from a different magmatic pulse than trachydacite and diorite.
The value of Ga/A and HFSE (Zr+Nb+Ce+Hf) for all rocks from study area is
comparable to the average A-type rocks. All rocks shows range from metaluminous to
weakly peraluminous in term of their A/CNK value. All rocks from Ramunia yield high
zircon saturation temperature value (826+ 5oC) and high content of high field strength
elements (e.x. Zr,Nb,Ce and Hf) which are clearly indicative of dry source derived or
low pressure incongruent melting. Based on geochemical, petrographical and high
saturation temperature and low pressure (~3.2kbar) calculated from thermometry shows
that all Rock from Ramunia may plausibly derived from low pressure melting of
granodiorite. Based on zircon U-Pb isotope age, rhyolite gave age about 238 + 2 Ma
which suggest that all rocks are related to subduction of the Palaeo-tethys ocean
underneath Indochina (volcanic arc). However the occurrences A-type give implication
that all rocks are formed during crustal extension due to oceanic slab rollback. The
under-plated mantle derived basalt will intrude into the lower to middle crust and
provide sufficient heat to melt the country rocks. The high heat yield by the mantle
derived basalt will contribute to the low pressure incongruent melting of the middle
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crust rocks (tonalite and granodiorite) which will formed the A-type magma and
gradually crystallized to be Ramunia volcanics. It is high possible that there are more
occurrence of the A-type rocks throughout Eastern belt province of Peninsular
Malaysia.
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