New insights into the petrogenesis of granitic rocks in southern Thailand, SE Asia tin belt: evidence from petrochemistry and geochronology

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ABSTRACT The granitic rocks in the Prachuap Khiri Khan Province, southern Thailand, SE Asia Tin Belt, comprise gneissic biotite monzogranite, porphyritic muscovite–biotite monzogranite, and porphyritic biotite monzogranite. Comprehensive field observations, petrography, mineral chemistry, and geochemistry establish gneissic biotite monzogranites as part of the Central Belt Granites (CBGs), while porphyritic muscovite–biotite monzogranite and porphyritic biotite monzogranite as part of the Western Belt Granites (WBGs). CBG and WBG granitic units exhibit peraluminous, alkali-calcic, and magnesian magmatic series traits, reflecting an S-type granite character resulting from crustal partial melting. Significantly, scatter correlations in variation diagrams, combined with the enrichment of Cs, Rb, Th, U, Pb, Nd, and P, and the depletion of Ba, Nb, and Ti contents, point towards an S-type granite signature formed during collisional events. Crystallization conditions reveal CBG gneissic biotite monzogranite encountered P–T conditions of 2.97–3.85 kbar/680°C–733°C/11.1–14.4 km, while WBG’s porphyritic muscovite–biotite monzogranite and porphyritic biotite monzogranite experienced 2.73–4.15 kbar/628°C–732°C/10.2–15.5 km and 2.47–3.80 kbar/651°C–728°C/9.2–14.2 km, respectively. Geochronological data indicate that CBG’s gneissic biotite monzogranite was emplaced from Early Cretaceous collision (128–119 Ma) of Indochina and Sibumasu terranes, while WBG’s porphyritic muscovite–biotite monzogranite and porphyritic biotite monzogranite were formed during the syn-collision of Sibumasu and West Burma terranes during Early Cretaceous (121–111 Ma) to Paleocene. Mineralogical and geochemical attributes of these granitic rocks exhibit strong relevance to Sn-W mineralization processes, indicative of a profound association.