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

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 <i>P–T</i> 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.

位于东南亚锡矿带的泰国南部巴蜀府的花岗岩类岩石，包括片麻状黑云母二长花岗岩（gneissic biotite monzogranite）、斑状白云母-黑云母二长花岗岩（porphyritic muscovite–biotite monzogranite）以及斑状黑云母二长花岗岩（porphyritic biotite monzogranite）。通过系统的野外地质观测、岩石学、矿物化学及地球化学研究，确定片麻状黑云母二长花岗岩属于中央带花岗岩（Central Belt Granites, CBGs），而斑状白云母-黑云母二长花岗岩与斑状黑云母二长花岗岩则归属于西部带花岗岩（Western Belt Granites, WBGs）。中央带与西部带花岗岩单元均表现出过铝质、碱钙质及镁质岩浆系列的地球化学特征，反映了由地壳部分熔融形成的S型花岗岩（S-type granite）成因属性。值得注意的是，变异图中的元素分散相关性，结合Cs、Rb、Th、U、Pb、Nd、P的富集以及Ba、Nb、Ti的亏损，表明其为碰撞事件中形成的S型花岗岩成因标识。结晶温压条件显示，中央带花岗岩的片麻状黑云母二长花岗岩的P-T条件为2.97~3.85千巴/680℃~733℃/11.1~14.4 km，而西部带花岗岩的斑状白云母-黑云母二长花岗岩与斑状黑云母二长花岗岩的结晶条件分别为2.73~4.15千巴/628℃~732℃/10.2~15.5 km与2.47~3.80千巴/651℃~728℃/9.2~14.2 km。年代学数据表明，中央带花岗岩的片麻状黑云母二长花岗岩的侵位时代为印支地体与锡布苏地体早白垩世碰撞时期（128~119 Ma），而西部带花岗岩的斑状白云母-黑云母二长花岗岩与斑状黑云母二长花岗岩则形成于早白垩世（121~111 Ma）至古新世期间锡布苏地体与西缅甸地体的同碰撞阶段。上述花岗岩类岩石的矿物学与地球化学特征与锡钨成矿过程具有显著相关性，暗示二者存在紧密的成因联系。