Late Triassic post-collisional granites related to Paleotethyan evolution in SE Thailand: Geochronological and geochemical constraints

Abstract

A set of new U–Pb geochronological, elemental and Sr–Nd–Hf isotopic data is presented to constrain the formation age and petrogenesis of granites in SE Thailand, which are significant for understanding eastern Paleotethyan tectonic evolution and regional correlation in SE Asia. Six granite samples from the Chonburi, Rayong–Bang Lamung and Chanthaburi plutons yielded similar crystallization ages of 222–218Ma. These granites can be geochemically classified into S-type (Group 1) and I-type (Group 2) granites. Both groups have similar chondrite-normalized REE and primitive mantle-normalized multi-element patterns but distinctly different Sr–Nd–Hf isotopic compositions. Group 1 is characterized by more enriched initial 87Sr/86Sr (i) ratios (0.7101–0.7272) and lower εNd (t) values (−12.0 to −13.2) compared with those of Group 2 with 87Sr/86Sr (i) of 0.7027–0.7053 and εNd (t) of −0.6 to −1.2. Consistently, zircons from Group 1 yield negative εHf (t) values of −7.3 to −27.4 and Mesoproterozoic or older Hf model ages (TDM=1.53–2.63Ga), distinct from those of Group 2 with positive εHf (t) values (+5.0–+11.3) and younger TDM (0.42–0.67Ga). Group 1 granites mainly originated from ancient greywackes but Group 2 from juvenile mafic crust with the input of meta-sedimentary component. These data, along with available observations, synthetically indicate that these granites formed in the post-collisional gravitational collapse setting of the thickened crust in response to the assemblage of the Indochina with Sibumasu blocks. They linked northerly and easterly to the Late Triassic granitoids in NW Thailand and East Malay Peninsula related to the Paleotethyan tectonic regime, respectively.