Reconstructing the East Palaeo-Tethyan assemblage boundary in west Indonesia: constraints from Triassic granitoids in the Bangka and Belitung islands

Abstract The geodynamic evolution of the Palaeo-Tethyan Ocean is key to understanding the development of Pangaea. The main continents of SE Asia were welded together in response to the closure of the Palaeo-Tethyan Ocean. However, the precise location of the sutures and timing of the collisions are poorly constrained, especially the southward continuation from Peninsular Malaysia into west Indonesia. This study presents new zircon U–Pb geochronological, petrological, elemental and Sr–Nd–Pb–Hf–O isotopic data in order to investigate the origin and tectonic setting of the granitoids from the Bangka and Belitung islands, west Indonesia. Although possessing different mineral compositions, the two groups of samples yield similar crystallization ages of c. 230–220 Ma and enriched Nd–Hf isotopic compositions (whole-rock ε Nd ( t ) = −9.6 to −2.4 and zircon ε Hf ( t ) = −12.1 to −0.1), and probably originated from melting of a mixed source of metagreywacke and metapelite with a subordinate meta-igneous component. Both granitic groups formed during post-collisional processes, and when this interpretation is combined with regional investigations on the granitic magmatism, the Bangka–Belitung granitoids may represent the southward continuation of the Main Range granitoids. If correct, the distribution of granitoids with distinct petrogenesis across both islands implies a location for the Palaeo-Tethyan suture zone between Bangka–Belitung and West Kalimantan.