Triassic Tectonic Affinity to Indochina‐East Malaya Block for West Sumatra and Paleo‐Tethys Implications: Constraints From Late Triassic Igneous Rocks

Abstract Mesozoic igneous rocks from Sumatra provide crucial insights into the temporal‐spatial connection with the Eastern Tethys Domain. This study presents new zircon ages and whole‐rock elemental data for the Late Triassic igneous rocks in West Sumatra. These igneous rocks yield consistent ages of 227–211 Ma. Granitoid and rhyolite exhibit A‐type affinities with high K 2 O and FeOt contents, and are depleted in HFSEs. They have similar ε Nd ( t ) values of −8.3 to −5.0, ε Hf ( t ) values of −8.0 to +1.4, and initial ratios for 206 Pb/ 204 Pb (18.71–19.17), 207 Pb/ 204 Pb (15.74–15.77) and 208 Pb/ 204 Pb (39.28–39.48). They were derived from an “ancient” meta‐mafic source with a juvenile mafic crust component. Mafic‐intermediate igneous rocks can be classified as medium‐ to high‐K calc‐alkaline series and are characterized by depletion in Nb, Ta, and Ti. Mafic‐intermediate volcanic rocks show higher ε Nd ( t ) values of −0.7 to +1.3 and ε Hf ( t ) values of +3.5 to +4.2 than the diabases with ε Nd ( t ) of −9.0 to −8.5 and ε Hf ( t ) of −5.5 to −1.2. All these igneous rocks share similar initial ratios for 206 Pb/ 204 Pb (18.62–18.84), 207 Pb/ 204 Pb (15.68–15.75) and 208 Pb/ 204 Pb (38.67–39.05), suggesting a metasomatized lithospheric mantle origin. These Late Triassic igneous rocks share similar isotopic compositions with the synchronous post‐collisional igneous rocks along the Eastern Paleo‐Tethys giant igneous belt and were formed in a post‐collisional extensional setting. Regional stratigraphy and detrital zircon observations indicate that West Sumatra constitutes the southern part of the Indochina‐East Malaya Block, and the Eastern Paleo‐Tethys zone likely extends into Sumatra.