Cretaceous Tethyan subduction in SE Borneo: Geochronological and geochemical constraints from the igneous rocks in the Meratus Complex

Abstract

• The igneous rocks in the Meratus Complex mainly formed at ∼115–140 Ma. • The Cretaceous Meratus mafic rocks originated from the slab-related wedge mantle. • The Cretaceous granitoids represent the product of wedge-originated juvenile crust. • Meratus Complex has a NW-Australian affinity and formed in an fore-arc setting. • The Meratus Neotethyan Ocean subducted beneath the Argo fragment until ∼100 Ma. SE Borneo lies at the junction of the Pacific and Tethyan realms. The Mesozoic geological record of the region is dominated by convergent plate margin activity, although the geological details and its broader role in the SE Asia evolution are poorly documented. This paper presents geochronological, whole-rock elemental and Sr-Nd-Pb isotopic data on the igneous rocks from the Meratus Complex in SE Borneo. The Meratus ophiolite might form at the Late Jurassic-Early Cretaceous (∼150–115 Ma), and the spatially-associated Haruyan Volcanics, Belawayan granitoids and their equivalents generated in the Early Cretaceous (∼140–107 Ma). The Haruyan and Pitap formations and their equivalents are dominated by Early Cretaceous (∼140–115 Ma) volcanic rocks and late Early Cretaceous (∼115–100 Ma) siliciclastic rocks, respectively. The mafic-intermediate igneous rocks in the Meratus Complex are characterized by MgO = 2.04–13.20 wt%, TiO 2 = 0.48–1.51 wt%, Nb/La = 0.09–0.42, ε Nd (t) = +4.6–+7.7, ( 206 Pb/ 204 Pb) i = 18.15–18.61, ( 207 Pb/ 204 Pb) i = 15.41–15.63 and ( 208 Pb/ 204 Pb) i = 38.03–38.63, and originated from the slab-related mantle wedge. The granitoids share similar elemental ratios and Sr-Nd-Pb isotopic compositions with the coeval mafic rocks, with Nb/La = 0.20–0.30, ε Nd (t) = +4.8–+6.0, Δ8/4 = 26.2–38.8 and Δ 7/4 = 5.0–7.7, representing the products of the wedge-originated juvenile crust. Synthesis of all data reveals a NW-Australian affinity for SE Borneo. The Early Cretaceous fore-arc tectonic setting extends southerly into the Bantimala (SW Sulawesi) and Luk Ulo (Central Java), constituting a united Early Cretaceous Central Indonesian accretionary zone. The Meratus Ocean subducted beneath the Argo fragment since ∼140 Ma and likely assembled with the Sundaland margin at ∼100 Ma in response to the Neotethyan consumption.