Late Cretaceous Nature of SW Borneo and Paleo-Pacific Subduction: New Insights from the Granitoids in the Schwaner Mountains

Cretaceous igneous rocks in SW Borneo are significant for investigating the Paleo-Pacific subduction and regional correlation. This paper presents new zircon ages and Sr-Nd-Pb-Hf-O isotopic and whole-rock geochemical data for the Cretaceous granitoids in the Schwaner Mountains. These granitoid samples yield formation ages of 92-80 Ma and can be geochemically subdivided into Group 1 biotite granite and granodiorite and Group 2 monzogranite. Group 1 has higher epsilon(Hf) (t) values of +1.2-+14.5 and lower delta O-18 values of 5.2-6.6 parts per thousand than Group 2 with epsilon(Hf) (t) and delta O-18 values of -1.5-+5.9 and 6.1-6.6 parts per thousand, respectively. Group 1 samples show variable epsilon(Nd) (t) values of -1.9-+1.7, (Pb-206/Pb-204)(i) ratios of 18.63-19.29, (Pb-207/Pb-204)(i) ratios of 15.62-15.69, and (Pb-208/Pb-204)(i) ratios of 38.67-39.49 and are the products of partial melting of newly underplated mafic rocks with a component of crustal rocks. Group 2 with slightly negative epsilon(Nd) (t) values of -1.1--1.5 was originated from partial melting of metasedimentary rocks with a juvenile mafic component. These granitoids were formed in a continental arc setting related to the Paleo-Pacific subduction during the Late Cretaceous and can compare with those contemporaneous I-type granites along the Kuching zone in NW Borneo. Those Late Cretaceous granitoids with A-type affinities from the easternmost Peninsular Malaysia and Singapore to the east of Sundaland might be formed in a back-arc extensional setting after the Paleo-Pacific subduction.

Automated summary

This paper presents new data on the Cretaceous granitoids in SW Borneo and discusses their significance in investigating the Paleo-Pacific subduction and regional correlation. The study shows that these granitoids were formed in a continental arc setting during the Late Cretaceous and can be compared to contemporaneous granites in NW Borneo. Additionally, Late Cretaceous granitoids with A-type affinities in eastern Peninsular Malaysia and Singapore might have formed in a back-arc extensional setting after the Paleo-Pacific subduction.