东北婆罗洲古地理重建:巴利奥宗(Baliojong) 大洋板块地层碎屑物源和年代学

The continuous subduction of palco-occans has resulted in the presence of numerous microplates in Southeast Asia, characterized by complex origins and tectonic evolution. This complexity poses significant challenges for paleogeographic reconstruction, particularly concerning the Northeast Borneo terrane, whose tectonic attributes and pre-Cenozoic paleogeography remain highly controversial. The Baliojong Ocean Plate stratigraphy outcropping in Northeast Borneo serves as a valuable record of palco-oceanic history, spanning from crustal spreading to subduction and extinction. In this study, we conducted detailed provenance and geochronological investigations on two turbiditc sections in the western part of the Baliojong Ocean Plate stratigraphy. By integrating whole-rock geochemistry, mineralogy, and zircon U-Pb geochronology-geochemistry-morphology, we determined the depositional ages and compositions, thereby revealing the subduction history and paleogeography of the overlying plates. Our results demonstrate significant differences between the two sections in terms of individual provenance and geochronological proxies. Turbidites in the eastern section (BF2) exhibit younger sedimentary ages, higher compositional maturity and detrital content, mafic-dominated source composition, and a greater abundance of larger-sized zircon grains of Caledonian and Indosinian ages compared to those in the western section (BF5). These lines of evidence clearly indicate that the two turbidite sequences are products of distinct accretionary periods. Combining our newly obtained maximum depositional age proxies based on detrital geochronology with published ages of radiolarian cherts and basalts, we interpret the deposition of the turbidite sequences to have occurred in the Late Cretaceous (~ 87 Ma and ~93 Ma). Comparison of the zircon U-Pb age signatures of the Baliojong turbiditcs with those of potential source areas in Borneo and surrounding plates suggests a provenance linkage to the zone encompassing the southern Indochina margin-East Malaya-Northwest Borneo. We interpret the location of the subduction zone, where the Baliojong Ocean Plate stratigraphy formed, to be closer to Sundaland than South China. The Late Cretaceous paleogeography of Northeast Borneo revealed in this study holds significant implications for reconstructing the Mesozoic subduction system in the South China Sea-Southeast Asia region.