Provenance of Cretaceous-Miocene sediments in Borneo: Implications for paleogeographic patterns and tectonic evolution

Abstract

Cretaceous-Miocene sedimentary rocks of northern Borneo contain a record of sediment routing linked to subduction of the paleo-Pacific and closure of the proto-South China Sea. How the sediment routing system responded to these changes continues to be debated, hindered by limited datasets. New Sr isotope data, combined with previous geochemical and chronological data, to determine the provenance of the Cretaceous-Miocene sediments in Borneo. Late Cretaceous-early Paleocene Lubok Antu Mélange, Lupar Formation and Layar Member of the Rajang Group in Sarawak, central Borneo have low ⁸⁷Sr/⁸⁶Sr ratios and high Ɛ_Nd values and are dominated by Cretaceous detrital zircon grains. The results consistent with sources from the collapsed upper Mesozoic magmatic belt on the Sunda Shelf. In the Paleocene-Eocene Kapit, Pelagus, Metah and Bawang Members of the Rajang Group, there is a decrease in Ɛ_Nd values and an accompanying increase in Permian-Triassic and pre-Permian zircon ages. These trends imply that materials eroded from the Eastern Province of Malay Peninsula became progressively more important to the Sarawak region after the early Paleocene. By contrast, to the east, Eocene strata in the Sabah region remain dominated by Cretaceous detrital zircons, sourced mainly from the Schwaner Mountains. Large numbers of Permian-Triassic detrital zircon ages in the Oligocene-middle Miocene strata of Sarawak and Sabah reflect a drainage network extending to older strata along the Malay Peninsula region since the late Eocene. These sources were cut off once South China Sea began to open, leaving the Schwaner Mountains and uplifted central Borneo as the dominant source of sediments in Sabah. The observed changes in sediment provenance between Sarawak in the west and Sabah in the east reflects changes in sediment routing that tracked subduction of the paleo-Pacific plate and the progressive closure of the proto-South China Sea during the late Cretaceous to middle Miocene.