4 research outputs found

    A late Oligocene tectono-volcanic event in East Kalimantan and the implications for tectonics and sedimentation in Borneo

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    New apatite fission-track data, K–Ar radiometric ages, and major and trace element geochem- istry from the northern part of the Kutai Basin, Borneo document a major regional tectono-volcanic episode. Apatite fission-track data from late Cretaceous sandstones indicate a period of rapid cooling in the late Oligocene. Cooling, initiated by a rapid temperature drop of over 40°C within c. 2 Ma might have been caused by increased denudation associated with tectonic movements. Rapid cooling is also concomitant with a phase of igneous activity. New K–Ar radiometric ages of andesitic–dacitic high-level intrusive rocks and associated volcanic rocks give ages of 23–18 Ma, which correlate with the regionally extensive late Oligocene–Miocene Sintang Intrusives Suite. These andesitic–dacitic high-level intrusive rocks also have geochemical characteristics of arc-related rocks. The sedimentary response to this tectono-volcanic event is the eastwards shift of the western basin margin and the inception of deltaic deposition around the newly re-defined basin margins. Up to 9 km of sediment was deposited in the basin during Miocene delta progradation, covering thick sequences of Palaeogene bathyal shales, providing an excellent décollement surface for later inversion. Elsewhere in Borneo and adjacent areas of SE Asia, major events recorded in the late Oligocene to early Miocene include major thrust imbrication and volcanic arc activity, the cause of which is unclear: Possibilities include the collision of Australia with the Philippine Sea Plate, the counter-clockwise rotation of Borneo in the Neogene and the initial impingement of blocks of South China origin with northern Borneo–south Palawan

    Provenance and tectonic setting of Miocene siliciclastic sediments, Sibuti formation, northwestern Borneo

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    Provenance and tectonic setting of sandstone and mudstone units of the Miocene Sibuti Formation from northwest Borneo have been studied based on the mineralogy, major and trace element geochemistry data. The X-ray diffraction (XRD) and scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) data revealed that the sandstones and mudstones were abundant in quartz, pyrite, clay, and heavy minerals such as zircon, rutile, and some detrital cassiterite. Geochemically, the sandstones and mudstones are classified into quartz arenite, litharenite, sublitharenite, arkose, and wacke. Quartz arenites are enriched with SiO2, Zr, and Th and depleted in Al2O3, CaO, and other elements compared to other sandstone types, indicating high maturity and intensive weathering. Chemical index of alteration (CIA: 77–90), plagioclase index of alteration (PIA: 86–100), and A-CN-K diagram suggest intense weathering in the source area. Elemental ratios such as La/Sc, Th/Sc, Cr/Th, La/Co, and Th/Co are similar to sediments derived from the felsic rocks. Also, the provenance discrimination diagrams suggest recycled continental nature of these clastic sediments which are mostly derived from metasedimentary source (Rajang Formation). Discriminant-function diagram for the tectonic discrimination of siliciclastic sediments revealed that the sediments of Sibuti Formation were derived from a collision zone, which is consistent with the geology of the study area
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