Geokimia Batuan Gunungapi di Pulau Timor Bagian Barat dan Impikasi Tektoniknya
DOI:
https://doi.org/10.33332/jgsm.geologi.v17i4.24Abstract
Geologi wilayah Timor bagian barat berasal dari tiga mintakat yaitu Mintakat Benua Australia, Mintakat Busur Banda dan batuan yang terendapkan setempat. Pengambilan dan analisis conto batuan di Sungai Fatu dan Kompleks Mutis serta tambahan data sekunder dari Sungai Metan, Pulau Atauro dan batuan hasil Deep Sea Drilling Project (DSDP) bertujuan untuk mengetahui batuan asal wilayah Timor berdasarkan data geokimia batuan gunungapi dan implikasi tektoniknya. Metodologi analisis geokimia yang digunakan adalah X-ray fluorescence (XRF) dan Inductively Coupled Plasma–Mass Spectrometry (ICP-MS) untuk mengetahui unsur utama, unsur jejak dan unsur tanah langka dari batuan gunungapi. Unsur-unsur ini digunakan untuk klasifikasi batuan dan lingkungan tektoniknya.
Hasil analisis geokimia conto batuan gunungapi dari Sungai Fatu dan DSDP berasal dari Benua Australia, sementara conto batuan dari Kompleks Mutis dan Sungai Metan menunjukkan Benua Asia atau Busur Banda seperti pada Pulau Atauro. Batuan basal dari Sungai Fatu terendapkan menjemari dengan batugamping Formasi Maubise berumur Perem dan merupakan Oceanic Island Basalt. Batuan basal dari Deep Sea Drilling Project (DSDP) secara geokimia termasuk subalkalin yang berasal dari pematang tengah samudera (Normal Mid Oceanic Ridge Basalt) berumur Jura.
Kompleks Mutis pada Oligosen Miosen mengawali kolisi antara Benua Asia dengan Benua Australia. Batuan metabasal Kompleks Mutis menunjukkan komposisi kalk-alkalin yang mencirikan busur kepulauan. Conto batuan dari Sungai Metan dan Pulau Atauro terutama menunjukkan komposisinya subalkaline. Puncak kegiatan kolisi terjadi pada Akhir Miosen – Awal Pliosen dan berlanjut hingga sekarang. Busur Banda bagian dalam sebagian gunungapinya sudah tidak aktif lagi seperti yang terjadi pada Pulau Atauro.
Kata kunci : geokimia, batuan gunungapi, mintakat, tektonik, kolisi, Timor
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