Karakteristik Geokimia Basal Alkali Formasi Manamas di Sungai Bihati, Baun, Pulau Timor

Abstract

ABSTRAK Batuan beku Formasi Manamas di Sungai Bihati, Baun merupakan salah satu singkapan batuan beku di Pulau Timor yang belum banyak diteliti berdasarkan karakter geokimia. Penelitian ini bertujuan untuk mengetahui genesa dan proses yang terjadi pada batuan beku Formasi Manamas dalam kerangka tektonik yang terjadi di Pulau Timor berdasarkan analisis petrografi dan geokimia. Analisis geokimia dilakukan dengan menggunakan X-ray Fluorescence (XRF) dan Inductively Coupled Plasma-mass Spectrometery (ICP-MS) untuk mengetahui senyawa utama, unsur jejak, dan unsur tanah jarang. Batuan beku Formasi Manamas berupa intrusi basal dengan afinitas alkali yang menunjukkan pola pengayaan unsur tanah jarang yang identik dengan Ocean Island Basalt (OIB). Penelitian ini membuktikan adanya dua mekanisme pengayaan unsur yang berbeda yaitu fluid related enrichment yang berkaitan dengan aktifitas subduksi lempeng Samudra Hindia di bawah Busur Banda dan melt related enrichment yang diperkirakan berasal dari sisa lempeng Samudra Hindia yang patah yang masuk kedalam zona reservoir OIB. Kedua magma lalu bercampur dan mengalami underplating di bawah Busur Banda. ABSTRACT The igneous rock of Manamas Formation in the Bihati River, Baun is one of the igneous rock outcrops in Timor Island that has not been widely studied based on its geochemical characteristic. This study aims to determine the genesis and processes that occur in the igneous rocks of the Manamas Formation within tectonic framework of Timor Island based on petrographic and geochemical analysis. X-ray Fluorescence (XRF) and Inductively Coupled Plasma-mass Spectrometery (ICP-MS) were used to determine the major elements, trace elements, and rare earth elements. The igneous rock of the Manamas Formation is a basalt intrusion with an alkaline affinity which shown an enrichment pattern of rare earth elements identical to Ocean Island Basalt (OIB). This study proves the existence of two different mechanisms of elemental enrichment, fluid related enrichment which related to the subduction activity of the Indian Ocean plate under the Banda Arc and also melt related enrichment which originated from the broken Indian Ocean plate which enters the OIB reservoir zone. The two different magmas then mix and underplating beneath the Banda Arc.

Petrogenesis and Geological Structure of Tantan Granitoid in Sungai Manau District, Merangin Regency, Jambi Province

“…Granite magma is usually associated with subduction areas due to the melting of part of the oceanic crust and continental crust, where the temperature and pressure are very high. Magma trapped under the crust will cause continental crust rocks (Sundaland), which contain continental sedimentary rocks, not to be metamorphosed so that it undergoes assimilation so that the magma shows the characteristics of high K 2 O, Na 2 O, and CaO [17]- [23]. It shows magma differentiation in Tantan Granitoid changing from basaltic or ultramafic primary to acidic magma.…”