The global significance of Krakatau Volcanic Complex and Way Kambas National Park is the best potential areas to be developed as part of a world heritage, particularly as UNESCO Global Geopark. Both of these objects are in the Lampung Province, Indonesia. Soon, it is necessary to identify and make an inventory of key sites that could become the theme of the area. The study of geodiversity and scientific valuation was carried out which referred to the Technical Guidelines for the Assessment of Indonesia Geological Heritage Resources, 2019. Based on these studies and assessments, there are 14 key sites to represent for Geopark Krakatau-Way Kambas themes. These sites are closely related to the evolution of tectonic activity in the Southern Sumatera as well as the dynamics of magmatism and paleovolcanism that have occurred since the Mesozoic which has signification in human history as world heritage.
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.
Manamas volcanic rock formed due to crustal thinning in fore arc setting. This research aims to provide information and the enrichment process of rare earth elements in Manamas Formation on the Timor Island and their tectonic implication. Manamas volcanic rock exposed in Bihati River, Baun, Timor consists of two different types of basalts, namely alkaline basalt and sub alkaline basalt. Analysis using ICP-MS method shows enrichment in large ion lithophile element and high field strength element. Subalkaline basalt has N-MORB patterns and alkaline basalt have OIB patterns. The Nb element is relatively impoverished that indicates influence of subduction activities. Thorium and uranium elements also show significant enrichment, due to sedimentary rocks contamination or continental crust or directly from the asthenosphere due to magma upwelling. The two distinctive patterns interpreted due to slab tear phenomenon beneath Timor Island during Australia oceanic plate subduction and recycled oceanic crust beneath Banda Arc.
Gunungapi Purba Soreang yang terletak di Kabupaten Bandung merupakan gunungapi yang tidak aktif dan tererosi kuat. Daerah ini memperlihatkan susunan litologi gunungapi strato-vulanik serta memiliki morfologi perbukitan bergelombang tak beraturan dan bukit-bukit soliter. Penelitian ini dilaksanakan untuk mengetahui hubungan geomorfologi dan geologi Gunungapi Purba Soreang dengan potensi keberadaan cebakan emas. Metode yang dilakukan adalah analisis geomorfologi, pemetaan vulkanostratigrafi dan analisis struktur geologi serta identifikasi zona alterasi dan mineralisasi. Berdasarkan peta morfografi dan kemiringan lereng, daerah penelitian menunjukan bentuk bentang alam khas gunungapi berupa bentuk yang menyerupai lingkaran atau circular feature yang dihasilkan oleh batuan intrusi, kubah lava, dan leher gunungapi purba, sebagai petunjuk lokasi sumber erupsi. Produk gunungapi purba Soreang memperlihatkan fasies sentral hingga distal dalam beberapa satuan gumuk dan khuluk. Litologi penyusun daerah ini di antaranya intrusi andesit dan diorit yang sebagian besar telah mengalami alterasi hidrotermal, perselingan lava dan breksi piroklastika dan tuff. Litologi ini menunjukkan bahwa Gunungapi Soreang merupakan jenis strato-vulanik. Di area Gunungapi Purba Soreang ini telah dilakukam eksplorasi potensi mineralisasi emas pada zona sentral. Pertambangan tradisional juga telah dilakukan oleh masyarakat lokal. Berdasarkan analisis terpadu bentang alam dengan litologi, perkiraan tubuh Gunungapi Purba Soreang dan zona sentral gunungapi tersebut dapat diidentifikasi. Hasil identifikasi tersebut digunakan untuk membantu penetapan area eksplorasi potensi cebakan emas di wilayah Soreang.
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