Petrogenesis of Volcanic Cones Intra Tondano Caldera, North Sulawesi
Ambarwati Puspanegara (a), Mirzam Abdurrachman (a), Mochamad Nugraha Kartadinata (b)

Geological Engineering Study Program, Faculty of Earth Sciences and
Technology, Bandung Institute of Technology (a), Centre of Volcanology and Geological
Hazard Mitigation (b)Please Just Try to Submit This Sample Abstract
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Abstract

Tondano Caldera is the result of an explosive eruption that was formed about 1.25 to 2
million years ago in North Sulawesi. After that, volcanic activity was still ongoing, marked
by the formation of volcanic cones in the Tondano Caldera, including Lokon Complex and
Tampusu Complex. Previous research at Tampusu Complex only discussed the geothermal
system in the surrounding area and for Lokon Complex it was necessary to update data
because from 1829 to 2015 there had been 37 eruptions. This study aims to map the
distribution of volcanic products, the history of the formation and evolution of magma, and
to determinethe tectonic setting based on petrogenesis studies.
Based on the volcanostratigraphic analysis, the study area was formed during 14 phases
of formation of khuluk and gumuk consisting of 10 khuluks and 6 gumuks. The
evolution of magma in the study area shows a repetition of magma differentiation
processes, primitive magma injection and magma assimilation which is reflected in
fluctuations in anorthite content and rock texture. Based on plagioclase microtexture
analysis, the processes that occur include decompression due to primitive magma,
crystal fractionation, self mixing due to convection, heating due to primitive magma
mixing, cooling due to eruption, and decompression during eruption. Analysis of spider
diagrams, bivariate and ternary diagrams between geochemical content, and
comparisons between trace elements shows that Lokon Complex and Tampusu
Complex are tectonically included in active continental margin with medium K calc
alkaline magma series from East Sangihe Subduction.

Keywords: Petrogenesis, Tondano Caldera, Lokon Complex, Tampusu Complex, magma evolution

Topic: Solid Earth Sciences