Structure Boundary Separating using Gravity Data for Central and Southern Parts of the East Java Basin Beneath the Quaternary Volcanic Deposits

Ardian Novianto,Sutanto Sutanto,Carolus Prasetyadi,Suharsono Suharsono,Jatmiko Setiawan

doi:10.46717/igj.55.1b.1ms-2022-02-17

Ardian Novianto, Sutanto Sutanto + Show 3 more

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https://doi.org/10.46717/igj.55.1b.1ms-2022-02-17

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Abstract

Stratigraphic interpretation shows that the relationship between Cenozoic volcanic rocks deposited in the Southern Mountains and marine clastic volcanic rocks in the Kendeng Basin possibly forms a stratigraphic transition bordered by the major fault that is yet to be defined. The thick Quaternary volcanic deposits obstruct field observation on the surface. Miocene outcrops in limited presence are found on the volcanic slope, positioned relatively more to the north than the same outcrop. This feature indicates major thrusting in southern Java that moved it to the north. The gravity data analysis was used to obtain the field observation and identify the subsurface geology. Total Horizontal Derivative analysis of the gravity data showed a major fault boundary with a relative west-east direction separating the high Bouguer anomaly area in the south from a large negative area of about -50 mGal in the north. Second Vertical Derivative analysis reconstructed the fault slope direction and showed a south-facing slope with a large angle. Based on the combination of the surface data and the subsurface analysis, the boundary is a major fault with a west-east direction on the south side of the Quaternary volcanic range and a south-facing slope. It is interpreted as the result of the compressive tectonics that formed the fold-thrust belt system.

Highlights

The physiographic of East Java, Indonesia, from the north to the south can be generally divided into three parts, namely Rembang, Kendeng, and Southern Mountains Zones (Smyth et al 2005; Smyth et al 2008)
The Southern Mountains were characterized by a high gravity anomaly between 130‒50 mGal, while the Kendeng Basin had a much lower value of up to -50 mGal
Eastern Java is formed by the compressive tectonics occurring in several periods in the Cenozoic due to the interaction between the Gondwana microcontinent and southeastern Sundaland

Summary

Introduction

The physiographic of East Java, Indonesia, from the north to the south can be generally divided into three parts, namely Rembang, Kendeng, and Southern Mountains Zones (Smyth et al 2005; Smyth et al 2008). The Kendeng Zone is separated from the Southern Mountains by an area composed of volcanoes and Quaternary volcanic deposits known as the Ngawi subzone (Setiaji et al 2016; Van Bemmelen, 1949) (Fig. 1). This zone is a sedimentary basin with a relative west-east orientation and divides East Java into three basins: the northern, central, and southern basins. The southernmost basin consists of Eocene-Miocene volcanic deposits known as the Early Cenozoic Southern Mountain Arc

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