Gravity-based 3D imaging of subsurface heat source and structural controls in the Pemali non-volcanic geothermal, Bangka Island, Indonesia

Putriani; Rahmat Nawi Siregar; Glenaldo Achmad Zhafran Evito

doi:10.58524/jograv.v1i1.104

Authors

Putriani Department of Physics, Institut Teknologi Sumatera Author
Rahmat Nawi Siregar Department of Physics, Institut Teknologi Sumatera Author https://orcid.org/0000-0001-5448-896X
Glenaldo Achmad Zhafran Evito School of Integrative and Global Majors, University of Tsukuba Author

DOI:

https://doi.org/10.58524/jograv.v1i1.104

Keywords:

Non-volcanic geothermal system, Satellite gravity data, 3D gravity inversion, Granite intrusion, Structural control

Abstract

The Southeast Asian Tin Belt is characterized by extensive granitoid intrusions that may act as long-lived heat sources for non-volcanic geothermal systems. On Bangka Island, Indonesia, hot spring manifestations in the Pemali area (North Bangka Regency) indicate active geothermal circulation unrelated to recent volcanism. This study aims to characterize the subsurface structure and identify the principal structural controls governing the Pemali geothermal system, with particular emphasis on delineating buried granite intrusions and associated fault zones that may facilitate heat transfer and fluid migration. Secondary satellite-derived gravity data (TOPEX) were analyzed through regional–residual separation and three-dimensional inversion modeling to reconstruct subsurface density distribution. The regional gravity anomaly ranges from 21.7 to 38.1 mGal and reflects deep-seated high-density basement or intrusive bodies consistent with granitoid emplacement. Residual anomalies vary from −2.4 to 1.5 mGal, indicating shallow lateral density contrasts. Prominent low residual gravity zones are interpreted as fractured and altered rocks with reduced density, likely associated with geothermal fluid pathways and structural discontinuities. These anomalies spatially correlate with surface thermal manifestations, suggesting structurally controlled geothermal circulation. The results support a conceptual model in which heat is conducted from subsurface granite bodies into overlying Tanjung Genting Formation rocks, while faults and fractures enhance permeability and fluid flow. This study demonstrates that integrated gravity inversion provides an effective reconnaissance tool for identifying heat sources and structural controls in non-volcanic geothermal settings, offering a geophysical basis for further detailed exploration in the Pemali geothermal prospect.

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