Subsurface delineation of Sukadana Basalt Province based on gravity method, Lampung, Indonesia

Abstract

Research subject. The geological profile of Sukadana Basalt Province as a large basalt outcrop in the back arc of Sumatra remains to be unclear. This also concerns the geological structures and their relationship with the Sundaland regional geology. Aim. To reveal the type and pattern of geological structures that controlled the Sukadana Basalt Province (SBP) to the surface, the distribution of Sukadana Basalt on subsurface and its relationship with Sundaland regional tectonics. Materials and Methods. A reprocessed bouguer anomaly map of Tanjungkarang quadrangle 1991 was used. Results. We found that the main eruption was located in the center of SBP. The forward modeling data show the thickness of SBP to reach 3,200 m. There are two Northwest-Southeast striking normal faults and one fissure controlling the development of SBP. These fractures served as the primary conduit for magma to ascend from the mantle to the Earth’s surface. We also found North-South striking normal faults and West-East dextral strike-slip fault that formed at Early Oligocene and indirectly supported the magma ascend to the surface. Conclusions. The North-South striking normal faults were correlated with the Sundaland oroclinal bending. These faults developed through the extrados zone, a large pull-apart area that caused the continental lithosphere to become thinner. Meanwhile, Quaternary-Northwest-Southeast striking fractures are correlated with the development of the Great Sumatra Fault. The formation of Northwest-Southeast striking fractures was affected by the Great Sumatra Fault movement, and the thinning of the back-arc crust affected by multi-extensional structures was implicated in the ascend of SBP’s magma to the surface.