Contrasting magmatic structures and tectonic controls from integrated gravity and magnetic data in the Bromo–Tengger–Semeru complex and the Lamongan Volcanic Field, East Java, Indonesia

Abstract

This study aims to clarify how contrasting tectonic regimes influence magma storage, connectivity, and emplacement in spatially adjacent volcanic systems within a single arc segment in East Java, Indonesia. We focus on the polygenetic Bromo–Tengger–Semeru (BTS) complex and the Lamongan Monogenetic Volcanic Field (LMVF), employing integrated gravity and magnetic approaches including Bouguer anomaly modeling, 3D Euler and 2D Werner deconvolution, constrained gravity inversion, and magnetic edge detection. A vertically extensive, lens-shaped high-density body is imaged beneath BTS between 5 and 20 km depth, with indications of lateral connectivity between Semeru and Bromo aligned along N-S compressional structures. In contrast, LMVF shows only shallow, dyke-like intrusions (<2.5 km) aligned with NW–SE and NE–SW faults, spatially correlated with maar lakes and cinder cones. These findings support a model in which compressional tectonics in BTS promote deep, laterally connected magma reservoirs, while extensional faulting in LMVF facilitates shallow, structurally guided intrusions. This comparative analysis highlights the role of tectonic segmentation in shaping magmatic structure and provides a replicable framework for integrated geophysical analysis of arc volcanism.