Structure and evolution of the Molucca Sea area: constraints based on interpretation of a combined sea-surface and satellite gravity dataset

Abstract

The paper presents an interpretation of the complete Bouguer gravity anomaly for the Molucca Sea area (northeast of Indonesia) in order to investigate the structure and interrelation of the main tectonic units of the region. Data on the gravity field and topography incorporate all available shipboard and satellite-derived data, including data collected during a 1994 R/V L’Atalante cruise in the Molucca Sea (MODEC). These data were compiled by weighted interpolation of surface and satellite data. The anomalous gravity field of the area contains components of different wavelengths, which we separated into regional and local anomalies using a spherical analogue of Kolmogorov–Wiener optimal (mean-square) filtering. Position and depth of the shallow lithospheric gravity sources were then estimated from the local field component by applying a new approach to Euler solution selection based on a recently developed fuzzy logic clustering method, called RODIN. The spatial distribution and depth of Euler solutions provide new information on the tectonic structure of the upper lithosphere resulting from the convergence of the Philippine Sea, Eurasian and Australian plates. The local Bouguer anomalies and dense clusters of Euler solutions make it easy to trace the Sangihe Trench further north, up to 5.5°N, joining it to the Pujada and Miangas ridges and to trace the Miangas Ridge southwards to its junction with the Central Ridge. Seismic data revealing compressive structure and dense shallow clusters of Euler solutions suggest that the Pujada Ridge overthrusts the Miangas Ridge from the west. Clusters of Euler solutions also clearly outline an ophiolite body of the Talaud Archipelago, show main thrust zones bounding it, and trace the southern termination of the Philippine Fault horsetail structure up to 5.5–6°N in the area southeast of Mindanao Island. Our results support the hypothesis that the Talaud Archipelago was formed in situ as an uplifted Central Ridge block. We suggest that the structure of the Archipelago and of the area to the east developed under compression caused by docking of the Snellius Plateau. The docking shifted the Philippine subduction zone eastwards and underthrust slivers of forearc lithosphere below the Talaud Archipelago.