Cenozoic tectonic and depth/age evolution of the Indonesian gateway and associated back-arc basins

Abstract

We reconstruct the tectonic and paleo-age and -depth history of the Indonesian seaway and associated southeast Asian back-arc basins to create a comprehensive paleogeographic framework for the region during the Cenozoic. We combine published tectonic models with revised models of the evolution of back-arc basins based on available marine magnetic anomaly data and a recently published high-resolution (1 min) marine gravity anomaly grid which reveals many fine-scale tectonic features previously not resolved. Reconstructions of the now-subducted Ceno-Tethys ocean floor are integrated with a revised absolute plate motion reference frame for the Indian Ocean based on moving hotspots. All marginal seas north of Australia formed in a back-arc setting, with the Caroline and Celebes seas opening north of a northward dipping subduction zone, and the Solomon Sea south of a southward dipping subduction zone north of Australia. We suggest that the evolution of the two sub-basins of the Caroline Sea from 36 to 25 Ma followed different seafloor spreading patterns, with the western sub-basin being influenced by the Manus hotspot. Our model suggests that collision between the Melanesian and the Caroline arcs led to cessation of oceanic crustal production in the Caroline Basin shortly before 25 Ma. Combined geophysical and geological observations suggest that several major tectonic events occurred north of Australia at around 45 Ma, roughly at the time when Australia started moving northwards at fast rates similar to the present. We suggest that this event is related to a relocation of the subduction zone NW of Australia under the Philippine Sea plate due to a collision and subsequent accretion of old Pacific plate material to the northward subducting Australian plate. Our gridded oceanic paleo-depth maps capture the history of marginal seas north of Australia, and the stepwise destruction of the Ceno-Tethys ocean floor in the northern Wharton Basin and the west Pacific, providing boundary conditions for both paleoceanograpic and geodynamic models. A regional analysis of basement depth anomalies reveals that median negative anomalous depth of several back-arc basins is of the order of 650–800 m, with a range of 300–1100 m, accompanied by negative regional heatflow anomalies, suggesting that mantle-driven dynamic topography plays a larger role in modulating regional basement depth than previously suggested. Regional shear wave mantle tomography cross sections highlight that all marginal basins that exhibit large negative dynamic topography are underlain by massive buried slab material in the lower portion of the upper mantle and/or below the transition zone, supporting the notion that the observed paired negative dynamic topography and heatflow anomalies are due to basin formation above slab burial grounds.