Benham Rise Unveiled: Morphology and Structure of an Eocene Large Igneous Province in the West Philippine Basin

Abstract:

Multibeam bathymetry with almost 100% coverage has revealed the morphology of Benham Rise, an oceanic plateau in the West Philippine Basin, for the first time. It consists of a main body measuring ~310 km by 330 km and three spurs extending 100-200 km from its eastern side. The main body is built on a shield platform with flanks consisting of ~3-15 km wide terraces with scarps as high as 100 m to 300 m. The platform is surmounted by a crest exhibiting caldera morphology with a diameter of ~150 km. Caldera features such as a breached rim, intra-caldera benches, and a resurgent dome suggest a multi-phase volcanic history consisting of both quiet and explosive eruptions.

The bathymetry and publicly available geological and geophysical data indicate three main stages in the formation of Benham Rise – shield-building, caldera formation, and post-caldera/late stage volcanism. The platform base is interpreted to have formed over a hotspot beneath the Central Basin Spreading Center during the shield-building phase between ~47.9 Ma to ~42.5 Ma. The arrowhead shaped Molave Spur is interpreted to have formed late in this stage along a ridge that propagated away from the hotspot. The caldera formation followed and is interpreted to have occurred before ~41.3-41.5 Ma when Benham Rise was still joined with Urdaneta Plateau. The Narra Spur was formed by late-stage hotspot related volcanism, as Benham Rise and Urdaneta Plateau separated, and ended with the eruptions of the Vinogradov Seamount at ~26 Ma.