Gravity Derived Moho Depths of East/Southeast Asia and Western Pacific

Abstract:

East and Southeast Asia and Western Pacific have extreme topography and both the youngest and oldest oceanic basins in the world, and are ideal places to understand oceanic basin evolution and continent-ocean interactions. Crustal structure is critical to understand the regional geodynamic processes. We present our recent inversion of Moho depths of East/Southeast Asia and Western Pacific from satellite gravity data. Because the marginal basins have experienced different cooling histories, we perform thermal correction after the simple Bouguer correction based on the plate cooling model. The model parameters are tested by varying the input plate thickness and mantle temperature with 5 km and 50°C steps, respectively. The evaluation criteria of thermal correction is that the regions with similar water depths have similar Moho depths. We find the best-fit plate thickness and mantle temperature are 95 km and 1300°C, respectively. The Moho undulations are then estimated from residual Bouguer gravity based on the Parker-Oldenburg algorithm. Because the study area convers distinct geological settings, we implement two gravity inversion strategies. In the first strategy, we use a constant density contrast of 0.38 g/cm³ across the Moho and a reference depth of 25 km for the entire study area. Using just one density contrast results in an obvious shallow Moho in continental region. In the second strategy, the study area is divided into four blocks, each covering either the continents or oceans mainly. Moho depths range approximately between 5 and 65 km. The average Moho depths of continental and continental shelf domains are about 35 and 23 km, respectively. Moho depths beneath the marginal basins are averaged at about 16 km. This large mean Moho depth is attributed to numerous seamounts, volcanic chains and ridges, where the Moho depths can be up to ~35 km. We find that the density contrast across the Moho varies between 0.33 and 0.40 g/cm³, approximately 0.40 g/cm³ in most continental domains and between 0.33 and 0.37 g/cm³ in oceanic domains.