Heat flow distribution and thermal structure of the Philippine Sea Plate and its adjacent areas

Research on the present geothermal state is an important way to understand the lithospheric geodynamics. We studied the heat flow (HF) distribution and the geothermal structure of the Philippine Sea Plate (PSP) and its adjacent area (100°E~155°E, 5°S~45°N) surrounded by the East China Sea, South China Sea and the West Pacific Ocean, which is aimed to provide thermal constraints for the dynamic mechanism and tectonic evolution of the PSP. Based on the observed seafloor HF data of the study area with the latest release of CRUST1.0 crustal layered model, the lithospheric geotherm was calculated using 1D steady-state heat conduction equation. However, the obtained numerous geotherms derived from the extrapolation through heat conduction equation strongly depended on the accuracy of the measured HF data, which is limited, unevenly distributed and easily affected by local factors. Therefore, as a meaningful comparison, the temperature distributions at 25 km and 50 km depth inferred from the upper mantle shear wave velocities structure (S2.9EA) are inverted. The HF distribution shows relatively high values in Ryuku Trench and nearby Izu-Boning Trench, where the crust thicken and the mantle uplift obviously as typical transition zones. The Mariana Trench located in the east (southeast) part and the Philippine Trench in the southwest both are with low HF, which is also illustrated in the upper mantle gravity map after temperature correction. The Central Basin Ridge is with unquestionable high HF, being perpendicular to which the value decreasing. The calculated temperature maps (at depth of 25 km and 50 km) by the two methods both present that the temperature in PSP is higher than that in the Western Pacific Ocean and the west Philippine Basin is lower than the east one, which consists well with the crust age. The west half parts both of the Philippine Basin and Parece Vela Basin show low temperature, but high value in Ryuku Trench, Nankai Through, Shikoku Basin, Amami Plateau, eastern Parece Vela Basin and most of Mariana Trough. The map also shows the low temperature feature nearby the Philippine subduction zone, the Benham Plateau as well as the Luzon, and the high temperature zone located in the Sulu Sea, which is clearly reflected in the magnetic anomalies. Certainly, there is also difference between the two kinds of temperature maps, mainly in Caroline Ridge, Yap Trench and Palau Trench. However, the temperature distribution obtained by these two methods is consistent well overall. This study is supported by the National Science Foundation of China (Grant No.: 40730317 and 40774060) and International Cooperation Projection in Science and Technology (Grant No.: 2010DFA24580).