Heat Flow Distribution in and around the Philippine Sea

Abstract

Heat flow measurements in the Philippine Sea area have been recentlyconducted not only across trench-arc-backarc systems, but also in backarc basins wherehydrothermal activity has been found and around accretionary prisms in order to clarify theirlocalized thermal features.
In most trench-arc-backarc systems, heat flow is commonly low fromtrench axis to forearc areas, whereas it is higher on backarc side. The Yap Arc system has asimilar heat flow profile to other arc systems, suggesting that its subducting activity is notyetceased. In the Nankai Trough, heat flow is locally high near the deformation front anddecreases landward. It is attributed to pore fluid flow in sediment layer and from deeper part.Anomalously high and variable heat flow along a fault at the western margin of Sagami Baycanbe explained by outflow of pore fluid driven by shallow heat source below.
Heat flow distribution in backarc basins is influenced by past orpresent hydrothermal activities, depending on their age. The relatively older Shikoku and ParaceVela basins have average heat flow values lower than those estimated from their age inthinly sedimented areas, whereas in the eastern half of the Parace Vela Basin they are uniformand concordant with those estimated from its age. The Mariana Trough and Izu-Bonin backarcdepressions are thought to be generally in a backarc spreading stage, and activehydrothermal venting with high and variable heat flow distribution was discovered near the axialpart. In the Okinawa Trough area which is presumed to be in a nascent stage of backarcrifting, hydrothermal ativities with active vents have also been found. A speculated pattern ofhydrothermal circulation is the discharge at topographic highs and the recharge of sea waterintosediment around the topographic low where heat flow values are low.
Comparison of heat flow distribution among these backarc basins forvarious spatial scales would be useful for better understanding of various kinds of geophysicalphenomena, such as cooling of lithosphere or hydrothermal activities.