Heat Flow Distribution Characteristics And Its Tectonic Significance Of China

The earth can beconsidered as a heat engine,sincea huge volume of inner heat drivesits evolution.Terrestrial heat flow,or surface heat flow,representing the earth's heat flux,is the only physical parameter that can be observed directly in the surface.Accordingly,heat flow holds important position in geothermal related studies.In addition,seeking for unconventional or new energies is the focus of energy science field worldwide,due to increasing shortage of fossil energy.As a clear energy potential,geothermal energy in the land and natural gas hydrate in the marine sediments,attract much attention recently.Heat flow regime of the continental and maritime areas of China would provide geothermal background for the assessment of geothermal energy and hydrate resource potential.Recently,we have determined 48 new heat flow data for the Tarim Basin,76 for the Bohai offshore area and 55 for the northern margin of the South China Sea.All the new data are integrated with previous data in this study,and 1009 data from 2132 totally are for the continental area.Grid processing method by areas of 1°×1°and GIS technology are used here to describe the heat flow pattern.This analysis not only attempts to overcome the shortage of arbitrary interpolation due to sparse coverage in heat flow determinations in previous compilations,but also integrates the land and sea areas of China for the first time.The average heat flow for the continental and maritime areas of China is 70.1±16.4mW/m2,and those for the continental and maritime areas of China are 61 mW/m2 and 75.5mW/m2,respectively.Heat flow for the maritime area is larger than that of the continental area.Heat flow pattern for the continental area is featured by high in the east and low in the west,and high in the southwest and low in the northwest;among which,the Bohai Bay Basin,coastal area in SE China and Southern Tibet have high heat flow anomalies.Whilst for the maritime area,high heat flow occurs in the south and west,but low in the north and east.For each sea in detail,both the Bohai Sea and Huanghai Sea have the similar heat flow with those in their adjacent onshore areas.The heat flow pattern in the East China Sea keeps NE striking and the Okinawa Trough is characterized by remarkably high heat flow,considering its affinity of back-arc basin.Heat flow increases gradually from the onshore to oceanic basin perpendicular to the coast.Regional extension associated with the Pacific plate subduction in east China and compression regime reduced by the Indo-Asia continental collision in the west account for the observed heat flow pattern.Geophysical analysis demonstrates that the transition and or gradient belt of the crustal thickness is also with high heat flow.The high heat flow anomalies are related to magmatism and present-day crustal activities such as the volcanism and earthquake.Crustal thinning process determines the heat flow in the maritime area and Cenozoic magmatism accounts for the heat flow pattern in the continental area.In summary,the average heat flow and its pattern presented in this study coincides with those in the last compilation,however,the regional pattern for different tectonic domains is much evident in this new compilation.More importantly,the average heat flow for the continental area of China is somewhat lower than the mean of global continental heat flow,and the heat flow for the China seas is also lower than those of the global oceans and other marginal seas,such as the Mediterranean Sea,Black Sea and Caspian Sea.This indicates geothermal regime of the continental and maritime areas of China is lower than global average.