Tectonic setting of deep geothermal system in island arc

我们在爪哇中部、苏门答腊南部和巽他岛弧的弗洛雷斯岛进行了三次MT测深。根据板块俯冲样式，将巽他弧的构造现状划分为三种类型。苏门答腊地区的特点是印度洋板块的斜向俯冲。Jawa - Sumbawa地区的特点是Jawa海沟的正常俯冲，而弗洛雷斯-帝汶地区的特点是弧与向北移动的澳大利亚大陆板块的碰撞，这些情况可能影响了被认为是火山和地热活动阶段的地壳结构。虽然地壳结构反映了这些现状以及各地区长期以来的构造演化，但现今地壳活动，如火山活动、地热活动和地震活动，也反映了现今的构造状况。本文试图勾画出强烈反映长期构造演化的地壳结构格架和与现今地壳活动有关的结构特征，二维电阻率结构显示，弧前侧地壳电阻率普遍较高，弧后侧地壳电阻率相对较低。这可能反映了地壳中的地热状况，并表明弧后一侧的温度梯度可能较高。在大火山之下出现了岩基，在岩基周围似乎发育有地热水循环带。苏门答腊岛地壳电阻率一般较低。拉分盆地的形成与斜向俯冲牵引下的走滑断层活动有关，区内火山和地热田发育。从而对岛弧深部地热资源的背景结构有了新的认识。

We have conducted three transects of MT soundings across central Java, south Sumatra and the Flores island in the Sunda arc. The present tectonic situation of the Sunda arc is divided by three types based on the plate subduction style. The Sumatra area is characterized by the oblique subduction of the Indian Ocean plate. The Jawa - Sumbawa area is characterized by the normal subduciton at Jawa trench and the Flores - Timor area is characterized by the collision of the arc with the northward moving the Australian continental plate.These situation may have affected a crust structure regarded as a stage of volcanic and geothermal activity. Although the crust structure has reflected these present situations as well as the tectonic evolution in each area for a long time, present crust activities, such as volcanic, geothermal and seismic activity, are reflecting present tectonic situation. We attempted to delineate the framework of the crust structure which strongly reflected long time tectonic revolution and the feature of structure relating to present crust activity in this study.The 2D resistivity structure revealed that the resistivity of the crust in the fore-arc side is genenrally higher, but back-arc side is relatively low. This may reflect the geothermal situation in the crust and shows the temperature gradient is probably higher in the back-arc side. The batholith was appeared beneath the big volcanoes and the geothermal water circulation zone seemed develop around the batholith. The resistivity of the crust tend to generally low in the Sumatra. The pull-a-part basins were formed associating with the activity of the transcurrent fault dragging by the oblique subuduction and the volcanoes and geothermal field developed in these area. We obtained these knowledge concerning the back ground structure of deep-seated geothermal resource in the island arc.