【摘要】 为了验证西南印度洋中脊50°E区域的残留熔融体与8~11 Ma前的岩浆供给活动的相关性,用有限元方法对洋壳模型进行热力学数值计算,以期解答超慢速洋中脊热液活动是由于古岩浆房长期持续供热,还是依赖周边热点提供持续的岩浆和热融熔问题.实验模拟了水平层状洋壳模型和地震试验得到的实际洋壳模型两种情况,对水平层状洋壳模型研究了上地幔有、无持续岩浆供给两种情况,对实际洋壳模型研究了一次岩浆供给的情况.结论如下:如果洋壳层底部没有持续热供应,岩浆房持续时间约为数千年或数万年;西南印度洋中脊中东段隆起区的热液活动和岩浆房最多持续存在0.8 Ma,现今热液活动的热源并不是8~11 Ma前的岩浆供给提供的.更多还原

【Abstract】 The Southwest Indian Ridge( SWIR) is characterized by ultra-slow spreading rate,lack of magma supply,thin crust,and extensive outcrops of serpentinized peridotite. Studies of axial crustal structure have been focused mostly on deep melt-poor ridge sections and little attention has been given to the central and shallowest portions of the SWIR,from the Prince Edward( 35. 5° E) to the Gallieni( 52. 3° E) fracture zones, where geochemical and geophysical data suggest the presence of a thicker crust. Both the extent of crustal thickening and the mechanism responsible for it are debated. Up to 10 km thick crust was determined by the study of 3-D wide-angle seismic experiment on the ridge section between49. 28° E and 50. 82° E. In order to learn if the thick crust and the crustal residual partial melting at SWIR 50° E influenced by the magma robust event happened at 8 ~ 11 Ma ago,whilst to find whether the ancient long lived magma chamber or the continually hot melt and magma supplied by surrounded hotspots make the activities of hydrothermal circulations at the ultra-slow spreading ridge,we simulate the thermal evolution process of the oceanic crust model by using the finite element method. The experiment includes two cases of oceanic crust with horizontal layers and oceanic crust obtained from seismic study,for the first case,we studied two situations of continued magma supply from the mantle and once magma supply from the mantle,for the second case,we studied one situation of once magma supply from the mantle. And our conclusions are as follows: If there is no continued magma supply,the magma chamber only last for several thousand or ten thousand years; and the hydrothermal circulations and magma chamber in the eastern shallow part of Southwest Indian Ridge will last at most 0. 8 Ma,which means the current hydrothermal circulations were not supplied by magma supply occurred at 8 ~ 11 Ma ago.更多还原