Electromagnetic and Tomographic Research of Melt below EPR

关于东太平洋海隆（EPR）周围的地球物理测量，美国斯克里普斯海洋研究所的R/V梅尔维尔号在1997年5月底至1997年7月初的一次研究巡航中成功地回收了四个海底电磁仪（OBEM），以获得一年多的海底电磁（EM）时间序列。在1996年5月中旬至1996年7月初的一次研究航行中，OBEM已安装在EPR的17 ° S处，这也是地幔电磁和层析成像（MELT）项目协调的一次国际航行。来自这些海底单位的EM数据现在正在与美国和澳大利亚团体同时收集的数据一起进行分析。分析和随后的建模/反演的目标是揭示超扩展中心下方熔体的EM结构。具体而言，这项研究的目的是通过在海底联合观测地震学和大地电磁学，量化熔体的几何形状、熔体比例和连通性。所收集的样品是火成岩或沉积岩，年龄为2，500至3，500 Ma。这些样品正在进行岩石学、地质学和古地磁学分析，以估计海底的构造活动和地球在科布伦森的地磁场，这些结果将与在澳大利亚（'95）和加拿大（' 96）收集的样品的结果相结合，以重建科布伦森地球的全球视图。

As for geophysical measurements around the East Pacific Rise (EPR four Ocean Bottom Electro Magnetometers (OBEMs) were successfully retrieved during a research cruise from the end of May/'97 through the beginning of July/'97 by R/V Melville of Scripps Institution of Oceangraphy, US,to yield electromagnetic (EM) time series at the seafloor for more than one year. The OBEMs have been installed at 17ﾟS of EPR during a previous research cruise from the middle of May/'96 through the beginning of July/'96, which was also an international cruise coordinated by Mantle ELectromagnetic and Tomography (MELT) Project. The EM data from these seafloor units are now being analyzed together with those simultaneously collected by US and Australian groups. The goal of the analyzes and subsequent modellings/inversions is reveal the EM structure of melt bodies just below the super spreading center. Specifically, this research aims at quantifying the geometry, melt fraction and connectedness of the melt bodies by a joint observation of seismics and magnetotellurics at the seafloor.In terms of study of the very old oceanic crust in Archaen, rock sampling was conducted in South Africa and Zimbabwe this year. The samples collected are either igneous or sedimentary rocks as old as 2,500 to 3,500 Ma. These samples are in the course of petrological, geological and paleomagnetic analyzes to yield estimates of the tectonic activity at the seafloor and Earth's geomagnetic field in Archaen, which will be combined with the results from the samples collected in Australia ('95) and in Canada ('96) to give reconstruction of a worldwide view of the Earth in Archaen.