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Marine magnetotelluric experiment across the central Mariana subduction-arc-back arc system

马里亚纳中部俯冲-弧背弧系统的海洋大地电磁实验

基本信息

批准号：
15340149
负责人：
SEAMA Nobukazu
金额：
$ 10.3万
依托单位：
Kobe University
依托单位国家：
日本
项目类别：
Grant-in-Aid for Scientific Research (B)
财政年份：
2003
资助国家：
日本
起止时间：
2003 至 2006
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-15340149/
关键词：
Subduction Zone Back-arc Basin Central Mariana area Upper mantle conductivity structure Ocean Bottom Electro-Magnetometers Magnetotelluric method マリアナ海域電気伝導度構造

项目摘要

We carried out a marine magnetotelluric transect across the central Mariana subduction-arc-back arc system using ocean bottom electro-magnetometers (OBEMs), ocean bottom electrometers (OBEs), and ocean bottom magnetometers (OBMs) to provide the electrical conductivity structure of the Mariana island-arc system extending from the Pacific ocean to the West Mariana Ridge (remnant arc) through the Marina Trough. Deployments of 33 OBEMs, 7 OBMs, and 7 OBEs were made at 40 sites across the central Mariana subduction-arc-back arc system during KR05-17 cruise. Observations using the instruments were made from December 2005 up to the recovery in September 2006. We successfully recovered 28 OBEMs, 7 OBMs, and 6 OBEs at 35 sites during KR06-12 cruise. We are still analyzing these data to estimate the upper mantle electrical conductivity structure, because the observation was delayed. But, these data will provide a comprehensive image of the conductivity structure for the central Mariana subduction-arc-back arc system, because the observation sites are so dense.We analyzed previous 9 OBEM data obtained from the same area. The resulting electrical resistivity structure shows an increase in conductivity at depths of about 70 km beneath the Mariana Trough and anisotropy at deeper depth. The low conductivity structure near Mariana Trough spreading axis implies that the onset of melting in the Mariana Trough back-arc basin is deeper than that of the typical MORB source region.Consideration of the effect of seafloor topography on ocean bottom magnetotelluric data is needed to estimate a reliable conductivity structure. We evaluated three different correction equations to correct the effect of seafloor topography with forward modeling, and we indicate the most an appropriate correction method based on a series of synthetic tests.

我们使用海底电磁计（OBEM）、海底静电计（OBE）和海底磁力计（OBM）对马里亚纳中部俯冲-弧-背弧系统进行了海洋大地电磁横断面测量，以提供从太平洋通过马里纳海槽延伸到西马里亚纳海岭（残余弧）的马里亚纳岛弧系统的电导率结构。 KR05-17 巡航期间，在马里亚纳中部俯冲-弧背弧系统的 40 个地点部署了 33 个 OBEM、7 个 OBM 和 7 个 OBE。使用仪器进行的观测从 2005 年 12 月开始一直到 2006 年 9 月回收。在 KR06-12 巡航期间，我们在 35 个地点成功回收了 28 个 OBEM、7 个 OBM 和 6 个 OBE。由于观测被延迟，我们仍在分析这些数据以估计上地幔的电导率结构。但是，由于观测地点非常密集，这些数据将为马里亚纳中部俯冲-弧-背弧系统的电导率结构提供全面的图像。我们分析了之前从同一区域获得的9个OBEM数据。由此产生的电阻率结构显示，在马里亚纳海槽下方约 70 公里的深度处，电导率有所增加，而在更深的深度处，则出现了各向异性。马里亚纳海槽扩张轴附近的低电导率结构意味着马里亚纳海槽弧后盆地的熔融起始位置比典型的MORB源区更深。需要考虑海底地形对海底大地电磁数据的影响来估计可靠的电导率结构。我们评估了三种不同的校正方程，以通过正演模型校正海底地形的影响，并基于一系列综合测试指出了最合适的校正方法。