Studies of the crustal formation and tectonics at ultra-slow spreading mid-oceanic ridges

该项目的目的是了解西南印度洋海岭的海底扩张构造、火山活动、地震活动和热液活动，这是一个超低速扩张系统。富士号巡航（法国-英国-日本海脊间巡航）于1997年10月7日至11月3日在西南海脊东部进行。观测的主要部分是TOBI深拖侧扫声纳观测（30 kHz，6 km条带）和海底地震仪对地壳结构和地震活动的观测。选择了两个一阶段，每个段长200 km，用于沿着轴拖曳。深拖箱测量设1个100 km * 100 km箱，包括离轴部分。TOBI侧扫图像较好地显示了火山特征和断层分布的细节。富士邮轮之主要业绩如下。(1)地壳的强烈不均匀性表明在该部分的中心集中的岩浆活动。(2)发现了一个70 km长的非火山岩段，其断裂样式复杂，但对这一段的扩张机制的认识还需要在该地区进行更多的调查。(3)海底地形对比强烈，在一个段的偏轴部分之间观察到火山构造的北方翼和缺乏火山构造的南翼。(4)大型深冲断裂对本区的伸展构造起主要作用。(5)OBS在该地区最大的一个区段观察到强烈的集中地震活动。

The objective of this program is to understand the sea floor spreadingtectonics, volcanism, earthquake activities, and hydrothermal activites of the Southwestern Indian Ridge, an ultraslow spreding system. The FUJI cruise (French-UK-Japan InterRidge cruise) was conducted from October 7 to November 3, 1997 at the eastern part of the Southwestern Ridge. The main parts of the measurements are TOBI deep-tow sidescan sonnar observation (30kHz, 6km swath) and the ocean bottom seismometer observation for the crustal structure and earthquake activities. Two first order segments with the length of 200 km each were selected for along axes towing. One 100km*100km box was set for the deep-tow box survey including offaxis part. The TOBI sidescan image well displayed the detail of volcanic features and fault distribution. The principal results of the FUJI cruise are as follows. (1) Intensive heterogeneity of the crusts were suggested by focused magmatism in the center of the segment. (2) A 70 km long non volcanic segment with a complex fault pattern was identified, although understanding of spreading mechanism of this part needs more survey in this area. (3) Strong contrast of sea bottom features between the offaxes parts of a segment is observed as the northern flank with volcanic construction and as the southern flank with pausity of volcanic construction. (4) Large dtachmen faults are observed suggesitng these type of faults have principal role on the spreading tectonics here. (5) Intensive focused seismic activity was observed y OBS at one of the largest segemts in the area.