Activities and Origin of Hotspot Volcanoes in Indian Ocean

(1)在1994年开始对留尼汪岛和毛里求斯岛进行初步调查之前，我们走访了巴黎物理研究所的科学家，直接就我们想要收集的岩石和其他地点获得了足够的信息。此外，我们还乘坐直升机从空中俯瞰留尼汪岛。通过1994年和1995年的调查，我们几乎可以从留尼汪岛、毛里求斯和罗德里格斯群岛收集到我们想要获得的各种样本。它们涵盖了时空范围内的样品，包括具有橄榄石斑晶和超镁铁质结核的玄武岩。(2)我们的三个小组在1995年对罗德里格斯岛进行了调查，发现该岛的地质情况在东西两部分之间存在差异，火山活动的中心似乎已经从西向东移动。岩浆似乎不是来自海脊系统。(3)通过与IPGP科学家的合作，作为火山物理研究，我们调查了尾波Q，发现它依赖于地震波的频率。Piton de la Fourneise火山周围的尾部Q已被发现与岛上的弧区和碰撞区的尾部Q相同。时间序列分析表明，Piton de la Fournase火山和Mt.富士火山受一个比伊豆-大岛火山和三宅岛-吉马火山更简单的系统控制。(4)采集的样品制备了薄片，并进行了岩石学、矿物学、化学和同位素分析，包括K-Ar定年。在我们积累了这样的数据之后，我们将讨论留尼汪岛热点的特征和起源。

(1) Before we started the preliminary survey of the Reunion and Mauritius Island in 1994, we had visited the scientists of the IPGP (Institut de Physique du Globe de Paris) and got sufficient information directly on the sites of rocks which we wanted to collect and others. Further, we surveyed the Reunion Island from the air by a helicopter. Through the survey in 1994 and 1995, we could collect almost all kinds of samples which we want to get from the Reunion, Mauritius and Rodrigues Islands. They cover samples which range in space and time and include basalts with olivine phenocrysts and ultramafic nodules.(2) Three of our group surveyed the Rodrigues Island in 1995 and found that the geology in this island is different between the eastern and western parts and the center of volcanic activity seems to have moved from the west to the east. The magmas do not seem to have been originated from the ridge system.(3) Through the cooperative works with the scientists of the IPGP,as a volcanophysical study, we investigated the coda Q and found that it depends on the frequency of seismic waves. The coda Q around the Piton de la Fournaise volcano has been found to be identical with those of the island are and collisional regions. The time-sequence analysis has revealed that the rhythm of volcanic eruption for the Piton de la Fournase volcano and Mt. Fuji is controlled by a simpler system than those of Izu-Oshima and Miyake-jima volcanoes.(4) For collected samples, thin sections were prepared and petrological, mineralogical, chemical and isotope analyzes including K-Ar dating are undertaken. After we accumulate such data, we will discuss the characteristics and origin of the Reunion hotspot.