Abstract:
The oceanic crust is formed by a combination of magmatic and tectonic processes at mid-ocean spreading centers. Under ultraslow spreading environment, however, observations of thin crust and mantle-derived peridotites on the seafloor suggests that a large portion of crust at ultraslow spreading ridges is formed mainly by tectonic processes, with little or absence of magmatism. Using three-dimensional seismic tomography at an ultraslow spreading Southwest Indian Ridge segment at 50.47°E, we discovered an extremely magmatic accretion of the oceanic crust. Our results reveal a low velocity anomaly (-0.6 km/s) at 4-8 km depth beneath the seafloor in the lower crust suggesting the presence of partial melt, which is accompanied by an unusually thick crust (~9.5 km), the thickest ever observed along mid-ocean ridges. We also observe a strong along-axis variation in crustal thickness from 9.5 to 4 km within 30-50 km distance, requiring a highly focused melt delivery from the mantle. We conclude that the extremely magmatic accretion is due to localized melt flow towards the center of the segment, which was enhanced by the significant along-axis variation in lithosphere thickness at the ultraslow spreading Southwest Indian Ridge.
主讲人简介：
陈永顺，“长江学者”特聘教授，1989年于美国普林斯顿大学地质和地球物理学系取得博士学位，先后在美国加州大学圣地亚哥分校Scripps海洋研究院、美国俄勒冈州立大学海洋研究院、日本爱媛大学理学部地球动力学研究中心任教，2001年10月起担任中国北京大学地球与空间科学学院、理论与应用地球物理研究所所长；2002获中国国家杰出青年科学基金；曾担任中国国家自然科学基金委员会第九届地球科学部专家评审组委员。社会职务：中国综合大洋钻探计划专家委员会委员、国际大洋中脊协会中国执委会主席、国际综合大洋钻探计划科学指导和评估委员会委员、海洋地球物理学杂志主编。
研究方向与领域：全球板块构造、海洋地球物理学、地球动力学
欢迎广大师生前往交流学习！
