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科学通报  2015 

超慢速扩张洋中脊NTD的蛇纹石化地幔:海底广角地震探测

DOI: 10.1360/N972014-01021, PP. 952-961

Keywords: 蛇纹石化地幔,非转换断层不连续,热液活动,超慢速扩张洋中脊,海底地震探测

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Abstract:

非转换断层不连续(NTD)在超慢速扩张洋中脊高频度出现,其地壳速度结构与相邻的岩浆扩张中心(NVR)差别明显.结合表层断层多和减薄的地壳,说明NTD在超慢速洋中脊扩张理论、热液活动甚至矿产资源方面有十分重要的意义.本文使用2条海底广角地震测线的数据,使用射线追踪正反演的方法,获得了西南印度洋中脊28~29扩张段之间NTD下方的地壳及上地幔速度结构.结果表明(1)NTD下方地壳较薄(3.2~4.5km),洋壳层2厚约2.0km,洋壳层3较薄(1.0km)甚至缺失;(2)洋壳层2表层速度横向差异大,表明存在较多断裂;(3)洋壳层3出现低速区,成因可能是受浅部大断裂或地幔蛇纹石化作用影响;(4)上地幔顶部速度存在低速异常(7.2km/s),结合NTD地壳较薄(

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