We recovered sedimentary and plutonic rocks from the off-ridge portion of the Southwest Indian Ridge (37°00.02ʹ E, 44°49.73ʹ S, 2165 m deep). The petrography, geochemistry, and geochronology of these plutonic rocks were analyzed. Ar–Ar dating of biotite in the plutonic rocks yielded early Paleozoic ages of approximately 475 and 490 Ma, indicating that these rocks are likely related to Antarctic orogenies during the late Neoproterozoic to early Paleozoic. In addition, the samples exhibited trace element compositions and low initial εNd values (−8 and −12) similar to those of rocks from western Dronning Maud Land and the Transantarctic Mountains, Antarctica. Such similarities suggest that these plutonic rocks from the off-ridge portion of the Southwest Indian ridge were derived from western Dronning Maud Land or the Transantarctic Mountains and deposited by melting icebergs as dropstones.

我们从西南印度洋脊（37°00.02ʹ E，44°49.73ʹ S，2165 m 深）的离脊部分回收了沉积岩和深成岩。分析了这些深成岩的岩石学、地球化学和地质年代学。深成岩中黑云母的 Ar-Ar 测年得出的早古生代年龄约为 475 和 490 Ma，表明这些岩石可能与新元古代晚期至古生代早期的南极造山运动有关。此外，样品表现出的微量元素组成和较低的初始 εNd 值（-8 和 -12）与来自西部 Dronning Maud Land 和南极洲横贯南极山脉的岩石相似。