Petrology, geochemistry, and geochronology of plutonic rocks from the present Southwest Indian Ridge: Implications for dropstone distribution in the Indian Ocean

We recovered sedimentary and plutonic rocks from the off-ridge portion of the Southwest Indian Ridge (37 degrees 00.02' E, 44 degrees 49.73' 5, 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 Neo-proterozoic to early Paleozoic. In addition, the samples exhibited trace element compositions and low initial epsilon Nd 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.