40Ar/39Ar ages of granitoid pebbles from IODP Expedition 382 Sites in Iceberg Alley, Scotia Sea, Antarctica

The eastern Scotia Sea is known as Iceberg Alley, where large numbers of icebergs are brought to the Antarctic Circumpolar Current via the Weddell Sea Gyre. Icebergs transported through Iceberg Alley today can have traveled in the coastal current from anywhere around the Antarctica margin, but are sourced mostly from the Weddell Sea sector. The Weddell Sea sector drains parts of the Peninsula, West, and East Antarctic Ice Sheets. Sites U1536 and U1537 in Dove Basin and U1538 in Pirie Basin provide nearly continuous records of climate and ice sheet variation through the last 3.3 million years. Although with lower recovery, Site U1536 extends into the Miocene and Site U1538 extends through the lower Pliocene. Large dropstones are very unusual in the latest 1 million years, and they become more abundant through the early Pleistocene and Pliocene. At the more northern site, U1538, abundant dropstones were found as young as 1.3 Ma, but at U1536 and U1537, high abundances are only found older than ~2.5 Ma. A variety of dropstone lithologies were observed and sampled during IODP Expedition 382. In this presentation we report on the 40Ar/39Ar results of hornblende or biotite from seventeen sampled dropstones of broadly granitoid composition and texture (diorite through granite). Two single step fusion and one step-heating experiments were conducted on each sample. Of the seventeen, five have ages consistent with Ross/Pan-African sources, ten have typical West Antarctica ages between 90 and 175 Ma, one is approximately 300 Ma and one has very complicated systematics that we tentatively interpret at Grenvillian with a substantial younger partial resetting. Combined with ongoing studies of the dispersed sand provenance as well as the potential sources around the Weddell, these data will help to elucidate the state of the ice sheets and ice shelves through the Neogene.