Provenance Investigations Using Magnetic Susceptibility of Pebble- to Cobble-Sized Clasts in the AND-2A Core, ANDRILL Southern McMurdo Sound Project, Antarctica

Magnetic susceptibilities of pebble- to cobble-sized clasts recovered in the ANDRILL SMS core (site AND-2A: 77° 45.488'S, 165° 16.605'E) (McMurdo Sound, Ross Sea) were measured on ice with a Bartington MS-2B susceptibility meter. Measurements were made on thin section billets or on clasts themselves when they were of suitable size for the instrument. The variability of the magnetic susceptibility is related both to variations in the primary magnetic mineral content of the source rocks as well as to secondary magnetic mineral formation/dissolution prior to and during the diagenetic process. Volcanic clasts, the dominant clast type thoughout the core, display the highest susceptibility values, but there is extreme heterogeneity of values within the same compositional type (i.e. felsic, intermediate, mafic). Given this, the susceptibilities of volcanic clasts in the AND-2A core are poorly suited for provenance studies. In contrast, the basement clasts (consisting of a variety of metasedimentary and intrusive rocks) can play an important role in defining ice provenance and dynamics. The textures and mineralogical compositions of intrusive and metamorphic rocks indicate the region between the Ferrar Glacier and the Mulock Glacier as the most likely provenance region. In order to better understand this result, we chose to undertake a magnetic petrology study on the most magnetic (Low-Field mass susceptibility, χ > 90*10-8 m3/kg) basement clasts sampled on ice. A comparison of the magnetic susceptibilities of our AND-2A clasts with samples collected from the outcrops of Southern Victoria Land (SVL) indicate that there is a good correlation between the highly magnetic metamorphic rocks of the region south of Ferrar Glacier and the most magnetic basement clasts in the core. In particular, the petrographic and magnetic features of metasedimentary clasts closely match both metasandstones from Baronick Glacier (Skelton Glacier area) and gneisses and schists from Hobbs Peak (Blue Glacier area), corroborating the inferences of the petrography-based provenance studies. These preliminary results point out the importance of mineral magnetic measurements in providing additional constrains and a useful data set for on-going provenance investigations of Cenozoic sediments recovered by recent ANDRILL drillholes in the McMurdo Sound area.