Nd isotopic anatomy of a pebble conglomerate from the Murihiku terrane of New Zealand: Record of a varied provenance along the Mesozoic Gondwanaland margin

We present Nd isotopic data from a Late Triassic (Rhetian; Otapirian local stage; 200-206 Ma) roundstone cobble conglomerate from near Gore, South Island, New Zealand. The sandstone matrix of this conglomerate has an initial ɛNd of + 3.0 and Sm/Nd of 0.219, values that are intermediate between the more radiogenic Nd isotopic and higher Sm / Nd ratios of older Murihiku siltstones and less radiogenic, lower Sm / Nd, younger siltstones. Clasts within this matrix are mainly volcanic: we analyzed basaltic-andesite, andesite and dacite pebbles along with a volcanogenic sandstone pebble and hypabyssal quartz diorite clast. These pebbles have initial ɛNd between + 3.7 and + 2.6, and are probably derived from a Late Triassic volcanic arc. A felsic plutonic pebble with an initial ɛNd of − 0.5 and crustal residence age of 1.0 Ga may record erosion of Gondwanaland Proterozoic basement. A mudstone rip-up clast may be composed of fine-grained cratonic detritus; it has a Nd crustal residence age of 1.1 Ga. This conglomerate, containing both arc-derived and older cratonic-derived clasts, captures in a single sample the contribution of mafic arc, felsic arc and craton-derived sedimentary rocks to bulk sediment Nd budgets recorded in the Murihiku terrane.