STRONTIUM, NEODYMIUM, AND LEAD ISOTOPIC AND TRACE-ELEMENT SIGNATURES OF THE EAST INDONESIAN SEDIMENTS - PROVENANCE AND IMPLICATIONS FOR BANDA ARC MAGMA GENESIS

We present new trace-element and Sr-Nd-Pb isotope data for 127 surface sediments and five sediments from DSDP Site 262, distributed along an d across the are-continent collision region of the Banda Are, East Ind onesia. The results are used to evaluate the role of subducted contine ntal material (SCM) in the genesis of the Banda Are magmas and to asse ss the extent to which geochemical and isotopic signatures of SCM are controlled by sediment provenance. In the surface sediments lead and n eodymium isotope ratios are variable: Pb-206/Pb-204 = 18.65-19.57; Nd- 143/Nd-144 = 0.51230-0.51190, with an increase in lead isotope ratios and a decrease in the Nd-143/Nd-144 ratio from northeast to southwest along the Panda Are. DSDP Site 262 sediments, farthest to the west in the Timer Trough, overlap with the surface sediments and have Pb-206/P b-204 = 18.89-19.23 and Nd-143/Nd-144 = 0.51200-0.51220. In contrast, the trace-element ratios and REE patterns of the sediments do not show systematic along-are variations and largely overlap with estimated Va lues for Upper Continental Crust, Post Archean Australian Shale (PAAS) , and ODP Site 765 sediments from the Argo Abyssal Plain. From the com bined isotopic and trace-element ratios in the terrigenous fraction of the sediments four major: provenance areas can be distinguished: Nort h New Guinea + Seram, South New Guinea, Timer, and northern Australia. The lead isotopic variations in the shelf and wedge sediments along t he Banda Are are parallel to similar variations in the volcanics; this is considered to be strong evidence for the incorporation of subducte d continental material in the are magmas. The trace-element characteri stics of both the volcanics and the sediments are also consistent with the involvement of sediments in the Banda Are magma genesis. The hint erland of the sediments is responsible for isotopic signatures created in the Panda Are mantle through recent subduction. This suggests that some of the mantle heterogeneities that are inferred from oceanic bas alts can be explained by differences in the provenance of (ancient) su bducted sediment.