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Strontium, neodymium, and lead isotopic and trace-element signatures of the East indonesian sediments: provenance and implications for banda arc magma genesis

1995; Elsevier BV; Volume: 59; Issue: 12 Linguagem: Inglês

10.1016/0016-7037(95)00151-4

1872-9533

Pieter Z. Vroon, Manfred J. van Bergen, G.J. Klaver, William M. White,

Geochemistry and Elemental Analysis

We present new trace-element and Sr-Nd-Pb isotope data for 127 surface sediments and five sediments from DSDP Site 262, distributed along and across the arc-continent collision region of the Banda Arc, East Indonesia. The results are used to evaluate the role of subducted continental material (SCM) in the genesis of the Banda Arc magmas and to assess the extent to which geochemical and isotopic signatures of SCM are controlled by sediment provenance. In the surface sediments lead and neodymium isotope ratios are variable: 206Pb/204Pb = 18.65–19.57; 143Nd/144Nd = 0.51230–0.51190, with an increase in lead isotope ratios and a decrease in the 143Nd/144Nd ratio from northeast to southwest along the Banda Arc. DSDP Site 262 sediments, farthest to the west in the Timor Trough, overlap with the surface sediments and have 206Pb/204Pb = 18.89–19.23 and 143Nd/144Nd = 0.51200–0.51220. In contrast, the trace-element ratios and REE patterns of the sediments do not show systematic along-arc variations and largely overlap with estimated values for Upper Continental Crust, Post Archean Australian Shale (PAAS), and ODP Site 765 sediments from the Argo Abyssal Plain. From the combined isotopic and trace-element ratios in the terrigenous fraction of the sediments four major provenance areas can be distinguished: North New Guinea + Seram, South New Guinea, Timor, and northern Australia. The lead isotopic variations in the shelf and wedge sediments along the Banda Arc are parallel to similar variations in the volcanics; this is considered to be strong evidence for the incorporation of subducted continental material in the arc magmas. The trace-element characteristics of both the volcanics and the sediments are also consistent with the involvement of sediments in the Banda Arc magma genesis. The hinterland of the sediments is responsible for isotopic signatures created in the Banda Arc mantle through recent subduction. This suggests that some of the mantle heterogeneities that are inferred from oceanic basalts can be explained by differences in the provenance of (ancient) subducted sediment.