Subduction and melting processes inferred from U series, Sr-Nd-Pb isotope, and trace element data, Bicol and Bataan arcs, Philippines

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doi: 10.1016/j.gca.2006.04.020
Author(s): DuFrane, S. Andrew; Asmerom, Yemane; Mukasa, Samuel B.; Morris, Julie D.; Dreyer, Brian M.
Author Affiliation(s): Primary:
University of New Mexico, Department of Earth and Planetary Sciences, Albuquerque, NM, United States
University of Michigan, United States
Washington University, United States
Volume Title: Geochimica et Cosmochimica Acta
Source: Geochimica et Cosmochimica Acta, 70(13), p.3401-3420. Publisher: Elsevier, New York, NY, International. ISSN: 0016-7037 CODEN: GCACAK
Note: In English. 92 refs.; illus., incl. 2 tables, sketch map
Summary: We present U-series, Sr-Nd-Pb isotope, and trace element data from the two principal volcanic chains on Luzon Island, developed over oppositely dipping subduction zones, to explore melting and mass transfer processes beneath arcs. The Bataan (western) and Bicol (eastern) arcs are currently subducting terrigenous and pelagic sediments, respectively, which have different trace element and isotopic compositions. The range of (230Th/238U) disequilibria for both arcs is 0.85-1.15; only lavas from Mt. Mayon (Bicol arc) have 230Th activity excesses. Bataan lavas have higher 87Sr/86Sr and lower 143Nd/144Nd than Bicol lavas (87Sr/86Sr=0.7042-0.7046, 143Nd/144Nd=0.51281-0.51290 vs. 87Sr/86Sr=0.70371-0.70391, 143Nd/144Nd=0.51295-0.51301) and both arcs show steep linear arrays towards sediment values on 207Pb/204Pb vs. 206Pb/204Pb diagrams. Analysis of incompatible element and isotopic data allows identification of a sediment component that, at least in part, was transferred as a partial melt to the mantle wedge peridotite. Between 1% and 5% sediment melt addition can explain the isotopic and trace element variability in the rocks from both arcs despite the differences in sediment supply. We therefore propose that sediment transfer to the mantle wedge is likely mechanically or thermally limited. It follows that most sediments are either accreted, reside in the sub-arc lithosphere, or are recycled into the convecting mantle. However, whole-sale sediment recycling into the upper mantle is unlikely in light of the global mid-ocean ridge basalt data. Fluid involvement is more difficult to characterize, but overall the Bicol arc appears to have more fluid influence than the Bataan arc. Rock suites from each arc can be related by a dynamic melting process that allows for 230Th ingrowth, either by dynamic or continuous flux melting, provided the initial (230Th/232Th) of the source is ∼0.6-0.7. The implication of either model is that inclined arrays on the U-Th equiline diagram may not have chronologic significance. Modeling also suggests that U-series disequilibria are influenced by the tectonic convergence rate, which dictates mantle matrix flow. Thus with slower matrix flow there is a greater degree of 230Th ingrowth. While other factors such as prior mantle depletion and addition of a subducted component may explain some aspects of U-series data, an overall global correlation between tectonic convergence rate and the extent of U-Th disequilibria may originate from melting processes. Abstract Copyright (2006) Elsevier, B.V.
Year of Publication: 2006
Research Program: DSDP Deep Sea Drilling Project
Key Words: 02 Geochemistry; Actinides; Alkaline earth metals; Asia; Bataan Arc; Bicol Arc; DSDP Site 291; DSDP Site 292; Deep Sea Drilling Project; Far East; Geochemistry; ICP mass spectra; Igneous rocks; Island arcs; Isotope ratios; Isotopes; Lava; Lead; Leg 31; Luzon; Magmatism; Marine sediments; Mass spectra; Melting; Metals; Mount Mayon; Nd-144/Nd-143; Neodymium; North Pacific; Northwest Pacific; Pacific Ocean; Pb-206/Pb-204; Peridotites; Philippine Islands; Plate tectonics; Plutonic rocks; Radioactive isotopes; Rare earths; Sediments; Spectra; Sr-87/Sr-86; Stable isotopes; Strontium; Subduction; Th/U; Trace elements; Ultramafics; Uranium; Volcanic rocks; West Pacific
Coordinates: N154906 N154907 E1243904 E1243902
N124825 N124827 E1274959 E1274951
Record ID: 2008044075
Copyright Information: GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands