Nd and Pb isotope evolution of deep water masses in the eastern Indian Ocean during the past 33 Myr

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Chemical Geology
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Feb 28
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New time series of Nd and Pb isotopes were generated from two hydrogenous ferromanganese crusts from the eastern Indian Ocean, which were dated by Be-10/Be-9 profiles and Co chronometry. The goal was to gain information on the nature and timing of variations of the deep water radiogenic isotope composition as a function of the evolution of the Indonesian Island Arcs since the Early Miocene, changes in ocean circulation related to the different stages of the closing of the Indonesian seaway for deep and intermediate water mass exchange since the Mid-Miocene, and enhanced Himalayan weathering since the Late Oligocene.A crust from 4119 m water depth in the Wharton Basin adjacent to Sumatra and the Java Trench (DODO 232D) has recorded a small variability in Nd isotope, but pronounced variations in Pb isotope composition over the past 17 Myr. Patterns and absolute values of the Nd and Pb isotope time series closely resemble the record of previously published crust SS663 from the central Indian Ocean, located some 2500 km SW of crust DODO 232D in the northern central Indian Ocean. In accordance with the interpretation derived from crust SS663, the Pb isotope composition of deep water in the Wharton Basin has apparently been mainly controlled by products of Himalayan erosion and weathering and to a lesser extent by the evolution of the Indonesian Island Arcs.The location of a second crust(VA16 13KD-1) from 2 100 m water depth on the Scott Plateau off NW Australia is beneath the present day outflow of Pacific-derived surface and thermocline water masses into the eastern Indian Ocean. The pattern of the Pb present day outflow of Pacific isotope time series of this crust and the observed changes in Pb isotope mixing relationships, which occurred at similar to 11.5 and similar to 3.5 Ma, reflect the combined influence of advection and mixing of water masses through the Indonesian Seaway and weathering of volcanic source rocks within the emerging Indonesian Island Arcs over the past 33 Myr. The Nd isotope time series shows a pattern similar to central and southwest Pacific crusts and is best explained by a mixture between Nd from water masses advected from the Indian and Southern Ocean and Nd released by weathering from the emerging Indonesian Island Arcs. (c) 2005 Elsevier B.V. All rights reserved.


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DOI 10.1016/j.chemgeo.2005.09.024