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Goldstein, S.L., 1986

Isotopic studies of continental and marine sediments, and igneous rocks of the Aleutian Islands arc

Bibliographic Reference

Goldstein, S.L., 1986, Isotopic studies of continental and marine sediments, and igneous rocks of the Aleutian Islands arc: New York City, New York, Columbia University, Teachers College, Ph.D. dissertation, 357 p., illust., maps.


Neodymium and strontium isotopic compositions are utilized to trace provenances of marine ferromanganese and detrital sediments, sediments from the major rivers on Earth, wind-blown dusts collected over the oceans, Amazon tributaries, and Aleutian igneous rocks. The amount of time the material in the detrital sediments has been resident in the continental crust is estimated. The samarium to neodymium ratios and neodymium isotopic compositions have been found to be uniform in products of large-scale erosion and transport, compared with the range of compositions in rocks at the surface of the Earth. The uniformity is largely independent of the lithological and tectonic diversity within major drainage basins. The total range of compositions in sediments from major rivers, wind-blown dusts, Amazon river tributaries, and Atlantic sediments are about the same. The uniformity reflects efficient mixing that has accompanied repeated cycles of erosion on the Earth's surface. Strontium, neodymium, and lead isotopic compositions of Aleutian igneous rocks cannot definitively resolve to what extent the elements in the magmas represent primary extraction from the mantle, or recycling from the crust. Combined with trace-element data, the case for a recycled component is stronger than the contrary case. A few principal conclusions are listed. (1) The average residence in the continental crust of material that is subject to erosion in the present day is about 1.7 billion years. (2) The continental crust is predominantly Proterozoic in age. (3) The Amazonian portion of the Guyana Shield has been part of the continental crust since the early Proterozoic. (4) The marine residence time of neodymium in the oceans is shorter than the mixing time of the oceans, but longer than the mixing times of individual ocean basins, therefore a few hundred to a thousand years. (5) The neodymium in the Atlantic Ocean is indistinguishable from present-day continental detritus. The Pacific contains a component derived from Pacific volcanism. (6) Island arc magmas contain components from the subducted oceanic crust, subducted sediment, and the upper mantle.

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