Strontium isotope geochemistry of late cretaceous granodiorites,Jamaica and Haiti,greater Antilles |
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| Authors: | LM Jones Raymond L Walker SE Kesler John F Lewis |
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| Institution: | 1. Research and Development Department, Continental Oil Company, Ponca City, OK 74601 U.S.A.;2. Oak Ridge National Laboratory, Oak Ridge, TN 37830 U.S.A.;3. Department of Geology, University of Michigan, Ann Arbor, MI 48109 U.S.A.;4. Department of Geology, George Washington University, Washington, DC 20052 U.S.A. |
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| Abstract: | Initial87Sr/86Sr ratios have been determined for a representative suite of Upper Cretaceous granodiorites and associated rocks from the Above Rocks composite stock in central Jamaica and the Terre-Neuve pluton in northwestern Haiti. The average initial87Sr/86Sr ratio for severn samples of the Terre-Neuve intrusion is 0.7036, with a range of 0.7026–0.7047. For two samples of the Above Rocks the initial ratios are 0.7033 and 0.7034. A third sample from this intrusive has an initial ratio of 0.7084, which is tenatively attributed to contamination. The initial87Sr/86Sr ratios indicate that neither ancient sialic crust nor sediments carried down a Benioff zone can be the primary source of the granodioritic magma. K/Rb ratios for these rocks range from 178 to 247, which are much lower than the average values (≥1000) for tholeiitic basalts. It is concluded that the magmas originated primarily by melting of downthrust oceanic crust or adjacent mantle material. |
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