Extreme Sr–Nd–Pb–Hf isotopic compositions exhibited by the Tinaquillo peridotite massif,Northern Venezuela: implications for geodynamic setting |
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Authors: | Sung Hi Choi Samuel B Mukasa Alexandre V Andronikov Maria C Marcano |
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Institution: | (1) Department Geological Sciences, University of Michigan, 2534 C.C. Little Building, 1100 N. University, Ann Arbor, MI 48109-1005, USA |
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Abstract: | An origin of the Tinaquillo Peridotite Complex in northern Venezuela, and a model for the tectonic framework of the boundary
zone between the southern Caribbean Plate margin and the South American Plate (SAP) during Late Jurassic to Mid-Cretaceous
time are developed using newly measured Sr, Nd, Pb and Hf isotopic compositions as well as major and trace element geochemistry
for some hornblendite veins and their spinel peridotite host rocks. Depleted geochemical characteristics, principally major
element concentrations, and Nd and Hf isotopes (e.g., εNd = + 27; εHf = +50; ca. 3.4 Ga-Nd model age) of the Tinaquillo peridotites suggest a genetic link between this complex and the Guiana
Shield farther to the south within Venezuela. Scattered zones within the Tinaquillo peridotite were overprinted by what we
interpret as channelized hydrous fluids (<∼3%) derived from the eastward-dipping subduction of the Farallon Plate beneath
the SAP in the Late Jurassic, leading to modification of the original Sr, Nd and Hf isotopic compositions as well as the incompatible
element concentrations. The hornblendite veins have Sr, Nd, Pb and Hf isotopic compositions, falling within the range of present-day
Pacific/Atlantic MORB, but trace element abundance patterns with combinations of arc- and MORB-like characteristics. These
results rule out the possibility of local melting of the host peridotites to produce magmas from which the hornblendite veins
formed. We suggest that during inception of the westward-dipping subduction of the Protocaribbean Plate immediately following
polarity reversal in the Mid-Cretaceous, melts infiltrated the mantle lithosphere and produced the veins. |
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