Dacite Genesis via both Slab Melting and Differentiation: Petrogenesis of La Yeguada Volcanic Complex, Panama |
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Authors: | DEFANT, MARC J. RICHERSON, PHIL M. DE BOER, JELLE Z. STEWART, ROBERT H. MAURY, REN? C. BELLON, HERV? DRUMMOND, MARK S. FEIGENSON, MARK D. JACKSON, THOMAS E. |
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Affiliation: | 1Department of Geology, University of South Florida Tampa, Florida 33620 2Department of Earth and Environmental Sciences, Wesleyan University Middletown, Connecticut 06457 3Laboratoire de P?trologie et UA1278, Universit? de Bretagne Occidentale 29287 Brest, France 4Laboratoire de G?ochimie et de G?ochronologie et UA 1278, Universit? de Bretagne Occidentale 29287 Brest, France 5Department of Geology, University of Alabama at Birmingham Birmingham, Alabama 35294 6Department of Geological Sciences, Rutgers, The State University New Brunswick, New Jersey 08903 |
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Abstract: | La Yeguada volcanioc complex (LYVC) is one of many major volcanoesthat represent the extension of the Central American arc inwestern Panama and that have resulted from current oblique subductionsouth of Panama. There are two major phases of calc-alkalinevolcanic activity at LYVC based on mapping and K-Ar radiometricdates. The first phase began at {small tilde} 13 Ma and ceasedat {small tilde} 7?5 Ma. This sequence, termed the old group,consists of basalts to rhyolites with typical arc mineralogies(OL, CPX, PL, MGT, and OPX). The samples have similar radiogenicSr and Nd values and appear to be related by fractional crystallizationwith assimilation and/or magma mixing involved in the differentiation.The parental basalts were probably derived from the metasomatizedmantle wedge via melting induced by fluids released from thesubducted lithosphere. There was an apparent period of minor volcanic activity from75 to 25 Ma (only one documented sample from thisperiod). The second phase (<2?5 Ma), termed the young group,consists only of dacites but with very different mineralogies(PL, MGT, AM, BI, with no PX) and geochemistries (e.g., highSr and low Y and HREE) compared with the old-group dacites (andandesites and rhyolites). The dacites cannot be related to theold group by various petrogenetic modeling techniques. Thesehigh-Al dacites have the characteristics of magmas derived fromthe partial melting of the subducted oceanic lithosphere witha hornblende eclogite residuum. This has been substantiatedby geochemical modeling. Samples similar to the young-group dacites in other arcs havebeen termed adakites and arc associated with the subductionof young hot crust which may explain why the slab melts. ThePanama basin has extremely high heat flow values, comparablewith those of the Galapagos ridge system. The change from normalarc volcanism to adakites suggests that the subducted oceaniccrust became hotter as time progressed. The subduction of anoceanic ridge or new ridge development along the Sandra Riftin the Panama basin can explain the change in volcanism withtime but more geophysical data are needed. |
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