San Quintín volcanic field, Baja California, Mexico: 'within-plate' magmatism following ridge subduction |
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| Authors: | M. Storey G. Rogers A.D. Saunders D.J. Terrell |
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| Affiliation: | Department of Geology, University of Lricester, Leicester LEI 7RH, UK;Isotope Geology Unit, Scottish Universities Research and Reactor Centre, East Kilbride, Glasgow G7.5 OQU, UK;Department of Geology, University of Leicester, Leicester LEI 7RH, UK;Instituto de Geofísica, Universidad National Autónoma de Mexico, Delegación Coyoacan, 04510 Mexico, DF, Mexico |
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| Abstract: | The Holocene San Quintín volcanic province in northern Baja California comprises spinel-lherzolite-bearing alkali basalts. Trace element (La/Nb = 0.57–0.73; K/Rb = 402–479; LaN/YbN= 8.4, 9.9) and isotopic ratios (87Sr/86r = 0.70323–0.70352; 143Nd/144Nd = 0.512924–0.512996; 206Pb/204Pb = 19.108, 19.250; 207Pb/204Pb = 15.567, 15.589; 208Pb/204Pb = 38.82, 38.85) show that the lavas are compositionally indistinguishable from some ocean island, plume-associated basalts such as Hawaii and the Azores, and testify to an asthenospheric source for the magmas. The occurrence in Baja of such lavas may be related to the nature of the cessation of plate subduction beneath the peninsula; at present, San Quintín (and volcanic provinces to the north) are underlain by a 'no-slab window', whereas immediately to the south, remanent oceanic lithosphere may be preserved as a relict slab. This may act as a bamer to the upward passage of diapirs or magmas from the asthenosphere. |
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