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| Format: | Artículo científico |
| Language: | en |
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Universitat de Barcelona
2006
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| Online Access: | https://www.redalyc.org/articulo.oa?id=50540202 |
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Table of Contents:
- Role of crustal melting in petrogenesis of the Cretaceous Water Island Formation (Virgin Islands, northeast Antilles Island arc) W.T. Jolly E.G. Lidiak Ciencias de la Tierra Antilles Virgin Islands Plagiorhyolite Water Island Fm Crustal melting The latest Aptian to earliest Albian (~115 Ma) Water Island Fm in the Virgin Islands contains some of the oldestknown arc-related strata in the Greater Antilles Island Arc. Hence, the unit is of considerable significance in tectonicreconstructions of initial subduction parameters along the long-lived destructive plate margin separatingthe North American and Caribbean Plates. Exposed Water Island strata are bimodal, consisting predominantlyof altered dacite and rhyolite (originally called keratophyre; 65-85% SiO2) and subordinate degraded (spilite;46-57% SiO2). TiO2 content of Water Island basalt averages approximately 0.5%, resembling borderline intermediate-Ti boninite basalts, consistent with low incompatible element abundances and low normalized lightrare earth elements (LREE) with respect to Sm. Trace element patterns of the felsic suite, characterized by pronouncednegative normalized anomalies for high field-strength elements (HFSE), low Sr/Y, and low absoluterare earth element (REE) abundances, and relatively flat normalized REE patterns, have analogues in plagiorhyolitesuites from bimodal Cenozoic arcs, including the western Aleutians, Izu-Bonin, the Kermadecs, and SouthSandwich. Relatively low incompatible element concentrations in plagiorhyolites and contrasting normalizedincompatible trace element patterns in basalts preclude an origin of Water Island plagiorhyolite through MORBtypefractional crystallization. Compositions are consistent instead with melting models involving partial fusionof amphibole-bearing gabbro at low pressures (within the stability range of plagioclase) in response to introductionof heat and aqueous flux by arc-related basalt melts and associated hydrothermal fluids during transmissionto the surface. Truncation of the basalt fractional crystallization trend at SiO2 = 57% indicates evolved islandarc basalt (IAB) crystal fractionates were gradually displaced from crustal magma conduits by more buoyantplagiorhyolite melt, and trapped in underplated, sub-crustal magma chambers. Basalts have low (Ce/Ce*)N(average Å 0.78), indicating the presence of significant pelagic sediment (0.5 to 1.5% Atlantic Cretaceouspelagic sediment, AKPS). One subunit of relatively high-HFSE plagiorhyolite has (Ce/Ce*)N near-expected values,but another with low-HFSE has slightly lower than expected (Ce/Ce*)N, consistent with a small sedimentcomponent. Absence of intermediate andesite from the Water Island Fm is inconsistent, however, with basaltrhyolitemagma mixing processes. Consequently, incorporation of sediment by low-HFSE plagiorhyolite isinferred to have resulted from re-melting of arc-related gabbro. 2006 artículo científico 1695-6133 https://www.redalyc.org/articulo.oa?id=50540202 en http://www.redalyc.org/revista.oa?id=505 Geologica Acta: an international earth science journal application/pdf Universitat de Barcelona Geologica Acta: an international earth science journal (España) Num.1-2 Vol.4