HR: 0800h
AN: V41B-1445    [Abstracts]
TI: Magmatic evolution of the Sarapiqui Miocene Arc, Costa Rica, Central America
AU: * Gazel, E
EM: egazel@eden.rutgers.edu
AF: Rutgers University, Department of Geological Sciences, Wright Geological Laboratory, 610 Taylor Road, Piscataway, NJ 08854-8066 United States
AU: Alvarado, G E
V41B-1445 AF: Instituto Costarricense de Electricidad, Department of Geology, San Jose, 10032-1000 Costa Rica
AU: Carr, M J
V41B-1445 AF: Rutgers University, Department of Geological Sciences, Wright Geological Laboratory, 610 Taylor Road, Piscataway, NJ 08854-8066 United States
AU: Obando, J
V41B-1445 AF: Geological Consultant, Hatillo 1, Calle Tempisque 130, San Jose, none Costa Rica
AU: Alfaro, A
V41B-1445 AF: Instituto Costarricense de Electricidad, Department of Geology, San Jose, 10032-1000 Costa Rica
AB: The Sarapiqu¡ Miocene Arc (22.2-11.4 Ma) is located in the modern back-arc region of northern Costa Rica, Central America. The arc basement is represented by serpentinized peridotites, Albian silicic pelagites, and Paleocene to Middle Eocene turbidites. Magmatic units vary from basalts to rhyolites and include lavas, pyroclastic deposits, and a few subvolcanic bodies. The magmatic evolution of the Sarapiqu¡ Miocene Arc consists of three distinct stages: 1) Jard¡n Basalts (22.2 Ma) showing a primary tendency with high MgO, Ni, Cr, and Nb, high initial La/Yb ratios, and low Ba/La which increase with the slab fluids addition; 2) Arrepentidos Basaltic-andesites, Chaparr¢n Pyroclasts, Hito Sar Basalts, Boca Tapada Gabro, and Chamorro Andesites, that represent the island arc evolution from 17.2 to 11.4 Ma; and 3) Crucitas Rhyolites (14.3 Ma) characterizated by low TiO2 and very high Ba/La ratios represent non-cogenetic, but contemporaneous felsic magmas produced by remelting of pre-existing intrusives. The REE patterns indicate a plagioclase rich, amphibole bearing source for this last unit. The Zr/Nb ratios (7-36) are evidence of the coalescing of a minor OIB source with a dominant MORB source, both modified by subduction. 87Sr/86Sr correlate positively with Ba/La; however, they are still within the OIB field. An inverse model using the REEs of the mafic units is consistent with a source mantle composition of garnet peridotite. All but one of the units show LILE enrichments and HFSE depletions typical of the island arc environment. The exception is a suite of near primary magmas, included in the Jardin Basalts, which probably originated by decompression melting. The Ba/La and La/Yb ratios of the Sarapiqui Miocene Arc are very similar to those of the modern Northern Costa Rican Arc, suggesting that the subduction fluid composition and the degree of partial melting have not changed significantly in the last 20 Ma.
DE: 1031 Subduction zone processes (3060, 3613, 8170, 8413)
DE: 8104 Continental margins: convergent
DE: 8185 Volcanic arcs
DE: 8413 Subduction zone processes (1031, 3060, 3613, 8170)
DE: 8486 Field relationships (1090, 3690)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005