HR: 11:50h
AN: T32A-07    [Abstracts]
TI: Adakitic-like volcanism in Southern Mexico and subduction of the Tehuantepec Ridge
AU: * Manea, M
EM: marina@geociencias.unam.mx
AF: Centro de Geociencias, UNAM, Campus Juriquilla, apdo postal 1-742, Queretaro, QRO 76001, Mexico
AU: Manea, V C
EM: vlad@geociencias.unam.mx
AF: Centro de Geociencias, UNAM, Campus Juriquilla, apdo postal 1-742, Queretaro, QRO 76001, Mexico
AU: Manea, V C
EM: vlad@geociencias.unam.mx
AF: Seismological Laboratory, Caltech, 1200E California Blvd., MS 252-21, Pasadena, CA 91125, United States
AB: The origin of El Chichón volcano is poorly understood, and our attempt in this study is to demonstrate that Tehuantepec Ridge, a major tectonic discontinuity on the Cocos plate, plays a key role in the slab dehydration budget and therefore in partial melting of the mantle beneath El Chichón. Using marine magnetic anomalies we show that the upper mantle beneath TR undergo partial serpentinization, a 5-7 km thick serpentinized root extending along TR and below the oceanic crust. Another key aspect of the magnetic anomaly over southern México is a long-wavelength (~150 km) high amplitude (~500 nT) magnetic anomaly located between the trench and the coast. Using a 2D joint magnetic-gravity forward model, constrained by the subduction P-T structure, slab geometry and seismicity, we find a highly magnetic and low-density source located at 40-130 km depth. We interpret this result as a serpentinized mantle wedge by fluids expelled from the subducting Cocos plate beneath southern Mexico. Such a deep hydrated mantle requires a low temperature wedge (T<600° C) because serpentine is stable below this temperature and also the magnetic properties are preserved for temperature less than the Currie point for magnetite (~580° C). This result explains the lack of volcanism in southern México where the slab depth is ~ 100 km. Using phase diagrams for sediments, basalt and peridotite, and the subduction P-T structure beneath El Chichón we find that sediments and basalt dehydrate ~ 50% at depths corresponding with the location of serpentinized mantle wedge, whereas the serpentinized root beneath TR strongly dehydrates (60-80%) at higher depths (170-180 km) comparable with the slab depth beneath El Chichón. We conclude that this strong deserpentinization pulse of mantle lithosphere beneath TR at great depths triggers arc melting, explaining the unusual location and probably the adakitic signature of El Chichón.
DE: 1219 Gravity anomalies and Earth structure (0920, 7205, 7240)
DE: 3005 Marine magnetics and paleomagnetics (1550)
DE: 3654 Ultra-high pressure metamorphism
DE: 8170 Subduction zone processes (1031, 3060, 3613, 8413)
DE: 8185 Volcanic arcs
SC: Tectonophysics [T]
MN: 2007 Joint Assembly