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Characterization and tectonic implications of Mesozoic-Cenozoicoceanic assemblages of Costa Rica and Western PanamaThe Pacific face of Costa Rica and western Panama has been extensively studied because of the wide occur-rence of oceanic assemblages. In Northern Costa Rica, the Santa Elena Nappe made by ultramafic and maficassociations overthrusts the Santa Rosa Accretionary Complex. The Nicoya Complex corresponds to a pre-Campanian oceanic plateau association, cropping out in the Nicoya Peninsula and the outer Herradura Block.The 89 Ma high MgO Tortugal Komatiitic Suite corresponds to 14-km long, 1.5-km wide body, with no clearrelation with to the NicoyaComplex. The Tulín Formation (Maastrichtian to Lower Eocene) forms the mainedifice of an accreted ancient oceanic island of the Herradura Block. The Quepos Block was formed by theaccretion of a late Cretaceous-Paleocene seamount. In the Osa and Burica peninsulas, Caño Island and Golfitoarea, a series of Upper Cretaceous to Eocene accreted plateau and seamount blocks crop out. In western Pana-ma, the oceanic assemblages range from Upper Cretaceous to Miocene, and their geochemical signature showtheir oceanic plateau association. The Costa Rica and western Panama oceanic assemblages correspond to afragmentary and disrupted Jurassic to Miocene sequences with a very complicated geological and geotectonichistory. Their presence could be interpreted as a result of accretionary processes rather than tectonic erosion;despite this last process is nowadays active in the Middle American Trench. The whole picture has not beencompleted yet, but apparently, most of the igneous rocks have a geochemical signature similar to the Galapagosmantle plume. The later has been acting in pulses, or otherwise the outcropping occurrences could be part of several plateaus somehow diachronically formed in the Pacific basin.

The eastern margin of North America has been shaped by a series of tectonic events including the Paleozoic Appalachian Orogeny and the breakup of Pangea during the Mesozoic. For the past ∼200 Ma, eastern North America has been a passive continental margin; however, there is evidence in the Central Appalachian Mountains for post-rifting modification of lithospheric structure. This evidence includes two co-located pulses of magmatism that post-date the rifting event (at 152 and 47 Ma) along with low seismic velocities, high seismic attenuation, and high electrical conductivity in the upper mantle. Here, we synthesize and evaluate constraints on the lithospheric evolution of the Central Appalachian Mountains. These include tomographic imaging of seismic velocities, seismic and electrical conductivity imaging along the Mid-Atlantic Geophysical Integrative Collaboration array, gravity and heat flow measurements, geochemical and petrological examination of Jurassic and Eocene magmatic rocks, and estimates of erosion rates from geomorphological data. We discuss and evaluate a set of possible mechanisms for lithospheric loss and intraplate volcanism beneath the region. Taken together, recent observations provide compelling evidence for lithospheric loss beneath the Central Appalachians; while they cannot uniquely identify the processes associated with this loss, they narrow the range of plausible models, with important implications for our understanding of intraplate volcanism and the evolution of continental lithosphere. Our preferred models invoke a combination of (perhaps episodic) lithospheric loss via Rayleigh-Taylor instabilities and subsequent small-scale mantle flow in combination with shear-driven upwelling that maintains the region of thin lithosphere and causes partial melting in the asthenosphere.

Melt inclusions (MI) are considered the best tool available for determining the pre-eruptive volatile contents of magmas. H2O and CO2 concentrations of the glass phase in MI are commonly used both as a barometer and to track magma degassing behavior during ascent due to the strong pressure dependence of H2O and CO2 solubilities in silicate melts. The often unstated and sometimes overlooked requirement for this method to be valid is that the glass phase in the MI must represent the composition of the melt that was trapped at depth in the volcanic plumbing system. However, melt inclusions commonly contain a vapor bubble that formed after trapping owing to differential shrinkage of the melt compared to the host crystal, and/or crystallization at the inclusion-host interface. Such bubbles may contain a substantial portion of volatiles, such as CO2, that were originally dissolved in the melt. In this study, we determined the contribution of CO2 in the vapor bubble to the overall CO2 content of MI based on quantitative Raman analysis of the vapor bubbles in MI from the 1959 Kilauea Iki (Hawaii), 1960 Kapoho (Hawaii), 1974 Fuego volcano (Guatemala), and 1977 Seguam Island (Alaska) eruptions. We found that the bubbles typically contain 40 to 90% of the total CO2 in the MI. Reconstructing the original CO2 content by adding the CO2 in the bubble back into the melt results in an increase in CO2 concentration by as much as an order of magnitude (thousands of parts per million). Reconstructed CO2 concentrations correspond to trapping pressures that are significantly greater than one would predict based on analysis of the volatiles in the glass alone. Trapping depths can be as much as 10 km deeper than estimates that ignore the CO2 in the bubble. In addition to CO2 in the vapor bubbles, many MI showed the presence of a carbonate mineral phase. Failure to recognize the carbonate during petrographic examination or analysis of the glass and to include its contained CO2 when reconstructing the CO2 content of the originally trapped melt will introduce additional errors into the calculated volatile budget. Our results emphasize that accurate determination of the pre-eruptive volatile content of melts based on analysis of melt inclusions must consider the volatiles contained in the bubble (and carbonates, if present). This can be accomplished either by analysis of the bubble and the glass followed by mass-balance reconstruction of the original volatile content of the melt, or by re-homogenization of the MI prior to conducting microanalysis of the quenched, glassy MI.

Primitive olivine-hosted melt inclusions (MI) are a useful means to estimate the pre-eruptive volatile contents of a volcanic melts but post-entrapment processes complicate this approach. In particular, crystallization of the host phase along the wall of the MI and diffusion of H through the host cause CO and potentially S or other volatiles to exsolve from the melt to a separate fluid bubble.

The complex geodynamic evolution of Aeolian Arc in the southern Tyrrhenian Sea resulted in melts with some of the most pronounced along the arc geochemical variation in incompatible trace elements and radiogenic isotopes worldwide, likely reflecting varia

In the interest of constraining the volatile budgets of the Earth's interior, melt inclusions are a valuable tool because they provide a geologically persistent record of melt volatile contents before they degas to the atmosphere during volcanic eruptions. However, melt inclusions require special care because of the possibility for volatile elements to diffuse from the glass into a separate fluid phase (bubble; e.g. CO2) or out of the olivine host (e.g. H2O)...