SEMINAR: MGG Student Seminar TODAY, Sean Murray and Marco Bagnardi

[Quinn Devlin <qdevlin@rsmas.miami.edu>]

MGG STUDENT SEMINAR

WEDNESDAY, APRIL 11
12:00 - 1:00 PM
SLAB SEMINAR ROOM



Multiply Substituted Isotopologues: What We Know and Where We are Going



Sean Murray, Peter K. Swart, Monica Arienzo,

Yulaika Hernawaiti, Don McNeill, Jim Klaus, Albertus Ditya

A new paleothermometer based on the multiple substitutions of rare isotopes into the molecular structure of CO2 is being developed to aid in extending the age and reducing the limitations on applicable samples to paleothermometry. These multiply substituted “clumped” isotopologues are derived from the phosphoric acid digestion of carbonate materials and show a water-independent link to temperature. This means that the clumped isotope paleothermometer does not require any isotopic understanding of the water the carbonate precipitated from. With this new technique, it has become possible to measure temperatures with an accuracy of ± 2 °C in samples dating back to the Precambrian.
            Being presented are two future projects that will utilize this new technique. The first is a controlled precipitation experiment producing calcites at different temperatures and precipitation rates. This is to address a disconnect found between predicted values, measured synthetic values, and natural organic/inorganic values which is possibly related to disequilibration of the calcite and water. We hope to further understand the factors that influence the clumped isotope values in calcites. The second is an application of the technique to short cores from the Dominican Republic. Two meteoric calcite lines were found using standard δ18O and δ13C which would indicate that two separate water masses with varying isotopic values influenced these samples. Our Preliminary data suggests an alternative theory that they were influenced by two different temperature waters.

SILL or DIKE? What fed the 2009 eruption at Fernandina Volcano, Galápagos?

Marco Bagnardi

            Fernandina Volcano forms the youngest and westernmost island of the Galápagos Archipelago, a group of volcanic islands located near the equator and 1000 km west of Ecuador. Twenty-five eruptions in the last two hundred years make Fernandina the most active volcano in the archipelago and one of the most active volcanoes in the world. Most eruptions occur along fissures fed by subvolcanic bodies that propagate from the central magmatic system and from reservoirs centered under the summit caldera. Eruptive fissures in the subaerial portion of the volcano form two distinct sets: (1) arcuate or circumferential fissures characterize the upper portion of the volcano around the caldera while (2) radial fissures are present on the lower flanks.
            Models of deformation from the 1995 and the 2009 radial fissure eruptions suggest that dikes with shallow dips fed them. In particular, InSAR data spanning the 2009 eruption indicate propagation of a sub-horizontal sill away from the summit region. As the sill propagated toward the flanks, it rotated slightly about a horizontal axis, resulting in a radial orientation but shallow dip upon reaching the surface. The initial formation of intrusions at Fernandina as shallowly dipping sills stands in contrast to intrusions into Hawaiian volcanoes, which are nearly always vertical dikes even close to summit regions.
            Dike propagation in a volcano is not a random process but it is controlled by the orientation of the principal stresses, with the dike orthogonal to the least compressive stress. We calculate stress changes within the volcanic edifice generated by the active geophysical processes (e.g., pressure changes in reservoir, dike emplacement) and we investigate what phenomena can produce a stress field compatible with the inferred dike geometries and the observed pattern of eruptive fissures.

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