Goldschmidt 2012 Conference Abstracts The Mayon Volcano (Philippines) Titan tholins: A synopsis of our plumbing system: Insights from current understanding of simulated crystal zoning patterns and volatile Titan aerosols 1* 2 1 contents MORGAN L. CABLE , SARAH M. HÖRST , ROBERT HODYSS , 1 3 1* 2 3 PATRICIA M. BEAUCHAMP , MARK A. SMITH AND PETER A. JOAN CABATO , FIDEL COSTA , CHRIS NEWHALL 1 WILLIS 1Earth Observatory of Singapore, [email protected] 1NASA Jet Propulsion Laboratory, California Institute of (* presenting author) Technology, Pasadena, USA, [email protected] (* 2Earth Observatory of Singapore, [email protected] presenting author) 3Earth Observatory of Singapore, [email protected] 2 University of Colorado, Boulder, USA, [email protected] 3 Mayon is a persistently degassing volcano, producing vulcanian- Universty of Houston, Houston, USA, [email protected] strombolian eruptions every few years, and perhaps a plinian eruption every century. We investigate the plumbing system beneath Mayon What Are Tholins? using phenocrysts, microlites and melt inclusions, which record Since the term ‘tholin’ was first applied by Carl Sagan to the processes in the magma chamber and conduit. We also inspect matrix dark organic residue formed from gas phase activation of cosmically glass composition to relate the magmatic history all the way to the last stages of cooling during an eruption. relevant mixtures, [1] many hundreds of papers have been published Eruptive products of Mayon are consistently basaltic andesite in on the generation and/or analysis of this material. In particular, the composition. Petrological data for this study are derived mostly from similarity of tholin optical properties to those of the Titan haze has bread-crust bombs of the 2000 eruption, which have inclusions of up caused new investigations into laboratory simulation of these to 40cm in size. These inclusions have the same bulk composition aerosols. Much has changed both in terms of our abilities to and phenocryst populations as the host rock, the difference lies only in their more crystalline matrix. The coarse microlites in the simulate conditions of the Titan atmosphere and to analyze the inclusions imply relatively slow degassing rates, revealing an upward samples produced. magma movement slower than that of an eruption, as would occur We will summarize work involving laboratory analogues of during convection in the conduit. Titan complex organic material (tholins) in the context of recent Similarity in the phenocrysts of the host and inclusions indicate discoveries. Our current understanding of Titan as a prebiotic the same magma at depth. Plagioclase phenocrysts show complex patterns, from oscillatory zoning to pervasive sieve textures that may system is constantly evolving, and recent data from the Cassini- occur multiple times in a single crystal. The most calcic end member Huygens mission has greatly improved physical and chemical resorbs more sodic zones, forming geometrically complex zones rich constraints on models of the atmosphere. However, laboratory in glass that result to the sieve texture. Clinopyroxene and experiments are still necessary to provide critical insight for orthopyroxene phenocrysts are also zoned, but show less complexity defining the next series of in situ experiments to perform on Titan, than the plagioclase. In many cases, pyroxene cores are more iron- rich than the rims, although iron-rich outermost rims are also which will better elucidate processes occurring in the atmosphere common. These textures and zonations can be explained by the and on the surface. mixing of at least two end-members in the reservoir, one more primitive (An80, Mg#75) and probably more volatile-rich than the Are Any Tholins Titan-Like? other (An60, Mg#65). The extent to which these patterns reflect a A variety of complex organic aerosols produced using gas phase single – versus multiple – replenishment, is unclear. Fe-Mg diffusion modelling in pyroxenes suggests timescales of activation techniques (cold plasma/corona discharge, hot less than 10 years between mafic injection and subsequent eruption. plasma/spark discharge, UV irradiation, etc.) have all been labeled Preliminary volatile data from melt inclusions in tephra fall deposits ‘tholins’, despite the fact that their physical and chemical properties of the 2000 eruption yield source depths of about 9km. Additional can be enormously different. This variability begs the question: volatile analyses of different Mayon eruption deposits are underway which, if any, of these tholins are truly Titan-like? to further characterise the inner workings of the volcano. We examine various tholin generation methods and compare the organic material produced to the expected composition of the aerosols in Titan’s haze and precipitates settled onto the surface. Tholins are assessed in terms of their optical properties, physical characteristics and chemical composition. We also investigate the possibility of additional chemistry occurring on the surface of Titan, and examine potential in situ analysis techniques that could be used on future landed missions to search for evidence of this chemistry. Finally, we develop a metric to classify tholins based on how effectively the relevant properties of the Titan atmosphere (temperature, pressure, energy density, etc.) are replicated during tholin formation. This metric should also help inform the next generation of chemical protocols and instrumentation for use on the surface or in the atmosphere of future Titan in situ missions. [1] Sagan (1979) Nature 277, 102-107. Mineralogical Magazine | www.minersoc.org 1534 Downloaded from http://pubs.geoscienceworld.org/minmag/article-pdf/76/6/1534/2919827/gsminmag.76.6.03-C.pdf by guest on 29 September 2021 Goldschmidt 2012 Conference Abstracts Oceanic gabbro signature in Petrologic evidence for rapid Mangaia melt inclusions exhumation of Alpine UHP rocks 1 1 2 R.A. CABRAL *, M.G. JACKSON , E.F. ROSE-KOGA , J.M.D. from > 100 km depth 3 2 4 5 DAY , K.T. KOGA , N. SHIMIZU , M.J. WHITEHOUSE , A. 1* 1 1 1 MARK J. CADDICK , ROBERT J. TRACY , NANCY L. ROSS PRICE 1Department of Geosciences, Virginia Tech, Blacksburg, Virginia, 1Boston University, Dept. Earth Sciences, Boston, MA 02215 United States, [email protected] (* presenting author) (*correspondence: [email protected]) 2Universite Blaise Pascal, Laboratoire Magmas et Volcans, CNRS, UMR 6524, Clermont-Ferrand, France We report on a whiteschist from the Brossasco Zone in the 3Scripps Institution of Oceanography, La Jolla, CA 92093-0244 Dora Maira UHP Alpine massif – a sample that preserves a 4Woods Hole Oceanographic Institution, Woods Hole, MA 02543 remarkably well-constrained record of its late-prograde to peak 5Swedish Museum of Natural History, Laboratory for Isotope pressure history, and allows exploration of the processes, Geology, SE-104 05, Stockholm, Sweden mechanisms and timescales of burial and exhumation in rocks reaching ultra-high pressure conditions. Thermodynamic modeling Lavas from Mangaia exhibit an extreme HIMU (high-μ, or high suggests that the abundance and composition of the major phases 238U/204Pb) signature that has been attributed to melting of ancient (garnet, kyanite, Mg-phengite, phlogopite, Na-phlogopite, recycled oceanic crust within ocean island basalt (OIB) mantle quartz/coesite, talc and rutile) are consistent with equilibration at sources [1]. In a landmark study, Saal et al. [2], measured extreme ~ 3.5 GPa, 775 ˚C. Well-preserved palisades-textured quartz around lead isotopic diversity in melt inclusions (MI) from Mangaia, large coesite inclusions in garnet attests to this high-pressure phase spanning half of the global range observed in OIBs. In Pb-isotopic of the rock’s history, whilst complete coe-qtz inversion during space, these MI display a trend towards an unradiogenic end member exhumation is reflected in the matrix. Unusual evidence of the path similar to MORB. However, the origin of Pb isotope diversity and the taken to reach maximum P and T can be inferred from asymmetric, identity of the unradiogenic end member could not be resolved due to high-Ca bands within pyrope-rich (~ prp92) garnet. These bands, lack of coupled major-trace-volatile element abundances for the MI. which mimic their host crystal’s shape and contain ~ 3 times higher This study examines homogenized olivine-hosted MI in Mangaia Xgro than the host, are sharply defined at their inner margin (towards lavas. We present the first coupled measurements of major-trace- the crystal core) but decay gradually to a low-Ca rim. We interpret volatile element abundances and Pb-isotopic measurements on the this as fractionation of Ca from a finite matrix source during garnet same MI. Critically, we identify Pb-isotopic variability in our MI, and growth. Thermodynamic constraints strongly indicate that the Pb-isotopic ratios correlate with ratios of major, trace, and volatile precursor host for this Ca was lawsonite, which is now entirely elements. For example, the anomalous MI with MORB-like Pb- absent from the sample but helps to constrain the early heating isotopic ratios exhibit geochemical signatures associated with oceanic history. gabbro, including elevated Sr/Nd, Ca/Al, Cl/La, and K/La. Indicators such as retained strain in matrix quartz crystals and It is difficult to constrain the origin—modern plate or ancient sharp boundaries in garnet zoning profiles suggest that exhumation recycled lithosphere—of the gabbroic signature. One hypothesis is