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Geochemistry/Mineralogy/Petrology (GMP)

The research programs in geochemistry at Brown address a wide variety of geological problems, utilizing observational, analytical, and experimental approaches. The principal active research areas presently are: geochronological and isotope tracer studies of tectonic processes in orogenic belts, including direct dating of deformational fabrics and shear zones; time-dependent aspects of a number of major long and short-term geological processes, especially mass transport and isotope diffusion rates in mineral structures and along mineral grain boundaries.

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Geochemistry

Igneous and metamorphic events are emphasized in studies of the behavior of elements and nuclides during the process of rock and mineral formation. Kinetic studies include diffusion and exchange of elements and isotopes in a fluid system (hydrothermal or magmatic), and application of oxygen and cation diffusion kinetics to cooling rates (and associated uplift and denudation rates) of igneous and metamorphic rocks in the Alps, Rockies, and New England. Geochronological methods are being developed to determine the ages and thermal histories of deformational events in the orogenic belt. Trace element and isotope geochemical studies are used to reconstruct the evolution of plutonic rock systems.

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Solid State Mineralogy

The mechanisms and kinetics of mineralogical processes on a microscopic scale give insight into large scale geological processes. Experimental samples, subjected to desired temperature, pressure, and chemical conditions, are analyzed by a combination of optical, x-ray diffraction, transmission electron microscopy, and chemical-isotopic methods. Current interests include grain boundary transport mechanisms and effects of crystal growth and interrelations of mineral deformation and kinetics during metamorphism. The latter involves collaborative studies with structural geologists Professors Jan Tullis and Greg Hirth.

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Petrology/Volcanology

Petrology research investigations include: field and experimental studies of the evolution of magmas under varying temperature, pressure and fugacities of oxygen, carbon dioxide and water; theoretical and experimental studies of the structure & solution characteristics of silicate melts; lab and theoretical studies of transport properties of silicate melts and transport processes in crystal-melt systems. Also being studied: origin and differentiation of lunar, Martian and terrestrial magmas, chemistry of magmas in equilibrium with sulfide & sulfate phases, magma ascent in calc-alkaline volcanic complexes, and controls on mineral-liquid element distributions.

Planetary petrology and volcanology at Brown focuses on petrological and volcanological processes that occur on the terrestrial-type planets other than Earth. This research compli-ments studies of similar processes that occur on Earth, and graduate students often add a planetary project to thesis research that is focused on Earth. The planetary science research is conducted on Earth’s Moon, Venus, Mars and the parent bodies of various igneous meteorites.

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GMP Labs

GMP's newest lab is a state-of-the-art trace metal-free clean laboratory for the chemical separation of various isotopes, and a melt inclusion laboratory for the preparation, re-homogenization and the determination of temperature of entrapment the of melt inclusions. In collaboration with other faculty at Brown, GMP is in the process of obtaining a Multi-Collector Inductively-Coupled-Plasma Mass Spectrometer (MC-ICPMS)

The geochemistry laboratories are well equipped for the application of chemical and particularly isotopic techniques to the solution of geologic problems. Equipment includes: automated mass spectrometers capable of analyzing both light and heavy elements, including O, C, Rb-Sr, Sm-Nd and U-Th-Pb, and all the necessary chemical and vacuum equipment to support mass spectrometer operations; a clean laboratory for the preparation of samples for isotopic analysis, including bombs and abraders for U-Pb zircon, monazite and sphene analyses; pressure vessels for experimental research, capable of operating continuously up to 1200°C and 3000 bars pressure; modern petrographic and binocular microscopes with conventional and digital photographic attachments; the usual ancillary gear used in mineral separation and sample preparation.

The thermal ionization mass spectrometer is an automated Finnigan-MAT 261 multicollector with 6 Faraday cups and an axial secondary electron multiplier (SEM), permitting simultaneous SEM/Faraday analysis of radiogenic Pb. There is also ready access to a Cameca electron microprobe and an XRF spectrometer for major and minor element analysis, both housed in the Department, and Cameca IMS-3f and Cameca 1270 ion microprobe microanalyzers housed at the Woods Hole Oceanographic Institution.

The facilities used by the experimental petrology/volcanology group include two experimental laboratories with numerous hydrothermal pressure vessels (Cold seal Rene and TZM), a 14 kb internally heated pressure vessel, two piston cylinder vessels, and sample preparation equipment. Analytical facilities include a CAMECA SX-100 electron microprobe, an XRF spectrometer for analysis of major and trace elements. There is a new FTIR spectrometer in the Department, and researchers here have ready access to the Cameca 3f ion probe and a new generation Cameca 1270 ion probe at Woods Hole.

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