0000000000205071
AUTHOR
Frank E. Brenker
Evidence for fractional condensation and reprocessing at high temperatures in CH chondrites
We performed a detailed study of silica-rich components (SRC) in the paired CH chondrites Acfer 182 and 207. These SRCs appear either as chondrules or fragments, and they contribute <0.1 vol% to the bulk meteorite. They usually contain a silica and a silicate portion. Both portions are, in most cases, cryptocrystalline and have bulk SiO2-concentrations between 65 and 85 wt%. The silicate generally has a pyroxene normative composition. The silica often appears as blebs within the silicate matrix or vice versa. If there are no blebs, silica and silicate still form rounded interfaces. The SRCs are depleted in refractory elements like Ca, Al, and Ti relative to CI. A few SRC- like objects are e…
Detection of a Ca-rich lithology in the Earth's deep (>300 km) convecting mantle
Earth's deep convecting upper mantle is believed to represent a rather homogenous geochemical reservoir of spinel or garnet lherzolite with primitive major element and moderately depleted trace element composition. Only where subduction occurs is this homogeneity disrupted by a suite of rocks ranging from eclogites/garnet pyroxenites (former oceanic crust) to residual harzburgites. In addition to these well documented peridotitic and metabasaltic rocks we have now discovered the presence of a chemically distinct reservoir in the deep convecting upper mantle. In situ structural analyses (micro X-ray diffraction and micro Raman spectroscopy) and three-dimensional trace element mapping (confoc…
Spectroscopic 2D-tomography: Residual pressure and strain around mineral inclusions in diamonds
We have studied high-pressure inclusions (Ca-silicates, coesite, graphite) in three large diamonds, one from the Kankan district, Guinea, and the other two from the Panda kimberlite, Ekati diamond mines, Canada. Using the in situ point-by-point mapping technique with a confocal Raman system, the mineralogy of the inclusions, as well as their area distribution pattern ( e.g. , of different Ca-silicate phases) and their order-disorder distribution pattern (shown for graphite/disordered carbon), were determined. Raman mapping of the host diamonds yielded 2D-tomographic pressure and strain distribution patterns and provided information on the residual pressure of the inclusions (∼ 2.3 GPa for a…
Origin of SiO2-rich components in ordinary chondrites
Abstract Silica-rich objects are common minor components in ordinary chondrites (OC), occurring as fragments and as chondrules. Their typical paragenesis is orthopyroxene + SiO 2 (with bulk SiO 2 >65 wt%) and occasionally with additional olivine and/or spinel. Individual silica-rich components (SRC) have previously been studied in various types of OCs, although there is only one comprehensive study of these objects by Brigham et al. [Brigham, C.A., Murrell, M.T., Yabuki, H., Ouyang, Z., El Goresy, A., 1986. Silica-bearing chondrules and clasts in ordinary chondrites. Geochim. Cosmochim. Acta 50, 1655–1666]. Several different explanations of how SRCs formed have been published. The main ques…
CO2-recycling to the deep convecting mantle
Institut fur Geowissenschaften, Johann Wolfgang Goethe-Universitat Frankfurt, 60054 Frankfurt, Germany (f.brenker@ em.uni-frankfurt.de) Max Planck Institute for Chemistry, Mainz, Germany (cvollmer@mpch-mainz.mpg.de) Ghent University, Department of Analytical Chemistry, Belgium (Laszlo.Vincze@UGent.be) University of Antwerp, Department of Chemistry, Belgium (bart.vekemans@ua.ac.be; koen.janssens@ua.ac.be) Institute of Experimental Physics, University of Debrecen, Hungary (szaloki@tigris.klte.hu) Institut fur Geowissenschaften, Johannes Gutenberg-Universitat, Mainz, Germany (nasdala@uni-mainz.de) KM Diamond Exploration Ltd., Vancouver, Canada (felixvkaminsky@cs.com)