Luvizotto et al., 2009 Rutilo en rocas metasedimentarias

Luvizotto et al., 2009 Rutilo en rocas metasedimentarias -...

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Unformatted text preview: ORIGINAL PAPER Rutile occurrence and trace element behavior in medium-grade metasedimentary rocks: example from the Erzgebirge, Germany George Luiz Luvizotto & Thomas Zack & Silke Triebold & Hilmar von Eynatten Received: 29 January 2009 /Accepted: 23 October 2009 /Published online: 13 November 2009 # The Author(s) 2009. This article is published with open access at Abstract Metamorphic textures in medium-grade (~500 – 550°C) metasedimentary rocks from the Erzgebirge give evidence of prograde rutile crystallization from ilmenite. Newly-crystallized grains occur as rutile-rich polycrystal- line aggregates that pseudomorph the shape of the ilmenites. In-situ trace element data (EMP and SIMS) show that rutiles from the higher-grade samples record large scatter in Nb content and have Nb/Ti ratios higher than coexisting ilmenite. This behavior can be predicted using prograde rutile crystallization from ilmenite and indicates that rutiles are reequilibrating their chemistry with remain- ing ilmenites. On the contrary, rutiles from the lowest grade samples (~480°C) have Nb/Ti ratios that are similar to the ones in ilmenite. Hence, rutiles from these samples did not equilibrate their chemistry with remaining ilmenites. Our data suggest that temperature may be one of the main factors determining whether or not the elements are able to diffuse between the phases and, therefore, reequilibrate. Newly-crystallized rutiles yield temperatures (from ~500 to 630°C, Zr-in-rutile thermometry) that are in agreement with the metamorphic conditions previously determined for the studied rocks. In quartzites from the medium-grade domain (~530°C), inherited detrital rutile grains are detected. They are identified by their distinct chemical composition (high Zr and Nb contents) and textures (single grains surrounded by fine grained ilmenites). Preliminary calculation, based on grain size distribution of rutile in medium-grade metapelites and quartzites that occur in the studied area, show that rutiles derived from quartzites can be anticipated to dominate the detrital rutile population, even if quartzites are a minor component of the exposure. Introduction Several studies have recently promoted the application of in-situ trace element analyses of accessory minerals as a tool to monitor geochemical processes in metamorphic and igneous rocks. This is a reflection of the continuous development of several in-situ analytical techniques ( i.e. , higher spatial resolution and lower detection limits) and the fact that accessory minerals are frequently the main carrier of trace elements used as tracer of geochemical processes Editorial handling: F. Gaidies and T. John G. L. Luvizotto ( * ) : T. Zack Institut für Geowissenschaften, Mineralogie, Universität Heidelberg, Im Neuenheimer Feld 236, 69120 Heidelberg, Germany e-mail: T. Zack e-mail: G. L. Luvizotto Geochemie, Max-Planck-Institute für Chemie, Joh.-Joachim-Becher-Weg 27,Joh....
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This note was uploaded on 03/19/2012 for the course GEOLOGY 6 taught by Professor Rm during the Spring '12 term at UNAM MX.

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Luvizotto et al., 2009 Rutilo en rocas metasedimentarias -...

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