Rutile occurrence and trace element behavior in medium-grade metasedimentary rocks: example from the Erzgebirge, Germany
| Autor: | Hilmar von Eynatten, George Luiz Luvizotto, Thomas Zack, Silke Triebold |
|---|---|
| Rok vydání: | 2009 |
| Předmět: |
education.field_of_study
010504 meteorology & atmospheric sciences Metamorphic rock Population Trace element Geochemistry Mineralogy metasedimentary rocks Erzgebirge Metamorphic textures [Rutile trace element] engineering.material 010502 geochemistry & geophysics 01 natural sciences Rutile trace element: metasedimentary rocks Geophysics Geochemistry and Petrology engineering Crystallite Pseudomorph education Chemical composition Ilmenite Geology 0105 earth and related environmental sciences |
| Zdroj: | Mineralogy and Petrology. 97:233-249 |
| ISSN: | 1438-1168 0930-0708 |
| DOI: | 10.1007/s00710-009-0092-z |
| Popis: | 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 polycrystalline 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 remaining 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. peerReviewed |
| Databáze: | OpenAIRE |
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