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| Titel |
Crustal xenoliths in post-collisional Variscan lamprophyres: records of late Variscan collision and orogenic extension |
| VerfasserIn |
Christian Soder, Thomas Ludwig, Winfried Schwarz, Mario Trieloff |
| Konferenz |
EGU General Assembly 2017
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 19 (2017) |
| Datensatznummer |
250145309
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| Publikation (Nr.) |
 EGU/EGU2017-9239.pdf |
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| Zusammenfassung |
| Crustal xenoliths entrained in post-collisional shoshonitic lamprophyres from the Variscan Odenwald (Mid-German Crystalline Zone, MGCZ) include felsic granulites (garnet, quartz, plagioclase, K-feldspar, biotite, omphacite, rutile) and basaltic eclogites (omphacite, garnet, quartz, kyanite, phengite, epidote, rutile). Classical thermobarometry, Zr-in-rutile thermometry and equilibrium phase diagrams reveal temperatures of 700–800°C and pressures of 1.7–1.8 GPa. Both lithologies record isothermal decompression resulting in partial melting at still elevated pressures (1.3–1.5 kbar) before entrainment into the magma. The development of diverse fine-grained microstructures is linked to the interaction with the rising melt.
The eclogitic garnet preserves compositional sector zonation patterns, which indicate rapid crystal growth, shortly followed by overgrowth/recrystallization during decompression. The preservation of these zonation patterns indicates crystallization immediately before the lamprophyre magmatism. These findings are supported by SIMS U-Pb dating of zircon rims, which gave ages of 330±3 Ma for both lithologies, indistinguishable from the published age of lamprophyre emplacement. Therefore, the xenoliths are a unique document of the late Variscan collisional process with marked crustal thickening to ~60 km and a subsequent decompression event.
Magmatic protolith ages are ~430 Ma for the basaltic eclogite and ~2.1 Ga for the felsic granulite. Silurian magmatism is well established within the MGCZ while the Paleoproterozoic age represents a hitherto unknown magmatic event. |
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