| Autor: |
Engvik, Ane K, Tveten, E., Bingen, B., Erambert, M., Feito, P., De Azavedo, S., VIOLA, GIULIO |
| Přispěvatelé: |
Engvik, Ane K, Tveten, E., Bingen, B., Viola, Giulio, Erambert, M., Feito, P., De Azavedo, S. |
| Jazyk: |
angličtina |
| Rok vydání: |
2007 |
| Předmět: |
|
| Popis: |
Pan-African high-pressure granulites occur as boudins and layers in the Lurio Belt in north-eastern Mozambique, eastern Africa. Mafic granulites contain the mineral assemblage garnet + clinopyroxene + plagioclase + quartz ± magnesiohastingsite. Garnet porphyroblasts are zoned with increasing almandine and spessartine contents and decreasing grossular and pyrope contents from core (Alm46Prp32 Grs21Sps2) to rim (Alm52Prp26 Grs19Sps3). This pattern is interpreted as a retrograde diffusion zoning with the preserved core chemistry representing the peak metamorphic composition. Mineral reaction textures occur in the form of monomineralic and composite plagioclase ± orthopyroxene ± amphibole ± biotite ± magnetite coronas around garnet porphyroblasts. Thermobarometry indicates peak metamorphic conditions of up to 1.57 ± 0.14 GPa and 949 ± 92 °C (stage I), corresponding to crustal depths of ∼55 km. Zircon yielded an U-Pb age of 557 ± 16 Ma, inferred to date crystallization of zircon during peak or immediately post-peak metamorphism. Formation of plagioclase + orthopyroxene-bearing coronas surrounding garnet indicates a near-isothermal decompression of the high-pressure granulites to lower pressure granulite facies conditions (stage II). Development of plagioclase + amphibole-coronas enclosing the same garnet porphyroblasts shows subsequent cooling into amphibolite facies conditions (stage III). Symplectitic textures of the corona assemblages indicate rapid decompression. The high-pressure granulite facies metamorphism of the Lurio Belt, followed by near-isothermal decompression and subsequent cooling, is in accordance with a long-lived tectonic history accompanied by high magmatic activity in the Lurio Belt during the late Neoproterozoic-early Palaeozoic East-African-Antarctic orogeny. © 2007 Blackwell Publishing Ltd. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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