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P– T– t evolution and textural evidence for decompression of Pan-African high-pressure granulites, Lurio Belt, north-eastern Mozambique.
- Source :
- Journal of Metamorphic Geology; Dec2007, Vol. 25 Issue 9, p935-952, 18p, 5 Diagrams, 7 Charts, 4 Graphs, 2 Maps
- Publication Year :
- 2007
-
Abstract
- 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 (Alm<subscript>46</subscript>Prp<subscript>32</subscript>Grs<subscript>21</subscript>Sps<subscript>2</subscript>) to rim (Alm<subscript>52</subscript>Prp<subscript>26</subscript>Grs<subscript>19</subscript>Sps<subscript>3</subscript>). 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. [ABSTRACT FROM AUTHOR]
- Subjects :
- GARNET
GEMS & precious stones
SILICATE minerals
AMPHIBOLES
ROCK-forming minerals
Subjects
Details
- Language :
- English
- ISSN :
- 02634929
- Volume :
- 25
- Issue :
- 9
- Database :
- Complementary Index
- Journal :
- Journal of Metamorphic Geology
- Publication Type :
- Academic Journal
- Accession number :
- 27463115
- Full Text :
- https://doi.org/10.1111/j.1525-1314.2007.00736.x