Magma homogenization during anatexis,ascent and/or emplacement? Constraints from the Variscan Weinsberg Granites |
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| Authors: | A Gerdes |
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| Institution: | Geochemisches Institut, Goldschmidtstr. 1, 37077 Göttingen, Germany,;NERC Isotope Geosciences Laboratory, Keyworth NG12 5GG, UK |
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| Abstract: | Recent studies have shown that melts and residues may not equilibrate during anatexis, and uncertainty exists about the scale on which magmas can be homogenized. This study of elemental and isotopic homogeneity of the South Bohemian Weinsberg granites (˜ 5000 km2) identifies three voluminous, relatively homogeneous magma batches. Each batch has different 87Sr/86Srinit (0.7080, 0.7093 and 0.7106), but all equilibrated at ˜ 327–329 Ma, very similar to the time of monazite crystallization. The data cannot entirely prove melt/residue equilibration during anatexis. However, elemental and isotopic compositions imply magma generation by partial melting of heterogeneous South Bohemian crust and chemical differentiation subsequent to Sr-isotope equilibration. Assuming relatively rapid ascent and solidification rates, magma homogenization must have occurred mostly just after partial melting, during melt segregation and accumulation in the deeper crust with slow prograde heating. Models of rapid crustal heating and instantaneous melt extraction are incompatible with the data. |
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