Rb-Sr and single - zircon grain 207Pb/206Pb chronology of the Monesterio granodiorite and related migmatites: Evidence of a Late Cambrian melting event int the Ossa-morena Zone, Iberian Massif

• Autores: P. Montero, Karmah Salman Monte, T. Zinger, Fernando Bea Barredo
• Localización: Estudios geológicos, ISSN 0367-0449, Vol. 55, Nº 1-2, 1999, págs. 3-8
• Idioma: inglés
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• Resumen

  • The Monesterio granodiorite, a small granodioritic body emplaced in a migmatitic complex in the SW of the Olivenza-Monesterio antiform, is a key plutonic body to understand the relationships among the magmatism, metamorphism, and deformation in the Ossa-Morena Zone, SW Iberian Massif. We dated the granodiorite with the single-zircon stepwise-evaporation 207Pb/206Pb method, and the related migmatization event with the Rb-Sr method on leucosomes. Our results indicate that the Monesterio granodiorite crystallised at 510 ± 7 Ma and its protolith had a component with Upper Proterozoic zircons with a minimum age of 1696 Ma. Leucosomes give a Rb-Sr age of 511 ± 40 Ma (MSWD = 1,7) with initial 87Sr/86Sr = 0.70914 ± 0.00048. The lower initial 87Sr/86Sr of the granodiorite and its calc-alkaline chemistry precludes it from having derived from the same protolith as the migmatites. The existente of different magmatic bodies in the Ossa-Morena Zone with ages clustering around 500-510 Ma reveals the existence of a significant melting event during the Late Cambrian that involved protoliths with very different geochemical and isotopic signatures