Phosphate mineral associations from the Tres Arroyos aplite-pegmatites (Badajoz, Spain): Petrography, mineral chemistry, and petrogenetic implications
In the Tres Arroyos granite-pegmatite system (Badajoz, Spain) a zoned aplite-pegmatite field occurs, with poorly evolved, intermediate and Li-rich dikes intruded into metasediments, close to the contact with the Nisa-Alburquerque granitic batholith. A high variety of Fe-Mn phosphates occur in the po...
| Autores: | , , , |
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| Tipo de recurso: | artículo |
| Fecha de publicación: | 2021 |
| País: | España |
| Institución: | Universidad del País Vasco |
| Repositorio: | Addi. Archivo Digital para la Docencia y la Investigación |
| OAI Identifier: | oai:addi.ehu.eus:10810/75571 |
| Acceso en línea: | http://hdl.handle.net/10810/75571 |
| Access Level: | acceso abierto |
| Palabra clave: | phosphates aplite-pegmatites Central Iberian Zone Tres Arroyos Iberian Massif |
| Sumario: | In the Tres Arroyos granite-pegmatite system (Badajoz, Spain) a zoned aplite-pegmatite field occurs, with poorly evolved, intermediate and Li-rich dikes intruded into metasediments, close to the contact with the Nisa-Alburquerque granitic batholith. A high variety of Fe-Mn phosphates occur in the poorly evolved aplite-pegmatites, and of Al-phosphates mainly in the intermediate and Li-rich dykes. The Fe/(Fe+Mn) ratio of the Fe-Mn phosphates is the highest one reported for aplite-pegmatite fields in the Central Iberian Zone, suggesting a low fractionation degree for the hosting poorly evolved aplite-pegmatites. In contrast, the high F contents observed in crystals of the amblygonite-montebrasite series from the intermediate and Li-rich aplite-pegmatites, indicates a higher fractionation degree for these dykes. The relatively common occurrence of phosphates in the three types of aplite-pegmatites from Tres Arroyos attests for a significant availability of P in the pegmatitic melt. In this granite- pegmatite system P first started behaving as a compatible element, hence favoring the crystallization of discrete phosphates, during the crystallization of the poorly evolved aplite-pegmatites. In more fractionated melts, where Fe-Mn-(Mg) contents were extremely depleted, P was still available, allowing the crystallization of the Al-phosphates, mainly of the amblygonite-montebrasite series, in the more evolved intermediate and Li-rich aplite-pegmatites. Subsolidus replacement of the early phosphate phases, such as those of the amblygonite-montebrasite series by lacroixite; together with the presence of late Ca- and Sr-bearing phosphates such as jahnsite-(CaMnFe), whiteite-(CaFeMg), mitridatite and goyazite, attest for an important activity of metasomatic fluids in the Tres Arroyos granite-pegmatite system. Consequently, variations in the phosphate mineral associations and in their chemical composition reflect well the fractional crystallization processes suffered by the pegmatitic melts from the poorly evolved up to the Li-rich dykes, as well as the subsolidus history of the Tres Arroyos system |
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