Mica and feldspar as indicators of the evolution of a highly evolved granite-pegmatite system in the Tres Arroyos area (Central Iberian Zone, Spain)

Autor: Alfonso Pesquera, Encarnación Roda-Robles, Pedro P. Gil-Crespo, Idoia Garate-Olave
Rok vydání: 2018
Předmět:
Zdroj: Journal of Iberian Geology. 44:375-403
ISSN: 1886-7995
1698-6180
DOI: 10.1007/s41513-018-0077-z
Popis: The aim of this study is to establish the petrogenetic links between the different granitic and aplopegmatitic units occurring in the Tres Arroyos granite-aplopegmatite system (Central Iberian Zone, Spain), from the textural and chemical variations in micas and feldspars. We aim to understand the differentiation mechanisms that allowed the extreme fractionation levels observed in the Li–F-richest dykes occurring in this aplopegmatite field. Major and trace elements in micas and feldspar from the different facies were analyzed by electron microprobe and LA-ICP-MS. Mica compositions define three different trends: muscovite-zinnwaldite-polylithionite, muscovite-trilithionite-polylithionite and biotite-zinnwaldite. The substitution mechanisms depend on the type of trend and on the stage of evolution. The K/Rb ratio and the Ba contents decrease in micas and K-feldspar with fractionation, whereas Li, Rb and Cs values increase. Lithium, Rb, Cs, Ba, Nb, and Ta show a clear tendency to get into the structure of the Fe-rich mica, whereas Be partitions preferably into the Al-micas. When Fe-micas are absent, Al-rich micas become the major sink for those trace elements. Phosphorus and Pb preferably get into the feldspars. In general, a linear and continuous variation of the K/Rb ratio with incompatible elements such as Cs, Rb or Li, and compatible such as Ba, both in micas and K-feldspar, supports a petrogenetic link between the Alburquerque batholith and the aplopegmatites via fractional crystallization.
Databáze: OpenAIRE
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