Abstract
Apatite can be used as an archive of processes occurring during the evolution of granitic magmas and as a pegmatite exploration tool. With this aim, a detailed compositional study of apatite was performed on different Variscan granites, pegmatites and quartz veins from the Central Iberian Zone. Manganese in granitic apatite increases with increasing evolution degree. Such Mn increase would not be related to changes in the fO2 during evolution but rather to a higher proportion of Mn in residual melts, joined to an increase in SiO2 content and peraluminosity. In the case of pegmatitic apatite, the fO2 and the polymerization degree of the melts seem not to have influenced the Mn and Fe contents but the higher availability of these transition elements and/or the lack of minerals competing for them. The subrounded Fe-Mn phosphate nodules, where apatite often occurs in P-rich pegmatites and P-rich quartz dykes, probably crystallized from a P-rich melt exsolved from the pegmatitic melt and where Fe, Mn and Cl would partition. The low Mn and Fe contents in the apatite from the quartz veins may be attributed either to the low availability of these elements in the late hydrothermal fluids derived from the granitic and pegmatitic melts, or to a high fO2. The Rare Earth Elements, Sr and Y are the main trace elements of the studied apatites. The REE contents of apatite decrease with the evolution of their hosting rocks. The REE patterns show in general strong tetrad effects that are probably not related to the fluids’ activity in the system. On the contrary, the fluids likely drive the non-CHARAC behavior of apatite from the most evolved granitic and pegmatitic units. Low fO2 conditions seem to be related to strong Eu anomalies observed for most of the apatites associated with different granitic units, barren and P-rich pegmatites. The positive Eu anomalies in some apatites from leucogranites and Li-rich pegmatites could reflect their early character, prior to the crystallization of feldspars. The increase in the Sr content in apatite from Li-rich pegmatites and B-P±F-rich leucogranites could be related to problems in accommodating this element in the albite structure, favoring its incorporation into apatite. The triangular plots ΣREE-Sr-Y and U–Th–Pb of apatites, as well as the Eu anomaly versus the TE1,3 diagram, seem to be potentially good as petrogenetic indicators, mainly for pegmatites and, to a lesser extent, for granites from the CIZ.
Funder
European Commission
Ministerio de Ciencia e Innovación
University of the Basque Country
Portuguese National Funds
Subject
Geology,Geotechnical Engineering and Engineering Geology
Reference157 articles.
1. Identifying accessory mineral saturation during differentiation in granitoid magmas: An integrated approach;Hoskin;J. Petrol.,2000
2. The geochemistry of phosphorus in granite rocks and the effect of aluminium;Bea;Lithos,1992
3. Apatite solubility in peraluminous liquids: Experimental data and an extension of the Harrison-Watson model;Pichavant;Geochim. Cosmochim. Acta,1992
4. Evidence for distinct stages of magma history recorded by the compositions of accessory apatite and zircon;Miles;Contrib. Mineral. Petrol.,2013
5. Lisowiec, K., Slaby, E., and Götze, J. Cathodoluminescence (CL) of apatite as an insight into magma mixing in the granitoid pluton of Karkonosze, Poland. Proceedings of the Conference on Raman and Luminescence Spectroscopy in the Earth Sciences.
Cited by
5 articles.
订阅此论文施引文献
订阅此论文施引文献,注册后可以免费订阅5篇论文的施引文献,订阅后可以查看论文全部施引文献