Experimental Crystallization of the Beauvoir Granite as a Model for the Evolution of Variscan Rare Metal Magmas

• Published in: Journal of petrology 2022-12, Vol.63 (12)
• Main Author: Pichavant, Michel
• Format: Article
• Language: English
• Subjects: Earth Sciences; Sciences of the Universe; Volcanology
• ISSN: 0022-3530; 1460-2415
• DOI: 10.1093/petrology/egac120

New experiments on the strongly peraluminous, Li-, P- and F-rich Beauvoir granite (Massif Central, France) provide a basis for understanding crystallization and chemical fractionation in Variscan rare metal magmas. Crystallization experiments were performed on two natural granite compositions under H2O-saturated conditions at 100, 200, and 300 MPa, from 540°C to 700°C and between ~NNO + 3 and NNO-1.4. Experimental charges were examined by SEM and their products (glasses and crystals) analyzed for major elements by EMPA. Trace element concentrations in selected glasses were determined by LA ICP-MS. Despite experimental durations commonly exceeding 1000 h and some up to 4000 h, kinetic problems were encountered in particular in the 100 MPa charges whereas, at 200 and 300 MPa, results consistent with previous melting experiments were obtained. Beauvoir melts crystallize quartz, plagioclase, K-feldspar and mica as major phases. At NNO-1.4, mica is a biotite, whereas it is a Li-mica between ~NNO+3 and NNO-1. Apatite, Fe-Ti oxides, either hematite or magnetite, topaz, amblygonite, cassiterite and columbite-tantalite appear as accessory phases between ~NNO + 3 and NNO + 1. Experimental plagioclases are albitic (An