Mineral Chemistry, Geobarometry and Oxygen Fugacity of the Granitic Rocks from the Itremo Domain, Central Madagascar

作     者：Désiré Alphonse Rakotondravaly Roger Randrianja Désiré Alphonse Rakotondravaly;Roger Randrianja

作者机构：Directorate of Operations Monitoring Ministry of Mines and Strategic Resources Antananarivo Madagascar Doctoral School of Engineering and Geosciences University of Antananarivo Antananarivo Madagascar 

出 版 物：《Journal of Geoscience and Environment Protection》 (地球科学和环境保护期刊（英文）)

年 卷 期：2022年第10卷第4期

页      面：145-166页

学科分类：0709[理学-地质学] 070901[理学-矿物学、岩石学、矿床学] 07[理学] 

主　　题：Itremo Granitic Monzonitic Mineral Chemistry Geobarometer Fugacity 

摘      要：Major and accessory minerals from the Ibity granite, Tsarasaotra monzonitic and granite dykes, and Antsahakely granite of the Itremo domain in the Precambrian basement of Madagascar were characterized by using microscopic observations and chemical analyses with the aim of understanding their chemical characteristics and estimating the crystallization pressure and oxygen fugacity of their host rocks. Plagioclases in these rocks are albite and oligoclase, while alkali feldspars are orthoclase. For the phlogopite-micas, Fe-biotite and Li-phengite are common for the Ibity and Antsahakely granites, Mg-biotite is common for the Ibity granite and the Tsarasaotra monzonitic and granite dykes, and siderophyllite and Zinnwaldite are specific to the Ibity granite. Phlogopite-micas in the studied rocks are mainly primary, accessorily re-equilibrated, and rarely secondary. Calcic amphiboles distributed in the Magnesio-and Ferro-hornblende are identified in the Tsarasaotra monzonitic, whereas amphibole is rare and absent in the other rocks. Igneous titanite is observed in the Ibity granite and in the Tsarasaotra monzonitic rocks, which have similar compositions to some REE oxide-rich titanites. Concerning the Fe-Ti oxide phases, the rhombohedral and spinel/trifer tetroxide phases are found in both the Tsarasaotra monzonitic and the Tsarasaotra granite dyke, the trifer tetroxide and spinel + wüstite phases are found only in the Ibity granite, and the pseudobrookite + rhombohedral phase is found only in the Tsarasaotra granite dyke. The epidote mineral, rarely found in the Antsahakely granite, could be an indicator of metamorphism or hydrothermal activity involved during the emplacement of this rock. Aluminum in hornblende geobarometer gave pressure ranges of around 5 kbar for the Tsarasaotra monzonitic rocks. The Titanite geobarometer gave pressures of 2.5 - 3.2 kbar for the Ibity granite, 2.9 kbar for the Tsarasaotra monzonitic, and 7.1 kbar for the Antsahakely granite. Both amph