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Q: affects anorthosite-suite rocks in the Morin terrane could be a distinct event after anorthosite intrusion (Scenario A), or the result of >300 m.y. of slow cooling (Scenario B). Anorthosite Fest. Through a Global Forum initiative at Brown University, Professor Lew Ashwal from Witwatersrand University in South Africa visited the Department of Geological Sciences from July 16 to 27th. The overall goal of the Forum was to initiate long-term research links with prominent universities around the globe. Lew is a world expert on terrestrial anorthosite formation and his visit sparked broad interest and support across Brown/MIT NLSI for discussions on the formation of lunar anorthosite. During Lew's visit, the current knowledge of the origin of both terrestrial and lunar anorthosites was reviewed and interdisciplinary research directions discussed. Anorthosite and labradorescence. Anorthosite is an igneous monomineralic rock that is composed of plagioclase feldspar (over 90% of the rock is composed of this mineral). Plagioclase is a very common mineral group, more than half of the Earth's crust is composed of it. Anorthosite in many cases is not light-colored at all. This is the result of tiny Fe-Ti oxide inclusions in plagioclase crystals that give them bluish-black hue. One fascinating aspect associated with many anorthosites is an effect called labradorescence. It is a special form of iridescence. of the western body of gabbroic anorthosite (Rose, 1960). The anorthosite probably originally formed by plagioclase floatation in mafic magma chamber at the base of the crust (Ashwal, 1993). The ores for med late during the crystallization of anorthosite by concentration of Fe-Ti oxides (Ashwal, 1993). metamorphism: (1) precipitation of metamorphic zircon from solid state reactions involving breakdown of Zr-bearing phases or (2) precipitation of partial intergranular melt, enriched in zirconium by partial reabsorbion of Lew Ashwal greeting an old friend. Credit: Brown/MIT. Lew's visit began with two extended lectures by him on terrestrial anorthosites, followed by a three-day field trip to anorthosite regions in the Adirondacks. A few people raised questions about how the new-found H2O in the lunar mantle would change our models of anorthosite formation. Also, the issue of how the very pure anorthosite (with scarce mafic minerals) widely observed across the Moon is formed was also discussed. In comparing the lunar anorthosites to terrestrial examples, it was unclear whether they were analogous to Archean anorthosites, which have similarly high An contents, but are thought to be derived from hydrous magmas. metamorphic zircon for mation in samples studied by Bingen et al. (2000), were not found in the thin sections (see also Davidson and v an Breemen, 1988). In the Ivry deposit, silica activity was high enough along the plagioclase boundaries to form zircon during cooling or metamorphism rather than baddeleyite or srilankite. Metamorphic Zircon in Fe-Ti Ores, Morin Anorthosite Complex (Grenville Province, Quebec) Anorthosite is a plutonic rock just as granite and gabbro and it is usually associated with the latter. Therefore we can conclude that despite being officially leucocratic it actually is usually associated with mafic rocks. Query: how is anorthosite formed
A:
The anorthosite probably originally formed by plagioclase floatation in mafic magma chamber at the base of the crust.