Syn-emplacement recrystallization and deformation microstructures in the Poe Mountain anorthosite,Wyoming

 Plagioclase recrystallization microstructures and petrofabrics in the unmetamorphosed, 1.43 Ga Poe Mountain anorthosite, Wyoming, are indicative of very high-temperature deformation and recrystallization during the emplacement of the anorthosite body. The Poe Mountain anorthosite consists of a core of recrystallized, massive anorthosite transitional with a series of layered anorthositic cumulates at the margin of the intrusion. Irregular grain boundaries and dissected grain microstructures in the massive core and transitional anorthosites suggest that the anorthositic rocks recrystallized by “fast” grain boundary migration and possibly subgrain rotation recrystallization, at very high temperatures (≈1050°C) during emplacement of the intrusion in the mid-crust (3 kbar). The deformation and recrystallization of the Poe Mountain anorthosite was continuous from subliquidus to subsolidus temperature conditions during the emplacement of the intrusion. Anorthosites with the lowest modal percentages of ferromagnesian minerals and Fe-Ti oxides are always the most recrystallized. This suggests that melt interstitial to the plagioclase-crystal framework was removed during deformation and recrystallization of the intrusion. Bulging of plagioclase grain boundaries around Fe-Ti oxides together with deformed oikocrystic ferromagnesian minerals and plagioclase chadacrysts indicate that the deformation and recrystallization of the intrusion continued after the crystallization of the interstitial melt minerals. Received: 28 February 1995/Accepted: 20 July 1995