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 indica tive 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 transitiona l with a series of layered anorthositic cumulates at the margin of the intrusion. Irregular grain boundaries and dissected grain microstruct ures in the massive core and transitional anorthosites suggest that th e anorthositic rocks recrystallized by ''fast'' grain boundary migrati on and possibly subgrain rotation recrystallization, at very high temp eratures (approximate to 1050 degrees C) during emplacement of the int rusion in the mid-crust (3 kbar). The deformation and recrystallizatio n of the Poe Mountain anorthosite was continuous from subliquidus to s ubsolidus temperature conditions during the emplacement of the intrusi on. Anorthosites with the lowest modal percentages of ferromagnesian m inerals and Fe-Ti oxides are always the most recrystallized. This sugg ests that melt interstitial to the plagioclase-crystal framework was r emoved during deformation and recrystallization of the intrusion Bulgi ng of plagioclase grain boundaries around Fe-Ti oxides together with d eformed oikocrystic ferromagnesian minerals and plagioclase chadacryst s indicate that the deformation and recrystallization of the intrusion continued after the crystallization of the interstitial melt minerals .