B. Lafrance et al., SYN-EMPLACEMENT RECRYSTALLIZATION AND DEFORMATION MICROSTRUCTURES IN THE POE MOUNTAIN ANORTHOSITE, WYOMING, Contributions to Mineralogy and Petrology, 122(4), 1996, pp. 431-440
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
.