KINEMATIC, PETROLOGIC, AND GEOCHRONOLOGIC CONSTRAINTS ON THE TIMING OF DEFORMATION AND METAMORPHISM IN THE DRESDEN STATION AREA, EASTERN ADIRONDACK MOUNTAINS, NY

Rocks from the northern portion of the Whitehall quadrangle and the Putnam quadrangle record the effects of multiple phases of deformation and metamorphism. In an outcrop along Hwy 22 in Dresden, khondalitic paragneisses contain the restitic mineral assemblage garnet-sillimanite-K-feldspar-plagioclase-quartz that formed during biotite dehydration melting. These gneisses exhibit a strong east-trending, gently plunging lineation. EMP monazite dates from these rocks cluster in three distinct populations: ~1179 Ma, ~ 1151 Ma, and 1050-1000 Ma. These dates correspond to reported ages for the Shawinigan Orogeny, intrusion of the AMCG suite, and post-Ottawan extension. Similar monazite dates are also found in a khondalitic paragneiss from just north of Whitehall. In the same outcrop a coronitic metagabbro truncates the foliation, has an apparent chilled margin against the khondalite, and is only weakly deformed indicating that it intruded after the khondalite was deformed. The coronitic metagabbro has coronas of opx, followed by grt-cpx symplectite, followed by garnet, around olivine and coronas of hornblende followed by garnet around ilmenite. The coronitic textures developed during a period of metamorphism that must be younger than that found in the khondalitic rocks. A lineated, pervasively recrystallized K-feldspar megacrystic granitoid occurs less than two kilometers to the north of the Dresden Station outcrop. The lineation in this rock also plunges gently to the east. U-Pb zircon SHRIMP-RG analyses yield a weighted mean age of 1155 +/- 15 Ma. This age is consistent with this unit belonging to the AMCG suite and indicates there was a period of post-emplacement deformation. Nearby mylonitic gabbroic to leucogabbroic rocks with variable amounts of hornblende, with west-verging, thrust sense kinematic indicators were also deformed at this time. These data are consistent with a garnet- and partial melt-forming period of granulite facies metamorphism prior to or during AMCG intrusion. This was followed by a second phase of metamorphism and deformation resulting the formation of the coronitic textures in massive gabbro and high-grade tectonites in more hydrated and weaker rock types.