GEOLOGY OF THE ROCK POND REGION, PHARAOH LAKE WILDERNESS AREA, ESSEX COUNTY, NY

The Adirondack Mountains encompass 27000 km² of domal uplift that represents the southern parts of a Mesoproterozoic Grenville Province. This region was involved in a series of orogenic events that ultimately led to the (~1 Ga) supercontinent Rodinia (McLelland et al., 2013). These tectonic pulses involved arc accretion, magmatism, and multiple stages of deformation (Regan et al., 2015). Understanding this structural evolution has major implications for constraining the emplacement and alteration mechanisms of the 1050 Ma Lyon Mountain Granite, which hosts magnetite-apatite deposits, locally with Rare Earth Elements (Valley et al., 2010). High resolution outcrop mapping (1:5000) in combination with in-situ microstructural, geochemical, and geochronological analyses have been carried out in order to provide insight into the nature and timing of tectonic events.

The Rock Pond area is characterized by inter-layered metapelites, quartzites, granitoid, and amphibolite/meta-gabbro and is interpreted to represent one of the older sequences of the Adirondack tectonostratigraphy (Walton and Waard, 1950). Metamorphic assemblages in paragneisses include Kspar + Bio + Grt + Sil and the assemblages in amphibolite include Hbl + Plag + Cpx, + Grt. A strong foliation (S₁) is deformed by two large-scale fold generations. The earlier phase (F₂) is characterized by isoclinal, steeply inclined, gently westward plunging folds with weak-to-moderate axial planar cleavage (S₂) that strikes westward and dips steeply to the south. Preferential growth of garnet along injected K-feldspar leucosome margins suggests syndeformational metamorphism and anatexis. The latter phase of deformation (F₃) resulted in isoclinal folding with N-S-striking steeply westward dipping axial planes and a southward plunging axis. The two fold generations are partitioned such that the northern part of the map area is dominated by F₂ folding and the southern part by F₃ folding. Future in-situ microprobe analyses will focus on constraining the relationship between structural fabrics, metamorphic reactions, and geochronology in order to integrate these deformation events into the tectonic framework of the Adirondack Mountains.