GEOCHEMISTRY AND TECTONIC IMPLICATIONS OF THE STORM KING GRANITE, HUDSON HIGHLANDS, NY

Twenty six samples of Middle Proterozoic Storm King Granite (Berkey, 1909) were collected within the Hudson Highlands, NY in order to understand their petrogenesis and tectonic implications for this region of the Grenville Province. The Storm King is a hornblende granite gneiss with a SHRIMP U/Pb zircon crystallization age of 1174±8 Ma (Ratcliffe and Aleinikoff, 2000) and occurs as late syntectonic sheets intruding the older metavolcanic and metasedimentary gneisses of the Hudson Highlands. Samples were collected from three localities: (1) the type-locality below Storm King Mountain near Cornwall, (2) at the base of Dunderberg Mountain above Jones Point, and (3) at Bear Mountain. All of the samples show the dominant regional gneissosity and upper amphibolite-granulite grade metamorphism of the surrounding ortho- and paragneisses.

Storm King Granite from these localities all have variably mild A-type granite chemical characteristics defined by high Fe/(Fe+Mg) (~0.9), K2O/Na2O (~1.5), high Ba (500-1800 ppm), Nb (10-40 ppm), Y (50-150 ppm), total REE (100-700 ppm) and low MgO (<0.3%), CaO (<2%), and Sr (30-150 ppm). REE patterns are LREE-enriched (La/YbN=5-18), but have flat MREE and HREE and relatively high HREE concentrations(~20-30x chondrite). The Bear Mountain samples show a slight negative Eu anomaly. The Dunderberg Mountain samples show no Eu anomaly while the Storm King Mountain samples range from slight positive to no Eu anomaly. The high MREE and HREE can be interpreted as the melting of garnet-free, mafic source rocks or shallow to mid-crustal levels. Most samples plot well within the within-plate granite (WPG) field while some plot on the border of the WPG and the volcanic arc granite (VAG) field on tectonic discrimination diagrams.

Based on data presented here, the Storm King Granite is geochemically similar to mildly A-type granites from Adirondack AMCG suites of roughly the same age (1180-1140 Ma, McLelland et al., 1996) and to A-type granitoids of the Byram Intrusive Suite of the New Jersey Highlands (Volkert et al., 2000). The age, the mild A-type affinity, and the similarity to Adirondack AMCG suites suggests a similar origin by shallow to mid-crustal heating during late- or post-Elzevirian lithospheric delamination and orogenic collapse.