REMAPPING AND GEOCHEMICAL ANALYSIS OF THE CROTON FALLS AND PEACH LAKE PLUTONS IN SOUTHERN NEW YORK AND PLACING THEM IN THE CONTEXT OF THE BEEMERVILLE-CORTLANDT TREND

The two plutonic bodies of Croton Falls and Peach Lake in southeast New York are sparsely documented intrusions laying to the northeast of the Cortlandt Complex. The two plutons are thought to be the easternmost end of the Beemerville-Cortlandt trend of intrusions through Northern New Jersey and Southern New York. The western Beemerville complex consists of alkaline silica-undersaturated rocks and then become dominated by slightly alkaline mafic-ultramafic rocks in the Rosetown and Cortlandt complex. Preliminary research and mapping done by Brock and Mose (1979) focused on the metamorphic effects in the surrounding Reading Prong. The plutons were field identified as mafic to ultramafic bodies with unrelated felsic pegmatite dikes, but no mineralogical or textural analyses was completed. More importantly, there is currently no geochemical data for the Croton Falls and Peach Lake plutons. The purpose of this research is to remap the plutons, determine the petrography and conduct geochemical analysis to understand the genetic relationship of these plutons within the Beemerville-Cortlandt trend. The data will be compared with geochemical data on lamprophyres within the Beemerville-Cortlandt trend from previous research to observe any potential relationships between the Peach Lake-Croton Falls plutons and the lamprophyres. During preliminary field analysis, the plutons consist of mostly amphibole-rich diorite and gabbro to ultramafic hornblendite. There is evidence for multiple intrusive events, which is more prominent in the Croton Falls pluton, as indicated by cross-cutting relationships of coarse- and fine-grained mafic units. The Peach Lake pluton had some units that appeared to have minor preferred foliations and possible evidence of magma mixing with xenoliths of gabbro found within dioritic bodies. The samples were analyzed by inductively coupled plasma–optical emission/mass spectrometry for bulk rock geochemistry. Preliminary geochemical results suggest a definitive similarity with the composition of the Cortlandt Complex. After petrographic analysis, the Croton Falls pluton consists of pyroxene hornblende gabbro to gabbronorite as well as hornblende gabbro which exhibited ad-heteradcumulate growth. The Peach Lake pluton was mostly pyroxene hornblende norites and gabbronorites.