GEOCHEMICAL ANALYSES OF MINERALS IN LAMPROPHYRES FROM THE CORTLANDT-BEEMERVILLE TREND, NEW JERSEY-NEW YORK

The Cortlandt-Beemerville Trend is a magmatic belt that intruded approximately 420-440 Ma. It spans roughly 100km with an east-west orientation through northern New Jersey and southern New York. Most of the belt is composed of ultramafic to mafic igneous rocks with a multitude of lamprophyre and other mafic dikes. Geologic maps produced by the New Jersey Geological Survey, New York Geological Survey, and United States Geological Survey have almost 200 dikes mapped throughout the Cortlandt-Beemerville Complex. These are mapped as lamprophyre dikes, mafic dikes, and felsic dikes. Many of these dikes have been mislabeled as the incorrect composition or incorrectly labeled as igneous intrusions when they are a different rock type (Shamus et al., 2018, Langschultz et al., 2019, Gulya et al., 2021). Lamprophyre dikes are mafic igneous rocks with an excessive amount of alkali elements. The goal of this project is to understand the origin of these dikes. There were 11 samples collected in the summer of 2022 and 16 samples collected in previous years. By getting the geochemistry of the samples we can determine whether the intrusions are lamprophyre dikes or other igneous rocks, indicating they likely come from crustal melting. Along with geochemical data, thin sections of the 27 samples will be made so that petrographic analysis can be done on them. Preliminary geochemical data show some samples that are marked as lamprophyre dikes have a silica content of greater than 54%, indicating they are mostly intermediate to felsic in composition. Between the geochemical data and petrographic analysis, the samples can be properly identified based on their composition and how they are related within the broader Cortlandt-Beemerville trend.