CONTINUING STUDIES INTO DIKES OF THE CORTLANDT-BEEMERVILLE TREND

The Cortlandt-Beemerville Trend, a magmatic belt intruding around 420-440 Ma, extends approximately 100 km in an east-west orientation through northern New Jersey and southern New York. Comprising mainly of ultramafic to mafic igneous rocks in several plutons, the belt also features numerous lamprophyre and other mafic alkaline dikes. Lamprophyre dikes, specifically, are mafic igneous rocks characterized by an excessive presence of alkali elements. Geological maps from the New Jersey Geological Survey, New York Geological Survey, and United States Geological Survey identify almost 200 dikes within the Cortlandt-Beemerville Complex, and were categorized as lamprophyre, mafic, or felsic dikes. Notably, some of these dikes have been mislabeled in terms of composition and are intermediate to felsic while others were identified as not even being igneous dikes but instead sedimentary units of unusual orientations (Shamus et al., 2018; Langschultz et al., 2019; Gulya et al., 2021; Rosal et al., 2022). The felsic dikes are believed to result from crustal melting induced by the Cortlandt-Beemerville intrusions. Some of the other lamprophyre dikes have defined a wide range of lamprophyre subtypes (i.e. minette vs. kersantites) and also display a diversity of chemical compositions. All of these findings have spurred further field and petrographic examinations of additional dikes. The objective of this project is to continue unraveling the origin of the dikes within the Cortlandt-Beemerville Trend and re-map these dikes. To that end, 13 dikes were sampled in summer of 2023 in New York and New Jersey. Analyzing the geochemistry of the samples is key to determining whether these intrusions are lamprophyre dikes or other types of igneous rocks, providing insights into their likely origin from crustal or mantle melting. In conjunction with the geochemical data, thin sections were created to facilitate petrographic analysis. The combined use of geochemical data and petrographic analysis is crucial for accurately identifying the samples and understanding their relationships within the broader Cortlandt-Beemerville trend. This is particularly true in trying to relate samples of the other alkaline mafic dikes that are not lamprophyres with the lamprophyres.