16-48 The Geochemical and Petrographic Analyses of "Mafic" Dikes in Northern New Jersey and Southern New York

Session: From Thin Section to Outcrop: Exploration of Undergraduate Research (Posters)

Presenting Author:

Authors:

Abstract:

This project focuses on the petrographic and geochemical analyses of “mafic” dikes throughout northern New Jersey and southern New York. These dikes have been suggested to be part of and related to the Cortlandt-Beemerville trend without strong evidence. This study serves to answer questions relating to the precise types of rocks present, the sources of these dikes, the degree of possible crustal contamination, and their relationship within the Cortlandt-Beemerville trend. Samples collected during the summer of 2024 and 2025 provide interesting insights into the generation of these features. Samples were collected based on different geological survey maps that previously identified lamprophyre, mafic, or “igneous” dikes over the last sixty years. Several of the mapped dikes were found to be misidentified as dark gray metasediments. Of the twelve samples analyzed, five were collected from the same outcrop covering an area of approximately 300 yds. Of those five samples, three of the dikes showed unique geochemical signatures suggesting the possibility of several different source magmas emplaced at different times, while two appeared similar. Other samples also showed complex geochemistries including a wide range of SiO2 wt%, varying levels of enrichment of incompatible elements, and the presence of some europium and niobium-tantalum depletion patterns. The overall geochemistry suggests that there is a diversity of rock types present and that they are not all related to one another and not even the larger plutons in the trend. 

© Copyright 2025 The Geological Society of America (GSA), all rights reserved.