GEOCHEMICAL INVESTIGATION OF DIKES ASSOCIATED WITH THE CORTLANDT-BEEMERVILLE TREND AND CHANGING PETROGENETIC PARADIGMS

The Cortlandt-Beemerville Trend is a magmatic belt comprised of alkaline to ultramafic rocks with various lamprophyre and felsic dike intrusions. The trend, which extends 100 km in an east-west direction from northwestern New Jersey to southern New York, is still poorly understood. The different intrusions are suggested to have been emplaced during the Ordovician period, between 420 Ma and 454 Ma (Eby, 2004; Zirakparvar et al., 2017). In two previous collaborative studies (Shamus et al., 2018; Langschultz et al., 2019), preliminary field work, petrography, and geochemical studies, including major and minor trace element geochemistry, were conducted on a number of dikes that were previously identified as lamprophyres, “mafic dikes”, or “igneous dikes” on geologic maps produced by the New Jersey Geological Survey, New York Geological Survey, and United States Geological Survey. This study continues these investigations by sampling additional dikes in New Jersey, but more critically, expanding into New York closer to the Cortlandt Complex. Of the mafic dikes that were found, 14 field samples were collected and sent to Bureau Veritas/Acme Laboratories for bulk rock inductively coupled plasma-emission/mass spectrometry (ICP-ES/MS). The cumulative results of these studies found that many of these intrusions were misidentified, as some of the dikes that were identified as igneous are actually intermediate to felsic in composition, and many of those identified as lamprophyres are not actually lamprophyres and do not appear to be related to either the Beemerville or Cortlandt complexes. Additionally, the trace element signatures of lamprophyres and the felsic-intermediate dikes do not appear to show any similarities, suggesting a different magmatic source. The lamprophyres do show significant similarities in trace element patterns to the Beemerville rocks analyzed by Eby (2004) but differ significantly from previously analyzed rocks of the Rosetown and Cortlandt complexes (Bender et al., 1984). As a result, it is suggested that a more significant re-examination of the geochemistry needs to be conducted in order to better elucidate the relationships between the lamprophyres, the felsic-intermediate dikes, and the rocks of the Beemerville and Cortlandt Complexes.