Paper No. 49-2
Presentation Time: 8:00 AM-12:00 PM
INVESTIGATING THE ORIGIN OF LAMPROPHYRE DIKES IN THE BEEMERVILLE COMPLEX, SUSSEX COUNTY, NEW JERSEY
The Cortlandt-Beemerville magmatic belt extends roughly 100 km from the eastern Cortlandt complex of southern New York into the western Beemerville complex of northern New Jersey. Swarms of lamprophyre dikes intrude through the Cortlandt complex and trend east-west into the Beemerville complex (Maxey, 1976). The lamprophyre dikes are hypothesized to have been emplaced roughly 420 Ma using only bulk rock major chemistry and cross-cutting relationships. The origin and association of lamprophyre dikes in the Beemerville complex are still poorly understood because these dikes have only been petrographically and geochemically examined in the immediate vicinity of Beemerville proper (Eby, 2004). In 2018, 7 mapped Beemerville lamprophyre dikes in Sussex county were analyzed using petrographic microscopy and bulk rock chemistry. The resulting data indicated that only 4 of the 7 sampled dikes were true lamprophyres (Shamus et al, 2018), and the other 3 dikes were intermediate to felsic with significantly large negative Ta and Nb anomalies and positive K anomalies; because of this, these dikes could not have resulted from fractionation of a single source. Instead, the felsic dikes have likely resulted from crustal melting, probably driven by heat from the Cortlandt-Beemerville intrusion. Those results drove this study to continue field and petrographic re-examination of more dikes. To that end, 16 additional lamprophyre dikes in the Beemerville proper were examined in the field and samples were collected to be analyzed using bulk rock major chemistry and petrographic analysis. Several of the 16 dikes collected using geologic maps produced by the New Jersey Geological Survey and United States Geological Survey mineralogically resemble the felsic dikes previously collected. In addition to this, several dike locations have been improperly mapped as no dike outcrops were present in their appropriate field location. The updated petrology of the 16 dikes will be discussed and compared to previous studies.