ORIGIN OF NORTHERN NEW JERSEY LAMPROPHYRE DIKES IN RELATION WITH THE BEEMERVILLE COMPLEX

The Beemerville Complex of northern New Jersey and the Cortlandt complex of southern New York are composed of carbonatites, mafic, ultramafic, ultrapotassic, and feldspathoid-bearing rocks consisting of two nepheline syenite bodies, and are associated with lamprophyre dikes (Maxey, 1976). There are approximately 50 outcrops located within Sussex County trending in an east-west orientation that intrude through the Proterozoic sequences, such as the Franklin Marble and the Ordovician Martinsburg Formation (e.g., Drake et al., 1996). These dikes can be located up to 30 km from the Beemerville Complex. The primary rock forming minerals of the lamprophyres found within Beemerville complex consist of medium grained phenocrysts of diopside-hedenbergite and biotite with a fine-grained matrix of nepheline, orthoclase, titanite, melanite, magnetite, apatite, and traces of pyrite (Maxey, 1976). Some of the lamprophyres contain ocelli that are composed of 75% orthoclase and 25% nepheline (Maxey, 1976). The age of the lamprophyre dikes is hypothesized to coincide with the Beemerville complex, forming during the Ordovician at approximately 420 Ma (Eby, 2004). However, previous studies were only based on the proximity, cross-cutting relationships, and bulk rock major element chemistry. The goal of this study is to determine whether most of the lamprophyres are related to the Beemerville Complex formation event based on whole rock trace and minor element geochemical analyses and to determine the precise origin of the lamprophyre dikes. Field samples were collected from 15 different dikes in Sussex and Morris Counties in order to test the diversity of these dikes. Samples were made into thin sections for petrographic examination of all the dikes and duplicates were sent for XRF and ICPMS analyses to provide the geochemical data.