Petrology, Geochemistry, And Tectonic Significance Of Mafic Dikes In Salem, MA

Abstract

Petrological and geochemical analysis of mafic dikes provides necessary information on the mantle-lithosphere interaction and overall geodynamic setting during magma formation. Numerous mafic dikes have been reported in the basement rocks of the Avalon terrane in Massachusetts. We present new petrological and geochemical results from mafic dikes intruding the Salem Gabbro-Diorite at the Salem Willows Park and Winter Island locations in Salem, MA. Field mapping reveals the mafic dikes are NE oriented with distinct margins in the Salem Gabbro-Diorite. Major element geochemistry indicates dikes are silica-undersaturated and lean tholeiitic, suggestive of a within-plate tectonic setting. Tectonic discriminant diagrams show the dikes plot between enriched mid-ocean ridge basalts and ocean island basalts. The spider diagrams display a diagnostic pattern of ocean-island basalts, and an abundance of incompatible trace elements such as Ba and Rb, which suggest an enriched magma source for these dikes. The dikes at the Salem Willows appear to corroborate best with the Mesozoic dike swarm of coastal Massachusetts as described in Ross (2020) using orientation, textural characteristics, and geochemical analysis. These dikes may further be related to what is known as the Central Atlantic Magmatic Province (CAMP) (Dorais, 2005), a Mesozoic-age flood basalt province which extends down coastal Canada and New England. Future K-Ar dating could be performed in order to conclusively determine a precise age for these dikes.