North-Central Section - 46th Annual Meeting (23–24 April 2012)

Paper No. 1
Presentation Time: 8:00 AM-11:40 AM


COOK, Margaret A., Geology Department, Augustana College, 639 38th Street, Rock Island, IL 61201,

The incipient rifting of the supercontinent Pangaea facilitated the emplacement of the Eastern North America (ENA) basalt provinces during the Mesozoic era. A generally uniform geochemical signature of high-titanium quartz-normative tholeiitic basalt (HTQ) magma is consistent throughout these flows. Previous research has concluded that these provinces were largely unchanged by crystal fractionation or crustal contamination and were directly extruded from shallow undepleted or enriched homogeneous mantle sources. However, a petrographic investigation of the Palisades intrusive diabase sheet has revealed unique magmatic differentiation features best explained by regional contamination, magma chamber recharge and at least two pulses of heterogeneous parent magma. The goal of this investigation is to analyse the extent of contamination within the Palisades sheet using radiogentic isotope data.

The identification and dating of these geochemical reversals were performed by strontium isotope data analyses on four samples. These samples include the floor sequence of initial injection, the concentrated zone of olivine at 10 m, an anomalous horizon above 70 m, and the final ceiling sequence of magma at 100 m. The results of these analyses are currently under evaluation by the accomplishment of final measurements. A thin-section examination was conducted on samples collected from partially assimilated xenoliths in Fort Lee, New Jersey. This evaluation has yielded evidence for in-situ remobilization of Lockatong shale and sandstone sediments that have contaminated the basal contact of the intrusive sheet.