GEOCHEMICAL CORRELATIONS BETWEEN DIKES AND FLOWS IN THE KEWEENAWAN FLOOD BASALT PROVINCE

Dike swarms are often the only remaining portions of ancient continental flood basalt provinces as erosive processes remove the thick flows that typify modern provinces. In the absence of sub-aerial basaltic flows, the chemical composition of dike swarms has been suggested as an analogue to the eroded basalts, however the degree to which a flood basalt lava-pile and dike swarms correlate remains poorly constrained. The Mamainse Point Formation, at 5250m thick, forms the most extensive and continuous portion of the ~1100Ma North American Keweenawan flood basalt province. Due to its continuity, the Mamainse Point Formation has recorded almost the entire petrogenetic evolution of the flood basalt province and contains extensive diking representing its magmatic plumbing system. The extensive dike swarm in the area, combined with the existing detailed chemostratigraphic sections, allow for a unique opportunity to correlate dike-swarms with their respective flows in a continental flood basalt province. 32 mafic dikes were sampled throughout the Mamainse Point Formation and surrounding Archean rocks. 25 samples were selected for whole rock analysis based on freshness. The initial results show an average loss on ignition of ~3%, confirming the freshness of the samples. The dikes also show an MgO range of ~3.9% to ~8.8% and a TiO₂ range of ~0.5% to ~3.9%. Initial analysis of the data shows a clustering of samples into high-Ti and low-Ti groups that correlates with divisions in other elements such as P₂O₅ and Zr. Preliminary data from dikes sampled throughout the Mamainse Point Formation and surrounding areas show strong major and trace element correlations with the previously identified chemostratigraphic sections of the erupted flood basalts. These data underline the geochemical similarities between the dikes and flows in the Mamainse Point Formation and suggest that dike swarm roots in other provinces may also reflect the chemistry of the eroded flood basalts.