FIELD INDICATORS OF DIKE LONGEVITY IN FLOOD BASALT PROVINCES

In this presentation I will show how one can roughly tell the duration of magmatic activity for feeder dikes, using field relations alone. The Columbia River Flood Basalt province is not only home to hundreds of mafic lava flows, but also hosts an abundance of feeder dikes to these flows. Thousands of dikes have been found, thousands more are probably near the surface but not exposed, or are exposed but yet found. Until recently, determining the active lifetime of each dike was not possible. New methods using paleomagnetism and thermochronology have overcome this barrier, and evaluation of the duration of magmatic activity for many dikes can now be determined. Here I present the ‘lifetimes’ of dozens of dikes from both the Columbia River Basalts and other flood basalt provinces. Over years of studying dike lifetimes, certain field relations and features that correlate with magmatic lifetime have become apparent. These include subtle features such as wall-rock and dike fracture patterns, dike geometry, and mineral indicators. Notably, more obvious features such as dike width and length do not correlate with magmatic lifetime.