RUI: Thermal Consequences and Textural Signatures of Reinjection in Mafic Sills

Slippery Rock University Of Pennsylvania, Slippery Rock PA

Investigators

Abstract

Just as volcanoes have alternating periods of eruption and repose, igneous intrusions can also have alternating periods of injection and crystallization. This study will provide a better understanding of the emplacement process and its effects in intrusive systems, specifically in mafic sills. The study will identify the diagnostic physical and chemical signatures of magma reinjection into a partially crystalline system and the specific textural characteristics of a reinjection horizon that can be used to determine its timing and thermal conditions. Diagnostic criteria for recognizing reinjections in mafic systems will allow this process to be positively identified in other intrusions and will place important constraints on models for magma chamber formation and evolution. In addition, the data to be developed (texture, composition, and mineralogy profiles) will be widely distributed as a resource for developing and testing petrologic hypotheses, and for recognizing additional processes beyond those specifically addressed in this study. The primary goal of this study is to define the detailed signature of reinjection events using a continuous drill core profile through a diabase sill (the Black Sturgeon sill) from Nipigon, Ontario. Petrographic data will include modal mineralogy, textures (crystal size distributions), and fabric (alignment factor). Geochemical data will include bulk-rock major and trace-element chemistry and mineral compositions. Preliminary results have been used to tentatively identify the positions and effects of several reinjection events in the Black Sturgeon sill. This project will document the fine-scale variations around these sites and locate and characterize other potential reinjection zones. These textural and compositional variations will provide a set of discrete criteria that can be used to demonstrate and document the existence of reinjection horizons in magmatic systems. Numerical cooling models will then be integrated with textural observations and with MELTS modeling to provide quantitative constraints on the emplacement history of the Black Sturgeon sill, including the timing and spatial distribution of the individual replenishment events.