We are exploring a billion year old tear in the Earth that in some ways resembles East Africa. However, the Mid-Continent Rift did not turn into an ocean (as many rifts do). Instead this event left a gash in the North American continent that runs in a horseshore through Lake Superior down through Michigan on one arm, and Iowa on the other. Into this tear in the Earth erupted vast volumes of basaltic magma over a billion years ago. 

Our primary goals in the region is to use the record of lavas erupted to probe what was going on in the crust and mantle during the ancient rifting events. We can collect lavas that stack on top of one another and thereby get a sense as to how the lava composition changes over time. This reveals insights into what melted to form the lavas and where the magmas that eventually became lavas resided in the crust before eruption. 

We have found that the source of the magmas which formed these rocks was a magma chamber that experienced many different eruption events and well as recharging events. We continue to explore these rocks.

The NSF award that funded this research has facilitated geological research in the central portion of the North American continent. The most pronounced geologic feature within this region is the billion-year old Mid-Continent Rift System, which was the primary focus of this study. This ancient feature represents one of the best-preserved examples of a region where a continent began to break apart, but failed. A modern example of this type of system would be the East African Rift System (e.g., Great Rift Valley in East Africa). The Mid-Continent Rift has within it layers of rock that preserve lavas in a well-constrained temporal sequence. By sampling each layer and analyzing its geochemical characteristics, we have provided new insights into how the lavas were generated, and how the lavas ponded within the crust before they erupted. Our project has applied modern modeling tools to the Main Phase of volcanism (sampled from the Upper Peninsula of Michigan), where we show distinct cycles of magmatic activity coincident with differing fluxes of magma from the mantle. We have also provided new radiogenic isotope data on lavas from throughout the entire lava sequence that allow us to establish which part of the mantle is contributing melt to the lavas. We have shown that as the Mid-Continent Rift develops, the initial source of lavas is from a plume of hot material that originated deep in the mantle, and that this source changes such that it is progressively shallower over time. Our project has also initiated other studies that continue after this award has terminated. Leveraging this award, an undergraduate secured additional (ongoing funding) to explore magma bodies associated with the Mid-Continent Rift in the eastern Lake Superior region. This work examines the potential sources and time of creation of these magma bodies. Given the already established mining operations in this area on such magma intrusions, this work has broader implications beyond the discipline. One of the most important outcomes of this proposal has been in training and development. The project supported a Ph.D. student, who will submit his work on the project as one of his dissertation chapters. The project also supported a M.S. student who has recently graduated. The location of this project within close proximity to MSU has allowed 11 undergraduate students to directly participate in research. The students learned how to construct a research project, in some cases plan a field campaign, design a project, collect geochemical data, analyze data, and communicate their findings in poster or oral presentation form. In addition, the samples analyzed by the projected supported ~15-20 students who worked in the lab - these students gained valuable experience in performing intricate tasks that require precision and accuracy. The result of this student participation is the communication of the research findings more broadly: 7 presentations were made by undergraduate students at the University-wide MSU Research and Arts Fair over three different years; 7 presentations were made by graduate and undergraduate students at regional scientific meetings; 9 presentations were made by MSU graduate, undergraduate, and faculty associated with the project at national/international meetings. Publications can be found here.