Imaging the electrical structure of the Great Lake Regions from 3D inversion of Lithoprobe and Earthscope Magnetotellurics data

Abstract:

The 1.1 Ga Midcontinent rift system in North America is a unique rift with extensive igneous rocks. Multiple studies have been carried on in order to understand the rift geometry and geological evolution. Combing the geological information, the previous Magnetotellurics result revealed that the conductive remnant mantle plume causing the midcontinent rift existed in the northwest Wisconsin and Western Lake Superior. Due to the limitation of the previous dataset, the northern extension of the high conductivity out of the US was not clear yet. Here, we constructed a three-dimensional resistivity model around the Great Lake regions combining Lithoprobe with Earthscope long period Magnetotellurics dataset. The study area covers the Midcontinent rift system in the south and the western Superior Craton in the north. At present, only the full impedance data were used. We will add the vertical transfer function data. In our preliminary results, we find a crustal conductor located around western Michigan, northmost Wisconsin, and northeastern Minnesota associated with the Midcontinent Rift, which has been imaging in previous Magnetotellurics results. An obvious high-conductivity mantle anomaly extending from Northern Wisconsin to central Ontario below 150 km appears in our model. It has a trend of NW-SE from Wisconsin to the boundary of the US and Canada and divides into two branches along NNW-SSE and approximately N-S, respectively. We are now working on the interpretation and geological evolution that associate with these electrical anomalies.