INTEGRATING THE CHRONOSTRATIGRAPHIC RECORD OF MIDCONTINENT RIFT VOLCANISM WITH THE HISTORY OF INTRUSIVE ACTIVITY

The Midcontinent Rift was the result of a protracted magmatic and extensional event in Laurentia's interior. While the overall duration of magmatic activity was protracted, there were rapid pulses of voluminous magmatism akin to what is typically revealed in shorter-duration large igneous provinces. An updated chronostratigraphic framework for the volcanics of the Midcontinent Rift was recently published that incorporated new age constraints developed using chemical abrasion ID-TIMS methods that enable high precision ²⁰⁶Pb/²³⁸U dates to be utilized (Swanson-Hysell et al. 2019). With such higher precision constraints, the timing and tempo of magmatic activity within the rift can be reevaluated. Of particular interest is to what extent the magmatic activity was continuous or punctuated by pulses. Key to evaluating this question is the timing of emplacement of intrusive rocks throughout the rift particularly the largest one — the Duluth Complex. Integrating the extrusive and intrusive records can be accomplished both through comparison of U-Pb dates as well as through comparison of paleomagnetic directions. The rapid progression of paleomagnetic pole positions associated with rapid equatorward motion of Laurentia enable paleomagnetic directions to give chronological insight. Paired geochronology and paleomagnetic data from the Duluth Complex confirm the interpretation of Paces and Miller (1993) that the layered series and the anorthositic series were rapidly emplaced. This emplacement was coeval with the eruption of the upper southeast sequence of the North Shore Volcanic Group. Taken together, these data further illuminate the voluminous pulse of melt generation ca. 1096 Ma — more than 10 million years after initial widespread magmatic activity.