T68 Evolution of the Midcontinent Rift: A Window into Proterozoic Environments, a Repository of Minerals, and a Lesson in Rifting II

Sunday, 4 November 2018
1:30 PM - 5:30 PM
Room 242

CONTROLS ON THE LOCALIZATION AND TIMING OF MINERALIZED INTRUSIONS WITHIN THE CA. 1.1 GA MIDCONTINENT RIFT SYSTEM

Paper number: T68-5
Program: Technical Sessions
Time: 2:30 PM – 2:45 PM

Authors

Abstract

North America’s ca. 1.1 Ga Midcontinent Rift (MCR) is one of the best preserved intra-continental rift systems of Precambrian age. It is host to the second largest layered intrusion in the world (Duluth Complex), as well as numerous mafic to ultramafic intrusions, some of which contain significant Ni-Cu mineralization (e.g., Eagle, Tamarack, and Thunder Bay North deposits). Many of these MCR-related intrusions have been dated by the U-Pb method, however: 1) the majority of these ages were obtained prior to the introduction of the chemical abrasion technique on single zircon grains, which often leads to greater precision and accuracy; 2) many ages are derived from only a few (2-3), primarily discordant, fractions of zircon and/or baddeleyite grains; and 3) several potential MCR intrusions have been discovered since the last major geochronological studies of the rift, revealed through a combination of geophysical methods and drilling, and remain undated. By more accurately refining the emplacement and crystallization ages of several MCR intrusions, and establishing robust U-Pb ages for newly-discovered bodies, we can better understand the dynamics of the MCR plumbing system and its secular evolution. At the deposit scale, high-resolution U-Pb ages may allow us to recognize whether particular intrusions were emplaced in one single magmatic pulse, or whether they represent long-lived conduits comprising multiple magmatic pulses. It may also reveal temporal constraints on the formation of mineralized intrusions within the MCR. Furthermore, combining high-precision ages with lithogeochemistry will allow us to test linkages between individual intrusions and distinct stages of the flood basalt sequence. In this presentation, we will discuss some of our recent geochronological results.

Geological Society of America Abstracts with Programs. Vol. 50, No. 6

doi: 10.1130/abs/2018AM-324035

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