Final inversion of the Midcontinent Rift during the Rigolet Phase of the Grenvillian Orogeny

Abstract Despite being a prominent continental-scale feature, the late Mesoproterozoic North American Midcontinent Rift did not result in break-up of Laurentia, and subsequently underwent structural inversion. The timing inversion is critical for constraining far-field effects orogenesis processes associated with rift's failure. Keweenaw fault northern Michigan (USA) major thrust structure rift inversion; it places ca. 1093 Ma volcanic rocks atop post-rift Jacobsville Formation, which folded its footwall. Previous detrital zircon (DZ) U-Pb geochronology conducted by laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) assigned 950 maximum age to Formation led researchers interpret deposition deformation as postdating 1090–980 Grenvillian Orogeny. In this study, we reproduced similar DZ dates using LA-ICP-MS then dated 19 youngest grains high-precision chemical abrasion–isotope dilution–thermal ionization mass (CA-ID-TIMS). CA-ID-TIMS at 992.51 ± 0.64 (2σ) redefines depositional overlaps date 985.5 35.8 late-kinematic calcite veins within brecciated zone. Collectively, these data are interpreted constrain final have occurred during 1010–980 Rigolet Phase Orogeny, following an earlier phase Ottawan Far-field propagated >500 km into continental interior phases