Dating the cooling of exhumed central uplifts of impact structures by the (U-Th)/He method: A case study at Manicouagan

Forty titanite grain fragments from 9 central uplift samples of metamorphosed anorthosite from the Manicouagan impact structure were dated by the (U-Th)/He technique. A (U-Th)/He central age of 207.1 +/- 6.4 Ma (2 standard error (SE), n = 40) has been determined. With 4 outlier ages removed the central age is refined to 208.9 +/- 5.1 Ma (2 SE). Both of these ages are within error of the previously determined U-Pb zircon age of 214 +/- 1 Ma (2 sigma) derived from the impact melt. Manicouagan's central uplift formed due to rapid elevation from similar to 7-10 km depth as part of the modification stage of the impact process, which has facilitated the dating of its emplacement due to resulting rapid exhumation and cooling and closure of the (U-Th)/He system in titanite. Correlation with the previous U-Pb zircon 214 +/- 1 Ma impact melt crystallization age indicates that the (U-Th)/He titanite dating technique offers a new approach to dating complex impact structures in the absence of viable melt sheets, or other melt products. The youngest ca. 195 Ma (U-Th)/He dates preserved in some titanite fragments are synchronous with Early Jurassic, rift-induced lithospheric thinning and associated igneous activity that defines the Central Atlantic Magmatic Province (CAMP). The (U-Th)/He titanite data from Manicouagan indicate that the influence of this regional event may extend west of the previously proposed limit of CAMP activity. (C) 2014 Elsevier B.V. All rights reserved.