Publication Details

McDannell:2018
Field Value
Title: Instability of the Southern Canadian Shield during the Late Proterozoic
Authors: Kalin T. McDannell, Peter K. Zeitler, David A. Schneider
Publication: Earth Planet. Sci. Lett., v. 490, p. .
Publish Date: January, 2018
DOI: 10.1016/j.epsl.2018.03.012
PDF: pdf
BibTEX Citation: McDannell:2018.bib

Abstract:

Cratons are generally considered to comprise lithosphere that has remained tectonically quiescent for billions of years. Direct evidence for stability is mainly founded in the Phanerozoic sediment record and low‐temperature thermochronology, but for significant parts of Canada, stability earlier in geologic time has been inferred due to the lack of an extensive rock record in both time and space. We used 40Ar/39Ar multi‐diffusion domain (MDD) analysis of K‐feldspar to constrain cratonic thermal histories across an intermediate (⁓0−350\circleC) temperature range in an attempt to link known high‐temperature geochronology that resolves the timing of orogenesis and metamorphism with lower temperature data suited for upper crustal burial and unroofing histories.This work is focused on understanding the transition from Archean Paleo proterozoic crustal growth to later intervals of stability,and how uninterrupted that record is throughout Earth’s Proterozoic “MiddleAge.”Intermediate‐temperature thermal histories of cratonic rocks at well constrained localities within the southern Canadian Shield of North America challenge the stability world view because our data indicate that these rocks were at elevated temperatures in the Proterozoic. Feldspars from granitic rocks collected at the surface cooled at rates of <0.\circleC/Ma subsequent to orogenesis, seemingly characteristic of cratonic lithosphere, But modeled thermal histories suggest that at ca.1.11.0 Ga these rocks were still near ≈0\circC– signaling either reheating, or prolonged residence at mid crustal depths assuming anorma l31 cratonic geothermal gradient. After 1 Ga, the regions we sampled then underwent further cooling 32 such that they were at or near the surface (<<\circleC) in the early Paleozoic. Explaining mid 33 crustal residence at 1 Ga is challenging. A widespread, prolonged reheating history via burial is 34 not supported by stratigraphic information, however assuming a pure lymonotonic history 35 requires >5 km of exhumation beginning at ca.1 Ga. A possible explanation maybe found in 36 McDannelletal. Late Proterozoic Instability of the Canadian Shield 2 evidence of magmatic under plating that thickened the crust, driving uplift and erosion.The 37 timing of this coincides with Mid Continent extension and Grenville orogenesis. 40Ar/39Ar MDD 38 data demonstrate that this technique can be successfully applied to older rocks and fill in a large 39 observational gap. These data also raise questions about the evolution of cratons during the 40 Proterozoic and the nature of cratonic stability through deep time