Geochronology of calcite‐filled joints, southeast Canada: Insight into Late Cretaceous deformation of eastern North America

Abstract

Resolving the timing of brittle tectonism is a challenge. We examined intra‐cratonic Middle Ordovician limestone bedrock that overlies Mesoproterozoic crystalline basement, which are both cut by ENE‐WSW trending fault zones that have historic M4‐5 earthquakes along their trace. Calcite‐filled mode I joints are ubiquitous within the strata, and are parallel to the modern stress field. Calcite δ18O and δ13C values are analogous to the bulk composition of Middle Ordovician limestones, and suggest vein formation from a source dominated by connate fluids of the host rock. U‐Pb geochronology of six calcite veins sealing ENE‐WSW oriented joints produced similar Cretaceous dates and were regressed together yielding a date of 96.8 ± 1.1 Ma (MSWD: 2.9). A Cenomanian age is consistent with the most recent reorientation of North America's compressive stress field, which is attributed to a change in spreading direction along the northern Mid‐Atlantic Ridge and is linked to a global plate reorganization event at ca. 105–100 Ma. These results suggest that the most recent redistribution of lateral stress was not a passive event, and generated brittle deformation and fluid flow at least 500 km inland of North America's Atlantic passive margin.

Reply to comment on "Geochronology of calcite‐filled joints, southeast Canada: Insight into Late Cretaceous deformation of eastern North America"

“…In the beginning of the Discussion section of Spalding et al. (2020), we cite widespread evidence on both sides of Atlantic Basin for increased sedimentation and topographic evolution during the middle to Late Cretaceous, both requiring uplift. We are in agreement that uplift occurred, but differ on the dominant mechanism and scale.…”

“…The veins in Spalding et al. (2020) are oriented NE‐SW, are pure calcite and are present in Middle Ordovician limestones; thus, these two sets of calcite veins are not comparable.…”

“…We welcome a scientific exchange with Davis et al. (2020) about our recent paper (Spalding et al., 2020) that was a product of the first author's MSc research (Spalding, 2017). The thesis contains an abundance of additional data not presented in the short research article, and endeavoured to highlight proper calcite vein characterization to better understand the microstructural relationships and the geochemical reservoirs of trace elements.…”

“…Consequently, “near‐surface” samples close to the trace of the hotspot experienced increased temperatures, whereas the Middle Ordovician limestone that was examined by Spalding et al. (2020) has not witnessed much, if any, of the elevated temperatures of the hotspot activity.…”

“…Spalding et al. (2020) argue that joint propagation and fluid flow in Middle Ordovician strata were initiated from a short‐lived increase in compressive stress at ca. 100 Ma as a consequence of a temporary increase in plate speed (Matthews et al., 2011).…”