Nd isotope mapping of the Frontenac Terrane in southwestern Grenville Province

Abstract

Nd isotope analyses are presented for granitoid rocks from the western part of Frontenac Terrane in the Grenville Province of Ontario. TDM ages show no correlation with the silica content of the rocks, but instead correlate with geographical location, suggesting that the TDM ages are indicative of regional crustal formation age, and do not result from mixing between sources with different provenance ages. Based on these observations, we identify a new crustal age boundary that follows the Desert Lake – Canoe Lake fault and the Rideau Lake fault, and hence a new juvenile crustal block (Westport domain). This domain is identified as part of the ensimatic back-arc rift zone that formed the juvenile segment of the Central Metasedimentary Belt in Ontario. However, additional sampling along the Ottawa River suggests that the juvenile Westport domain does not extend into Quebec. Instead, a narrower ensialic rift zone is represented by the Marble domain in Quebec. Based on comparison with the Taupo volcanic zone and the northern Red Sea as modern analogues, we suggest that the transition from a wide ensimatic rift zone in Ontario to a narrow ensialic rift in Quebec was accommodated by transtensional motion along a zone of diffuse shear east of Ottawa.

3‐D geophysical modeling of a buried, simple impact crater: Holleford impact structure, Ontario, Canada

“…Overlay of the Bouguer gravity on the DEM (Figure 5c) shows gravity lows (~ 1.5 mGal) to the south of the structure rim and below Knowlton Lake where lower‐density Paleozoic sediments thicken within a structural depression in the Precambrian basement surface. The gravity low below Knowlton Lake corresponds with a northwest‐trending magnetic anomaly that defines the Canoe Lake‐Desert Lake fault (Dickin & Strong, 2021) (Figures 1b and 4a).…”

“…(b) Regional geology map showing location of Holleford study area (~9 km 2 ; Figure 1). The structure lies close to the limit of Paleozoic cover and is underlain by Mesoproterozoic basement rocks of the Grenville Province Frontenac Terrane (modified from Dickin & Strong, 2021; Magnus & Easton, 2015). The Desert Lake‐Canoe Lake fault marks a major normal basement fault that extends below Knowlton Lake.…”

“…Within the Holleford study area, basement is composed of interbedded marble, quartzo‐feldspathic gneiss, granulite, and amphibolite units that strike northeastward and dip southeastward (Figure 1b). To the east of Holleford, the western shoreline of Knowlton Lake marks the location of a major northeast‐trending, down‐to‐the‐east normal fault (Desert Lake‐Canoe Lake Fault; Figure 1b) (Dickin & Strong, 2021; Easton, 2001).…”