BS in Earth Sciences
Natural Resources Management and Environmental Sciences Department
Studies of pre-Grenvillian (1.4–1.3 Ga) plutons offer insight into the dynamics of arc amalgamation and backarc rifting prior to continental collision in the Ottawan orogeny. The Central Metasedimentary Belt boundary thrust zone (CMBbtz) is a northeast–southwest trending thrust zone consisting of metaplutonic thrust sheets enveloped in gneissic tectonites and calcitic– dolomitic marbles. Tonalitic CMBbtz thrust sheets (Dysart and Redstone) are made up of upper amphibolite-facies, foliation-concordant metatonalites (+ amphibole ± biotite ± accessory zircon and titanite) and amphibolites (± biotite ± clinopyroxene), and are located in the southern Ontario Grenville Province. These thrust sheets are thought to have formed and amalgamated onto the Laurentian margin prior to Ottawan orogeny. Major and trace element analysis show the metatonalites have calc-alkaline affinity and amphibolites have both calc-alkaline and tholeiitic affinities suggesting a continental arc environment. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) geochronology of zircon from the two thrust sheets yield igneous ages of ca. 1350–1300 Ma, Dysart amphibolites yield a 1086 Ma Ottawan metamorphic age, and Dysart tonalites record metamorphic zircon growth at ca. 1150–1100 Ma. This last metamorphic event has not been documented in the CMBbtz, but correlates well with thermal events in the allochthonous Parry Sound domain to the west, as do ca. 1350 Ma igneous ages of tonalities in both areas. These data support the hypothesis that the CMBbtz and Parry Sound domain may have been initially linked. Widespread ca. 1350 Ma crust along with distinct 1460– 1400 Ma TDM model ages is consistent with a shared genesis of the Dysart–Mount Holly suite in New York and Vermont, and support the correlation between the CMBbtz thrust sheets and the Adirondack Highlands–Mount Holly belt as a rifted continental arc.