Isotopic evidence for the crustal evolution of the Frontenac Arch in the Grenville Province of Ontario, Canada

Abstract

Nine late-tectonic granitoid bodies from the Central Metasedimentary Belt (CMB) of the Grenville Province were studied by the Sr, Nd and O isotopic systems. They occur on either side of the Rideau Lake Fault (RLF). Four bodies south of the fault were dated by the U-Pb zircon method. Three of the ages are tightly constrained at 1166 ± 3 Ma. This is in contrast to ages reported for late-tectonic plutons north of the fault between 1090 and 1076 Ma. t Nd DM model ages range from 1211 to 1480 Ma, indicating that the plutons were derived from a mixed source involving older crust. Exposed pelitic and psammitic metasediments in the area have t DM ages averaging 1790 Ma. The observed Sr-Nd-O relationships indicate that marble was involved in the evolution of the granitoids. The granites are chemically similar to the Mid-Proterozoic anorogenic plutons that occur elsewhere in North America. Their crystallization ages are not found elsewhere in the CMB in Ontario, but they are similar to ages found to the east in the Adirondacks, New York. This suggests that the Frontenac-Adirondack area represents a separate Penokean-age block assembled with the rest of the CMB ∼ 1070 Ma ago.