New U-Pb Zircon Ages Reveal a Long-Lived Magmatic History for the Harvey-Cardiff Domain of the Composite Arc Belt of the Grenville Province In Ontario

The geologic history of Harvey-Cardiff domain in the western Composite Arc Belt (CAB) is poorly understood. New geochronological and geochemical data collected in Cavendish Township in SW Harvey-Cardiff domain indicates a long-lived, geochemically diverse, history from 1290 to 1030 Ma.

The oldest rocks are tonalite gneisses of the Anstruther and Burleigh gneiss complexes, previously dated at 1290 Ma. Next youngest are the alkalic Glamorgan (Trooper Lake) gabbro, previously dated at 1246±3 Ma; and syenite and nepheline-syenite suite rocks emplaced between 1242 and 1219 Ma. A deformed quartz monzodiorite pluton, geochemically distinct from syenite and younger alaskite suite rocks, is currently undated.

Two “alaskite” suite plutons in the domain were dated: the syntectonic, monzogranitic Junction pluton yielded a U-Pb zircon age of 1221.0±1.6 Ma, whereas a deformed K-feldspar megacrystic granodiorite body in the deformation zone that forms the boundary between the Harvey-Cardiff and Bancroft domains, yielded an age of 1211.3±1.6 Ma, which places a maximum age on domain boundary formation. Also, an age of 1229 Ma was reported by Burr and Carr (1994) from a granite body in the Anstruther gneiss. All are roughly 20 to 30 m.y. younger than typical alaskite suite ages from elsewhere in the CAB (1240-1245 Ma).

Plutons of a previously unknown late granite suite, characterized by higher K2O (4.6-7.7 wt%) and Th (25-55 ppm), yield a U-Pb zircon age of 1067±4 Ma. Although similar in age to plutons of the ultrapotassic Kensington-Skootamatta suite of the Frontenac-Adirondack Belt, chemically the late granites are most like the 1066 Ma Barbers Lake granite, and it is possible that 2 geochemically distinct plutonic suites were emplaced into CAB at circa 1070 Ma. A syenogranite pegmatite vein hosting the former Cavendish U mine yielded a U-Pb age of 1059.2±3.7 Ma, suggesting a temporal link between late granite and pegmatite emplacement.