Geochronological studies of precambrian rocks from the southern district of Keewatin / Геохронологические исследования докембрийских горных пород из южного района Кииватен

Results and conclusions are presented of U-Pb, Rb-Sr and K-Ar studies in three areas of southern District of Keewatin. The results of U-Pb studies on zircon are generally complex and age interpretations are not necessarily unique. The geology, more fully described elsewhere, is summarized in this report.
Aneikuni-Yathkyed lakes area. U-Pb age results on zircon indicate that the age of the volcanic-granitoid basement is in the range 2650 to 2680 Ma. K-Ar ages on hornblende and biotite in the Archean basement rocks are commonly ca. 1700 Ma, typical of ages re-set by the Hudsonian Orogeny. There is, however an area of at least 7000 km2 where K-Ar ages on hornblende approximate 2450 Ma and K-Ar ages on biotite range from 2425 to 1975 Ma, indicating minor or no effect of the Hudsonian Orogeny. The age of the Christopher Island formation of the Dubawnt Group is bracketed by a previously published U-Pb zircon age of 1753 + 31-2 Ma on granite intrusive into the formation and by a K-Ar age of 1984 ± 78 Ma on hornblende from a pre-Dubawnt Group quartz monzonite pluton.
Edehon-Hyde lakes area. U-Pb age results on zircon from the granulite terrane are interpreted as follows. I. Granodiorite gneiss, age of emplacement of plutonic precursor to gneiss, 2544 + /1/-8 Ma. 2. Granodiorite gneiss 2 km northeast, age of plutonic predecessor to gneiss, possibly 3190 Ma (minimum age 2702 Ma). 3. Well bandedparagneiss adjacent to granodiorite gneiss (2, above), age of migmatization of paragneiss, 2786 ±41 Ma. North of the granulite terrane, weakly foliated granodiorite gneiss yields a U-Pb zircon age of 2737 + 131-9 Ma. Rb-Sr measurements on the Archean rocks did not generally provide diagnostic results. A Rb-Sr isochron age of 1912 ± 42 Ma was obtained on granite to quartz monzonite stocks intrusive into the basement rocks. K-Ar ages on the Archean rocks in this region are generally in the range 1700 to 1785 Ma.
Kasba gneiss area. East of Kasba Lake, U-Pb measurements on zircon from two locations of Kasba gneiss, supported by Rb-Sr whole-rock model ages, provide an early Archean age ca. 3270 Ma. Less than 20 km distant, two additional specimens from the same unit yield less reliable zircon ages ca. 2780 Ma, and Rb-Sr whole-rock model ages of 2037 and 2457 Ma suggesting rejuvenation by Proterozoic events. Biotite and hornblende K-Ar ages range from 1740 to 1891 Ma. <...>