AGES AND PETROGENETIC SIGNIFICANCE OF IGNEOUS MANGERITE-CHARNOCKITE SUITES ASSOCIATED WITH MASSIF ANORTHOSITES, GRENVILLE PROVINCE

U-Pb zircon ages of zircon fractions of major anorthosite-mangerite-charnockite-granite (AMCG) igneous suites imply that this magmatism inaugurated what is widely regarded as the Grenvillian event between about 1.16 and 1.12 Ga ago. Pre-Grenvillian AMCG suites about 1.36 and 1.64 Ga old have much more restricted distribution. An apparent time lag of about 0.05 to 0.10 Ga is indicated between culmination of AMCG magmatism and the widely recognized Grenvillian metamorphic peak. The time lag is consistent with conductive heating of thick subcontinental lithosphere that began with initiation of AMCG magmatism and continued until geotherms rose sufficiently to produce granulites in much of the lower to middle crust. -from Authors