Petrology and age of the A-type Mulock granite batholith, northern Grenville Province, Ontario

Abstract The Mulock granite batholith is exposed over 530 km 2 in the northern part of the Grenville Province, 25 km north of North Bay, Ontario. The batholith has a UPb zircon emplacement age of 1244+4/-3 Ma. Two regional tectonic events affected the batholith: (1) moderate-grade regional metamorphism; and (2) shearing and mylonitization related to the Grenville Front Tectonic Zone which slices across the northern third of the batholith. A suite of fine-to coarse-grained, pink, gneissic granites containing accessory fluorite and with colour indices between 1 and 27, dominate the batholith and are cut by abundant aplite dikes. Anorthosite dikes cut the granites and aplite in the central part of the batholith. The granites were originally alkali feldspar granite and syenogranite, and the coarser-grained varieties were originally hypersolvus. The suite is mainly metaluminous to marginally peraluminous; peralkaline varieties are rare. Most of the suite is subalkalic, but subordinate alkalic granites enriched in biotite and ferrohastingsite are early phases. The suite shows all the major and trace element compositions and elemental ratios diagnostic of A-type granite suites. Metamorphism altered the primary distribution of some of the trace elements, particulary Rb and F. The granites crystallized under relatively low pressures (