The Boullé Complex was introduced in the Jeannin Lake area (Charette et al., 2016) to group a package of porphyraceous intermediate intrusions circumscribed to a thrust sheet of the Rachel-Laporte Lithotectonic Domain; hence it is a structural complex.

The Boullé Complex consists of K-feldspar porphyritic intermediate intrusive rocks and syenogranite, all moderately magnetic and well foliated to protomylonitic. The different facies are generally observed together on outcrops and it was not possible to differentiate them at mapping scale 1:250 000.

Porphyraceous rock contains 15-20% microcline phenocrystals 0.5-2 cm long. Their composition varies from monzonite to quartz monzodiorite, including monzodiorite. Monzogranite is also locally observed. Intermediate rocks are partially recrystallized and dark grey with pink flecks in fresh exposure. They contain 25-35% ferromagnesian minerals including greenish brown biotite, locally chloritized, and hornblende. K-feldspar is also found in the matrix. Quartz is sparse (<3%) and plagioclase is variably sericitized. Myrmekitic textures are common and accessory minerals are relatively abundant. These include sphene, epidote, opaque minerals, apatite and allanite. Monzogranite is pale pink and contains up to 30% centimetric microcline phenocrystals and only 10% ferromagnesian minerals consisting of biotite.

Syenogranite is partially recrystallized, medium grained, very well foliated or lineated, and pink. It contains 3-7% greenish brown biotite, locally chloritized, which forms small millimetric to centimetric clusters. Quartz regularly forms small, discontinuous millimetric bands and exhibits undulatory extinction in thin sections. Muscovite and hematite are observed as accessory minerals. Centimetre to metre-wide layers or elongated enclaves of the porphyraceous facies are commonly observed in syenogranite.

Thickness and distribution

The Boullé Complex is located in the NW part of the Jeannin Lake area (Charette et al., 2016), where it forms a thrust sheet ~30 km long by 8 km wide elongated in a NW-SE direction within the Rachel-Laporte Lithotectonic Domain. It covers an estimated area of 149 km².

Dating

An age of 2690 Ma was obtained in a monzonite of the Boullé Complex. Protoliths of gneiss or deformed intrusive rocks that form thrust sheets of the Rachel-Laporte Domain are all Archean (2668-2883 Ma; Lafrance and Vanier). These thrust sheets are interpreted as having overthrusted Paleoproterozoic rocks during the New Quebec Orogenesis (1.82-1.77 Ga; Machado et al., 1989).