Background

Description

Thickness and Distribution

The De Pas Supersuite is a polyphase syntectonic intrusion NNW-SSE to N-S oriented that extends over 440 km long and 25 to 55 km wide within the George Lithotectonic Domain (Charette et al., 2018). Rocks assigned to De Pas Supersuite are also present in the eastern part of the Baleine Lithotectonic Domain, which is just west of the George Domain. The De Pas Supersuite is associated with a strong positive regional aeromagnetic anomaly crossing the centre of the SECP. In its western part, however, some of the rocks assigned to De Pas Supersuite are non-magnetic and are located outside this regional anomaly.

With an area of 14 138 km², the De Pas Supersuite is the largest unit in the SECP. The granitic suite (11 656 km²) largely dominates the charnockitic suite (2482 km²).

Dating

U-Pb dating indicates a crystallization age for the De Pas Supersuite between 1840 and 1810 Ma (Krogh, 1986; Dunphy and Skulski, 1996; James et al., 1996; James and Dunning, 2000) and more specifically between 1840 and 1823 Ma for the De Pas Granitic Suite (Dunphy and Skulski, 1996).

More recent work on the Ministère’s 1/250 000 mapping between 2011 and 2016 yielded ages between 1861 Ma and 1813 Ma. Readers can refer to the granitic and charnockitic suites of the De Pas Supersuite for more details on these dates. Recent dating confirms the conclusions of Dunphy and Skulski (1996) and James et al. (1996) that the two magmatic suites of the De Pas Supersuite have a contemporary emplacement. In addition, this evolution is partly synchronous with the development of major regional shear corridors, particularly the Rivière George Shear Zone, along which the De Pas intruded.

Stratigraphic Relationship(s)

The De Pas Supersuite is interpreted by several authors to be associated with a Proterozoic magmatic arc environment connected to a subduction zone developed during the New Quebec Orogenesis (Dunphy and Skulsky, 1996; Martelain et al., 1998; Simard et al., 2013). Wardle et al. (1990, 2002) note that the magmatic arc could also be associated with a syncollisional component in the hinterland of the New Quebec Orogen.

The Ministère’s mapping work highlighted the transitional nature of the north-south contact between the two suites that make up the De Pas Supersuite. Thus, the main units of each of these suites, that is, the porphyraceous units (pPdep2 and pPcde2), have similar textural and mineralogical characteristics. Orthopyroxene, well preserved in the southern sector, is increasingly altered and completely replaced by a mix of serpentine and amphibole moving northward to an amphibole-biotite assemblage. Several outcrops exhibit rocks with and without orthopyroxene that show no cross-cutting relationships between them. It is therefore possible that the southern portion of the De Pas Supersuite represents a deeper portion of the intrusion that allowed the crystallization of orthopyroxene and the formation of charnockite, whereas the northern portion would be a more superficial part. It is also possible that the transition from orthopyroxene rock to orthopyroxene-free rock from south to north is a change in crystallization conditions, as the CO₂-rich magma moves to a richer H₂O magma.

Paleontology

Does not apply.

References