Background

Description

Wabash Complex 1 (mPwab1): Migmatitized Paragneiss, Sedimentary Migmatite and Granite

Wabash Complex 2 (mPwab2): Paragneiss, Quarzite and Quartzitic Wacke

This unit consists of rusty biotite ± graphite ± garnet ± sillimanite ± pyrrhotite ± pyrite paragneiss, minor quantities of impure quartzite in millimetric beds and pyrite-chalcopyrite-garnet quartzitic wacke. Rusty paragneiss are the most abundant facies of this unit. These fine to medium-grained and rust-coloured metapelites are easily recognizable in the field. 

Wabash Complex 3 (mPwab3): Calcitic to Dolomitic Marble and Calcosilicate Rocks

This unit consists of medium to coarse-grained calcitic to dolomitic marble with whitish to greyish fresh surface. Marble outcrops were mapped in earlier work (Lee, 1972). These marbles form thin, greyish to pinkish lenses, interbedded in biotite-graphite paragneiss. Minerals observed in all marbles in the area are calcite (55-65%), dolomite (≤10%), diopside (5-20%), biotite (<2%), quartz with undulatory extinction (3-10%) and trace minerals such as apatite, actinolite and feldspars. This unit also contains minor amounts of rusty graphite-garnet paragneiss, calcosilicate rock boudins and centimetric to metric horizons of impure quartzite. Quarzite horizons are interstratified with marbles in rusty paragneiss. A pegmatite dyke approximately 6 m wide containing orthopyroxene, clinopyroxene and sulphides (pyrite and pyrrhotite, 1-2%) intrudes into quartzose facies of this unit.

Wabash Complex 4 (mPwab4): Amphibolite and Garnetite Accompanied by Quartzofeldspathic Rocks and Ultrametamorphic Granitoids

This unit consists of several facies that cannot be individualized at the 1:50,000 scale: amphibolite and garnetite, quartzofeldspathic rock and ultrametamorphic granitoids.

Unit mPwab5 consists of probable volcano-sedimentary rocks associated with iron formations.

Iron formations are banded and consist of several alternating facies rich in silicates, oxides, chert or garnet (garnetite). The silicate facies iron formation, the most important in terms of surface area, is fine grained and clinopyroxene-rich. It occurs as 20 to 30 cm thick bands and is composed mainly of clinopyroxene (80%) and plagioclase. This unit typically has contents of 52-53% SiO₂, 17-25.5% Fe₂O₃t and 4-10.6% MgO. The sulphide facies iron formation also occurs as 20 to 30 cm thick bands. The rock is composed of garnet, pyrrhotite, pyrite and sphalerite and is heavily rusted in altered surface. Contents are 29% SiO₂, 10% Fe₂O₃t, 5.6% MgO and 3% S.

Chert is visible in places and consists of 1 to 2 cm thick continuous bands composed solely of recrystallized, fine-grained greyish quartz. Garnetite occurs as 5 to 50 cm bands. It is fine grained and has a porphyroblastic texture associated with the presence of garnet crystals up to 0.5 cm in diameter. It is composed of 40-50% garnet, plagioclase, quartz and accessory pyrite and chalcopyrite. Garnetite contains 46.7-53.7% SiO₂, 16.05-24.4% Fe₂O₃t and 11.8-16.15% Al₂O₃.

The volcano-sedimentary package consists of mafic gneiss, quartzofeldspathic gneiss, felsic to intermediate plagioclase-crystal rocks and fragmentary porphyritic felsic rocks (lapilli tuff). Fine-grained mafic gneiss forms approximately 5 m thick horizons composed of clinopyroxene and plagioclase. This facies is characterized by alternating leucoratic and melanocratic bands. Melanocratic bands are subparallel and may represent deformed pillow margins. Mafic gneiss contains 48-50% SiO₂, 0.45-0.59% K₂O and 13.5-15% FeO. On the modified Alteration Box Plot (Large et al., 2001; Trépanier, 2011), samples plot in the fresh basalt field. In the SiO₂ vs. K₂O+Na₂O diagram (Le Bas et al., 1986), these rocks fall in the tholeiitic basalt field. The rare earth element diagram is quite flat with contents up to 20 times the chondritic values (McDonough and Sun, 1995).

Quartzofeldspathic gneiss was only recognized on one outcrop. It is fine grained, whitish in altered surface and greenish in fresh exposure. It forms a horizon approximately 2 m thick and is composed of quartz and feldspar accompanied by acessory pyrite. This felsic to intermediate rock has high deformation (mylonitization). Gneiss contains 68.3% SiO₂, 6.9% K₂O and 1.8% Fe₂O₃3t. On the Nb/Y vs Zr/TiO₂ diagram (Winchester and Floyd, 1977), rocks are classified as rhyolites. The rare earth element diagram has a negative slope with light rare earth enrichment relative to heavy rare earths.

Fragmentary felsic rock is the most abundant facies of the volcano-sedimentary package. It occurs as horizons of variable thickness on all the outcrops of the volcano-sedimentary package. This fine-grained lithology contains fragments made of amalgamated crystals of K-feldspar, plagioclase and clinopyroxene. The matrix is composed of biotite, green hornblende and clinopyroxene. Carbonates and epidote are acessory minerals. This fragmentary rock contains 53-58% SiO₂, 2.5-4% K₂O and 7.1-13.7% Fe₂O₃t. In order to determine these rocks’ protolith which represent a typical and exclusive facies of this area, they were plotted in the Nb/Y vs Zr/TiO₂ diagram of Winchester and Floyd (1977) which indicates rhyodacitic composition.

Under the microscope, mafic minerals form millimetric horizons, while plagioclase crystals are rounded and recrystallized. Carbonates are located in fractures or occur as subhedral crystals, and K-feldspar is perthitic. Centimetric “xenotliths” (1-10 cm) are present on some fragmentary rock outcrops. These xenotliths are fine grained and mafic. Since they are only associated with fragmentary rocks, they could be interpreted as “fiammes”. This interpretation seems to support the hypothesis that these rocks are lapilli tuffs. These mafic fragments are fine grained and mainly composed of clinopyroxene, and some plagioclase and quartz. Chloritization and hematitization are observed at the fragment edges. Some apatite crystals are also associated with chlorite.

Thickness and Distribution

The Wabash Complex was identified by Moukhsil et al. (2015) during mapping of the Parent region (sheets 32B01, 32B02, 31O15 and south of 31O10). It was also observed west of Parent when mapping the Clova region (sheets 32B03, 31O11, 31O13; Moukhsil et al., 2016) and east in the Wemotaci region (sheets 31P11, 31P12, 31P13 and 31P14; Moukhsil and Côté, 2017)

Dating

Stratigraphic Relationship(s)

Some lithological units of this complex form metric to decametric tectonic slices in the Lacoste Magmatic Suite and in the Dugré, Pope, Vermillon and Hibbard plutonic suites. They also occur as enclaves in syenitic units of the region. They are intruded by pegmatite dykes and the Roc Suite. 

Paleontology

Does not apply.

References