Background

Description

Travers Suite 1 (mPtra1): Gabbronorite, Hypersthene Diorite, Mangerite and Minor Amounts of K-Feldspar-Hypersthene Granite

Travers Suite 2 (mPtra2): Mangerite, Syenite, Orthopyroxene Syenite, Minor Amounts of Syenogranite and Granite

Mangerite is composed of orthopyroxene, plagioclase, K-feldspar, apatite, quartz, zircon and opaque minerals. Plagioclase is perthitic. Orthopyroxene is urilitized, biotitized and has undergone severe hydrothermal alteration, giving it a brownish colour under the microscope (in natural light). Ferromagnesian minerals are concentrated in clusters. In these, you can see inclusions of opaque minerals, zircon and apatite. Biotite appears to be an alteration product of amphibole. Syenite is composed of amphibole, biotite, K-feldspar, plagioclase, clinopyroxene, zircon, titanite and opaque minerals. This rock is porphyritic due to the presence of antiperthitic K-feldspar and has mortar texture. Titanite is located on the edge of opaque minerals. Finally, apatite is either disseminated or as inclusions in ferromagnesian minerals. K-feldspar granite also contains plagioclase, quartz, opaque minerals, zircon and allanite. This medium-grained rock has a small percentage of ferromagnesian minerals. Quartz locally shows myrmekitic texture. Allanite is scarce, occurring as small subcircular crystals surrounded by concentric fractures.

Travers Suite 3 (mPtra3): Granite, Syenogranite, Minor Amounts of Gabbronorite, Monzonite and Quartz Syenite

Granite and syenogranite are fine to medium grained and are composed of K-feldspar, plagioclase, quartz, biotite, clinopyroxene, zircon, apatite and opaque minerals. Biotite is found in large poikilitic tabular crystals containing quartz, or in small alteration crystals that affect clinopyroxene parallel to cleavage. K-feldspar is antiperthitic and quartz is locally myrmekitic. Granite is K-feldspar porphyritic. Rocks in this unit are heavily deformed in places, giving them a cataclastic texture. In addition, in deformation zones, plagioclase is highly sericitized and white mica (muscovite) crystals are observed. Gabbronorite has the same composition as that of unit mPtra2. Quarz syenite is medium grained and contains amphibole, microcline, sodic plagioclase and trace orthopyroxene. The unit contains centimetric to metric paragneiss enclaves.

Travers Suite 4 (mPtra4): Syenite, Orthopyroxene Syenite, Quartz Syenite, Akali Feldspar Granite, Quartz Monzonite, Syenogranite

Unit mPtra4 consists mainly of pinkish syenitic facies marked by a percentage variation in quartz, biotite, amphibole and especially orthopyroxene. These syenitic facies are generally k-feldspar porphyritic. The latter is perthitic and locally sericitized. There are carbonates in places. Alkali feldspar granite and quartz monzonite are generally medium grained and composed of biotite, hornblende, K-feldspar and plagioclase. Orthopyroxene, apatite, zircon and opaque minerals are ancessory minerals. Locally, this unit also includes salmon-pink porphyritic biotite-hornblende-K-feldspar-plagioclase syenogranite.

From a geochemical perspective, the Travers Suite consists of mafic to felsic rocks with SiO₂ contents ranging from 52.4 to 76.69% and K₂O contents from 0.9 to 5.39%. The majority of rocks in this suite are metaluminous (Maniar and Piccoli, 1989) and type I (igneous origin; Chappell and White, 1974). In addition, mafic rocks are of calc-alkaline affinity, and intermediate and felsic rocks are calc-alkaline (potassium rich) to shoshonitic (Peccerillo and Taylor, 1976).

Thickness and distribution

The Travers Suite consists of two plutons located in the northeast portion of sheet 31P16, which likely extend into adjcacent sheets. The fourth unit (mPtra4) predominantly occurs as more or less thick dykes roughly N-S oriented. It intrudes into other units of the same suite.

Dating

Stratigraphic Relationship(s)

The Travers Suite intrudes into the La Bostonnais Complex and contains klippes of the Montauban Group.

Paleontology

Does not apply.

References