|Author:||Charette and Beaudette, 2018|
|Type area:||Frichet River (NTS sheet 35F13)|
|Geological province:||Churchill Province|
|Geological subdivision:||Ungava Orogen / Narsajuaq Arc|
|Lithology:||Mafic intrusive rock|
Table des matières
The Frichet Suite was introduced by Charette and Beaudette (2018) to describe the coarse-grained, locally porphyraceous and recrystallized mafic intrusions of the Narsajuaq Arc. The name of this suite comes from the river of the same name near the largest intrusion of hypersthene jotunite and diorite.
The majority of the Frichet Suite consists of orthopyroxene-clinopyroxene jotunite and diorite. These lithologies, usually coarse-grained, are white and black in altered surface and have a characteristic granoblastic speckled appearance. This appearance is produced by centimetric clusters of greenish and brownish mafic minerals and, in places, by a porphyraceous texture. These 0.5 to 2 cm porphyroids are formed by recrystallization of plagioclase phenocrystals. Jotunite varies from a foliated appearance to a massive one in the core of larger intrusions. When the rock is deformed, mafic mineral clusters and plagioclase phenocrystals form lenses stretched in foliation. Mafic minerals make up between 20 and 45% of the rock and sometimes have a heterogeneous distribution. Orthopyroxene is commonly fractured and partially replaced by biotite or iddingsite. Orthopyroxene and clinopyroxene are found in the core of recrystallized hornblende crystal clusters. Hornblende is the main mafic mineral and is locally replaced by biotite. Few accessory minerals are observed in this lithology (e.g., magnetite, pyrite, apatite, chlorite, carbonate and zircon). In the matrix, plagioclase crystals are well recrystallized and are moderate to strongly saussuritized.
On some outcrops, other intrusive lithologies associated with jotunite are observed. The first is a coarse-grained leucogabbronorite, less rich than jotunite in mafic minerals (5-25%) and including, like jotunite, centimetric clusters of mafic minerals giving a speckled appearance to the rock. The second, of gabbroic composition, contains up to 60% mafic minerals, is homogeneous, varies from medium to coarse grained and distinguished from other lithologies by the absence of the porphyraceous and speckled textures. Jotunite also contains ultramafic horizons (websterite, olivine websterite locally) and garnet gabbronorite enclaves.
The Frichet Suite appears as a large sigmoid mass in NTS sheet 35F13 (>35 km by 3 km) as well as small plutons stretched along the regional foliation (approximately 5 km by 1 km). These plutons concentrate within or near the Sugluk Suture. At the contact with the latter, the jotunite forms an elongated mass oriented east-west and is in contact with the granulitic gneiss of uncertain origin of the Pingasualuit Complex (pPpgs2a).
This unit is generally spatially associated with porphyraceous or porphyroclastic felsic-intermediate units of the Suluraaq Suite (pPslq). Intrusive rocks of the Frichet and Suluraaq suites both forms competent masses in the vicinity of the Sugluk Suture deformation zone. Both of these could be cogenetic. The Frichet Suite intrusions cut gabbronorite, gabbro and diorite of the Pingasualuit Complex (pPpgs1a). These are also observed as enclaves in the mafic intrusions.
Does not apply.