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Horseshoe Complex
Stratigraphic label: [arch][ppro]hrs
Map symbol: ApPhrs

First published: 20 October 2016
Last modified:

 

 

 

  DISCLAIMER: This English version is translated from the original French. In case of any discrepancy, the French version shall prevail. 

Informal subdivision(s)
Numbering does not necessarily reflect the stratigraphic position.
 
None
 
Author: Charette et al., 2016
Age: Archean; Paleoproterozoic
Stratotype: None
Type area: Jeannin Lake area (NTS sheet 24B)
Geological province: Churchill Province
Geological subdivision: Rachel-Laporte Lithotectonic Domain
Lithology: Monzonite
Category: Lithodemic
Rank: Complex
Status: Formal
Use: Active
Related unit(s)

None

Background

The Horseshoe Complex was introduced in the Jeannin Lake area (Charette et al., 2016) to group intermediate intrusions circumscribed to a thrust sheet of the Rachel-Laporte Lithotectonic Domain. Hence, it is a structural complex. A homogeneous and massive granitic to granodioritic gneiss unit, which is locally porphyraceous, was described by Penrose (1978) in the Horseshoe Lake area. Penrose mentions that these gneiss are similar to those found in remobilized Archean bedrocks.

 

Description

The Horseshoe Complex consists mainly of monzonite, quartz monzonite and monzodiorite, but there are also some quartz diorite, gabbro and pyroxenite. Intermediate rocks inject mafic and ultramafic rocks that take a local brecciated appearance. The different lithologies are partially recrystallized, moderately to highly magnetic, well foliated and fine to medium grained.

 

Intermediate rocks have a pink and black (or white and black) mottled appearance. Ferromagnesian minerals (15-25%) form millimetric to centimetric clusters consisting of brown to green biotite and epidote with some hornblende locally. K-feldspar regularly forms recrystallized and stretched clusters (0.5-1 cm) that may be former phenocrystals, although some coarser perthitic microcline crystals are also preserved locally. Quartz forms small anhedral zones consisting of subgrains with undulatory extinction. Rocks are usually altered with partial chloritization of biotite and sericitization, epidotization and hematitization of plagioclase. Accessory minerals are abundant (2-4%) and next to ferromagnesian clusters. They include apatite, sphene, opaque minerals, hematite and allanite (in the core of epidote) as well as, more locally, zircon and carbonate.

Mafic and ultramafic rocks consist of black or dark green amphibolized gabbro and pyroxenite. Gabbro contains ~60% ferromagnesian minerals consisting of hornblende, epidote and chlorite. The rock is fractured and highly altered with injections of millimetric to centimetric magnetite-epidote ± pyrite veinlets. Pyroxenite is composed of a mixture of amphibole (actinolite and tremolite) zones and felts, chlorite and phlogopite. It also includes many opaque mineral grains (magnetite) and small carbonate crystal clusters.

 

Thickness and distribution

The Horseshoe Complex is located in the NW portion of the Jeannin Lake area (Charette et al., 2016), where it forms an NW-SE oriented, 18 km-long by 8 km-wide thrust sheet in the Rachel-Laporte Lithotectonic Domain. In the SE extension of this complex, a smaller slice (4 km by 2 km) was also assigned to this unit. The Rachel-Laporte Domain represents the eastern part of New Quebec Orogen.

 

Dating

Rocks of the Giton Complex have not been dated. However, in the Ungava Bay (Simard et al., 2013) and Saffray Lake (Lafrance et al., 2014) areas, protoliths of gneiss and deformed intrusive rocks that form thrust sheets of the Rachel-Laporte Domain are all Archean (2668-2883 Ma). These various thrust sheets are interpreted as having overthrusted Paleoproterozoic rocks during the New Quebec Orogenesis (1.82-1.77 Ga).

Stratigraphic Relationship(s)

The Horseshoe Complex consists of Archean rocks circumscribed to a thrust sheet from the Archean basement which would have been emplaced on Paleoproterozoic volcano-sedimentary rocks of the Rachel-Laporte Lithotectonic Domain during the New Quebec Orogenesis. It is therefore in fault contact with volcano-sedimentary rocks of the Laporte Supersuite.

Paleontology

Does not apply.

References

Author(s) Title Year of Publication Hyperlink (EXAMINE or Other)
CHARETTE, B. – LAFRANCE, I. – MATHIEU, G. Géologie de la région du lac Jeannin (SNRC 24B). Ministère de l’Énergie et des Ressources naturelles, Québec. 2016

Electronic geological report

LAFRANCE, I. – SIMARD, M. – BANDYAYERA, D. Géologie de la région du lac Saffray (SNRC 24G-24F). Ministère des Ressources naturelles, Québec; RG 2014-02, 49 pages. 2014 RG 2014-02
PENROSE, B. Géologie de la région du lac Horseshoe, Territoire du Nouveau-Québec. Ministère des Richesses naturelles; DPV-573, 35 pages. 1978 DPV-573
SIMARD, M. – LAFRANCE, I. – HAMMOUCHE, H. – LEGOUIX, C. Géologie de la région de Kuujjuaq et de la Baie d’Ungava (SNRC 24J et 24K). Ministère des Ressources naturelles, Québec; RG 2013-04, 60 pages. 2013 RG 2013-04

 

 

11 février 2020