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Highfall Complex
Stratigraphic label: [arch][ppro]hig
Map symbol: ApPhig

First published: 23 July 2018
Last modified: 13 January 2020

 

 

 

  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.
 
ApPhig3 Amphibolitized diorite and gabbro
ApPhig2 Granite
ApPhig1 Porphyraceous monzogranite and quartz monzonite
 
Author: Lafrance et al., 2014
Age: Archean; Paleoproterozoic
Stratotype: None
Type area: Saffray Lake area (NTS sheet 24G)
Geological province: Churchill Province
Geological subdivision: Rachel-Laporte Lithotectonic Domain
Lithology: Potassic felsic intrusions
Category: Lithodemic
Rank: Complex
Status: Formal
Use: Active
Related unit(s)

None

Background

The Highfall Complex was defined by Lafrance et al. (2014) in the Saffray Lake area (sheet 24G) to group potassic intrusions circumscribed to a thrust sheet of the Rachel-Laporte Lithotectonic Domain. It is thus a structural complex. Clark (1980) had also described greyish and pinkish granitic intrusions in the area, having or not an augen texture.

 

Description

The Highfall Complex consists of three units: 1) porphyraceous monzogranite and quartz monzonite (ApPhig1); 2) granite (ApPhig2); and 3) amphibolitized diorite and gabbro (ApPhig3).

 

Highfall Complex 1 (ApPhig1): Porphyraceous Monzogranite and Quartz Monzonite

Porphyraceous rocks of unit ApPhig1 are homogeneous, very well foliated and have a high magnetic susceptibility. They are greyish, medium to coarse grained, and contain 10-30% pink K-feldspar phenocrystals 0.5-3 cm. Phenocrystals are partially recrystallized and very well aligned in foliation. In places, they are highly stretched and appear as discontinuous bands. Ferromagnesian minerals (10-25%) commonly combine into lenticular clusters a few millimetres wide, composed mainly of brown to green biotite with lesser amounts of hornblende (4-6%), epidote (2-4%) and magnetite (1-3%). Accessory minerals (3-6%) are usually attached to ferromagnesian mineral clusters and consist of sphene, apatite, allanite, muscovite and small zircon grains as inclusions in biotite. Sericite, carbonates and epidote are alteration minerals observed in feldspar crystals.

 

Highfall Complex 2 (ApPhig2): Granite

Unit ApPhig2 granite is the youngest phase of the Highfall Complex. It contains decimetric to metric enclaves of other units of the complex and occurs as centimetric to metric injections within unit ApPhig1. Granite is pinkish, medium grained, even grained and well foliated. Quartz, microcline and plagioclase contents are similar. Granite contains 2-12% ferromagnesian minerals consisting of brown biotite, locally chloritized, with some hornblende, epidote and fine magnetite. Accessory minerals are the same as in unit ApPhig1, but in smaller amounts.

 

Highfall Complex 3 (ApPhig3): Amphibolitized Diorite and Gabbro

Potassic rocks of units ApPhig1 and ApPhig2 contain boudinaged enclaves, centimetre to metre-wide, of melanocratic rocks stretched parallel to foliation. Some of these enclaves form klippes of significant width compiled from the work of Clark (1980) and assigned to unit ApPhig3. This author describes these klippes as consisting of amphibolitized, foliated, fine to medium-grained diorite and gabbro, composed mostly of plagioclase with some biotite.

 

Thickness and distribution

The Highfall Complex is located in the NW part of the Saffray Lake area (Lafrance et al., 2014), where it forms a thrust sheet ~35 km long by 12 km wide elongated in a NW-SE direction within the Rachel-Laporte Lithotectonic Domain. It represents the eastern part of the New Quebec Orogen.

 

Dating

The Archean age obtained in quartz monzonite is similar to that of granitic gneiss of the Rénia Complex, just north of the Highfall Complex.

Unit Sample Number Isotopic System Mineral Crystallization Age (Ma) (+) (-) Reference(s)
ApPhig1 12-DB-1029 U-Pb Zircon 2705 8 8 Davis et al., 2015

Stratigraphic Relationship(s)

The Highfall Complex is part of a large thrust sheet separated in half by a thrust fault delineating two complexes: the Rénia Complex in the north and the Highfall Complex in the south. This sheet is composed of rocks that would originate from the Archean basement, and would have been emplaced within Paleoproterozoic volcano-sedimentary rocks of the Rachel-Laporte Lithotectonic Domain during the New Quebec Orogenesis (1.82-1.77 Ga). It is therefore in fault contact with Laporte Supersuite units. The northern section of the sheet is interpreted as having partially overthrusted the southern section towards the end of deformation.

Paleontology

Does not apply.

References

Author(s) Title Year of Publication Hyperlink (EXAMINE or Other)
CLARK, T. Région de la rivière Koksoak (Nouveau-Québec). Ministère de l’Énergie et des Ressources naturelles, Québec; DPV-781, 20 pages, 1 plan. 1980 DPV 781

DAVIS, D.W. – MOUKHSIL, A., – LAFRANCE, I. – HAMMOUCHE, H. – GOUTIER, J. – PILOTE, P. – TALLA TAKAM, F.

Datations U-Pb dans les provinces du Supérieur, de Churchill et de Grenville effectuées au JSGL en 2012-2013. Ministère de l’Énergie et des Ressources naturelles, Québec; RP 2014-07, 56 pages.

2015 RP 2014-07
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

 

 

 

10 février 2020