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David Member
Stratigraphic label: [narc]dd
Map symbol: nAdd

First published: 5 december 2018
Last modified:

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Translation of original French

Informal subdivision(s)
Numbering does not necessarily reflect the stratigraphic position.
 
nAdd2 Flow breccia and andesitic hyaloclastite
nAdd1 Andesitic basalt
 
Author:Leclerc et al., 2011
Age:Neoarchean
Reference section:Good reference outcrops are accessible on Road 167, along David Creek, at the south entrance to the town of Chibougamau (UTM NAD 83, zone 18: 543695 mE, 5527426 mN)
Type area:Area from David Lake (NTS sheet 32G16) to the east of Roberge Lake (sheet 32H13), north of Chibougamau Lake
Geological province:Superior Province
Geological subdivision:Abitibi Subprovince
Lithology:Mafic volcanic rocks
Type:Lithostratigraphic
Rank:Member
Status:Formal
Use:Active
Related unit(s)

Background

The David Member (Leclerc et al., 2011) refers to massive, pillowed and brecciated aphyric andesitic basalts and andesites (nAdd1) of the upper Obatogamau Formation, north of the Lac Doré Intrusive Suite. It originally corresponded to the lower division of the former Gilman Formation (Leclerc et al., 2008).

 

Description

 

David Member 1 (nAdd1): Andesitic Basalt

Andesitic basalt is typically aphyric, dark green in fresh exposure and medium green in altered surface. Flows can reach a thickness of 60 m (Allard, 1976) and are typically composed of pillowed (~50%) and massive (~25%) mafic volcanic rocks intruded by comagmatic gabbroic sills (~25%). A minor (<1%) brecciated facies is present locally. Flow breccias also form centimetre to metre-thick lenses interbedded with massive and pillowed flows.

Reference outcrops at the southern entrance to the town of Chibougamau expose dark green, locally amygdaloidal, pillow basalts and tiny brecciated horizons containing hyaloclasts (0.5-1 m). Basalts are cut by medium-grained gabbro sills.

 

David Member 2 (nAdd2): Flow Breccia and Andesitic Hyaloclastite

In the Petit Gilman Lake area south of the town of Chibougamau, lenses of brecciated material are observed over 30 m thick and extend laterally for several hundred metres. They are interbedded with ankeritized chlorite-sericite schist strips of the Lac Sauvage Shear Zone.

 

Thickness and Distribution

The David Member is generally <1 km thick, but much thicker in the area south of Chibougamau due to tectonic recurrences along numerous reverse shear zones in the Lac Sauvage deformation corridor. Rocks of the David Member extend from northern David Lake (sheet 32G16) to eastern Roberge Lake (sheet 32H13).

Dating

None. 

Stratigraphic Relationship(s)

Volcanic rocks at the David Member’s base are cut by rocks of the Lac Doré Intrusive Suite, although primary cross-cutting relationships are generally obscured by deformation (Lac Sauvage Shear Zone, Bordière du Lac Doré Shear Zone; Daigneault and Allard, 1990). The David Member’s summit corresponds to the contact with volcaniclastic rocks of the Waconichi Formation’s Allard Member.

Paleontology

Does not apply.

References

Author(s)TitleYear of PublicationHyperlink (EXAMINE or Other)
DAIGNEAULT, R. – ALLARD, G.O.Le Complexe du lac Doré et son environnement géologique (région de Chibougamau – Sous-province de l’Abitibi). Ministère de l’Énergie et des Ressources, Québec; MM 89-03, 275 pages.1990MM 89-03
LECLERC, F. – BÉDARD, J.H. – HARRIS, L.B. – GOULET, N. – HOULE, P. – ROY, P.Nouvelles subdivisions de la Formation de Gilman, Groupe de Roy, région de Chibougamau, Sous-province de l’Abitibi, Québec : résultats préliminaires. Current Researches, Geological Survey of Canada; 2008-7, 20 pages.2008Source
LECLERC, F. – BÉDARD, J.H. – HARRIS, L.B. – MCNICOLL, V. – GOULET, N. – ROY, P. – HOULE, P.Tholeiitic to calc-alkaline cyclic volcanism in the Roy Group, Chibougamau area, Abitibi Greenstone Belt – Revised stratigraphy and implications for VHMS exploration. Canadian Journal of Earth Sciences; volume 48, pages 661–694.2011Source

 

30 août 2019