|Reference section:||The official reference section was proposed by Allard for the IGC Congress (Allard, 1972) and described in the CIM excursion Guidebook (Allard, 1984). It begins in the anorthositic zone (UTM NAD83, zone 18: 564780 mE, 5515720 mN) and ends in the granophyric zone (UTM NAD83, zone 18: 564369 mE, 5513649 mN)|
|Type area:||East of Armitage Lake (southeastern portion of sheet 32G16-200-0102)|
|Geological province:||Superior Province|
|Geological subdivision:||Abitibi Subprovince|
|Lithology:||Mafic to ultramafic intrusive rocks|
Table des matières
The large Lac Doré stratiform and differentiated mafic to ultramafic intrusion was originally identified as the Lac Doré Complex (Allard, 1956; Allard, 1976). This name, which emphasized the analogy with Bushveld or Stillwater-type layered stratiform complexes, was maintained by Daigneault and Allard (1990) for historical reasons, despite the recommendations of the North American Stratigraphic Code to use the term “complex” (Articles 37d and 38; MER, 1986). The most recent version of the North American Stratigraphic Code (NASC, 2005) maintains that it is incorrect to use the term “complex” to refer to “various types of rock belonging to a single class”. For this reason, we are proposing to amend the nomenclature of the Lac Doré Complex in accordance with sections 31 to 41 of the North American Stratigraphic Code: (a) the Lac Doré Complex is renamed the Lac Doré Intrusive Suite (referred to in the rest of the text as LDIS); (b) the Lac Doré Lower Series, Lac Doré Layered Series and Lac Doré Upper Series become the Lac Doré Lower Unit, Lac Doré Layered Unit and Lac Doré Upper Unit respectively; and (c) the Layered Zone, included in the Layered Series (former nomenclature), is now referred to as the “layered zone” and is considered an informal lithodeme.
The Lac Doré Intrusive Suite (LDIS) is a stratiform synvolcanic intrusion of mafic to ultramafic composition hosted in volcanic rocks of the Obatogamau and Waconichi formations. The LDIS stratigraphy is based on the work of Allard (1967) and Allard and Caty (1969). It includes the Lac Doré Lower Unit (nAcdi), Lac Doré Layered Unit (nAcdl) and Lac Doré Upper Unit (nAcds). East of the Grenville Front Tectonic Zone, mafic to ultramafic intrusive rocks, which are deformed and metamorphosed to the amphibolite facies, were also attributed to the LDIS (Allard, 1979, 1981; Ciesielski and Madore, 1989; Bandyayera et al., 2005).
The Lac Doré Intrusive Suite occupies the axial section of the Chibougamau Anticline and outcrops over 5 to 7 km thick and >53 km long (Daigneault and Allard, 1990).
A quartz pyroxenite sample from the layered zone (Lac Doré Layered Unit) yielded an age of 2728.3 +1.2/-1.1 Ma and a granophyre sample from the granophyric zone (Lac Doré Upper Unit) yielded an age of 2727.0 ±1.3 Ma (Mortensen, 1993).
|Isotopic System||Mineral||Crystallization Age (Ma)||(+)||(-)||Reference(s)|
Does not apply.