|Author:||Beauchamp and Massei, 2018|
|Type area:||Bohier Island area (NTS sheet 33A01)|
|Geological province:||Superior Province|
|Geological subdivision:||Opinaca Subprovince|
Table des matières
Rocks of the Martel Pluton were originally part of the Lac Barou Massif described by Hocq (1985). This massif was broken down into several units by Beauchamp and Massei following the summer 2017 mapping work conducted by the Ministère. They separated rocks of the Martel Pluton which, unlike other granites of the Otish Mountains, have a banded appearance and more sericite.
The Martel Pluton entirely consists of fairly light grey-white granite, locally with tints of greenish in altered surface and light pinkish white in fresh exposure. This granite is medium to coarse-grained, massive to slightly foliated, with pegmatitic clusters in places. The Martel Pluton is distinguished from other granites in the area by the amount of white mica it contains, and by the banded aspect it gives it. It contains 1% to 4% primary and well-crystallized muscovite. Locally, muscovite is observed in thin section as symplektitic bundles (17-SB-4044), marking rapid and primary crystallization. White mica also appears as veinlets. These veinlets actually represent fractures that opened during a brittle deformation event, which were then filled with secondary sericite. Early ductile deformation is also marked by the oscillatory extinction of quartz. The rock also contains 1-2% garnet and about 1% biotite. It is not uncommon to see a graphic structure on outcrop. The main alterations are weak to moderate hematitization and damouritization, both of which affect plagioclase.
The chemical composition of the Martel Pluton rocks is very homogeneous and is marked by a low content in Fe2O3T (0.75-1.94%) and MgO (0.06-0.21%) as well as a higher K2O content (3.91-5.14%) than other felsic intrusions in the region (Barou Intrusion, Cadieux Pluton, Île Bohier Pluton, Kaaispaach Suite, Misasque Pluton). At the trace element level, the samples analyzed are distinguished by their very low contents in Sr (13 to 43 ppm), Ba (18 to 98 ppm) and V (below the detection limit). The Martel Pluton is peraluminous and similar to S-type granitoids (Maniar and Piccoli, 1989). It is primarily of transitional affinity (Ross and Bédard, 2009). In the diagram Y+Nb vs. Rb (Pearce et al., 1984), rocks of the Martel Pluton plot in the field of volcanic arc granites.
The rare earths diagram is relatively flat, except for a large negative Eu anomaly. The profiles show a slight enrichment in heavy rare earth elements because of garnet in the rock. In addition, the total concentration of rare earth elements is much lower than that of other granites in the area, with contents ranging from 18 to 39 ppm.
The Martel Pluton was observed in the extreme west of the terrain of the Otish Mountains, over about 15 km. It is therefore located in the western portion of NTS sheet 33A01 and likely continues in sheet 33A02.
Map relationships indicate that the Martel Pluton developed after the Barou Intrusion (nAbru). It is also posterior to the Laguiche Complex (nAlgi). Contacts are intrusive with these two units. The Martel Pluton is also cut by a diabase dyke belonging to the Mistassini Dyke Swarm (Namib).
Does not apply.