|Author:||Charette and Beaudette, 2018|
|Type area:||Ivitaarqiap Lake area (NTS sheet 35K06)|
|Geological province:||Churchill Province|
|Geological subdivision:||Ungava Orogen / Narsajuaq Arc|
|Lithology:||Hypersthene felsic intrusive rock|
Table des matières
The Navvaataaq Suite, introduced by Charette and Beaudette (2018), includes orthopyroxene felsic intrusive rocks that intrude into foliated to gneissic banded granulitic rocks of the Narsajuaq Arc. The unit name originates from Navvaataaq Lake, which is located near the largest intrusion of opdalite and enderbite within the arc (NTS sheets 35K05 and 35K06). Previously, lithologies of this suite were assigned to unit pPNAR1 of the Older plutonic suite and unit pPNAR4 of the Younger plutonic suite described by St-Onge and Lucas (1992) and St-Onge et al. (1992).
The Navvaataaq Suite (pPnav1) consists of opdalite and enderbite, medium to coarse grained, leucoratic and massive to foliated. A common feature of these rocks is the concentration of mafic minerals in millimetric to centimetric discontinuous laminae or in clusters, producing a speckled appearance. Within these clusters, brownish orthopyroxene cores are usually observed with the naked eye. Intrusive rocks generally have heterogeneous appearance that is produced at the outcrop scale by variations in size (usually medium to coarse-grained, or locally fine-grained), altered surface colour (beige, beige-green, green, brown-green, brownish, brownish beige, pinkish beige) and proportion of mafic minerals (5-20%). The petrographic study indicates that these intrusive rocks locally have a homogeneous composition ranging from enderbite to opdalite, locally charnockite, or are formed of two diffuse phases, occurring as undulating bands or clusters, which are difficult to distinguish in outcrop. One of these phases is charnockitic and the other is opdalitic or enderbitic. The charnockitic phase is slightly coarser grained and includes quartz zones or clusters. In outcrop, the heterogeneous appearance is sometimes amplified by the presence of 2 to 30% of variably assimilated mafic-ultramafic enclaves and by the presence of 5 to 20% pinkish or whitish centimetric bands in diffuse contact in orthopyroxene felsic rocks. These bands are irregular, discontinuous and straight-lined or undulating. They may be conformable to or cut foliation. Locally, small (1-2 cm) phenocrystals of K-feldspar or plagioclase are present.
Microscopic photographic study supports the intrusive nature of this suite that is not recrystallized or is only recrystallized locally. Quartz usually occurs as irregular zones, interstitial between subhedral to anhedral crystals of plagioclase and K-feldspar. Plagioclase is anti-perthitic and myrmekites are present in the matrix or are concentrated on the rims of mafic mineral clusters and laminae. The majority of these clusters and laminae are composed of intergrown biotite flakes and hornblende, matted or as poikilitic crystals. Apatite and magnetite are usually associated with mafic minerals. When present in the mineral assemblage, orthopyroxene is associated with mafic clusters and laminae and is partially to be completely replaced by iddingsite, biotite, chlorite, calcite, or a fine-grained assemblage of these minerals. In some places, orthopyroxene appears to be completely replaced by fibrous amphibole clusters, indicating uralitization of orthopyroxene, or is surrounded by poikilitic anhedral or matted hornblende. Clinopyroxene occurs in some samples as better preserved crystals, or is locally partially replaced by hornblende. Few secondary minerals are present in intrusive rocks of the Navvaataaq Suite. Euhedral zircons and allanite occur as trace minerals.
Opdalite and enderbite of the Navvaataaq Suite occur in the central-west and northwest portion of the Narsajuaq Arc as subconformable, folded intrusions within the foliated to gneissic granulitic rocks of the Pingasualuit Complex (pPpgs) and the Siurartuuq Suite (pPsir) or as large kilometric masses containing several klippes of these lithologies.
A medium-grained, foliated and speckled opdalite, present in a kilometric intrusive mass assigned to the pPnav1 unit, was sampled by Charette and Beaudette (2018) to date the Navvaataaq Suite. The analytical results are pending. No other datings are available at this time.
Intrusive rocks of the pPnav1 unit usually occur as intrusions forming conformable to subconformable, regular decimetric to metric horizons in hypersthene quartz diorite and hypersthene diorite of the Pingasualuit Complex 1 (pPpgs1) unit. In the larger intrusion masses associated with the Navvaataaq Suite, lithologies of this complex are present in variably assimilated enclaves. Also, enderbite and opdalite of the pPnav1 unit are in sharp to diffuse contact and cut granoblastic potassic rocks of the Siurartuuq Suite (pPsir1). Field observations indicate that the Navvaataaq Suite is late with respect to granoblastic charnockite.
Does not apply.