The Montauban region, south-central Grenville Province, is known for its small, stratiform, polymetallic Au-Ag-Zn-Pb ore deposits. The amphibolite-facies orebodies and hydrothermally altered wall rocks occur within the ca. 1.45 Ga Montauban group, a sequence dominated by quartzofeldspathic gneiss with minor quartzite and amphibolite, locally pillowed metabasalt, and sporadic outcrops of marble and calc-silicate rocks. Occurrences of lapilli tuff are reported, namely from the structural footwall-stratigraphic hanging wall of the orebodies. This is the first unequivocal example of felsic volcanic rocks in the Montauban group. Proximal lapilli tuff and vesicular basaltic pillow lava occur with thinly bedded intermediate to felsic rocks interpreted as distal pyroclastic subaqueous fallout deposits, and laterally intercalated epiclastic sediments. Such volcanic rocks are consistent with deposition of the Montauban group in a shallow submarine environment at the late stage of an andesitic to felsic volcanic cycle, a common occurrence in mature island-arc or backarc settings where Au-rich volcanogenic sulphide deposits are formed.
In the Aguanish Complex of the eastern Grenville Province, foliation trajectories, along with the contacts between migmatized orthogneissic sheets, define kilometer-scale domes. We present a detailed structural analysis of three of these domes with an emphasis on the distribution of the principal stretching axes derived from conjugate flanking shear bands (melt-filled extensional shear bands). Noteworthy structural elements formed synchronously with the development of the domes are (1) maximum and minimum stretching axes are distributed tangentially along the envelopes of domes and radially toward the cores of domes, respectively; (2) a radial distribution of elongation lineations in the core of the...
The Barrow River bedrock geology map is the product of targeted mapping carried out during the summer of 2010, enhanced by radiometric age-dating as well as high-resolution aeromagnetic and radiometric surveys completed over previously published geological maps of the Paleoproterozoic Penrhyn Group and its Archean basement in southeastern Melville Peninsula, Nunavut. The high-resolution aeromagnetic survey was utilized to project lithological boundaries beneath Quaternary cover. The map shows complex basement-cover relationships characterized by multiple generations of thrusting and folding in a thick-skinned tectonic regime, followed by dextral transpression along the southern edge of the Penrhyn Group. A late-Archean tectonometamorphic event is recorded by ca. 2.55 Ga monazite in basement gneiss. Onset of rifting prior to deposition of the Penrhyn Group may be indicated by the emplacement of a bimodal suite of granite and leucogabbro-anorthosite at ca. 2.02 Ga. Penrhyn Group units are tentatively correlated with the Piling Group on Baffin Island.
The Central Gneiss Belt comprises parautochthonous gneisses overlain by northwest-transported allochthonous terranes originating from the pre-Grenvillian Laurentian margin or from farther outboard as inferred for the Parry Sound allochthon. In the Huntsville region, orthogneisses of the Algonquin allochthon yielded U-Pb zircon igneous crystallization ages at 1444 +12 -8 , 1442 +9 -8 , and 1432 +54 -98 Ma. In absence of direct evidence for older intrusions, the association of these plutonic rocks with gneisses giving Nd crustal residence ages of ca. 1.7 Ga sets the Algonquin allochthon apart from the underlying parautochthon, and from the overlying Muskoka allochthon. Orthogneisses from the latter also give zircon igneous ages at 1453 ± 6 Ma and 1427 +16 -13 Ma, with no older memory. These ages closely correspond to the Nd model ages of associated gneisses, testifying to the juvenile nature of this terrane. Plutonic ages from the Algonquin and Muskoka allochthons are older than those of the Parry Sound allochthon to the northwest, thereby confirming its exotic nature. The importance, distribution, and nature of 1475-1410 Ma plutonism down structural section from the juvenile Muskoka allochthon, via the more mature Algonquin allochthon, into the parautochthon and Grenville foreland, testify to the development of an ensialic arc along that part of the Laurentian margin tectonically incorporated in the Central Gneiss Belt. Furthermore, the age and structural relationship require Grenvillian break-back thrust reactivation to account for the high structural position of the Muskoka allochthon, which was part of the Laurentian ramp during overthrusting of the younger and farther travelled Parry Sound allochthon.
Aeromagnetic images of the northern Minto block show broad (40-100 km) positive anomalies divided by narrow (10-20 km) linear þtroughsþ. Reconnaissance mapping reveals supracrustal remnants within the troughs, separated by pyroxene-bearing granitoid massifs. Previous work in the þGoudalie trendþ documented the Vizien, Qalluviartuuq, and Duquet belts. To the east of the belts (80 km) is the 220-km long, segmented Pelican-Nantais belt of mafic, intermediate and felsic volcanic rocks and immature sedimentary rocks, metamorphosed at amphibolite and granulite facies. The map pattern of the central part of the Pelican-Nantais belt resembles a regional-scale sheath fold. Reconnaissance in the Faribault-Leridon belts, 75 km farther to the east, showed mainly mafic volcanic rocks, gabbro, and some peridotite, associated with quartz-rich sedimentary units. Plutonic units comprise variably pyroxene- or hornblende-biotite- bearing tonalite, granodiorite, and granite.
The Lake Minogami carbonate breccia (LMCB) exhibits field characteristics similar to those of a carbonatite diatreme, but a geochemical signature reflecting derivation from nearby marbles. The rocks display a very fine grained calcite matrix containing mechanically abraded rounded rock fragments. The breccia shows mineralogy and geochemistry distinct from carbonatites, namely a high SiO2 content (÷30%), low abundances of compatible and incompatible trace elements and limited REE fractionation. In addition, breccia samples show REE normalized patterns parallel to those of nearby tectonic marble and comparable 13C and 18O values. These features provide strong evidence for the derivation of the Lake Minogami carbonate breccia matrix by remobilization of a marble protolith. The presence of microfractures filled by calcite in both rock fragments and xenocrysts, rare subgrains and neoblasts around xenocrysts, as well as bent twins and kinks in matrix calcite provide additional support for a tectonic origin.
