A reinterpretation of the stratigraphy and deformation of the Aillik Group, Makkovik, Labrador

摘要

The Aillik Group of Aphebian volcanic and sedimentary rocks is situated in the Makkovik Sub-province of Labrador, north of the Grenville Front. Its lithology, in the vicinity of Makkovik, has been completely reinterpreted and the first formal stratigraphic subdivision of the group defined, with introduction of new names. The previously unrecognised sequence of deformational events and associated metamorphism has been delineated. -- The 8500 m. (25,000 ft.) thick Aillik Group consists of cratogenic flow-banded and porphyritic rhyolite lava's, (previously mapped as quartzites), minor interbedded basalt lavas, polymictic and rhyolite conglomerates,and quartz-poor arkoses (also previously mapped as quartzites). The group is subdivided into six formations. The lowest (Nesbit Harbour Formation), comprising 800 m. to 2000 m. (2400 - 6000 ft.) of conglomerate with minor arkoses and basalt lavas, is conformably overlain by the Makkovik Formation of 2000 m. to 7000 m. (6000 - 21,000 ft.) of rhyolite lavas, with minor tuffs, conglomerates and arkoses. This is conformably overlain by two stratigraphically equivalent (?) formations:- the 2000 m. (6000 ft.) thick Pomiadluk Formation of interbedded rhyolite, conglomerate and tuff in the northeast; and the 2000 m. (6000 ft.) thick Manak Bay Formation of arkose and minor basalt lava in the southeast. -- West of this sequence, and separated from it by a major tectonic slide (and the associated, structurally defined, Ranger Bight complex of amphibolites), is the 3000 m. (9000 ft.) thick Big Island Formation of interbedded rhyolite, arkose, conglomerate and basalt lava. -- The Aillik Group is intruded by several major syntectonic granitic to gabbroic plutons including a large, rhymically layered, hornblende gabbro (appinite?) intrusion, the Adlavik Igneous Complex. -- Four deformations are recognised, of which the second produced penetrative fabrics and large, upright, northeast trending, folds. The others developed only local structures and fabrics, and one major interference dome. The second deformation resulted in different amounts (r = 1 to 5) and types (k = 1 to oo ) of strain, (which is not lithologically controlled), in different areas. The entire area is shown to possibly occur within a major zone of strike-slip (simple-shear) movement. -- Metamorphism has remained in the amphibolite and greenschist facies throughout tectonism. -- The Aillik Group is unconformably overlain by the Jurassic Ford's Bight Conglomerate.