Geology and U-Pb geochronology of the Annidale Group, southern New Brunswick: Lower Ordovician volcanic and sedimentary rocks formed near the southeastern margin of lapetus Ocean

Abstract

Geological mapping and U-Pb (zircon) dating have led to the discovery of distinctive Lower Ordovician volcano-sedimentary rocks in the Annidale area of southern New Brunswick. These rocks are included in a newly defined group, herein termed the Annidale Group, which is divided into three fault bounded(?) units of partially overlapping age. These units are named the East Scotch Settlement Formation, the Lawson Brook Formation and the Canaan Forks sequence, from south to north. The East Scotch Settlement Formation contains a steeply dipping succession of mixed mafic and felsic volcanic rocks and a variety of clastic and volcanogenic sedimentary rocks. The Lawson Brook Formation constitutes a shallowly to moderately north-dipping succession dominated by felsic volcanic rocks. The Canaan Forks sequence, most of which constitutes a shallowly to moderately north-dipping succession, is dominated by clastic sedimentary rocks. Structurally, much of the Annidale Group is characterized by intense shearing produced by numerous vertical northeast- and northwest-trending faults and by southward- and northward-directed thrust faults. In the vicinity of these structural features, the East Scotch Settlement Formation is further characterized by pervasive carbonatization that is commonly accompanied by base-metal- and gold-bearing silicification and high chromium-mica alteration zones.
 
 Zircons from a felsic dome in the East Scotch Settlement Formation and from felsic schists in the Lawson Brook Formation yield U-Pb dates of 493 ± 2 Ma and 497 ±10 Ma, respectively. Based on these dates and constituent lithologies, the Annidale Group is tentatively correlated with parts of the Cookson Group to the southwest.
 
 RÉSUMÉ
 La cartographie géologique et les datations U-Pb sur les zircons ont mené à la découverte de roches volcaniques et sédimentaires distinctives, de l’Ordovicien intérieur, dans la région d 'Annidale du sud du Nouveau-Brunswick. Ces roches sont comprises dans un Groupe nouvellement défini, nommé ici le Group d'Annidale, qui est divisé en trois unités possiblement bordées par des failles et dont les âges se recouvrent partiellement. Ces unités sont nommées, du nord au sud: la Formation de East Scotch Settlement, la Formation du Ruisseau Lawson et la séquence de Can nan Forks. La Formation de East Scotch Settlement contient une succession à pendage abrupt de volcanites mafiques et felsiques et un assemblage varié de roches sédimentaires clastiques et volcanogènes. La Formation du Ruisseau Lawson consiste en une succession à pendage faible ou modéré vers le nord dominée par les volcanites felsiques. La séquence de Cannan Forks, dont la majeure partie est une succession à pendage faible ou modéré vers le nord, est dominée par les roches sédimentaires clastiques. Structuralement, une bonne partie du Groupe d'Annidale est caractérisée par un cisaillcment intense produit par de nombreuses failles verticales nord et nord-est et par des failles de chevauchement vers le sud et le nord. A proximité de ces failles, la Formation de East Scotch Settlement est caractérisée par une carbonatation intense qui est commundment accompagnée par une silicification porteuse de métaux de base et d'or et de zones d'altération à mica chromifere.
 
 Les zircons d'un dome felsique dans la Formation de East Scotch Settlement et de schistes felsiques dans la Formation du Ruisseau Lawson ont donné des âges U-Pb de 493 ± 2 Ma et 497 ± 10 Ma, respectivement. Sur la base de ces datations et de similarity lithologiques, le Groupe d'Annidale est tentativement corré1é avec des parties du Groupes de Cookson, situé au sud-ouest.
 
 [Traduit par le journal]

A Review of Proterozoic to Early Paleozoic Lithotectonic Terranes in New Brunswick, Canada and their Tectonic Evolution during Penobscot, Taconic, Salinic and Acadian Orogenesis

“…First predicted by Fyffe and Fricker (1987), the widespread occurrence of Cambrian to Lower Ordovician volcanic rocks in southern New Brunswick has now been confirmed by mapping and follow-up radiometric dating (McLeod et al 1992;Johnson and McLeod 1996;Johnson et al 2009). Remnants of this Penobscot arc-backarc system can now be traced with confidence for some 300 km from the Penobscot Bay area of coastal Maine to the Belleisle Bay area in New Brunswick (Fig.…”

“…They consist of a thick succession of dominantly pillowed mafic flows, black shale, and greyish green siltstone that have been intruded by massive, grey to black, flow-banded, feldspar-phyric, subvolcanic felsic domes ). These volcanic domes bear a striking resemblance to those in the Middle Cambrian Castine Volcanics (504 ± 3 Ma) of coastal Maine, but a U-Pb zircon date on one of the Lawson Brook domes yielded a younger Late Cambrian age of 493 ± 2 Ma (McLeod et al 1992;Ruitenberg et al 1993). Highly strained schistose felsic and mafic rocks, which are thought to represent a deep structural level of the Lawson Brook Formation, are exposed farther north in a small inlier surrounded by Carboniferous strata.…”

“…Highly strained schistose felsic and mafic rocks, which are thought to represent a deep structural level of the Lawson Brook Formation, are exposed farther north in a small inlier surrounded by Carboniferous strata. Felsic rocks within this highly strained unit yielded igneous zircons that gave a U-Pb date of 497 ± 10 Ma (McLeod et al 1992) and an 40Ar/39Ar date of 444 ± 5 Ma on metamorphic muscovite ).…”

“…Since 1990, in particular, a large amount of new stratigraphic, geochemical, geochronological, and structural data have been collected by van Staal and co-workers at the Geological Survey of Canada; Sandra Barr and students at Acadia University; Damian Nance at Ohio University; and staff of the Geological Surveys Branch at the New Brunswick Department of Natural Resources. This work involved detailed mapping of dozens of quadrangles throughout southern New Brunswick (Fyffe and Riva 1990;McLeod et al 1992McLeod et al , 2001McLeod 1995McLeod , 1997White 1996a, b, 1999;Johnson and McLeod 1996;White and Barr 1996;Currie and McNicoll 1999;Fyffe et al 1999;Fyffe 2001Fyffe , 2005Fyffe and Grant 2001;Barr et al 2002) and northern New Brunswick (Wilson 1990(Wilson , 2000(Wilson , 2002van Staal and Fyffe 1995;van Staal et al 2003;.…”

Archived U-Pb (zircon) dates from southern New Brunswick

“…Some of the U-Pb dates and related analytical data have been published in their entirety (McLeod et al 1992;Ruitenberg et al 1993), whereas others have been incompletely published as isochron diagrams (Johnson and McLeod 1996) or quoted as personal communications. The purpose of this paper is to present all dates and data for those not yet published in their entirety.…”