Contrasting geology in the Pocologan River and Long Reach areas: implications for the New River belt and correlations in southern New Brunswick and Maine

Abstract

The Pocologan River and Long Reach areas are situated in the New River belt, which comprises the westernmost exposures of Neoproterozoic rocks in southern New Brunswick. Previous mapping in the southwestern part of the New River belt indicated that Neoproterozoic and Cambrian rocks in the Pocologan River area are different from coeval strata in the Caledonia belt (Avalon /one sensu stracto) in the Saint John area. Recent mapping in the Long Reach area has shown that there are significant lithological changes across the Robin Hood Lake fault, which bisects the New River belt into northeastern (Long Reach) and southwestern (Pocologan River) segments. Neoproterozoic and Cambrian rocks in the Long Reach area are directly comparable to those in the Caledonia belt, demonstrating that the New River belt is composite.
 
 Recent data have also shown that Early Cambrian volcanic activity in the Pocologan River area is broadly contemporaneous with epeirogenic events related to a major sequence boundary in the Avalonian cover sequence. This suggests that the northeastern and southwestern segments of the composite New River belt may have experienced a similar tectonic event, possibly as separate but adjacent continental fragments or as geographically isolated parts of one Gondwanan terrane. The lithological similarity of late Early to (?) Middle Cambrian quartzose sedimentary strata in the Pocologan River area to Middle Cambrian rocks in the St. Croix belt in Maine also supports the suggestion that the St. Croix belt is part of this composite terrane.
 
 RÉSUMÉ
 Les secteurs de la riviére Pocologan et de Long Reach sont situes dans la ceinture de New River, qui englobe les affleurements les plus à I'ouest des roches du Protérozoique supéricur du Sud du Nouveau-Brunswick. Des travaux de cartographic antérieurs dans Ie sud-ouest de la ceinture de New River ont révé;lé que les roches du Protérozoique supeérieur et du Cambrien du secteur de la riviére Pocologan constituaient des exemplaires uniques de stretcs contemporaines de la ceinture de Caledonia (zone d'Avalon au sens strict) dans la région de Saint-Jean. Des travaux de cartographic recents dans le secteur de Long Reach ont révélé des changements lithologiques marqués a travers la faille du lac Robin Hood, qui subdivise la ceinture de New River en deux segments : les segments nord-est (Long Reach) et sud-ouest (riviere Pocologan). Les roches du Protérozoique supérieur et du Cambrien du secteur de Long Reach sont directement comparable? à celles de la ceinture de Caledonia, ce qui démontre que la ceinture de New River constitue unc ceinture composite.
 
 Des donées récentes ont également rétvélé que I'activitié volcanique du Cambrien inférieur dans le secteur de la riviére Pocologan a en gros été contemporaine aux phénomenes épirogéniques apparentés à une Iimite de séquence importante dans la séquence de couverture avalonnienne. Cela laisse supposer que les segments nord-est et sud-ouest de la ceinture composite de New River pourraient avoir été soumis a un phénomene tectonique analogue, possiblement en tant que fragments continentaux distincts mais adjacents ou de parties géographiquement isolées d'un terrane du Gondwana. La similarity lithologique des strates seédimentaires quartzeuses de la fin du Cambrien précoce au Cambrien moyen (?) dans le secteur de la riviére Pocologan avec les roches du Cambrien moyen de la ceinture de St. Croix au Maine appuie par ailleurs l’hypothése que la ceinture de St. Croix fail partie de ce terrane composite.
 
 Traduit par la rédaction

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

“…The geology of the internally faulted New River terrane varies considerably along and across strike, as shown by Johnson and McLeod (1996), Johnson (2001), and Johnson et al (2009). Extensive surface exposures of New River basement rocks occur in three fault panels marked as A, B, and C on Figure 3.…”

“…3, 4). Thus, the Beulah Camp Formation appears to occur higher in the stratigraphic section than the Browns Flat Formation and to be Early Cambrian or possibly latest Neoproterozoic in age (McCutcheon 1981;Greenough et al 1985;Landing and Westrop 1996;Johnson 2001).…”

“…A rhyolitic tuff from Gorhams Bluff (Fig. 3) yielded a Neoproterozoic U-Pb zircon date of 554 ± 6 Ma (Johnson 2001;McLeod et al 2003), demonstrating that the Lobster Brook Formation is considerably younger than the Lingley Plutonic Suite with which it is in fault contact.…”

“…3) where, in the Long Reach area, they belong to the Lingley Plutonic Suite (Johnson 2001;Johnson and Barr 2004). The Lingley suite comprises granodiorite, tonalite, and quartz diorite along with red leucogranite and quartz-feldspar porphyry (Currie 1987;Johnson 2001).…”

“…3) where, in the Long Reach area, they belong to the Lingley Plutonic Suite (Johnson 2001;Johnson and Barr 2004). The Lingley suite comprises granodiorite, tonalite, and quartz diorite along with red leucogranite and quartz-feldspar porphyry (Currie 1987;Johnson 2001). Neoproterozoic U-Pb zircon dates of 625 ± 2 Ma and 629 ± 1.0 Ma have been obtained from the granodioritic and granitic phases, respectively (Currie and McNicoll 1999).…”