Some Aspects of the Pre-Carboniferous Geology of Saint John, New Brunswick

Field relations, petrography, and age of plutonic units in the Saint John area of southern New Brunswick

“…On the basis of Rb-Sr and U-Pb data, Olszewski and Gaudette (1982) concluded that the Brookville Gneiss is older than a postulated 800 Ma metamorphic and plutonic event (represented by the Golden Grove Suite). Currie et al (1981) and many subsequent workers (e.g., Currie, 1987;Nance, 1987) interpreted the gneiss to represent the continental basement upon which the overlying Green Head Group accumulated. However, recent U-Pb dates from the orthogneissic and paragneissic components of the Brookville Gneiss indicate a Late Precambrian protolith age (White et al, 1990a, b;Bevier et al, 1990), much younger than the Middle Riphean (Neohelikian) age proposed by Hofmann (1974) for the Green Head Group on the basis of stromatolites.…”

“…Diffuse leucogranitic areas within the Brookville paragneiss, as described by Currie et al (1981), may represent leucosomes produced during high-grade metamorphism of the Brookville Gneiss. It seems doubtful that the discordant zircon age of 465 Ma for one of these granitic areas (Olszewski et al, 1980;Currie et al, 1981) is significant.…”

“…However, they also suggested that the plutonic rocks may be as young as Devonian. They assigned names to many of the individ ual plutons in their Golden Grove Intrusives, terminology subse quently adopted with various modifications by later workers (Wardle, 1978;Ruitenberg et al, 1979;Currie et al, 1981;Deveau, 1989). Alcock (1938) upgraded the Green Head Formation to group status.…”

“…Based on results of K-Ar and Rb-Sr dating by numerous workers, Ruitenberg et al (1979) concluded that the plutons associated with the Green Head Group range in age from Late Precambrian to Early Paleozoic whereas intrusive rocks in the Coldbrook Group are Early Ordovician. Currie et al (1981) used the term Brookville Gneiss to refer to all gneisses in the Saint John area and interpreted the gneisses to be Archean basement, reactivated and diapirically emplaced into the Green Head Group during the intrusion of the Golden Grove Suite. Currie et al (1981) also described the plutons of the Golden Grove Suite, modifying the units of Hayes and Howell (1937) and introducing some new pluton names (see below).…”

“…Currie et al (1981) used the term Brookville Gneiss to refer to all gneisses in the Saint John area and interpreted the gneisses to be Archean basement, reactivated and diapirically emplaced into the Green Head Group during the intrusion of the Golden Grove Suite. Currie et al (1981) also described the plutons of the Golden Grove Suite, modifying the units of Hayes and Howell (1937) and introducing some new pluton names (see below). On the basis of Rb-Sr and U-Pb data, Olszewski and Gaudette (1982) concluded that the Brookville Gneiss is older than a postulated 800 Ma metamorphic and plutonic event (represented by the Golden Grove Suite).…”