New U-Pb (zircon) age and geochemistry of the Wedgeport pluton, Meguma terrane, Nova Scotia

Abstract

A new U-Pb (zircon) age of 357 ±1 Ma for the Wedgeport pluton in the Meguma terrane of southwestern Nova Scotia confi rms that it is younger than other granitoid plutons of the Meguma terrane but not as young as the ca. 316 Ma age based on previous geochronological work. The pluton consists of mainly homogeneous biotite monzogranite characterized by abundant accessory phases including garnet, zircon, epidote, titanite, and ilmenite. Major minerals are quartz, plagioclase (albite-oligoclase), and perthitic microcline. The pluton has consistently high SiO 2 content (average ca. 75%) but shows some internal variation consistent with fractional crystallization of feldspar and biotite, together with accessory phases such as zircon. Tectonic setting during emplacement of the pluton was likely within plate, but classifi cation is ambiguous because the pluton has characteristics of all three granite types. Peraluminous composition and presence of ilmenite and aluminous minerals such as Fe-rich biotite and garnet suggest S-type affi nity, but other characteristics such as high-level emplacement, accessory fl uorite, and some chemical characteristics (high Ga/Al ratio, elevated Nb and Y) indicate A-type affi nity, whereas abundant titanite and overall chemical character is compatible with felsic I-type composition. The granite has specialized characteristics such as elevated Rb relative to Sr and Ba, and high U and Th compared to all of the average granite types. High ε Nd values (+2 to+3) indicate a relatively primitive source compared to other plutons of the Meguma terrane. The Wedgeport pluton appears to be unique in the Meguma terrane in both age and composition, although similar plutons may occur in inboard terranes of the Appalachian orogen. RÉSUMÉUne nouvelle datation au U-Pb (à partir de zircon) situant à environ 357 Ma le pluton de Wedgeport à l'intérieur du terrane de Meguma dans le Sud-Ouest de la Nouvelle-Écosse, confi rme qu'il est plus récent que les autres plutons granitiques du terrane de Meguma, mais qu'il a plus des 316 Ma qu'on lui avait attribués dans le cadre de travaux géochronologiques antérieurs. Le pluton est constitué de monzogranite à biotite principalement homogène caractérisé par des phases accessoires abondantes, notamment du grenat, du zircon, de l'épidote, de la titanite et de l'ilménite. Les principaux minéraux présents sont le quartz, le feldspath plagioclase (albite-oligoclase) et la microcline perthitique. Le pluton a une teneur constamment élevée en SiO 2 (en moyenne environ 75 %), mais il présente une certaine variation interne correspondant à une cristallisation fractionnée des feldspaths et de la biotite, ainsi que des phases accessoires, dont du zircon. L'intrusion du pluton est probablement survenue dans un cadre tectonique intra-plaque, mais sa classifi cation est ambiguë parce que le pluton possède des caractéristiques des trois types de granites. Sa composition hyperalumineuse et la présence d'ilménite et de minéraux alumineux, comme de la biotite riche en fer et du grenat, lais...

Nature and Origin of an LCT-Suite Pegmatite With Late-Stage Sodium Enrichment, Brazil Lake, Yarmouth County, Nova Scotia. Ii. Implications of Stable Isotopes ( 18o, d) for Magma Source, Internal Crystallization and Nature of Sodium Metasomatism

“…The age of the pegmatite contrasts with the timing of intrusive events in the region (see Fig. 1) at 440 Ma (Brenton pluton), 380-376 Ma (South Mountain Batholith) and 357-361 Ma (Wedge Port pluton) (Keppie & Krogh 2000, MacLean et al 2003, Kontak et al 2008. Thus, emplacement of the BLP corresponds to a period of magmatic quiescence in this part of the Meguma Terrane.…”

U-Pb tantalite, Re-Os molybdenite, and 40Ar/39Ar muscovite dating of the Brazil Lake pegmatite, Nova Scotia: a possible shear-zone related origin for an LCT-type pegmatite

“…Regarding the younger tantalite ages, we note the following relevant information: (1) the emplacement of the Wedgeport pluton at 357 Ma (MacLean et al 2003); (2) Moynihan (2003). Thus, the younger U-Pb tantalite ages may refl ect widespread hydrothermal activity previously undetected in this part of the Meguma terrane that relates to a widespread thermal and/or magmatic event.…”

“…In light of this observation, it is relevant to note that the Wedgeport pluton (Fig. 1), located south of the BLP, was re-dated recently using U-Pb zircon and yielded an age of 357 Ma (MacLean et al 2003). This pluton has A-type chemical affi nities and, most importantly, has spatially-related pegmatite and chalcophile-lithophile element mineralization.…”

“…Relevant to this study are the following: (1) 439 ± 4 Ma mafi c-felsic volcanic rocks of the White Rock Formation and the co-magmatic Brenton Pluton (U-Pb zircon; Keppie & Krogh 2000;MacDonald et al 2002); (2) Kontak et al 1995;Culshaw & Reynolds 1997); and (4) emplacement of the Wedgeport Pluton at 357 Ma (U-Pb zircon; MacLean et al 2003).…”

Field relations and petrology of the Trafalgar Plutonic Suite and comparisons with other Devonian granitoid plutons in the Meguma terrane, Nova Scotia, Canada

“…1), intruded the Meguma terrane at about 375-372 Ma. These mainly peraluminous plutons were strongly contaminated by abundant xenoliths and country rock assimilation, although the amount of contamination varies within individual plutons (e.g., MacLean et al 2003;Clarke 2007;Erdmann et al 2007Erdmann et al , 2009MacDonald and Clarke 2017). The granitic bodies were emplaced at moderate to shallow depths and were rapidly exhumed, forming narrow contact metamorphic aureoles surrounding the individual plutons (Mahoney 1996;Dostal et al 2006;Jamieson et al 2012).…”