U–Pb geochronologic constraints on the crustal evolution of the Long Range Inlier, Newfoundland

Abstract

The Long Range Mountains of Newfoundland expose the northeastern most basement inlier of the Appalachian Orogen. U-Pb results for two samples of basement gneiss reveal crustal formation ages of 1466 ± 10 Ma (Western Brook Pond charnockite) and 1530 ± 8 Ma (Cat Arm Road gneiss), indicating an affinity with Pinwarian magmatism (1510-1450 Ma) in Labrador. A third sample of basement gneiss from the Cat Arm Road dam site yielded a minimum formation age of 1631 Ma. These basement gneisses were intruded by granite plutons during two periods of Grenvillian magmatism; Group I at 1032-1022 Ma and Group II at 993-985 Ma. Group I intrusions include the 1032.0 ± 1.5 Ma Lomond River granite and the 1022.0 ± 2.0 Ma Lake Michel igneous suite; Group II intrusions include the 999 ± 4 Ma Potato Hill charnockite, 993 ± 7 Ma Horse Chops granite, 984.9 ± 1.6 Ma Cloud River granite, and may include the Apsy granite. The metamorphic history of the Long Range Inlier is complex and three discrete Proterozoic metamorphic events can be delineated on the basis of field relationships and U-Pb dates for metamorphic minerals. M 1 metamorphism is a regional high-grade event that occurred prior to 1032 Ma, the emplacement age for the unmetamorphosed Lomond River granite. M 2 and M 3 occurred at 1022 and 989 Ma, respectively; coinciding with the two main periods of Grenvillian magmatism. The Precambrian crustal evolution of the Long Range Inlier is very similar to the Pinware terrane of Labrador, consistent with a single contiguous terrane presently separated by the Gulf of St. Lawrence. A surprising discovery from this study is identification of the first known occurrence of Silurian mafic magmatism in the Long Range Inlier, the 430.5 ± 2.5 Ma Taylor Brook gabbro.

Evidence of Late Ediacaran Hyperextension of the Laurentian Iapetan Margin in the Birchy Complex, Baie Verte Peninsula, Northwest Newfoundland: Implications for the Opening of Iapetus, Formation of Peri-Laurentian Microcontinents and Taconic – Grampian Orogenesis

“…In general, most of the detrital zircons analyzed (Fig. 6G) yield Mesoproterozoic ages (1.0 -1.5 Ga), and display a prominent Grenvillian peak typical of the Laurentian basement widely exposed in the Grenville province of southern Labrador and unconformably underlying parts of the Humber margin in western Newfoundland (Heaman et al 2002;Gower et al 2008). Smaller Paleoproterozoic (1.8 -2.0 Ga) and Neoarchean (2.4 -3.0 Ga) peaks are also consistent with a proximal Laurentian provenance.…”

The timing of gold mineralization in White Bay, western Newfoundland: Evidence from 40Ar/39Ar studies of mafic dykes that predate and postdate mineralization

“…The porphyritic granodiorite host rock subsequently gave an imprecise U-Pb zircon age (lower intercept) of 1006 ± 82 Ma (Heaman et al 2003). Kerr et al (2006) attempted to date the gold mineralization directly using Re-Os isotopic analysis of pyrite and arsenopyrite.…”

“…The Sops Arm Group is mostly in fault contact with older rocks, but an unconformable relationship to trondhjemite of the Southern White Bay Allochthon is preserved in one location. Silurian and older rocks are intruded by granitoid rocks of the Gull Lake Intrusive Suite (398 + 27/-7 Ma; Erdmer 1986) and the Devils Room granite (425 ± 10 Ma; Heaman et al 2003). Carboniferous sedimentary rocks unconformably overlie all of the older rocks, including granite of the Gull Lake Intrusive Suite.…”

“…1500 and ca. 980 Ma (Heaman et al 2003). These rocks are cut by the late Precambrian Long Range mafic dykes (ca.…”

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

“…A measured amount of 205 205 Pb/ 235 235 U tracer solution was added to the acid mixture in each vessel prior to digestion. Purifi cation of Pb and U from the dissolved tantalite fragments was accomplished using anion exchange chromatography with an HBr/HCl procedure similar to that reported for Fe-bearing minerals such as titanite or rutile (e.g., Heaman et al 2002). The purifi ed uranium and lead aliquots were loaded together onto out-gassed Re fi laments in a mixture of phosphoric acid and silica gel.…”