Geochemistry and U–Pb zircon age of comenditic metafelsites of the Tibbit Hill Formation, Quebec Appalachians

Abstract

Metafelsites in Waterloo area, Quebec, represent the only known silicic volcanic rocks in the predominantly basaltic Tibbit Hill Formation. Low-grade metamorphism accompanied by hydration and albitization has converted the felsic volcanic rocks mainly to muscovite–quartz–albite schists. The volcanic parent of these metafelsites was formed partly as lava flows and partly as tuffs. The principal compositional type was a comendite. A component of intermediate rocks is also present but its extent is undetermined and probably minor. U–Pb zircon studies of the metafelsites have yielded a reliable age of [Formula: see text]. This Early Cambrian age is probably representative of the age of the Tibbit Hill Formation as a whole.The Tibbit Hill Formation accumulated at one of the clearest examples of a RRR (rift–rift–rift) triple junction–the Sutton Mountains triple junction–of the continental rift system formed as a prelude to the opening of the Iapetus Ocean. Its volcanic rocks are products of the youngest major episode of rift-related volcanism known from the continental margin of Laurentia. The volcanic event may have occurred as a harbinger of the onset of sea-floor spreading at the Sutton Mountains triple junction.

Paleozoic orogens in New England, USA

“…These include the Tibbitt Hill Greenstones (Kumarapeli 1976;Kumarapeli et al 1981Kumarapeli et al , 1989Doolan et al 1982;Coish et al 1985;Ratcliffe 1987) exposed in northern Vermont and southern Quebec, for which a U-Pb zircon age of 554 Ma has been obtained on an interbedded felsite (Kumarapeli et al 1989). The rift setting is suggested by a large positive gravity anomaly, supposedly reflecting an ancient triple junction in a location just southeast of Montreal, in which the Ottawa-Bon-nechere graben would correspond to the failed arm.…”

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

“…However, rift-related magmatism continued throughout the northern Appalachians for another 20 my (to ca. 550 Ma; Kumarapeli et al 1989;Bédard and Stevenson 1999;Hodych and Cox 2007;Burton and Southworth 2010, and references therein) and the thermal subsidence of Laurentia's (para)autochthonous rifted margin took place at least 40-50 my later (525-520 Ma; Bond et al 1984;Williams and Hiscott 1987;Waldron and van Staal 2001;Hibbard et al 2007). The apparent conflict between paleomagnetic and geological data posed a major conundrum and called into question models of late Neoproterozoic opening of Iapetus.…”

A Mechanism for Tectonic Inheritance at Transform Faults of the Iapetan Margin of Laurentia

“…Southwest of the Missisquoi transform in the southwesternmost part of the Quebec embayment, alluvial deposits (Pinnacle Formation), as much as 3.5 km thick, are locally interlayered with metabasalt (554 +4/-2 Ma, Tibbit Hill Formation) (Coish et al 1985;Kumarapeli et al 1989;Cherichetti et al 1998). The synrift deposits thin southward away from the transform along the rifted margin and are interlayered locally with volcanic rocks (571 ± 5 Ma, Pinney Hollow Formation) (Stanley and Ratcliffe 1985;Rankin et al 1989;Walsh and Aleinikoff 1999).…”

“…Abrupt along-strike variations in shelf and slope stratigraphy in western Newfoundland indicate that the rift margin on the St. Lawrence promontory was segmented by trans- (Fokin 2003;Tollo et al 2004), SO-Southern Oklahoma volcanic-plutonic complex (Wright et al 1996;Hanson et al 2009Hanson et al , 2013bThomas et al 2012), SR-Striped Rock pluton (Essex 1992), SV-Stewartsville pluton (Fokin 2003), TH-Tibbit Hill metavolcanics (Kumarapeli et al 1989), WO-White Oak Creek pluton (Fokin 2003).…”