Gravity and magnetic anomalies of the Sutton Mountains region, Quebec and Vermont: expressions of rift volcanics related to the opening of Iapetus

Abstract

Prominent, nearly coincident, positive gravity and magnetic anomalies occur in the Sutton Mountains region, centered about 100 km east of Montreal, Quebec. Several lines of evidence indicate that the gravity anomaly stems from two principal sources: a deep (mid and lower crustal) source of speculative origin and a shallow source identifiable with a narrow belt of late Precambrian -early Cambrian metavolcanic rocks, the Tibbit Hill volcanics. The magnetic anomaly seems to be produced mainly by the metavolcanic rocks. Three-dimensional modelling of a residual gravity anomaly, supplemented by two-dimensional modelling of the magnetic anomaly, shows that the seemingly minor belt of metavolcanic rocks constitutes the surface expression of a thick (maximum thickness -8 km) pile of dominantly mafic volcanics, which are only slightly exposed at the present level of erosion.The Tibbit Hill volcanics are regarded as products of rift-related volcanism that occurred at an rrr triple junction developed during the early stages of the opening of the Iapetus Ocean. The Ottawa graben is probably the failed of this triple junction. The emplacement of the Grenville dike swarm whose trend is nearly coincident with that of the Ottawa graben was probably coeval with the volcanism in the Sutton Mountains region. The present work shows that the volcanism in the region was on a much larger scale than hitherto recognized.On observe des anomalies prokminentes, presque coincidentes, de gravitC positive et de magnCtisme dans la rtgion des monts Sutton, dont le centre se situe a environ 100km a l'est de MontrCal au QuCbec. Plusieurs lignes d'kvidence indiquent que I'anomalie de gravitC provient de deux sources principales; une source profonde (partie mtdiane ou profonde de la create) d'origine incertaine et une source peu profonde qu'on identifie a une zone Ctroite de roches mCtavolcaniques, les volcaniques de Tibbit Hill, datant de la fin du PrCcambrien au debut du Cambrien. L'anomalie magnetique semble provenir surtout des roches mCtavolcaniques. Un modkle en trois dimensions d'une anomalie de gravitC rtsiduelle, complCtt par un modkle en deux dimensions de I'anomalie magnetique, montre que la zone apparemment nCgligeable des roches mCtavolcaniques constitue I'expression en surface d'un empilement Cpais (maximum de 8 km environ) de roches volcaniques surtout mafiques qui n'est que trks legkrement expos6 au niveau actuel d'trosion.

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.…”

Geochemistry and petrogenesis of the Tibbit Hill metavolcanic suite of the Appalachian fold belt, Quebec-Vermont; a plume-related and fractionated assemblage

“…The relatively narrow (less than 10 km) belt of THF outcrop areas shown in figure 1 represents inliers of the THF exposed at structural culminations of a major anticlinal axis. That these seemingly minor outcrop areas are merely the surface expression of a large volcanic mass, about 250 km long, up to 45 km wide and up to 8 km thick, has been demonstrated by analysis of the associated gravity and magnetic anomalies (Kumarapeli, Goodacre, and Thomas, 1981). The triangular-shaped area which represents the subsurface extension of the Tibbit Hill volcanic mass occurs in the apical area of the Sutton Mountains salient ( fig.…”

“…This has led to the suggestion that the Tibbit Hill volcanism took place just before the onset of seafloor spreading and not during rift initiation some 35 Ma earlier (Kamo, Krogh, and Kumarapeli, 1995). Secondly, it is the clearest example of eruption at an RRR (rift-rift-rift) triple junction (the Sutton Mountains triple junction) in a setting similar to that of the Afar triangle (Kumarapeli, Goodacre, and Thomas, 1981). The rifting event took place as a prelude to the opening of the Iapetus ocean.…”

U-Pb zircon age of metafelsite from the Pinney Hollow Formation; implications for the development of the Vermont Appalachians

“…Considering the chemical overlap between zones 2 and 3 and the lack of ages from zones 1 and 4, it is difficult to establish conclusively the complete temporal span of rifting with only the 554 and 571 Ma ages. The ϩ54 mGal gravity anomaly associated with the Tibbit Hill suggests that it is one of the largest masses of rift volcanic rock in the Appalachians (Kumarapeli, Goodacre, and Thomas, 1981). It is still possible that rocks older than 554 Ma exist at the unexposed depths of the Tibbit Hill, and that rocks younger than 571 Ma exist in the Pinney Hollow.…”