Petrogenesis of the Elzevir batholith and related trondhjemitic intrusions in the grenville province of eastern Ontario, Canada

A newly recognized suite of trondhjemite-tonalite and dacitic gneiss forms a 10 krn wide belt of rocks within the Mount Holly Complex in the central part of the Green Mountain massif of Vermont. Field relationships and chemistry indicate that these gneisses are calc-alkaline, volcanic, and hypabyssal plutonic rocks older than the Middle Proterozoic regional deformation that affected the Mount Holly Complex. U-Pb zircon dates indicate ages as great as 1.35 Ga for crystallization of the volcanic protoliths and for intrusion of crosscutting trondhjemite. Tonalitic plutonism continued until 1.31 Ga.Map-scale contacts between the trondhjemitic-tonalitic4acitic gneisses and the paragneiss sequence of the Mount Holly Complex are sharp, suggesting that the volcanic rocks of the trondhjemite-tonalite suite underlie the paragneiss units and do not intrude them. These relationships suggest that the trondhjemite-tonalite suite is either considerably older than, and unconformable beneath, the paragneiss cover rocks or represents a volcanic edifice slightly older than the deposition of the sedimentary precursor to the paragneiss units. The paragneiss and tonalite-trondhjemite gneisses are both intruded by younger granitoids that were intruded at about 1.25 Ga during strong dynamothermal metamorphism.The trondhjemitic gneisses of the Mount Holly Complex of Vermont have high A1,0, and low Yb contents and light rareearth element enrichment patterns that are more characteristic of continental than oceanic volcanic arcs. The Mount Holly intrusives and volcanics may have formed during 1.35-1.31 Ga ensialic volcanic-arc activity, contemporaneous with ensimatic arc activity during the early part of the Elzevirian phase of the Grenville orogeny. In Vermont, later deformation and granite intrusion at about 1.25 Ga coincide with the major pulse of the Elzevirian orogeny and associated trondhjemitic plutonism in the Central Metasedimentary Belt of eastern Canada.Une skquence nouvellement indentifiCe de gneiss trondhjkmitique-tonalitique et dacitique forme une bande lithologique large de 10 km dans le complexe du Mount Holly, occupant la partie centrale du massif de Green Mountain, Vermont. Les recoupements sur le terrain et la gkochimie rkvelent que ce gneiss sont des roches calco-alcalines, volcaniques, plutoniques de semi-profondeur, plus vieilles que la dkformation rkgional qui a eu lieu au Protkrozolque moyen et qui a dkrangk le complexe du Mount Holly. L'Bge maximum de la cristallisation des protolithes volcaniques et de l'intrusion de la trondhjCmite recoupant le socle a Ctk ktabli par le chronomktre U-Pb sur zircon B 1,35 Ga. Le plutonisme tonalitique a eu lieu jusqu'h 1,31 Ga.Les contacts entre gneiss trondhjemitique-tonalitique-dacicitique et la sequence de paragneiss du complexe du Mount Holly, vus h 1'Cchelle de la cartographie gkologique, sont nets et ils indiquent que les roches volcaniques de la sequence de trondhjemite-tonalite sont sous-jacentes aux unitCs de paragneiss et ne les recoupent pas. Ces relations suggerent que ...

Section: Comparison With Calc-alkaline Plutons and Volcanic Rocks Of mentioning

confidence: 96%

Section: Comparison With Calc-alkaline Plutons and Volcanic Rocks Of mentioning

confidence: 97%

Trondhjemitic, 1.35–1.31 Ga gneisses of the Mount Holly Complex of Vermont: evidence for an Elzevirian event in the Grenville Basement of the United States Appalachians

Ratcliffe¹,

Aleinikoff²,

Burton³

et al. 1991

“…The Elzevir batholith is part of the early ca. 1240 Ma (Bell and Blenkinsop 1980;Silver and Lumbers 1966) suite of large, calc-alkalic, tonalite-granodiorite intrusions that includes the Weslemkoon, Northbrook, Cross Lake, and White Lake plutons (Pride and Moore 1983). The Elzevir was intruded into upper greenschist to amphibolite grade metabasalts of the Tudor Formation (Sethurarnen and Moore 1973).…”

Section: Geological Setting and Previous Geochronologymentioning

confidence: 98%

“…1) in the CMB of the Grenville Supergroup in eastern Ontario, in the eastern part of the Hastings Basin (Elzevir terrane), approximately 30 km east of the Thanet and Cordova gabbros studied by Berger and York (1981b) and by Lopez-Martinez and York (1983). The geology of the area has been studied in detail by Connelly (1985), Pride and Moore (1983), Moore and Thompson (1980), Carmichael et al (1978), Condie and Moore (1977), Brown et al (1975), Kamilli (1974), Sethuramen and Moore (1973), and Lumbers (1967,1964). The geochronology of the region has recently been sumrnarized by Easton (1986).…”

Section: Geological Setting and Previous Geochronologymentioning

confidence: 99%

An ⁴⁰Ar/³⁹Ar geochronological study of the Elzevir batholith and its bearing on the tectonothermal history of the southwestern Grenville Province, Canada

Hanes¹,

Clark²,

Archibald³

1988

Results of 40Ar/39~r step heating for muscovite, potassium feldspar, and plagioclase from the Ca. 1240 Ma Elzevir trondhjemite in the Central Metasedimentary Belt of the Canadian Grenville Province have been combined with earlier data and used to deduce a thermal history for the eastern Elzevir terrane following the Ottawan orogeny (1050-950 Ma). Muscovite yielded precise plateau dates of ca. 900 Ma, whereas the potassium feldspar displayed disturbed age spectra with Ca. 730-760 Ma dates for broad "plateau" regions. This age difference could be explained by slow cooling or by thermal overprinting at 760-800 Ma that has updated the microcline. The plagioclase spectra provide evidence for a low-temperature hydrothermal event Ca. 380 Ma ago that has generated sericite in saussurite and has caused partial argon loss from the microcline. This result agrees with the other plagioclase thermochronometry and paleomagnetism on the Cordova gabbro 25 km to the West but provides a lower estimate for the upper age bracket of this event. It is suggested that earlier models of protracted, post-700 Ma cooling of this part of the Grenville orogen may be a consequence of variable updating of plagioclase by this Devonian alteration event.Results of 40Ar/3yAr step heating for muscovite and microcline from the Bark Lake diorite in the Bancroft terrane are in agreement with earlier work in this area, and the cooling path of the Elzevir trondhjemite is seen to be indistinguishable, within the limitations of the method, from that of the Bark Lake diorite in the time period 1050-750 Ma.Les résultats des analyses de libération par paliers thermiques de 40Ar/3yAr pour la muscovite, le feldspath potassique et le plagioclase extraits de la trondhjémite d'Elzevir, âgée approximativement de 1240 Ma, de la ceinture métasédimentaire centrale de la province de Grenville, Canada, ont été combinés à d'autres données disponibles et utilisés pour reconstituer l'histoire thermique de l'est du terrane d'Elzevir après l'orogenèse de I'Ottawien (1050-950 Ma). La muscovite a fourni des âges-plateaux bien définis autour de 900 Ma, tandis que le feldspath potassique offrait des spectres d'âges 730-760 Ma calculés sur les parties larges des plateaux. La différence entre ces âges peut s'expliquer par un refroidissement lent ou une surimpression thermique à 760-780 Ma qui aurait rajeuni le microcline. Les spectres du plagioclase fournissent des indices d'un événement hydrothermal de basse température datant d'il y a environ 380 Ma et qui a produit la séricite au sein de la saussurite et provoqué la fuite partielle de l'argon du microcline. Ces résultats s'accordent bien avec les données thermochronométriques et paléomagnétiques des plagioclases obtenues pour le gabbro de Cordova situé à 25 km plus à l'ouest, cependant ils donnent une évaluation plus basse à la limite supérieure de la fourchette des âges correspondant à cet événement. Nous croyons, selon les modèles antérieurs d'un refroidissement prolongé, postérieur à 700 Ma, que cette partie de l'orogenèse de...

“…4a) (Easton 1986;Windley 1986). The arc, now situated on the leading edge of the plate, was intruded by the calc-alkaline Elzevir batholith, which has trace-element patterns similar to those of batholiths in modern Andean-type continental margins (Pride and Moore 1983). The 1120-1039 Ma Ottawan Orogeny (Easton 1986, Fig.…”

Section: I the Grenville Orogenic Beltmentioning

confidence: 98%

Anorogenic magmatism and the Grenvillian Orogeny

Windley¹

1989

The Grenvillian Orogeny was preceded by extensive anorogenic volcanism and plutonism in the period 1500–1300 Ma in the form of rhyolites, epizonal granites, anorthosites, gabbros, alkaline complexes, and basic dykes. An analogue for the mid-Proterozoic anorogenic complexes is provided by the 2000 km by 200 km belt of anorogenic complexes in the Hoggar, Niger, and Nigeria, which contain anorthosites, gabbros, and peralkaline granites and were generated in a Cambrian to Jurassic rift that farther south led to the formation of the South Atlantic. An analogue for the 1 × 106 km2 area of 1500–1350 Ma rhyolites (and associated epizonal granites) that underlie the mid-continental United States is provided by the 1.7 × 106 km2 area of Jurassic Tobifera rhyolites in Argentina, which were extruded on the stretched continental margin of South America immediately preceding the opening of the South Atlantic. The mid-Proterozoic complexes were intruded close to the continental margin of the Grenvillian ocean and were commonly superimposed by the craton-directed thrusts that characterized the final stages of the Grenvillian Orogeny. The bulk of the Keweenawan rift and associated anorogenic magmatism formed about 1100 Ma at the same time as the Ottawan Orogeny in Ontario, which probably resulted from the collision of the island arc of the Central Metasedimentary Belt attached to the continental block in the east with the continental block to the west. The most appropriate modern equivalent would be the Rhine Graben, which formed at the same time as the main Alpine compression.