The Prospect Rock thrust: western limit of the Taconian accretionary prism in the northern Green Mountain anticlinorium, Vermont

Abstract

This paper presents evidence for an early Taconian, west-directed fault in northern Vermont, the Prospect Rock thrust, which represents the trace of the contact between the Taconian oceanic accretionary prism (Dunnage Zone) and less allochthonous, continental margin rocks (Humber Zone). Mapping at 1 : 24 000 over the last decade has led to reassessment of units within the Camels Hump Group, resulting in newly defined lithotectonic packages: the Green Mountain slice and the Prospect Rock slice. Rocks in these slices may be of similar age, but those in the Green Mountain slice were originally deposited as more proximal sediments and remained on the Humber side of the sub duction zone, whereas those in the Prospect Rock slice were transferred by underplating to the accretionary prism. Both slices contain ultramafics. Motion on the Prospect Rock thrust (D1) preceded Taconian garnet-grade metamorphism and subsequent east-directed back-folding. However, D1 structures were diachronous across the orogen. Late Taconian (D2) structures record a change from east-verging back-folds in northern Vermont and southern Quebec to west-verging folds farther south. The Prospect Rock thrust does not correspond exactly to Cameron's line nor to the Baie Verte – Brompton line as originally defined. However, our understanding of the geometry of the Prospect Rock thrust demonstrates that the Dunnage Zone extends farther west than previously recognized and may also explain features farther to the east.

K–Ar age constraints on the evolution of polydeformed fold–thrust belts: The case of the Northern Appalachians (southern Quebec)

“…Such an interpretation is consistent with the extensional collapse model suggested by Pinet et al (1996a,b) to account for hinterland-directed motion in the southern Quebec Appalachians. From a regional perspective, similar hinterland-directed transport along back-thrust faults and downto-the-east normal faults that correlate chronologically with D 3 deformation in southern Quebec has been documented near the IHZ-EHZ boundary in Newfoundland (Waldron et al, 2003;Bradley, 2005) and New England (Thompson and Thompson, 2003).…”

Supra–subduction zone extensional magmatism in Vermont and adjacent Quebec: Implications for early Paleozoic Appalachian tectonics

“…The base of the Rowe-Hawley belt has been interpreted to be the Taconic-age Prospect Rock Fault (Fig. 2)-a west-directed thrust (Thompson et al, 1999;Thompson and Thompson, 2003). The Burgess Branch fault zone (Fig.…”

“…The northern Vermont RoweHawley belt consists primarily of metasedimentary and metaigneous rocks from the Ottauquechee, Stowe, Moretown (western and eastern members), and Cram Hill Formations (lithologic descriptions are given in Fig. 2 N above albite porphyroblast-bearing rocks of Hazens Notch ( Zhn) and Fayston ( Zf) --C C Formations (Thompson and Thompson, 2003) as well as the intervening Belvidere Mountain (ophiolitic) and Tillotson Peak (blueschistbearing) mafic complexes (Laird et al, 1984;Gale, 1986;Laird et al, 2001). The base of the Rowe-Hawley belt has been interpreted to be the Taconic-age Prospect Rock Fault (Fig.…”

The Ocean – Continent Transition Zones Along the Appalachian – Caledonian Margin of Laurentia: Examples of Large-Scale Hyperextension During the Opening of the Iapetus Ocean

“…8) are composed of albite-bearing schists (e.g. the non-graphitic Fayston Formation and the graphitic Hazens Notch Formation) and rare greenstone horizons (Thompson and Thompson 2003). The Hazens Notch and Ottauquechee formations also contain serpentinized ultramafic and talc -carbonate bodies.…”

“…The Hazens Notch and Ottauquechee formations also contain serpentinized ultramafic and talc -carbonate bodies. The Fayston, Hazens Notch and Ottauquechee formations are interpreted by Thompson and Thompson (2003) and Kim et al (2003) to represent metamorphosed rift clastics and slope-rise deposits spanning the Late Neoproterozoic to Cambrian Iapetan rift -drift transition, and are likely correlatives of the riftdrift facies exposed within the Sutton Mountains (Colpron et al 1994) and Notre Dame Mountains anticlinoria in southern Quebec. The geochemistry of the greenstones within the Green Mountain Slice and the Sutton Mountains anticlinorium suggests that they formed during rifting (Coish et al 1985;Colpron et al 1994).…”