TECTONIC EVOLUTION OF THE ROWE-HAWLEY BELT IN CENTRAL AND NORTHERN VERMONT

The Pre-Silurian Rowe-Hawley Belt (RHB) in central and northern VT is a tectonic assemblage of continental margin, oceanic, and suprasubduction zone rocks that were juxtaposed during the Ordovician Taconian Orogeny and also deformed and metmorphosed by the Devonian Acadian Orogeny. The RHB is bounded by the Green Mt. Belt (west) and to the Conn. Valley Belt (east). The RHB correlates with the Dunnage and eastern Internal Humber zones of S. Quebec. Recent bedrock geologic maps of the RHB provide a detailed framework to integrate petrological and geochemical data with.

We divided the RHB into fault-bounded lithotectonic slices that lie at different structural levels. From structurally lowest (west) to structurally highest (east) these slices are: 1) Belvidere Mt. (ophiolitic) and Tillotson Peak (blueschist) complexes, 2) Prospect Rock Slice, 3) Hyde Park Slice, 4) Mt. Norris Slice (MNS), 5) Worcester Mt. Complex, and 6) Moretown Fm. Slice (separable into Dumpling Hill and Wrightsville slices in central VT).

Although Taconian F1 and F2 folds are both isoclinal, F2 folds are reclined. F3 and F4 Acadian folds are gently plunging open- tight asymmetric folds with axial planar crenulation cleavages; F5 folds are open folds.

Trace and REE geochemistry indicates that mafic rocks in the RHB formed in incipient MORB (Type 1), late rift (Type 2), rift (Type 3) or suprasubduction zone extensional basin (Type 4) tectonic settings. The western RHB is dominantly composed of types 1 and 2 whereas Type 4 comprise the eastern RHB and MNS; Type 3 are of limited extent.

Laird et al. (1984; 1993) determined that increases in the NaSiCa-1Al-1 (PL) substitution in amphibole and plagioclase and the Al2Mg-1Si-1 (TK) substitution in amphibole and chlorite were proxies for respective metamorphic pressure and temperature increases. PL and TK values derived from the cores and rims of amphiboles from mafic rocks were grouped into Pressure Facies. The western RHB slices are dominantly med-high P whereas the Moretown Fm. slices are low P.

We conclude that: A) western RHB slices formed in a late rift-incipient MORB tectonic setting and were metamorphosed at med-high to high P, B) eastern RHB and MNS slices have a suprasubduction zone extensional basin origin and were metamorphosed at low P, C) there is a suture between the western and eastern RHB.