THE SURRY COMPLEX (SURRY SLURRY): ROOT ZONE OF THE PENOBSCOT OROGEN?

Exposures along the Gulf of Maine bear critically on the tectonic evolution of the Gondwanan margin of Iapetus, especially because relationships between the Gander and Avalon Zones in Newfoundland are obscured by the post-Ordovician Dover Fault. In the Ellsworth terrane, ductilely-deformed schists locally enclose meter-scale to kilometer-scale competent blocks of volcanic and ultramafic rocks. Here, the Surry complex refers to a structural complex that extends between North Haven Island and Ellsworth and comprises lithodemic units such as the Ellsworth Schist, Serpentinite of Deer Isle, North Haven Greenstone, and, perhaps, the Castine Volcanics. The Serpentinite of Deer Isle has a harzburgite protolith, contains elongated and pulled-apart orthopyroxenes, and represents a slice of upper mantle; its margins are highly sheared, and adjacent rocks include foliated gabbro, mafic pillow breccia, and felsic and mafic tuffs. Deformation of the complex is highly heterogeneous; locally, the main fabric of the Ellsworth Schist indicates top-to-the northwest thrusting. Ellsworth Schist is overlain by Castine Volcanics via presumed angular unconformity, and North Haven Greenstone is overlain by fossiliferous shallow-marine sediments of Llandovery age. Felsic volcanic units in the complex have yielded Cambrian ages. North of Ellsworth and at the head of Morgan Bay, quartz-rich metasediments, previously included in the Ellsworth Schist, resemble lithologies of the Gander Zone. Whether or not the Deer Isle serpentinite was partially exhumed during an early extensional phase related to back-arc rifting, its present occurrence implies an Early Paleozoic subduction zone. The Surry complex may correlate with the GRUB line and related rocks that structurally overlie the Gander Zone of central Newfoundland. We propose that the Penobscot unconformity at its type locality (Shin Brook, northern Maine) may record the far-field loading effect of plate convergence near the Gondwanan margin, i.e., northwest-directed allochthons rooted in the Surry complex.