Early to Middle Devonian granitic and volcanic rocks from the central Gulf of Maine

• Published in: Lithos 2011-10, Vol.126 (3), p.455-465
• Main Authors: Barr, Sandra M., Mortensen, James K., Thompson, Margaret D., Hermes, O. Don, White, Chris E.
• Format: Article
• Language: English
• Subjects: Alkali feldspar granite; Alkaline rocks; Avalonia; Gulf of Maine; Syenogranite
• ISSN: 0024-4937; 1872-6143
• DOI: 10.1016/j.lithos.2011.06.009

Cashes Ledge igneous suite in the central Gulf of Maine is represented by 10 granitic and two felsic tuff samples collected from bedrock outcrops using the submersible Alvin in 1971–1972 and archived at the Woods Hole Oceanographic Institute. Laser ablation ICP-MS analyses of zircon grains yielded crystallization ages of 414.9 ± 1.1 Ma and 399.7 ± 1.5 Ma for two alkali feldspar granite samples, 407.0 ± 1.9 Ma for a syenogranite sample, and 384.4 ± 2.3 Ma and 383.9 ± 1.6 Ma for two felsic tuff samples. The samples contain iron-rich mafic minerals, including aegirine-augite, grunerite/ferroedenite, and annite. Most of the samples are alkaline to slightly peralkaline, with high concentrations of SiO 2, Y, Zr, Nb, and REE, strong negative Eu anomalies, and positive epsilon Nd values (1.8 to 3.7). The suite resembles part of a belt of similar Silurian–Devonian rocks with ages between 426 and 370 Ma now recognized in the central part of Avalonia in southeastern New England. They formed in a long-lived, likely extensional regime linked to subduction and subsequent complex transcurrent motions among Ganderia, Avalonia, and Meguma, culminating in the closure of the Rheic Ocean. ► Mainly alkaline to weakly –peralkaline granitic and volcanic rocks outcrop in the central Gulf of Maine. ► Five U–Pb (zircon) ages obtained by LA-ICP-MS range from 415 to 384 Ma. ► Similar Silurian–Devonian alkaline/peralkaline rocks occur in Avalonia in SE New England. ► These rocks suggest long-lived extension during microcontinent accretion in the northern Appalachian orogen.