THE APPLEDORE ISLAND DIORITE OF THE RYE COMPLEX, COASTAL NEW HAMPSHIRE AND MAINE: DETERMINING THE IDENTITY OF AN ENIGMATIC TERRANE

The Rye Complex of coastal New Hampshire and Maine is a peri-Gondwanan terrrane of uncertain origin. Appledore Island of the Isles of Shoals hosts a dioritic intrusion with continental rift tholeiite compositions. Minor amounts of coeval granitic rocks with syn-collisional compositions display mingling relationships with the diorite at the margin of the pluton. The 361 Ma diorite has similar major, trace, and isotopic compositions to those of the basalts and intrusive rocks of the Maritimes Basin of Canada and the Narragansett Basin in Massachusetts and Rhode Island. The ages of the interplate volcanic rocks of the Narragansett Basin are ~ 370 Ma whereas those of the Maritimes Basin range from 375 to 330 Ma, bracketing the age of the Appledore Island diorite. These interplate tectonic setting rocks reflect regional extension during the Late Devonian to Early Carboniferous, producing successor basins to the Acadian Orogeny. It appears that the geochemical and age similarities between the Appledore Island diorite and the mafic igneous rocks of the successor basins indicates that the Rye Complex is a fragment of one of these successor basin blocks that was transposed by movement along the Norembaga Fault System to its position adjacent to the Merrimack Trough rocks of New Hampshire and Maine. Isotopic analyses of the granitic rocks are currently being conducted with the aim to determine a Ganderian or Avalonian source of the crustal melts.