Constraints on the tectonic evolution of the southern New River terrane and its relationship to other terranes in southern New Brunswick.

摘要

The narrow, fault-bounded New River terrane contains the northwesternmost exposures of Neoproterozoic rocks known in southern New Brunswick. Through mapping, structural, and petrological studies, this study has focused on unravelling relationships among Neoproterozoic and younger rocks in the southern part of the terrane. The Neoproterozoic rocks are here divided into the ca. 620 Ma Blacks Harbour Granodiorite and Beaver Harbour Porphyry, and the ca. 555 Ma units, which include both volcanic and co-magmatic high-level intrusive rocks. Both the ca. 620 Ma and ca. 555 Ma suites are shown here to exhibit chemical signatures characteristic of formation in continental margin subduction settings. The ca. 555 Ma units are overlain by, and in faulted contact with, Early-Middle Cambrian volcanic and siliciclastic rocks of the Simpsons Island and Mosquito Lake Road formations, and Silurian-Devonian sedimentary rocks of the Mascarene Group. The Blacks Harbour Granodiorite and Beaver Harbour Porphyry are unconformably overlain by the Late Devonian Perry Formation, and faulted against Cambrian sedimentary rocks of the Buckmans Creek Formation. Most of the rock units in the southern New River terrane are similar in age and petrology to units in the northern part of the terrane, and hence are interpreted to be comagmatic with them. Broad similarities also exist between the New River terrane and other areas of southern New Brunswick, but making direct links remains enigmatic. The ca. 620 Ma and ca. 555 Ma volcanic arcs in the New River terrane are interpreted to have undergone separate deformational histories throughout the Early Paleozoic, and were juxtaposed along the Letang Harbour Fault - Robin Hood Lake Fault no earlier than Late Devonian.