A paleomagnetic investigation of the Middle Ordovician Tetagouche Group in northern New Brunswick was undertaken to determine the paleogeo~aphi~ position of the Miramichi Terrane. Stepwise thermal demagnetization of pillow basahs reveals a high-temperature characteristic ~gnet~tion with a mean direction of B = W, Z = +69", k = 22, aas = 13" (tih-corrected, N= 7 sites; 73 samples). A positive fold test and the presence of antipodal normal and reversed polarity directions indicate that this ancient direction is Ordovician in age, with a paleopole position of 52"N, 352"E. The corresponding pateolatitude of 535 places these vokanic rocks near the southern margin of the Iapetus Ocean, at paleolatitudes similar to those revealed by Avalon for the Middle to Late Ordovician. The mafic and felsic volcanic rocks and marine sedimentary rocks of the Tetagouche and Fournier groups have been interpreted to be remnants of a rifted continental margin and a Middle Ordovician back-arc basin. Our results show that the process of rifting and back-arc basin formation occurred at the Avalonian margin of Iapetus, which implies that Ordovician subduction was not restricted to the Laurentian margin, but also marks the southern margin of Japetus.