AVALONIAN PROXIMITY OF THE ORDOVICIAN MIRAMICHI TERRANE, NORTHERN NEW-BRUNSWICK, NORTHERN APPALACHIANS - PALEOMAGNETIC EVIDENCE FOR RIFTINGAND BACK-ARC BASIN FORMATION AT THE SOUTHERN MARGIN OF IAPETUS

A paleomagnetic investigation of the Middle Ordovician Tetagouche Grou p in northern New Brunswick was undertaken to determine the paleogeogr aphic position of the Miramichi Terrane. Stepwise thermal demagnetizat ion of pillow basalts reveals a high-temperature characteristic magnet ization with a mean direction of D = 060-degrees, I = +69-degrees, k = 22, alpha95 = 13-degrees (tilt-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-degrees-N, 352-degrees-E. The corresponding paleolatitude of 53-degrees-S places these volcanic roc ks near the southern margin of the Iapetus Ocean, at paleolatitudes si milar to those revealed by Avalon for the Middle to Late Ordovician. T he mafic and felsic volcanic rocks and marine sedimentary rocks of the Tetagouche and Fournier groups have been interpreted to be remnants o f a rifted continental margin and a Middle Ordovician back-arc basin. Our results show that the process of rifting and back-arc basin format ion occurred at the Avalonian margin of iapetus, which implies that Or dovician subduction was not restricted to the Laurentian margin, hut a lso marks the southern margin of Iapetus.