PALEOMAGNETISM OF THE PENNINGTON MOUNTAIN TERRANE - A NEAR-LAURENTIANBACK-ARC BASIN IN THE MAINE APPALACHIANS

Paleomagnetic studies of volcanic terranes in the Appalachians provide quantitative data on the Ordovician paleogeography of the Iapetus oce an. New paleomagnetic results from submarine volcanics of the Middle t o Late Ordovician Winterville Formation of Maine further constrain the evolution of lapetus. Ten sites yield a tilt corrected direction of D /I = 327/-21 (alpha(95) = 9.3, k = 27.9); the corresponding paleomagne tic pole calculated for the average site location (46.8 degrees N, 291 .3 degrees E) is located at 26 degrees N, 148 degrees E (d(p) = 5 degr ees, d(m) = 10 degrees, A(95)=7.7). A Silurian conglomerate (Frenchvil le Formation) test is inconclusive due to a strong present-day field o verprint which obscures any primary remanence. The presence of a posit ive tilt test, however, supports the conclusion that the characteristi c magnetization of the Winterville Formation is a prefolding, primary magnetization. An Ordovician paleolatitude of II 11 +/- 5 degrees for the Pennington Mountain terrane of northern Maine is indistinguishable from that of the Laurentian margin (15-20 degrees) during the Middle to Late Ordovician. The paleolatitude of the Pennington Mountain terra ne is also similar to, but slightly more equatorial than that of the p reviously studied Bluffer Pond Formation of the nearby Munsungun terra ne (18 +/- 9 degrees). We conclude that the Ordovician Pennington Moun tain and Munsungun volcanic terranes of Maine were formed and acquired their characteristic magnetization near the Laurentian margin. The pa leolatitudes of these terranes are also similar to that obtained from the Stacyville volcanics of the more outboard Lunksoos terrane (20 +/- 8 degrees), but they contrast strongly with the Ordovician Miramichi terrane of northern New Brunswick that yielded a paleolatitude of 51 d egrees (+ 21,-16 degrees). These results from Maine support the presen ce of one or more backarc basins adjacent to the Laurentian margin dur ing the Middle to Late Ordovician.