PALEOMAGNETISM OF THE ORDOVICIAN BLUFFER POND FORMATION - PALEOGEOGRAPHIC IMPLICATIONS FOR THE MUNSUNGUN TERRANE OF NORTHERN MAINE

The Munsungun area of northern Maine is an early Paleozoic terrane wit hin the Central Mobile Belt (CMB) of the northern Appalachians. The Bl uffer Pond Formation of the Munsungun Terrane is composed primarily of pillow basalt and gabbro with minor intercalated sediments and has a maximum thickness of 1230 m. This unit is of early-Late Ordovician (Ca radocian) age, based on paleontological data, and folding most likely occurred during the Devonian (Acadian Orogeny). This region has been m etamorphosed to subgreenschist facies. Samples for paleomagnetic study have been obtained from 15 sites of pillow basalt and seven sites of gabbro within the Bluffer Pond Formation. Natural remanent magnetizati on (NRM) directions are similar to the expected present-day field dire ction and are interpreted to be strongly affected by a viscous overpri nt. Detailed stepwise thermal demagnetization fails to adequately reso lve a partial overprint direction with intermediate blocking temperatu re, but stable endpoints combined with great circles do isolate a char acteristic high-temperature component carried by magnetite as indicate d by unblocking temperatures and rock magnetic experiments. After tilt correction the formation mean calculated from pillow basalt sites onl y is D = 339-degrees, I = -33-degrees (k = 12, alpha95 = 14-degrees, n = 11), with a corresponding paleopole of 23-degrees-N, 133-degrees-E (deltap = 90, deltam = 160), calculated for an average site location o f 46.5-degrees-N, 291-degrees-E. When both pillow basalt and gabbro si tes are used to calculate a tilt-corrected formation mean, the result is D = 339-degrees, 1 = -28-degrees (k = 12, alpha95 = 12-degrees, n = 14), and this characteristic component passes a tectonic tilt test. T he calculated paleopole (26-degrees-N, 134-degrees-E; deltap = 7-degre es, deltam = 13-degrees) from pillows and gabbros falls near (but not on) the Ordovician apparent polar wander path segment for North Americ a and yields a paleolatitude (180 +/- 9-degrees-S) similar to that of the Lunksoos Terrane which is located farther to the southeast within the CMB of Maine. The Laurentian margin at this time was located at pa leolatitudes of 15-20-degrees-S. The paleogeographic implication of th is result is that the Munsungun Terrane was located near the Laurentia n margin within the lapetus Ocean and this near-continent location is consistent with a marginal or back arc basin tectonic environment for the extrusion of the Bluffer Pond volcanics.