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Tectonic history of the Lunksoos Composite Terrane in the Maine Appalachians
Author(s) -
Wellensiek M. Reid,
Pluijm Ben A.,
Van der Voo Rob,
Johnson Rex J. E.
Publication year - 1990
Publication title -
tectonics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.465
H-Index - 134
eISSN - 1944-9194
pISSN - 0278-7407
DOI - 10.1029/tc009i004p00719
Subject(s) - terrane , geology , ordovician , paleomagnetism , paleontology , volcanic rock , paleozoic , sequence (biology) , tectonics , volcano , biology , genetics
Several Ordovician volcanic terranes are preserved between the Paleozoic North American margin and the Avalon Terrane in the northern Appalachians of Maine. They have been interpreted as remnants of an island arc on the basis of their current position in the Appalachians or as ocean islands near the margin of Avalon on the basis of paleontologic data. A study of one of these terranes, the Lunksoos terrane in northern Maine, was undertaken through a combination of paleomagnetic and structural analyses in order to understand its tectonic evolution. Paleomagnetic study of the pre‐Caradoeian (pre‐Late Ordovician) Stacyville volcanics revealed three components of magnetization. The final magnetization removed (D=90°, I=36°, α95=11.8°) is interpreted to be primary and yields a paleolatitude of approximately 20°S; however, a Late Ordovician remagnetization cannot be excluded. The Stacyville volcanics now overlie a Cambrian and Lower Ordovician sequence (the Grand Pitch and Shin Brook formations) that is believed to have been deposited at the southern side of Iapetus, possibly near the margin of Avalon. During the Middle and Late Ordovieian, Avalon was at paleolatitude s higher than 40°S, while the volcanics were either formed or remagnetized at a paleolatitude of 20°S. The pre‐Caradocian Stacyville volcanics therefore could not have been deposited directly on the Grand Pitch‐Shin Brook sequence but must have been tectonically emplaced. The Rockabema Diorite which intrudes the entire Cambro‐Ordovician sequence constrains the timing of this emplacement to be pre‐late Early Silurian. These relationships indicate that the Lunksoos area is a composite terrane within the Maine Appalachians. The tectonic emplacement scenario is unnecessary if the Grand Pitch and Shin Brook formations were not located on the south side of Iapetus during the Ordovician. This alternative, however, poses conflicts with the interpretation of faunal affinities.