The Alleghanian Orogeny from Start to Finish: As Chronicled by the Narragansett Basin, Southeastern New England
Daniel Murray, University of Rhode Island
The Avalon zone of New England consists of a collage of terranes accreted onto ancestral eastern North America during Mid-to Late Paleozoic times. In New England the Alleghanian orogeny represents the final amalgamation of this zone against Laurentia during the assemblage of Pangaea. For most terrains affected by the Alleghanian orogeny in New England the evidence for that event is seen as either an overprinting of earlier Neoproterozoic or Paleozoic orogenic fabrics, or as a faintly and poorly constrained imprint on granitoids. An exception is the Narragansett basin (NB), a Devonian to earliest Permian basin that has been variably deformed and metamorphosed, and intruded by the Narragansett Pier Granite (NPG). Abundant megaflora, radiometric dates, and structural and petrologic analysis of the NB provide the basis for a detailed and nuanced chronology for the Alleghanian orogeny This presentation will summarize that diverse data and use it to place constraints on models for Alleghanian tectonism, as it affected southeastern New England. It is also noteworthy that the NB is unique in that it contains coal that ranges from anthracite in the north to graphite in the south. This progressive metamorphism of organic material in the context of orogenesis is nowhere else so well preserved, as will also be seen in the presentation.
Our understanding of the Narragansett basin draws from the collective efforts of many individuals, and there is an extensive literature to that effect. Below are two recent articles that not only summarize current thinking, but also provide entrées to primary sources.
Fetherston, D., Murray, D.P., and Wintsch, R.P., 2014, Alleghanian metamorphism of the southern Narragansett Basin, RI: Hinged burial and exhumation. Guidebook to geologic field studies in Rhode Island and adjacent areas. New England Intercollegiate Geologic Conference 106th Annual Meeting, p. B5-1 – B5-19.
Murray, D.P., Skehan, J.W., and Raben, J., 2004, Tectonostratigraphic relationships and coalification trends in the Narragansett and Norfolk basins, New England: Journal of Geodynamics, 37, pp. 583-611.