The Accretions of Gander, Nashoba, and Avalon onto the Laurentian Margin Martha Parsons

explanatory Essay
2211 words
2211 words

I. INTRODUCTION A significant portion of New England was formed as a result of an accretionary orogen. Southeastern New England is marked by a series of terranes that accreted onto the Laurentian supercontinent during the Silurian and Devonian. The Terranes of Gander, Nashoba, Avalon, and Meguma are present from west to east in eastern Massachusetts and all of are Gondwanan provenance. Their modern-day juxtaposition suggests that the marginal Gondwanan micro-continents collided sequentially from west to east, expanding the Laurentian continent with each respective collision. As each subsequent plate collided, an intervening subduction zone died and a new subduction zone was created to the east. The oblique collision of the Avalon Terrane into Laurentia followed the accretions of the Gander and Nashoba Terranes and preceded the accretion of Meguma. The collision was marked by uplift, mylonitic metamorphism, and calc-alkaline Nashoba plutonism as the Iapetus Ocean subducted under the Nashoba and eventually the Avalon collided obliquely into the continental margin. The area composed of the Gander, Nashoba, Avalon, and Meguma Terranes has been extensively studied for many years. However, it was only recently that the terranes were recognized as distinct geologic entities with unique tectonic histories thus there is still much debate regarding the tectonic model which brought these terranes together (Hon et al., 2007). This paper will address the geology of the peri-Gondwanan terranes and propose a potential tectonic model for the accretional orogenic events. It will also primarily focus on the juxtaposition between the Nashoba and Avalon Terranes. II. TECTONIC SETTING Global Tectonics The most recent complete supercontinent cycl... ... middle of paper ... ...J.C. (2004) Mylonites and Brittle Shear Zones Along the Western Edge of the Avalon Terrane West of Boston, NEIGC Field Trip Guide. Marshak, S. (2009) Essentials of Geology, 3rd ed. New York: W.W. Norton & Company, ch. 11, p. 298-320. Skehan, J.W., Rast, N., Kohut, E., Hepburn, J.C., and Grimes, S.W. (1998) Precambrian and Paleozoic Mylonites of the Boston Avalon, NEIGC Field Trip Guide. Stroud, M.M., Markwort, R.J., and Hepburn, J.C. (2009) Refining Temporal Constraints on Metamorphism in the Nashoba Terrane, Southeastern New England, Through Monazite Dating. Lithosphere, vol. 1, p. 337-342. Van Staal, C.R., Whalen, J.B., Valverde-Vaquero, P., Zagorevski, A., and Rogers, N. (2009) Pre-Carboniferous, Episodic Accretion-Related, Orogenesis along the Laurentian Margin of the Northern Appalachians. Geological Society, London, Special Publications, vol. 327, p. 271-316.

In this essay, the author

  • Explains that new england was formed as a result of an accretionary orogen. the terranes of gander, nashoba, avalon, and meguma are present from west to east in eastern massachusetts.
  • States that the paper will address the geology of the peri-gondwanan terranes and propose a potential tectonic model for accretional orogenic events.
  • Explains how the proterozoic break-up of rodinia and the formation of pangaea caused significant tectonic collision and rifting along their margins.
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