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

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.

• 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.
• Explains that eastern massachusetts is composed of a series of fault-bounded peri-gondwanan terranes that collided into the laurentian continent.
• Explains that correlations of both the avalon and meguma terranes are present in modern-day europe indicating that accretion occurred prior to rifting.
• Explains that the gander terrane is the westernmost terran in massachusetts. it is composed of proterozoic to cambrian volcanic and volcano-sedimentary rocks and rifted off of amazonian gondwana.
• Explains that the nashoba terrane is bounded by the bloody bluff fault zone to the southeast and the newbury-clinton
• Explains that uranium-lead analysis of monazites found in the fish brook gneiss indicates active metamorphism until at least the mid-silurian and argon analysis reveals cooling to temperatures below 500°c during the mississippian.
• Describes newbury volcanic complex, composed of unmetamorphosed calc-alkaline basalts, andesites and rhyolites, distinct from both the avalon and nashoba terranes.
• Explains the geologic and geochemical similarity of the avalon terrane to newfoundland's. it was dominated by two periods of magmatism with intervening amagmatic sedimentation.
• Explains that the ordovician to devonian period of compositionally different magmatism occurred in two plutonic suites: the lexington suite and the cambridge reservoir suite.
• Explains that the tectonic boundary between the nashoba and avalon terranes was formed by accretion. it is composed of three distinct deformational zones of spatial similarity but temporal and characteristic differentiation.
• Explains that the burlington mylonite zone is a left-lateral ductile shear zone formed deep within the crust resulting from transpressional deformation.
• Explains that the kendal green mylonite zone is a right-lateral ductile shear zone and the bloody bluff fault zone.
• Explains that gander, nashoba, avalon, and meguma originated as part of the gondwanan supercontinent and subsequently joined the laurentian continent.
• Explains that the most simplified and logical version of these collisions describes a series of active or inactive volcanic arc ribbons that accreted sequentially ceasing an intervening subduction zone to the west
• Explains that avalonia originated as a suprasubduction related volcanic arc on the gondwanan margin forming the early calc-alkaline magmatism present today.
• Describes the works of cheney, hepburn, and frost, who published field trip guidebook for the northeastern united states.
• Introduces hepburn, j.c., hill, m. and hon, r. (1987) the avalonian and nashoba terranes, eastern massachusetts, usa.
• Explains kay, a., kohut, e.j. and hepburn, j.c.
• Explains marshak's essentials of geology, 3rd ed. new york: w.w. norton & company.
• Explains van staal, whalen, valverde-vaquero, zagorevski, and rogers. pre-carboniferous, episodic accretion-related, orogenesis along the laurentian margin of the northern appalachians.