Northeastern Section - 54th Annual Meeting - 2019

Paper No. 12-5
Presentation Time: 2:50 PM


LUDMAN, Allan, School of Earth and Environmental Sciences, Queens College (CUNY), 65-30 Kissena Boulevard, Flushing, NY 11367

Bob Wintsch’s eclectic interests and ingenious approaches to "intractable" problems have led to important advances in several areas. These will undoubtedly continue in his Connecticut “retirement” but we might all profit if he invests intellectual capital a bit farther north.

Nature of orogen-parallel differential exhumation in Maine and New Brunswick. The NE to SW transition from shallow to deep crustal conditions is well documented in rocks of New England but more complex regional exhumation is recorded in Maine and New Brunswick. (1) Fabrics in the easternmost Norumbega fault system (NFS) indicate shallow crustal (sub-chlorite) deformation. Deeper crustal levels are exposed to the southwest-- greenschist conditions in eastern Maine and amphibolite conditions in mid-coastal Maine -- but revert to greenschist conditions in the Portland area. (2) Unrelated to the NFS, Cambro-Ordovician Miramichi rocks in northern New Brunswick record subduction to blueschist conditions (van Staal et al., 2008) at the same time that correlative rocks exposed at the surface supplied sediment to adjacent basins (Ludman et al., 2017). Farther southwest, low-grade Miramichi rocks terminate just northeast of amphibolite facies correlative rocks of the Casco Bay Group.

Crystallization of coarse-grained granitic plutons emplaced in the upper crust. The Deblois pluton is one of the largest post-Acadian granitic plutons in Maine. It is very coarse grained despite the fact that it was emplaced at shallow crustal levels and cooled so rapidly that U-Pb zircon and Ar/Ar hornblende and biotite ages overlap. A dry magma is indicated by the lack of hydrothermal alteration, presence of only a few aplite dikes, and lack of pegmatites. How was this coarse-grained texture produced?

Origin and evolution of the Central Maine basin. A thick sequence of deep-water Late Ordovician through Devonian turbidites deposited in the Central Maine basin blankets much of Maine. The intensely telescoped basin is 160 km wide today; restoring it to its pre-deformation geometry suggests an initial width of more than 500 km. Tectonic models suggest the absence of oceanic crust beneath the basin during deposition but possible modern analogues are typically much smaller. Bob’s years in Taiwan and experience with modern foreland and fore-arc basins can be put to good use here.

  • Ludman 12-5.pdf (6.5 MB)