29 Petrologic, Structural, and Tectonic Interpretations in Northern New England I: A Session Honoring the Work of Jo Laird and Peter J. Thompson

Monday, 19 March 2018
8:00 AM - 12:00 PM
Emerald Ballroom III

THE "ME-NH" TRANSECT FROM THE MIGMATIZED CENTRAL MAINE BELT IN WESTERN MAINE TO THE BRONSON HILL ANTICLINORIUM IN NORTHERN NEW HAMPSHIRE

Paper number: 29-1
Program: Theme Sessions
Time: 8:00 AM – 8:20 AM

Authors

Abstract

This paper is imbued with the spirit of the "NH-VT" transect across the northern Appalachians annually led by Jo Laird, Pete Thompson, and Wally Bothner and enjoyed by legions of UNH grad students. New 7.5' bedrock quadrangle mapping, supported by the Maine and New Hampshire Geological Surveys through the U.S.G.S. StateMap program, forms a near continuous E-W transect of updated bedrock geology across the Central Maine Belt (CMB) to the Bronson Hill Anticlinorium (BHA) along the U.S Rte. 2 corridor; the "ME-NH" transect.

In the Gilead and Bethel, Maine quads, a highly migmatized CMB Rangeley stratigraphy has been defined with poor topping control that is intruded by diorites, granites, and pegmatites. Detrital zircons yield maximum depositional ages of circa 422-433 Ma while crystallization ages for two-mica granites yield ages of 349-355 Ma. The sequence of events in this part of the CMB is: (1) end of Rangeley Stratigraphy deposition at 422-433 Ma; (2) Acadian nappe-stage folding and the onset of regional metamorphism; (3) widespread migmatization occurring around 376 Ma; (4) Neoacadian open, reclined refolding: (5) Neoacadian emplacement of the Songo Pluton and associated diorites at 364 Ma; (6) Neoacadian two-mica granite emplacement at circa 350 Ma; (7) Alleghanian emplacement of the Sebago-type plutons at 294; and (8) intrusion of pegmatites around 260 Ma.

In the NH quadrangles the Mahoosuc Fault separates migmatized CMB Silurian Rangeley Formation from the BHA Ordovician Ammonoosuc Volcanics. The Moose River Fault separates the Ammonoosuc Volcanics from the Oliverian Jefferson Dome. Internal to the Dome are several dip-slip ductile shear zones. The BHA sequence sits unconformably (Penobscot?) above the Cambrian Albee Formation. Detrital zircons for the Albee yielded maximum depositional ages of 522 Ma and 545 Ma. Jefferson Dome gneisses yielded Ordovician crystallization zircon ages of 440 Ma and 447 Ma with one unexpectedly yielding a Carboniferous age of 334 Ma. Detrital zircon ages of a metasedimentary xenolith within the Jefferson Dome gave a maximum sedimentation age of 429 Ma suggesting the enveloping intrusion is no older than Silurian. Though we have improved our understanding of the "ME-NH" transect we have also uncovered many new areas of future work that the next generation of students will enjoy.

Geological Society of America Abstracts with Programs. Vol. 50, No. 2

doi: 10.1130/abs/2018NE-311147

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