Tectono-metamorphic history of southern New Hampshire and southeastern Vermont

Conference · Tue Jan 01 04:00:00 EST 1985 · Geol. Soc. Am., Abstr. Programs; (United States)

OSTI ID:6877476

Chamberlain, C P; Lyons, J B; Thompson, Jr, J B; Rosenfeld, J L; Downie, E

A major boundary between two Acadian metamorphic terranes is marked by a band of low-grade rocks in the Connecticut River valley coinciding with the Monroe Line (ML) and separating higher-grade rocks in two distinct lithostratigraphic terranes. To the west, Cambro-Devonian rocks in the Vermont sequence overlie Grenvillian basement, whereas to the east a different Cambro-Dev. sequence rests upon Hadrynian basement. These terranes were assembled no later than the early Devonian. The eastern terrane, consisting of the Bronson Hill Anticlinorium(BHA) and Merrimack Synclinorium (MS), is bounded on the east by the older Massabesic Gneiss (650-480 my) and Ord (.) Merrimack Group. This southeastern terrane was in contact with the MS by the early Devonian because there is no break in metamorphism across the terrane boundary. Metamorphism in the western terrane (Vermont) is synkinematic and peaks in the Staur-Ky zone. The earliest metamorphism is believed to be Taconian and represents the thermal decay of relict blueschist metamorphism observed to the northwest and the accretion of an island-arc. The earliest metamorphism in the eastern terrane (BHA-MS) is Acadian and is associated with nappe formation and synkinematic plutons. Continued Acadian crustal shortening in the MS resulted in a pressure increase (from 3.8 to 7 kb), with rocks reaching peak metamorphism in the Sil-Mus up to Kspar-Cord zones. The authors suggest that this high-grade metamorphism was the result of a high transient heat flux initiated by crustal stretching in the MS during the Silurian and early Devonian when 8 km of clastics were deposited in a rapidly subsiding trough.

• Research Organization: Harvard Univ., Cambridge, MA (USA)
• OSTI ID: 6877476
• Report Number(s): CONF-8510489-
• Conference Information: Journal Name: Geol. Soc. Am., Abstr. Programs; (United States) Journal Volume: 17
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580100* -- Geology & Hydrology-- (-1989)
580201 -- Geophysics-- Seismology & Tectonics-- (1980-1989)
BASEMENT ROCK
FEDERAL REGION I
GEOLOGIC AGES
GEOLOGIC HISTORY
GEOLOGY
LITHOLOGY
METAMORPHIC ROCKS
METAMORPHISM
NEW HAMPSHIRE
NORTH AMERICA
PALEOZOIC ERA
PETROGENESIS
ROCKS
STRATIGRAPHY
TECTONICS
USA
VERMONT