Characterization of the crust of Maine by seismic reflection and refraction
Major structural features of the crust of Main and adjacent Quebec appear in both seismic reflection and refraction profiles gathered in 1983 and 1984 through US-Canada cooperative experiments and associated gravity, magnetic, and geologic studies. Excepting gabbroic plutons, the upper crust is sialic throughout Maine with velocity 5.7-6.3 km/sec; below approx.22 km, velocity increases to 6.8-7.2 km/sec. Crustal thinning, from 40 km in the NW to 35 km in the SE, accounts for all the increase in the regional gravity field to the SE. The crust-mantle transition is gradational but yields multiple strong Moho reflections and clear Pn arrivals. Seismic data permit five different kinds of continental crust (terranes) to be characterized. The terranes are separated by boundaries that penetrate most of the crust. No ancient oceanic crust was identified. In northwestern Maine, crust II with the Chain Lakes Massif and superposed ophiolite was obducted in the Taconian orogeny onto sialic (Grenville.) Crust I. Crust II is in steep contact with high grade sialic metamorphic rocks of crust III approx.10 km SE of the NW border of the Merrimack synclinorium. The contact is covered by approx.12 km of Silurian and Devonian metasedimentary rocks. Crust III contacts crust IV along the Norumbega fault zone; high grade Precambrian and lower Paleozoic metasedimentary rocks thrust southeastward make up the upper part of crust IV. Crust IV contacts crust V along the Turtle Head fault zone in Penobscot Bay. In Crust V approx.12 km of bimodal Lower Paleozoic volcanic rocks cover Precambrian rocks at medium grade. The irregular shapes of granitic plutons were determined to depths of 6-10 km.
- Research Organization:
- Geologic Survey, Reston, VA (USA)
- OSTI ID:
- 6169820
- Report Number(s):
- CONF-8510489-
- Journal Information:
- Geol. Soc. Am., Abstr. Programs; (United States), Vol. 36; Conference: 98. annual meeting of the Geological Society of America, Orlando, FL, USA, 28 Oct 1985
- Country of Publication:
- United States
- Language:
- English
Similar Records
Chain Lakes massif, west central Maine: northern Appalachian basement or suspect terrane
Metamorphism of tectonic terranes in the eastern marginal zone of the Appalachian orogen, New England
Related Subjects
CONTINENTAL CRUST
MAPPING
SEISMIC SURVEYS
MAINE
GRAVITY SURVEYS
MAGNETIC SURVEYS
PETROLOGY
PLUTONIC ROCKS
SEISMIC WAVES
EARTH CRUST
FEDERAL REGION I
GEOLOGY
GEOPHYSICAL SURVEYS
IGNEOUS ROCKS
NORTH AMERICA
ROCKS
SURVEYS
USA
580300* - Mineralogy
Petrology
& Rock Mechanics- (-1989)
580203 - Geophysics- Geophysical Survey Methods- (1980-1989)