Progressive low pressure metamorphism of metapelitic rocks from the Casco Bay area, southwestern Maine

Conference · Mon Mar 01 00:00:00 EST 1993 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5934672

Grover, T W ^[1]; Lang, H M ^[2]; Gordon, T M ^[1]

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1. Univ. of Calgary, Alberta (Canada). Dept. of Geology and Geophysics
2. West Virginia Univ., Morgantown, WV (United States). Dept. of Geology and Geography

A prograde sequence of metapelitic rocks occurs in the Casco Bay area, southwestern Maine. Excellent exposure along the coast of Orrs Island, Harpswell Neck, and Small Point have allowed for the delineation of several metamorphic zones which show an increase in metamorphic grade from west to east across the area. These zones are, in order of increasing metamorphic grade, a garnet zone, a staurolite zone, a staurolite + andalusite zone and a sillimanite [plus minus] andalusite [plus minus] staurolite zone. The widespread occurrence of coexisting andalusite + sillimanite in the highest grade portion of the area, along with the presence of andalusite [plus minus] sillimanite veins on Hermit Island suggest peak metamorphism was near the andalusite-sillimanite transition. Staurolite is also found in apparent textural equilibrium in many of the sillimanite-bearing samples. Metamorphic pressures and temperatures were determined using the approach of Gordon. Peak temperatures range from [approx] 440C in garnet zone rocks to [approx] 510C in sillimanite [plus minus] andalusite zone rocks. Metamorphic pressures are [approx] 3-3.5 kbars. These P-T estimates are consistent with those determined using GeO-Calc. In contrast with the static style of metamorphism reported in central and western Maine, metamorphism in the Casco Bay area, located east of the Norumbega Fault, was synchronous with deformation. The same sequence of porphyroblast growth reported for the Orrs Island-Harpswell Neck area is also found in the Small Point area, suggesting the same metamorphic event affected the entire region. However, coarse grained muscovite pseudomorphs after andalusite or staurolite in rocks with stable andalusite and staurolite are found in the Small Point area suggesting these rocks have a polymetamorphic history. Evidence for polymetamorphism is not found elsewhere in the area.

• OSTI ID: 5934672
• Report Number(s): CONF-9303211-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 25:2; Conference: 28. annual Geological Society of America (GSA) Northeastern Section meeting, Burlington, VT (United States), 22-24 Mar 1993; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
GEOLOGIC DEPOSITS
GEOBAROMETRY
GEOTHERMOMETRY
PARAGENESIS
MAINE
METAMORPHIC ROCKS
BAYS
DEFORMATION
GARNETS
GEOLOGIC HISTORY
METAMORPHISM
MINERALOGY
PETROGENESIS
COASTAL WATERS
DEVELOPED COUNTRIES
GEOLOGY
MINERALS
NORTH AMERICA
OXYGEN COMPOUNDS
PETROLOGY
ROCKS
SILICATE MINERALS
SILICATES
SILICON COMPOUNDS
SURFACE WATERS
USA
580000* - Geosciences