[sup 40]Ar/[sup 39]Ar evidence for delayed post-Acadian cooling in the southernmost Connecticut Valley Synclinorium

Conference · Wed Jan 01 00:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5807210

Moecher, D P ^[1]; Cosca, M A ^[2]

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1. Univ. of Kentucky, Lexington, KY (United States). Dept. of Geological Science
2. Univ. Lausanne (Switzerland)

Available Ar-40/Ar-39 data for the Connecticut Valley Synclinorium (CVS) of the New England segment of the Appalachian Orogen indicate rapid post-Acadian cooling. However, new data indicate this pattern does not extend the entire length of the CVS. Ar-40/Ar-39 ages obtained from hornblende and muscovite in The Straits Schist indicate delayed cooling and a more complex post-Acadian thermal history. Data for the Seymour area are consistent with the studies above for the vicinity of the Waterbury Dome. The data farther south indicate one or more of the following: (1) slow (2--3C/Ma) post-Acadian cooling and uplift through the Permian; (2) post-Acadian cooling through Hbl closure in the Mississippian with a subsequent Alleghanian metamorphism that did not exceed 500 C; or (3) post-Acadian cooling with subsequent metamorphism that approached 500 C or involved ductile recrystallization, partly resetting hornblende and totally resetting muscovite south of Derby. Petrologic evidence supporting (2) or (3) consists of widespread but not pervasive greenschist facies retrogression of Hbl + Pl + Sph assemblages in amphibolites to Act + Ep, and Grt + Ky + St assemblages in metapelites to Chl + Bt + Qz. The present data cannot resolve between (2) or (3). However, both are consistent with results of a study in the Bridgeport Synform that yield (1) a U-Pb monazite age of 296 [+-] 2 Ma from the Ansonia Leucogranite, implying the occurrence of an Alleghanian thermal event that promoted monazite growth; and, (2) a U-Pb cooling age of 360 Ma from sphene in the Pumpkin Ground Granodiorite, indicating that Alleghanian events did not exceed ca. 550 C.

• OSTI ID: 5807210
• Report Number(s): CONF-921058-; CODEN: GAAPBC
• Journal Information: Geological Society of America, Abstracts with Programs; (United States), Vol. 24:7; Conference: 1992 annual meeting of the Geological Society of America (GSA), Cincinnati, OH (United States), 26-29 Oct 1992; ISSN 0016-7592
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
APPALACHIAN BASIN
GEOTHERMOMETRY
AGE ESTIMATION
ARGON 39
ARGON 40
CONNECTICUT
COOLING
GEOLOGIC HISTORY
ISOTOPE RATIO
METAMORPHISM
RESERVOIR TEMPERATURE
ARGON ISOTOPES
BETA DECAY RADIOISOTOPES
BETA-MINUS DECAY RADIOISOTOPES
DEVELOPED COUNTRIES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC STRUCTURES
ISOTOPES
LIGHT NUCLEI
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NUCLEI
RADIOISOTOPES
SEDIMENTARY BASINS
STABLE ISOTOPES
USA
YEARS LIVING RADIOISOTOPES
580000* - Geosciences