Multiple generations of monazite growth in metapelites of the Wepawaug Schist, southern Connecticut

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

OSTI ID:5809438

Lanzirotti, A; Hanson, G N ^[1]

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1. State Univ. of New York, Stony Brook, NY (United States). Dept. of Earth and Space Sciences

The Wepawaug Schist, part of the Orange Milford Belt of southern Connecticut, consists dominantly of micaceous phyllites and schists. A progression in metamorphic zonation from chlorite through kyanite grade occurs within 3 km. There were previously no constraints on either the depositional age of the Wepawaug Schist or the time of metamorphism. Concordant U-Pb sphene ages of 457 [+-] 3 Ma for the Woodbridge granite, which cuts the Wepawaug Schist, mean that the metapelites are older than late Ordovician. Kyanite grade rocks contain two distinct monazite populations within a single outcrop: (1) Crystals from a graphitic schist are clear, round, and xenoblastic. They have [approximately]0.9 wt.% Th, Sm/Nd = 0.12--0.14, and display pronounced chemical zonation. These give normality discordant U-Pb ages that define an upper intercept age of 420 [+-] 12 Ma. (2) In a less graphitic schist they are light yellow, idioblastic, tabular crystals that cut muscovites. They have Sm/Nd = 0.16 and [approximately] 2.6 wt.% Th and give concordant U-Pb ages of 377 [+-] 3 Ma. The authors suggest that the Wepawaug Schist is older than 457 Ma and was affected by two events which resulted in monazite growth, one during the Middle Devonian (377 Ma) and one in the Late Silurian (420 Ma).

• OSTI ID: 5809438
• 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
CONNECTICUT
GEOLOGIC FORMATIONS
AGE ESTIMATION
METAMORPHISM
DEVONIAN PERIOD
ISOTOPE DATING
LEAD
MONAZITES
SCHISTS
SILURIAN PERIOD
URANIUM
ACTINIDES
DEVELOPED COUNTRIES
ELEMENTS
GEOLOGIC AGES
MATERIALS
METALS
METAMORPHIC ROCKS
MINERALS
NORTH AMERICA
PALEOZOIC ERA
PHOSPHATE MINERALS
RADIOACTIVE MATERIALS
RADIOACTIVE MINERALS
RARE EARTH COMPOUNDS
ROCKS
THORIUM MINERALS
USA
580000* - Geosciences