U-Pb garnet, sphene, monazite, and rutile ages: Implications for the duration of high-grade metamorphism and cooling histories, Adirondack Mts. , New York

Journal Article · Wed May 01 04:00:00 EDT 1991 · Journal of Geology; (USA)

DOI:https://doi.org/10.1086/629503· OSTI ID:5541883

Mezger, K; Rawnsley, C M; Hanson, G N ^[1]; Bohlen, S R ^[2]

---

1. State Univ. of New York, Stony Brook (USA)
2. Geological Survey, Menlo Park, CA (USA)

Garnet ages for the Lowlands range from 1,168-1,127 Ma, those from the central and southern Highlands from 1,154-1,013 Ma. Metamorphism in the Highlands may not have occurred as a single event but rather in several discrete thermal pulses. An age of 1,153 {plus minus} 3 Ma was determined for garnets in the syn-regional metamorphic contact aureole of the Diana syenite, consistent with that of the syenite intrusion, 1 155 {plus minus} 4 Ma. Garnets just outside the contact aureole give an age of 1,168 {plus minus} 6 Ma. In the Lowlands, monazite yielded an age of 1,161 {plus minus} 1 Ma, rutiles yielded ages of 1,005 {plus minus} 2 Ma and 953 {plus minus} 4 Ma, and sphene ages range from 1,156 to 1,103 Ma. In the Highlands, monazite yielded an age of 1,033 {plus minus} 1 Ma, rutiles yielded ages of 911 {plus minus} 2 Ma and 885 {plus minus} 2 and sphenes from 1,033 Ma to 991 Ma. The rutile and monazite ages indicate that both terranes cooled at time-integrated rates of ca. 1.5C/Ma for at least 150 Ma following the last phase of high-grade metamorphism. The Lowlands cooled to ca. 400C by ca. 1,000 Ma and the Highlands by ca. 900 Ma. The mineral ages indicate that metamorphic pressures and temperatures recorded by thermobarometry correspond to conditions attained polychronically over 150 Ma or more. Mineral ages combined with temperature estimates for peak metamorphism indicate that the closure temperature for the U-Pb system is >800C in garnet, 640-730C in monazite, and 500-670C in sphene.

• OSTI ID: 5541883
• Journal Information: Journal of Geology; (USA), Journal Name: Journal of Geology; (USA) Vol. 99:3; ISSN JGEOA; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACTINIDE COMPOUNDS
ACTINIDE ISOTOPES
ADIRONDACK MOUNTAINS
AGE ESTIMATION
APPALACHIAN MOUNTAINS
CHALCOGENIDES
COOLING
DEVELOPED COUNTRIES
FEDERAL REGION II
FLUIDS
GARNETS
GEOLOGIC FORMATIONS
INCLUSIONS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LEAD ISOTOPES
MATERIALS
METAMORPHISM
MINERALIZATION
MINERALS
MONAZITES
MOUNTAINS
NEW YORK
NORTH AMERICA
OXIDE MINERALS
OXIDES
OXYGEN COMPOUNDS
PHOSPHATES
PHOSPHORUS COMPOUNDS
RADIOACTIVE MATERIALS
RADIOACTIVE MINERALS
RARE EARTH COMPOUNDS
RESERVOIR FLUIDS
RESERVOIR PRESSURE
RESERVOIR TEMPERATURE
RUTILE
SILICATES
SILICON COMPOUNDS
THORIUM COMPOUNDS
THORIUM MINERALS
THORIUM PHOSPHATES
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS
URANIUM ISOTOPES
USA