Evidence for multiple metamorphic events in the Adirondack Mountains, N. Y
Field evidence consisting of: (1) rotated, foliated xenoliths, (2) country rock foliation truncated by isoclinally folded igneous intrusions bearing granulite facies assemblages document one, or more, early dynamothermal event(s) of regional scale and high grade. Early metamorphism resulted in pronounced linear and planar fabric throughout the Adirondacks and preceded the emplacement of the anorthosite-mangerite-charnockite-granite-alaskite (AMCA) suite which contains xenoliths of the metamorphosed rocks. Olivine metagabbros, believed to be approximately contemporaneous with the AMCA-suite, also crosscut and contain xenoliths of, strongly foliated metasediments. These intrusive rocks caused contact metamorphism in the metasediments which locally exhibit both anatectite and restite assemblages. Subsequently, this already complex framework underwent three phases of folding, including an early recumbent isoclinical event, and was metamorphosed to granulite facies P,T conditions. The age of the early metamorphism cannot yet be narrowly constrained, but isotopic results suggest that it may be as young as approx. 1200 Ma or older than approx. 1420 Ma. U-Pb zircon ages indicate emplacement of the AMCA-(metagabbro)-suite in the interval 1160-1130 Ma and place the peak of granulite facies metamorphism between 1070-1025 Ma. The anorogenic character of the AMCA-suite, and the occurrence of metadiabase dike swarms within it, are further evidence of the separate nature of the metamorphic events that precede and postdate AMCA emplacement.
- Research Organization:
- Colgate Univ., Hamilton, NY (USA)
- OSTI ID:
- 7024339
- Journal Information:
- J. Geol.; (United States), Vol. 96:3
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ADIRONDACK MOUNTAINS
GEOLOGIC HISTORY
METAMORPHISM
AGE ESTIMATION
ANORTHOSITES
GRANITES
INTRUSION
ISOTOPE DATING
LEAD
RESERVOIR PRESSURE
RESERVOIR TEMPERATURE
TECTONICS
URANIUM
ACTINIDES
APPALACHIAN MOUNTAINS
ELEMENTS
GABBROS
IGNEOUS ROCKS
METALS
MOUNTAINS
PLUTONIC ROCKS
ROCKS
580100* - Geology & Hydrology- (-1989)