H漫画

The Meguma terrane experienced a complex tectonothermal history. ⁴⁰Ar-³⁹Ar data on slates, amphiboles, and micas indicate that regional metamorphism was initiated about 400 Ma BP. Plutons were intruded approximately 386-360 Ma BP. The Southern Satellite plutons appear to be of similar age to the South Mountain batholith. An overprinting event which peaked about 320-300 Ma BP was much more extensive than previously considered. Information from fission track dating of apatite, and K-feldspar age spectra have been combined to put constraints on the timing, duration, and temperature of overprinting. The effects were most severe in the southwest, where domains of economic mineralization are located. Although opening of the Bay of Fundy rift about 210 Ma BP was accompanied by basaltic magmatism, the thermal effects of this event were mild in the Meguma terrane. Fission track ages from apatite suggest that final cooling below 100 ^o C occurred about 190-170 Ma BP, soon after magmatism associated with opening of the present Atlantic Ocean.

Overprinted mica and K-feldspar samples seem incapable of yielding meaningful data on closure temperature by the vacuum diffusion technique of Berger and York (1981). Quantification of discordance in ⁴⁰Ar-³⁹Ar age spectra provides a useful framework for evaluating information contained in such spectra, and for testing reproducibility in the⁴⁰Ar-³⁹Ar step-heating technique.

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Pages: 429
Supervisor:听 Peter Reynolds / Gunter Muecke