A hornblende sample from this complex has an apparent 40Ar/39Ar age of 495 ± 5 my. The 40Ar/39Ar data was obtained in a stepwise outgassing experiment. If, as has been suggested, the Brighton complex represents Layer 3 of a former oceanic crust, then the latter was produced in this region about 495 my ago (that is, in the Lower Ordovician).

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