40Ar/39Ar and U-Pb mineral ages from the Brookville Gneiss: implications for terrane analysis and evolution of Avalonian "basement' in southern New Brunswick

Abstract

New 40Ar/39Ar hornblende and U-Pb zircon data from units previously thought to represent basement to the Avalon composite terrane in southern New Brunswick yield latest Precambrian or early Cambrian metamorphic cooling ages and a late Precambrian protolith age. The results conflict with previous interpretations of the Brookville Gneiss and the metasedimentary Green Head Group as a mobilized Proterozoic basement-cover succession upon which an Avalonian ensialic arc developed at c.600-635 Ma. Instead, the age of the orthogneiss matches that of the arc, and the orthogneiss protolith is likely to have been originally intrusive into the Green Head Group. -from Authors