Journal article

40Ar/39Ar and K-Ar ages: early Paleozoic metamorphism and deformation in the Narooma accretionary complex, NSW

E Prendergast, R Offler, D Phillips, H Zwingmann

AUSTRALIAN JOURNAL OF EARTH SCIENCES | TAYLOR & FRANCIS LTD | Published : 2011

Abstract

White micas in slates from an imbricated sequence of deformed turbidites, and clast-in-matrixmelanges that form the Narooma accretionary complex at Batemans Bay, record apparent 40Ar/39Ar whole rock ages in the range 450 to 500 Ma, with intermediate-temperature average ages of 471±13 Ma and 476±11 Ma (2 standard deviations). By contrast, two K-Ar whole rock ages are 430.9±8.6 Ma and 449.2±9.0 Ma. Fractions (<2, 3-5 and 10-20 μm) from the same samples show a progressive increase in age with grainsize (<2 μm=413.1±8.3-404.7±8.1 Ma; 3-5 μm=417.1±8.3 Ma; 10-20 μm=434±8.6-437.5±8.8 Ma 2 standard deviations). The older whole rock 40Ar/39Ar ages are attributed to recoil loss of 39Ar. The cleavage f..

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