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1998 - The MacEachern - Ponfsord Memorial Award

Cambrian to early-Devonian meta-sedimentary rocks of the Halifax and
Goldenville formations of the Meguma Group and the overlying White Rock and
Torbrook formations form the rart of the Meguma Terrane that underlies southwest Nova
Scotia in the Digby area. An ⁴⁰Ar/³⁹ Ar study utilizing laserprobe techniques on single
muscovite grains and stepwise heating on whole rock samples was used to examine the
provenance and metamorphism of the Meguma Group, and the White Rock and Torbrook
formations in the Digby area. Single grain muscovite analyses from the Goldenville
Formation showed a single population that ranged from 519 to 593 Ma, with an average
of 551 卤 6.3 Ma, a range that does not overlap with the whole rock spectrum ages of
approximately 250 to 450 Ma. Halifax Formation single grain muscovite analyses gave
ages that ranged from 344 to 591 Ma and overlap the range of ages found in the Halifax Formation whole rock spectra. The single grain muscovite analyses from the White Rock Formation encompassed an age range from 448 Ma to 533 Ma. The whole rock spectra for the Meguma Group and White Rock formations generally gave age ranges increasing with %³⁹ Ar released from 250 to 600 Ma, with plateau-like spectra indicating a regional metamorphic overprinting in some samples at approximately 400 Ma. The Torbrook Formation sample gave a whole rock spectrum increasing in a stepwise fashion between 275 Ma and 380 Ma. Microprobe data indicates that all the analyzed single grains are compositionally muscovite. The results from this study indicate a provenance age of
approximately 560 to 600 Ma for the Cambrian to Ordovician Halifax and Goldenville
formations. Results from the Silurian White Rock Fom1ation are interpreted to indicate a
detrital age of ca. 500 Ma with detritus possibly from the Meguma Group or A val on
Terrane. A whole rock anal6sis from the Lower Devonian Torbrook Formation yielded
an age of ca. 370 Ma. The ⁴⁰Ar/³⁹ Ar ages from this study showed evidence of resetting
due to regional metamorphism and deformation related to the Devonian Acadian
Orogeny and the late syntectonic intrusion of the ca. 370 Ma South Mountain Batholith.

Keywords:
Pages: 68
Supervisor: Peter Reynolds and Chris White

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