LE3 .A278 2000

2000

Barr, Sandra

Acadia University

Master of Science

Masters

Geology

Earth & Environmental Sciences

The White Rock Formation in the Yarmouth area occurs in a faulted synclinal structure underlain by the Halifax Formation. The formation is divided into 7 stratigraphic units based on field mapping, petrographic study and published geophysical maps. All units are commonly intruded by mafic dykes and/or sills that also occur in the adjacent Halifax Formation. Metamorphic grade is greenschist to amphibolite facies. The Brenton Pluton occurs on the eastern limb of the syncline and appears to be in faulted contact with the basal unit of the White Rock Formation on the west and slate of the Halifax Formation on the east. The chemistry of mafic volcanic rocks indicates an alkalic affinity and a within plate tectonic setting. The felsic volcanic rocks are chemically similar to the Brenton Pluton and both have characteristics of within-plate A-type granites. The mafic volcanic rocks are comagmatic with the mafic dykes and sills and with the felsic rocks, but Sm-Nd data ([epsilon]Nd +1.37) indicate a crustal influence in the felsic rocks. Volcanic rocks in the Yarmouth area are chemically similar to those elsewhere in the White Rock Formation. A felsic tuff from near the top of the formation yields a U-Pb age of 438 +3/-2 Ma, which supports an Early Silurian age for the formation and provides a constraint for stratigraphic correlation with other areas in western Nova Scotia. A regional geochemical comparison with the Arisaig Group indicates similar tectonic settings but chemically different sources. The geochemistry of the White Rock Formation and Brenton Pluton indicate a continental extensional environment in the Meguma terrane during the Silurian.

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