Structural geology, metamorphic petrology and argon-40/argon-39 geochronology of the Yarmouth area, southwest Nova Scotia.

摘要

Lower Palaeozoic rocks of the Meguma terrane were extensively deformed and metamorphosed during the Devonian Acadian orogeny, which resulted from oblique collision with the Neoproterozoic Avalon terrane. In the Yarmouth area of southwest Nova Scotia, the Cambrian-Ordovician Goldenville and Halifax (HF) formations are overlain the Silurian White Rock Formation (WRF), which forms the core of an axially-stretched, SW-plunging Acadian (D1) syncline. Acadian structures are well-preserved in the core of the syncline, which is dominated by mafic volcanogenic rocks. On the steep limbs, D1 structures in dominantly metasedimentary outer parts of the WRF and underlying HF are overprinted in broad shear zones, previously recognised as manifestations of the Carboniferous Alleghenian orogeny (D2).; D2 shear zones are wide (3--5 km), strike-parallel regions of pervasive, greenschist-facies, polyphase ductile strain, with foliation (S2) sub-parallel to their boundaries.; Metamorphic grade ranges from biotite zone in the Goldenville Formation and central parts of the WRF to staurolite-andalusite zone within each of the D2 shear zones.; The presence of higher-grade rocks within Alleghenian shear zones is interpreted to reflect differential exhumation of M1 assemblages, possibly as a result of variable pure shear during D2 (325 Ma) transpression. (Abstract shortened by UMI.)