Pradeep Bhatnagar

1996 - The MacEachern - Ponsford Memorial Award

B. Sc. Honours Thesis

Structural Geology and Deformation of the Meguma Group at the Northeastern Contact of the South Mountain Batholith, Halifax Area

(PDF - 258 Mb)

Structural mapping and petrographic analyses were conducted to document the
structural geology and deformation of the Meguma Group country rocks adjacent to the
Halifax Pluton of the South Mountain Batholith (SMB) near Halifax, Nova Scotia.
Intrusion of the Devonian South Mountain Batholith caused local deformation and
metamorphism of the Cambrian-Ordovician Meguma Group. The mapped portion of the
SMB-Meguma contact of this study has been subdivided into two parts based on the style
of emplacement. Passive emplacement, occurring south of the Williams Lake area, is
characterized by regional structures preserved up to the SMB contact (e.g., bedding,
cleavage, bedding-cleavage intersection lineations, and minor folds), stoping, and dyking.
Evidence that suggests active emplacement, occurring north of the Williams Lake area,
includes: the Kearney Lake Transverse Anticline, deflection of bedding and the Halifax/Goldenville contact, steepening of the bedding-cleavage intersection lineations towards the SMB, schistose fabric near the SMB-Meguma contact, sulphide stretching lineations, mineral lineations, boudinaged dykes, and extensional fractures. The transition from deformed country rocks to country rocks with preserved regional structures may
represent a change in structural level of the Halifax Pluton from pluton wall to pluton
roof. Petrographic analysis has identified pre-to syn-tectonic cordierite, pre- and posttectonic andalusite, and syn- to post-tectonic sillimanite. Subvertical to vertical
boudinaged dykes, metamorphic (schistose) fabrics, stretching lineations, mineral
lineations, and pulled apart andalusite grains indicate subvertical to vertical stretching of
the Meguma Group. The curvature of bedding and the Halifax-Goldenville contact and
steepening of bedding-cleavage intersection lineations and increase in strain towards the
SMB, are consistent with downwards movement of the Meguma Group. Granite filled
extensional fractures indicate a shear sense of granite (SMB) side down. A subvertical to
vertical simple shear zone accommodates both the downward movement of the granite
and the downward movement of the country rocks. Lopolith emplacement by floor
depression is a possible emplacement model for the SMB. This study proposes that the
change in style of emplacement, deformation, and downwards displacement of the
country rock, are related to the various modes of emplacement of the SMB which may
change with time and different structural levels ofthe batholith.

Keywords: South Mountain Batholith, Halifax Pluton, Meguma Group, emplacement, deformation, metamorphism, downward movement, extensional fractures, country rocks
Pages: 120
Supervisor:Nicholas Culshaw