Strain-induced mineral growth in ductile shear zones and a preliminary study of ductile shearing in western Newfoundland

Abstract

In the Fleur de Lys and the Central Gneiss terranes the presence of strain-induced mineral growth characteristic of ductile shear zones within zones of rocks with mylonitic fabrics indicates the existence of major belts of layer-parallel ductile shearing with complex evolutionary sequences. Kinematic markers in several of these shear belts indicate that shearing movements on initially probably gently inclined surfaces, directed not normal to the axial trend of the orogen but parallel to it, are tectonically important in western Newfoundland. The shear belts are in excess of 1 km thick, and one well-exposed example exhibits a pattern in which zones of the highest strain anastomose on the map scale.The base of the Fleur de Lys Supergroup is marked by one such major zone of shearing (décollement) in which kinematic indicators record movements directed to the north and to the south, before the regional attitude of the rocks was steepened. Along the Baie Verte Line, earlier north- and south-directed movements in the Fleur de Lys were succeeded by reverse movements towards the east, over the Dunnage Terrane.

Taconic Metamorphism Preserved in the Baie Verte Peninsula, Newfoundland Appalachians: Geochronological Evidence for Ophiolite Obduction and Subduction and Exhumation of the Leading Edge of the Laurentian (Humber) Margin During Closure of the Taconic Seaway

“…D 2 shear zones, some of which reused earlier D 1 faults, are locally associated with attenuated limbs of major F 2 folds. Kinematics of these shear zones are generally complex or obscured by superimposed strains, especially adjacent to long-lived faults associated with the Baie Verte Line (Hibbard 1983;Piasecki 1988;Goodwin and Williams 1996). Shear zones occurring at the mylonitic contacts between the East Pond Metamorphic Suite and the Fleur de Lys Supergroup (Piasecki 1988) were folded by F 2 folds, so that their kinematics and timing are uncertain.…”

“…Kinematics of these shear zones are generally complex or obscured by superimposed strains, especially adjacent to long-lived faults associated with the Baie Verte Line (Hibbard 1983;Piasecki 1988;Goodwin and Williams 1996). Shear zones occurring at the mylonitic contacts between the East Pond Metamorphic Suite and the Fleur de Lys Supergroup (Piasecki 1988) were folded by F 2 folds, so that their kinematics and timing are uncertain. D 2 faults are ESE-directed along the contact between the BVOT and the Burlington plutonic suite (Kidd 1974), however, the vergence of D 2 structures in the northwest part of the Birchy Complex and adjacent Rattling Brook Group (where post-D 2 strain is generally weaker) suggest northwest-directed transport (Kidd 1974;Bursnall 1975;Hibbard 1983).…”

“…D 3 shear zones locally accommodated southeast-directed thrusting, in part reactivating D 2 faults (Fig. 2;Bursnall 1975;Piasecki 1988). The subvertical S 3 foliation varies from a non-penetrative crenulation cleavage to a penetrative schistosity.…”

Ode to Field Geology of Williams: Fleur de Lys Nectar Still Fermenting on Belle Isle

“…But what have remained undetermined are the age and even the very existence of possible basement to the Fleur de Lys sedimentary rocks of the Burlington Peninsula (e.g. Piasecki 1987Piasecki , 1988. Hibbard (1983), amongst others, remained undecided and 'lumped' the rocks of the western Burlington Peninsula into a relatively conformable Fleur de Lys Supergroup sequence, including 'my basement' rocks, which he renamed the East Pond Metamorphic suite (EPMS), and subsequent workers appear to have avoided testing the wisdom of this.…”

“…de Wit (1972) suggested the conglomerate was of fluvial origin and unconformably overlies a remobilized basement of gneiss and granite (de Wit 1980). These rocks were later renamed the East Pond Metamorphic Suite (EPMS) by Hibbard (1983) and incorporated by him (and Piasecki 1987(and Piasecki , 1988 into the FdLS (i.e. the EPMS of Hibbard is the infrastructure of both the highly tectonized and metamorphosed basement and cover of the FdLS; Piasecki was less precise about the tectonostratigraphy, but incorporated the conglomerate into the EPMS basement, and separated it from the FdLS).…”