North‐west propagation of the Grenville orogen: Grenvillian structure and metamorphism near Key Harbour, Georgian Bay, Ontario, Canada*

Contractional displacements on front-parallel structures have resulted in a rise in metamorphic grade towards the interior of the orogen.

“Grenvillian planar fabrics in the Parautochthonous belt are generally subparallel to the Grenville Front, and contractional displacements on frontparallel structures have resulted in a rise in metamorphic grade towards the interior of the orogen (Haggart et al. 1993; Rivers et al. 1993; Jamieson et al. 1995).”

Grenvillian planar fabrics in the Parautochthonous belt are generally subparallel to the Grenville Front.

“Grenvillian planar fabrics in the Parautochthonous belt are generally subparallel to the Grenville Front, and contractional displacements on frontparallel structures have resulted in a rise in metamorphic grade towards the interior of the orogen (Haggart et al. 1993; Rivers et al. 1993; Jamieson et al. 1995).”

In the GFTZ in Ontario, evidence for two high-grade metamorphic events has been recorded at c45 1060 Ma and c45 980 Ma (Ottawa and Rigolet orogenies, respectively).

“In contrast, in the GFTZ in Ontario, evidence for two high-grade metamorphic events has been recorded at c45 1060 Ma and c45 980 Ma (Ottawa and Rigolet orogenies, respectively; Jamieson et al. 1995).”

In the southern Parautochthonous belt in Ontario, P-T conditions of c45 1200 MPa / 800°C, developed at c45 1060 Ma during the Ottawa orogeny, were followed by a period of isothermal decompression.

“In the southern Parautochthonous belt in Ontario, P-T conditions of c45 1200 MPa / 800°C, developed at c45 1060 Ma during the Ottawa orogeny, were followed by a period of isothermal decompression (Anovitz and Essene 1990; Jamieson et al. 1995).”

In cross-section A, the Mid-Parautochthon detachment system is known as the Boundary shear, a broad, moderately dipping zone of intensely flattened ductile gneiss in which oblique-normal kinematic indicators overprint older thrust structures.

“In A, where it is known as the Boundary shear, it is a broad, moderately dipping zone of intensely flattened ductile gneiss in which oblique-normal kinematic indicators overprint older thrust structures (Jamieson et al. 1995).”

In cross-section A, there is widespread evidence of Ottawan (c. 1060-1020 Ma) metamorphism in the southern Parautochthonous belt prior to reworking during the Rigolet orogeny.

“In cross-section A, there is widespread evidence of Ottawan ( c45 1060-1020 Ma) metamorphism in the southern Parautochthonous belt prior to reworking during the Rigolet orogeny (Jamieson et al, 1995)”