Lithoprobe line 55: integration of out-of-plane seismic results with surface structure, metamorphism, and geochronology, and the tectonic evolution of the eastern Grenville Province

Lelukuau terrane is overlain by Tshenukutish terrane along a southeast-dipping normal-sense shear zone.

“It is overlain by Tshenukutish terrane along a southeast-dipping normal-sense shear zone (Hynes et al. 2000).”

Lelukuau and Tshenukutish terranes, located on the north shore of Manicouagan Reservoir, comprise the Manicouagan Imbricate zone, and its mapped extension into the southern part of the reservoir is described by Eaton et al. (1995) and Hynes et al. (2000).

“These terranes, located on the north shore of Manicouagan Reservoir, comprise the Manicouagan Imbricate zone (Indares et al. 1998, 2000), and its mapped extension into the southern part of the reservoir is described by Eaton et al. (1995) and Hynes et al. (2000).”

In cross-section D, the thrust-sense Highway shear zone carries rocks in its hanging wall that were metamorphosed at c. 1011-989 Ma.

“In cross-section D, the thrust-sense Highway shear zone carries rocks in its hanging wall that were metamorphosed at c45 1011-989 Ma (Hynes et al. 2000).”

At depth, the Grenville Front is a listric structure that soles out in the crust-mantle boundary.

“At depth, it is a listric structure that soles out in the crust-mantle boundary (Hynes et al. 2000; White et al. 2000).”

Hart Jaune and Berthé terranes together comprise a north-vergent, fold-thrust stack, with the Berthé anorthosite occupying the core of a km-scale sheath fold in the centre of the stack.

“Hart Jaune and Berthé terranes together comprise a north-vergent, fold-thrust stack, with the Berthé anorthosite occupying the core of a km-scale sheath fold in the centre of the stack (Hynes et al. 2000).”

Hart Jaune terrane consists predominantly of gneisses that preserve evidence for two granulite-facies metamorphic events at 1470 Ma and 989 Ma (Pinwarian and Rigolet orogenies, respectively).

“Hart Jaune terrane consists predominantly of gneisses that preserve evidence for two granulite-facies metamorphic events at 1470 Ma and 989 Ma (Pinwarian and Rigolet orogenies, respectively; Scott and Hynes 1994; Hynes and St-Jean 1997; Hynes et al. 2000).”

Coeval normal faulting along the Upper Allochthon detachment above the HP belt, leading to unroofing by tectonic extrusion, resulted in widespread preservation of the HP mineralogy and texture.

“Coeval normal faulting along the Upper Allochthon detachment above the HP belt, leading to unroofing by tectonic extrusion, resulted in widespread preservation of the HP mineralogy and texture (Hynes et al. 2000).”

Hynes et al. (2000) showed that the southwesterly continuation of the Hart Jaune shear zone (the Highway shear zone) was imaged in the Lithoprobe deep seismic reflection experiment and could be traced to at least 10 km below the present erosion surface.

“Hynes et al. (2000) showed that its southwesterly continuation (known as Highway shear zone) was imaged in the Lithoprobe deep seismic reflection experiment and could be traced to at least 10 km below the present erosion surface.”

The Archean craton comprised a mechanically competent buttress or ramp that focused extrusion of the HP rocks above it in the central Grenville Province.

“The restriction of Archean rocks to the footwall of the HP belt in the central Grenville Province is significant and is compatible with the inference that the Archean craton comprised a mechanically competent buttress or ramp that focused extrusion of the HP rocks above it (e.g., Hynes and Eaton 1999; Hynes et al. 2000).”

In the central Grenville Province, extension took place above the HP belt.

“extension took place above the HP belt”

In the central Grenville Province, extension took place above the HP belt and was coeval with thrust transport of the HP belt onto the footwall ramp, leading to unroofing by tectonic extrusion.

“In contrast, in the central Grenville Province extension took place above the HP belt and was coeval with thrust transport of the HP belt onto the footwall ramp, leading to unroofing by tectonic extrusion (Hynes et al. 2000).”

In the central Grenville Province, thrusting and extensional shearing were approximately coeval.

“in the central Grenville Province, thrusting and extensional shearing were approximately coeval”

Extension above the HP belt in the central Grenville Province led to tectonic extrusion of the HP rocks.

“leading to tectonic extrusion of the HP rocks (Hynes et al. 2000)”

The Molson Lake terrane, also derived from Laurentian crust, formed outboard of the Knob Lake Group, and its present location structurally above the Gagnon terrane implies that the crustal-scale development of the Grenville Orogen took place by foreland-propagating understacking.

“The Molson Lake terrane, also derived from Laurentian crust [Rivers et al., 2002], formed outboard of the Knob Lake Group and its present location structurally above the Gagnon terrane implies that the crustal-scale development of the Grenville Orogen took place by foreland-propagating understacking [Hynes et al., 2000].”

The Lac Joseph terrane and structurally equivalent terranes farther east in Labrador are inferred to have been emplaced into their present locations by normal faulting.

“The Lac Joseph terrane and structurally equivalent terranes farther east in Labrador are inferred to have been emplaced into their present locations by normal faulting (Figure 15e) [Hynes et al., 2000].”

Shortening ceased when the top of the Archean basement became incorporated into the thrust wedge.

“Hynes et al. [2000] showed that Archean crust formed the footwall to the crustal-scale ramp and Figure 17b illustrates that shortening ceased when the top of the Archean basement became incorporated into the thrust wedge.”