Trans-Hudson Orogeny - Sequence of Events

Sequence of Events

Marine evidence indicates that the area initially opened to form an ocean called the Manikewan Ocean. Faulting, sedimentary and igneous rocks all indicate that divergence formed a rift valley that continued to spread until it resulted in a passive margin in which there was no tectonic activity. Shallow marine deposits formed on the continental shelves, and oceanic crust formed on the margins of the continental cratons as the divergence continued. Eventually the divergence stopped, then reversed direction, and collision occurred between continental land masses. During the Wopmay orogeny, subduction occurred as oceanic crust of the Slave craton was subducted beneath an eastward moving continental plate. Likewise, during the Trans-Hudson orogeny, rifting at first separated the Superior craton from the rest of the continent. Then the Superior craton reversed its direction and the ocean basin began to close. A subduction zone formed as the oceanic crust of the Superior craton was subducted beneath the Hearne and Wyoming craton with the Sask craton in the middle. Volcanic arcs developed as the cratons collided, eventually resulting in the THO mountain building (orogeny).

During the opening and then closure of the Manikewan Ocean, the following sequence of events occurred:

1. Deposition of passive margin sequences, beginning at ca. 2.16 Ga.
2. Ocean closure beginning at ca. 1.92 Ga in the western THO, leading to the formation of the La Ronge/Lynn Lake, the Flin Flon Domain/Glennie island arcs, and the Pelican Thrust located between the two volcanic arc complexes and the Archaen Sask craton.
3. Beginning at about 1.88 Ga, accretion of the La Ronge/Lynn Lake arcs to the Hearne craton margin and related deposition of an extensive molasse/foredeep sequence. This event was contemporaneous with intraoceanic accretion leading to the formation of the Flin Flon/Glennie accretionary complex.
4. Continental arc magmatism along the SE margin of the Churchill plate between 1.86 Ga and 1.85 Ga.
5. Cessation of continental arc magmatism at about 1.850 Ga, perhaps related to collision of the Flin Flon/Glennie complex (western THO) and Narsajuaq arc (Baffin segment), with the Churchill plate.
6. Opening of the Kissinew back-arc basin during the interval 1.85-1.84 Ga, with the Flin Flon complex now forming part of the active arc and Granville Lake Structural Zone forming part of the remnant arc.
7. Collision between the Sask Craton and Churchill Plate, beginning at ca. 1.84 Ga, leading to the inversion of the Kisseynew basin and deposition of molasse deposits.
8. Terminal collision involving the Superior craton, beginning at ca. 1.83 Ga and ongoing until approximately 1.77 Ga. (Corrigan, 2004).).
9. The final stages of continental collision where marked by 1.84-1.82 Ga. magma generation within the Kisseynew domain related to interaction between the Sask craton and the Flin Flon–Glennie complex, and a 1.82-1.79 Ga. collision of the Rae and Superior cratons. A decrease in subduction angle likely resulted from northward-directed subduction of more buoyant crust, with associated changes in thermal conditions leading to melting over a wide area. Ultimately subduction ceased, and the slab foundered into the mantle, potentially resulting in the generation of alkalic and potassic magmas within the Rae and Hearne cratons.