The odyssey of the Cache Creek terrane, Canadian Cordillera: Implications for accretionary orogens, tectonic setting of Panthalassa, the Pacific superwell, and break-up of Pangea

Abstract

The Cache Creek terrane (CCT) of the Canadian Cordillera consists of accreted seamounts that originated adjacent to the Tethys Ocean in the Permian. We utilize Potential Translation Path plots to place quantitative constraints on the location of the CCT seamounts through time, including limiting the regions within which accretion events occurred. We assume a starting point for the CCT seamounts in the easternmost Tethys at 280 Ma. Using reasonable translation rates (11 cm/a), accretion to the StikiniaQuesnellia oceanic arc, which occurred at about 230 Ma, took place in western Panthalassa, consistent with the mixed Tethyan fauna of the arc. Subsequent collision with a continental terrane, which occurred at about 180 Ma, took place in central Panthalassa, N 4000 km west of North America yielding a composite ribbon continent. Westward subduction of oceanic lithosphere continuous with the North American continent from 180 to 150 Ma facilitated docking of the ribbon continent with the North American plate.The paleogeographic constraints provided by the CCT indicate that much of the Canadian Cordilleran accretionary orogen is exotic. The accreting crustal block, a composite ribbon continent, grew through repeated collisional events within Panthalassa prior to docking with the North American plate. CCT's odyssey requires the presence of subduction zones within Panthalassa and indicates that the tectonic setting of the Panthalassa superocean differed substantially from the current Pacific basin, with its central spreading ridge and marginal outward dipping subduction zones. A substantial volume of oceanic lithosphere was subducted during CCT's transit of Panthalassa. Blanketing of the core by these cold oceanic slabs enhanced heat transfer out of the core into the lowermost mantle, and may have been responsible for the Cretaceous Normal Superchron, the coeval Pacific-centred mid-Cretaceous superplume event, and its lingering progeny, the Pacific Superswell. Far field tensile stress attributable to the pull of the slab subducting beneath the ribbon continent from 180 to 150 Ma instigated the opening of the Atlantic, initiating the dispersal phase of the supercontinent cycle by breaking apart Pangea. Docking of the ribbon continent with the North American plate at 150 Ma terminated the slab pull induced stress, resulting in a drastic reduction in the rate of spreading within the growing Atlantic Ocean.

Geology, Mantle Tomography, and Inclination Corrected Paleogeographic Trajectories Support Westward Subduction During Cretaceous Orogenesis in the North American Cordillera

“…Over the years a few workers (Moores 1970;Mattauer et al 1983;Chamberlain and Lambert 1985;Lambert and Chamberlain 1988;Moores 1998) proposed alternative models involving collision of North America with various arcs above westward-dipping subduction zones but they failed to garner traction in the community. Some more recent models for Cordilleran development, created to better explain the overall development of the orogen, posit that the leading edge of North America was subducted to the west beneath an exotic ribbon continent during Cretaceous orogenesis (Johnston and Borel 2007;Johnston 2008;Hildebrand 2009Hildebrand , 2013. Testing these models is difficult because there were no alternating magnetic anomalies produced during the lengthy Cretaceous superchron and huge tracts of the easternmost floor of the Pacific Ocean basin were subducted (Engebretson et al 1985;Atwater 1989).…”

“…The evidence suggests that it was mostly assembled by 160 Ma, but ultimately amalgamated by 100 Ma, when a basin of unknown nature and width that separated the eastern and western halves of the Peninsular Ranges batholith, the Sierra Nevada, and the Coast Plutonic complex, closed (Kistler 1990;Kimbrough et al 2001;Lackey et al 2008;Gehrels et al 2009;Hildebrand 2013). The North American platform terrace was unaffected by any of these events; either the more outboard collisions were sufficiently small or local that they did not affect the North American margin, or, more likely given the number, variety, and extent of terranes, there was an intervening ocean basin (Johnston and Borel 2007;Johnston 2008;Hildebrand 2009Hildebrand , 2013. That the North American platform terrace was unaffected by these events forms a key part of the evidence that the Cordilleran Ribbon Continent and North America were separate entities until they collided -initially during the Sevier event and later during Laramide terminal collision.…”

The Tooth of Time: The North American Cordillera from Tanya Atwater to Karin Sigloch

“…9), assuming average plate velocities of 1°/Myr (11 cm/yr). The paths are constrained by the accretion of the seamounts ~230 Ma to the StikiniaQuesnellia magmatic arc situated in western Panthalassa, >4000 km west of North America, and their collective accretion to the inferred pericratonic Nisling terrane ~180 Ma and to North America itself by Late Jurassic (Fernie Group) time (Johnston and Borel 2007). Their "Odyssey of the Cache Creek terrane" implies repeated subduction of large oceanic slabs in western tropical Panthalassa between 280 and 150 Ma.…”

“…The viability of these connections depends on the transit times of slabs to the CMB and plumes to the surface. They contended (Johnston and Borel 2007) that "westward subduction of oceanic lithosphere, starting at 180 Ma, that was part of the same plate as Pangea, closed the ocean basin separating the supercontinent from the terranes amalgamated within Panthalassa", and they speculate that slab pull associated with this subduction contributed to the breakup of Pangea. At this point, Stephen and I had never met, so I invited him to Harvard for a departmental seminar, in hopes that seismic tomographers in Cambridge might rise to the challenge of imaging the former intra-Panthalassic slab graveyard.…”

“…Conversely, why is there so little evidence of pre-Laramide (pre-125 Ma) tectonism and volcanism in the Rocky Mountains if a subduction zone existed on the continental margin at that time (Hildebrand 2009)? From time to time, iconoclastic scenarios have been invoked to account for these and other problems with the standard model. Some scenarios postulate that the Laramide orogeny resulted from west-dipping subduction and collision of a passive North American margin with a pre-assembled arc-bearing composite terrane (Moores 1970(Moores , 1998Tempelman-Kluit 1979;Mattauer et al 1983;Chamberlain and Lambert 1985;Lambert and Chamberlain 1988;Johnston 2001Johnston , 2008Johnston and Borel 2007;Hildebrand 2009Hildebrand , 2013. The two most recent iconoclasts, Stephen Johnston (University of Victoria) and Robert Hildebrand (University of California -Davis), arrived at nearly the same scenario independently, starting from different backgrounds and parts of the Cordillera.…”