Mantle and geological evidence for a Late Jurassic – Cretaceous suture spanning North America
Crustal blocks accreted to North America form two major belts which are separated by a tract of collapsed Jura-Cretaceous basins extending from Alaska to Mexico. Evidence of oceanic lithosphere that once underlay these basins is rare at the earth’s surface. Most of the lithosphere was subducted, whi...
| Published in: | GSA Bulletin |
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| Main Authors: | , |
| Format: | Article in Journal/Newspaper |
| Language: | unknown |
| Published: |
Geological Society of America
2017
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| Subjects: | |
| Online Access: | https://doi.org/10.1130/B31529.1 https://ora.ox.ac.uk/objects/uuid:0edbd710-ba27-4aa4-a257-d79b43a84781 |
| Summary: | Crustal blocks accreted to North America form two major belts which are separated by a tract of collapsed Jura-Cretaceous basins extending from Alaska to Mexico. Evidence of oceanic lithosphere that once underlay these basins is rare at the earth’s surface. Most of the lithosphere was subducted, which accounts for the general difficulty of reconstructing oceanic regions from surface evidence. However, this seafloor was not destroyed; it remains in the mantle beneath North America and is visible to seismic tomography, revealing configurations of arc-trench positions back to the breakup of Pangea. The double uncertainty of where trenches ran and how subducting lithosphere deformed while sinking in the mantle is surmountable, owing to the presence of a special-case slab geometry. Wall-like, linear slab belts exceeding 10,000 km in length appear to trace out intra-oceanic subduction zones that were stationary over tens of millions of years, and beneath which lithosphere sank almost vertically. This hypothesis sets up an absolute lower-mantle reference frame. Combined with a complete Atlantic spreading record that paleo-positions North America in this reference frame, the slab geometries permit detailed predictions of where and when ocean basins at the leading edge of westward-drifting North America were subducted, how intra-oceanic subduction zones were overridden, and how their associated arcs and basement terranes were sutured to the continent. An unconventional paleogeography is predicted in which mid- to late Mesozoic arcs grew in a long-lived archipelago located 2000-4000 km west of Pangean North America (while also consistent with the conventional view of a continental arc in early Mesozoic times). The Farallon Ocean subducted beneath the outboard (western) edge of the archipelago, whereas North America converged on the archipelago by westward subduction of an intervening, major ocean, the Mezcalera-Angayucham Oceans. The most conspicuous geologic prediction is that of an oceanic suture which must run along ... |
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