Mantle and geological evidence for a Late Jurassic−Cretaceous suture spanning North America

Abstract

Crustal blocks accreted to North America form two major belts that are separated by a tract of collapsed Jurassic-Cretaceous basins extending from Alaska to Mexico. Evidence of oceanic lithosphere that once underlay these basins is rare at 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 positions paleo-North America in this reference frame, the slab geometries permit detailed predictions of where and when ocean basins at the leading edge of westwarddrifting 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 Ocean. The most conspicuous geologic prediction is that of an oceanic suture that must run along the entire western margin of North America. It formed diachronously between ca. 155 Ma and ca. 50 Ma, analogous to diachro nous suturing of southwest Pacific arcs to the northward-migrating Australian continent today. We proceed to demonstrate that this suture prediction fits the spatio-temporal evidence for the collapse of at least 11 Middle Jurassic to Late Cretaceous basins wedged between the Intermontane and Insular-Guerrero superterranes, about half of which are known to contain mantle rocks. These relatively late suturing ages run counter to the Middle Jurassic or older timing required and asserted by the prevailing, Andean-analogue model for the North American Cordillera. We show that the arguments against late suturing are controvertible, and we present multiple lines of direct evidence for late suturing, consistent with geophysical observations. We refer to our close integration of surface and subsurface evidence from geology and geophysics as "tomotectonic analysis." This type of analysis provides a str...

Evidence for Whole Mantle Convection Driving Cordilleran Tectonics

“…However, these mechanisms are regional in scale and are not intended to explain the many first‐order changes that affect the entire length of the Cordillera. Less conventional models for the Cordillera, proposing changes in subduction polarity and the nature of arc magmatism (continental versus oceanic) as well as the assembly of much of the Cordillera as an outboard terrane (Hildebrand, ; Johnston, ; Sigloch & Mihalynuk, ), are more consistent with our analysis of these first‐order changes. In particular, the 10,000‐km‐long, “mantle wall” of subducted slabs beneath North America appears to trace out a zone of meridional mantle downwelling, and possibly intraoceanic subduction zones, that were stationary over tens of millions of years (Sigloch & Mihalynuk, , ).…”

Along‐Strike Variation in the Magmatic Tempo of the Coast Mountains Batholith, British Columbia, and Implications for Processes Controlling Episodicity in Arcs

“…The paleogeography of the batholith and associated terranes remains uncertain. Most studies recognize two or more arcs or arc fragments prior to mid‐Cretaceous time (Gehrels et al, ; McClelland, Gehrels, Samson, et al, ; Monger et al, ; van der Heyden, ; Sigloch & Mihalynuk, , ). Doubling of a single arc by ~1,000 km of Early Cretaceous sinistral translation is invoked to explain the pre‐mid‐Cretaceous magmatic and sedimentologic patterns in and adjacent to the batholith (Gehrels et al, ; Monger et al, ; Yokelson et al, ).…”

“…Doubling of a single arc by ~1,000 km of Early Cretaceous sinistral translation is invoked to explain the pre‐mid‐Cretaceous magmatic and sedimentologic patterns in and adjacent to the batholith (Gehrels et al, ; Monger et al, ; Yokelson et al, ). Collision of multiple arcs is proposed by Sigloch and Mihalynuk (, ) to reconcile surface geology with tomography. Common to the models, however, is the interpretation that a single Late Cretaceous to early Tertiary batholith formed above an east‐dipping subduction zone.…”

The Dynamic History of 220 Million Years of Subduction Below Mexico: A Correlation Between Slab Geometry and Overriding Plate Deformation Based on Geology, Paleomagnetism, and Seismic Tomography

“…Many authors have interpreted the Vizcaíno‐Cedros ophiolite and arc complexes as allochthonous intraoceanic terranes that accreted to the North American margin by Late Jurassic time, formed either above a Triassic‐Jurassic westward dipping (Boles & Landis, ; Busby‐Spera, ; Critelli et al, ; Sigloch & Mihalynuk, ) or eastward dipping subduction zone (Barnes, ; Rangin, ). However, based on the absence of a Triassic intraoceanic arc, an accretionary prism or crustal suture east of the ophiolite, as well as the lack of evidence of major crustal shortening or a collision, Kimbrough and Moore () instead argued that forearc rifting models developed for the Californian ophiolite belt to the north (Saleeby, , ; Stern & Bloomer, ) may better explain the formation of the Vizcaíno‐Cedros ophiolite and arc complexes.…”

“…Recent frames have attempted to provide such control using correlation of surface geology to deep mantle structure (Torsvik & Cocks, ; van der Meer et al, ) but remain subject to large uncertainties. As a consequence, correlations of seismic tomography to Mesozoic Cordilleran subduction records have led to paleogeographic interpretations that are markedly different for pre‐mid‐Cretaceous times, which are best summarized by scenarios with (Shephard et al, ; van der Meer et al, ) or without (Sigloch & Mihalynuk, , ) subduction directly under the North American continental margin.…”