~85 Ma Sevier orogeny Classic “Andean margin” Arc -arc -fold-and-thrust -foredeep 100 km Jones et al., Figure 2a Jones et al., Geosphere 2011 ~80 Ma Sevier orogeny Classic “Andean margin” fading Arc -arc dying Sierra Nevada, Mojave?, Penninsular Ranges -fold-and-thrust stops, southern Nevada -foredeep broadens ? Farallon A34-32o (84-73 Ma) Jones et al., Figure 2b Jones et al., Geosphere 2011 ~75 Ma Sevier/Laramide Arc? orogeny Classic “Andean margin” disrupted -arc dead Sierra Nevada, Nevada -arc? in Mojave; eastward in Mexico -fold-and-thrust stops, southern Nevada -foreland deformation starts -foredeep nearly gone, sedimentation sweeps to east Farallon A34-32o (84-73 Ma) Arc? Jones et al., Figure 2c Jones et al., Geosphere 2011 ~70 Ma Laramide orogeny Arc? -limited volcanism in west typically peraluminous (crustal melts?) -Colorado Mineral Belt established -fold-and-thrust stops, southern Nevada-Arizona -foreland deformation substantial -foredeep limited, COMB sedimentation focused to east 100 km Farallon A32-30o (73-67 Ma) Arc? Jones et al., Figure 2d Jones et al., Geosphere 2011 ~65 Ma Laramide orogeny Arc? -limited volcanism in west typically peraluminous (crustal melts?) -Colorado Mineral Belt active -fold-and-thrust stops, southern Nevada-Arizona -foreland deformation well- defined -thrust-belt foredeep absent, COMB sedimentation focused in Ireteba pluton local basins 100 km Farallon A30-27 (67-62 Ma) Arc Jones et al., Figure 2e Jones et al., Geosphere 2011 Torsvik et al., G^3, 2019 Henderson et al.' Farallon Aseismic Ridges, Laramide Orogeny lP5 J• Y -/1 Present•A-%=.- !,-,.•Hlsex ,--"•• _Hess • 0 • • • 30•N ••', •awaiian' %•-- •?. OøN , •-,• ;.%Hotspot Z• • • . -.•;•' :•_COcOs • O'N:• •..- + % + '•Hotspot ••• - OøN • ' Wilkes- - • ' ' Hotspot 180•W 90•W 180øW 90'W (b) 154 Ma Chron M21 30'N 30øN • Farallon Izanagi •% O'N OøN / Pacific 180:'W 90'W , , (f) 123 Ma Chron M 1 56Ma Kula/ -.,,'• 30øN 30øN Chron•""'••••2 • , "' Izanagi• Farallon Pacifi O'N OøN / Pacific + •'•'•'•'-":'?:'•' ';•';"•••'.•,• Farallon 180øW 90øW 180øW 90øW Fig. 3. Reconstructions of the lithospheric plates with Hendersonrespect to etthe al., Tectonics, 1984 hot spots, and formation of hot spot-produced volcanic edifices on the Pacific and Farallon plates at the spreading ridge. Hot spots are held fixed and the oceanic and continental plates are moved with respect to the hot spots from 154 Ma to 56 Ma. Large symbols show locations of the active hot spots in each frame, heavy lines show the tracks left on the oceanic plates by their motion over the hot spots. The large symbols are solid when the hot spots were located on the Pacific plate and open when the hot spots were located on the Kula plate. (a) The present location of the Lynn Seamount hot spot, the Wilkes hot spot, and the Hawaiian hot spot on the Pacific plate. (b)-(f) Reconstructions of plates, continents, and aseismic ridges. Locations of aseismic ridges showu subducted beneath North America are uncorrected for the dip of the slab. Barbed line marks the trench axis. Very heavy lines mark the ridge axes. This is a Mercator projection. NATURE GEOSCIENCE DOI: 10.1038/NGEO829 LETTERS A’ SNB: Sierra Nevada batholith 223 270 Fig. 3 SCB: Southern California batholith 315 section line PRB: Peninsular Ranges batholith Approximate location of trench 68 belt thrust SNB 72 evier Active margin S Strike-slip 79 zone 1 134 Intra-arc 76 ductile shear belts Shallow flat Colorado subduction 80 Approximate trace Plateau of San Andreas fault /Gulf of California 84 179 223 Early Palaeogene Sierra Madre Occidental arc SCB 223 Late Cretaceous eastern 88 batholitic belt Early Cretaceous western batholithic belt 179 Cretaceous to Early Tertiary forearc basin 55 A Franciscan subduction Farallon complex plate Laramide foreland 60 Late Cretaceous/Early Palaeogene 134 dextral transpression of Front Ranges belt 223 Late Cretaceous/Early Palaeogene 65 normal shortening of Wyoming belts PRB Early Palaeogene mainly thin-skinned (km) thrusting of Mexican belt 0100 200 300 400 Position of main Centre of putative Isotherms (¬40 °C): putative conjugates conjugates through time (Myr BP) 179 80 Myr BP slab contour at given depth (in km) Shatsky at 80 Myr BP 80 Shatsky Liu et al., Nature Geosc, 2010 Hess at 60 Myr BP 60 Hess 179 60 Myr BP slab contour at given depth (in km) Figure 2 Palinspastic map showing the southwest Cordilleran active margin and the Laramide foreland for the end of Cretaceous time3 with the | temperature field overlain. Contours (same as Fig. 1; light blue for 80 Myr BP, red for 60 Myr BP) and predicted positions of the putative Shatsky and Hess conjugate plateaux (inside the 179 km contour) are from the inverse model. Filled circles represent the volumetric centre of the putative Shatsky (light blue) and Hess (red) conjugate plateaux at given age during their subduction beneath North America. Line AA0 indicates the surface trace of the cross-sections shown in Fig. 3. these areas (Fig. 3a,b). Collectively, our study suggests that initial subducting Inca plateau in Peru23, where broad surface subsidence subduction of the plateau should have caused the slab to flatten is observed above the flat slab (Supplementary S2). because of the extra buoyancy associated with its thick crust, Laramide uplifts, at local scales, initiated along thrust faults but continuing flattening would mostly result from the increased during flat-slab underplating11 (Fig. 2). Subsequent regional-scale plate coupling with a possibly weakened mantle wedge21. As uplifts, however, are associated with removal of the plateau from the Shatsky conjugate translated beneath the Colorado Plateau beneath the Laramide province. The flat-slab associated with the region (Fig. 2), the oceanic crust is deep enough to undergo the Shatsky conjugate gradually sank deeper into the mantle as it basalt–eclogite phase transformation, during which the plateau migrated to the northeast. Both horizontal removal of flat slab loses its positive buoyancy22. Both the overall negative slab density from beneath the Colorado Plateau region after 80 Myr bp and anomaly and enhanced plate coupling during shallow subduction the overall diminishing negative dynamic topography associated drag the surface downward (Fig. 3a). A present-day analogy is the with cold slabs (Fig. 3b,c) led the surface to rebound in a NATURE GEOSCIENCE ADVANCE ONLINE PUBLICATION www.nature.com/naturegeoscience 3 | | 542 W.A. Yonkee, A.B. Weil / Earth-Science Reviews 150 (2015) 531–593 Yonkee & Weil, Earth Sci Rev, 2015 Fig. 6. Schematic lithospheric cross sections, shown for: A — Late Jurassic (~150 Ma); B — Early Cretaceous (~100 Ma); C — Late Cretaceous (~80 Ma); and D — Paleogene (~50 Ma) times. The Late Jurassic was marked by development of an E-dipping subduction zone, increased igneous activity along the magmatic arc, and initial shortening in the western part of the orogenic system. The Early Cretaceous included development of an accretionary complex, growth of the magmatic arc, crustal thickening in the hinterland, thin-skin shortening of the western Sevier belt, and sedimentation within a foreland basin. The Late Cretaceous included decreasing subduction angle (along with early development of a flat-slab segment to the south), a flare-up followed by shutdown of the magmatic arc, lower crustal thickening beneath a hinterland plateau, shortening in the eastern Sevier belt, and broad dynamic subsidence of the Western Interior Seaway. The Paleogene included rapid subduction and NE-underthrusting of the flat-slab segment, minor extension in the thickened hinterland, final shortening in the eastern Sevier belt, and uplift of Laramide arches that disrupted the foreland basin. zircon and geochemical signatures compared to temporally correlative coarser volcaniclastics with maximum depositional ages as young as forearc strata of the Great Valley Group, with Early Cretaceous sediment 123 Ma, which underwent blueschist metamorphism at 117 Ma. The sources mostly from accreted terranes and Jurassic volcanics, and Late Yolla Bolly terrane consists mostly of clastics with maximum deposi- Cretaceous sources mostly from more deeply eroded parts of the tional ages of ~120–110 Ma, along with a slab of ~170 Ma oceanic basalt magmatic arc (Dumitru et al., 2015). and chert, which underwent lower blueschist metamorphism at The eastern belt includes from east to west, the South Fork Mountain ~110 Ma (Dumitru et al., 2010, 2015). Limited accretion prior to schist, Valentine Formation, and Yolla Bolly terrane. The eastern belt 125 Ma may reflect thin trench fill during early arc growth, whereas was juxtaposed against the structurally overlying Coast Range ophiolite rapid accretion after ~125 Ma appears associated with thicker trench and Great Valley Group of the forearc basin along the Coast Range fault fill derived from the growing arc. The central belt consists mostly of mé- zone, which is interpreted to have initiated along the subduction zone at lange comprised of disrupted volcaniclastic mudstone, sandstone, and ~160 Ma and been subsequently reactivated as a normal fault that exotic blocks, which likely formed by a combination of sedimentary helped exhume the accretionary complex and generate accommodation (Wakabayashi, 2015) and tectonic (Cloos, 1982)processes,andsubse- space for deposition of forearc strata (Unruh et al., 2007; Ernst, 2011). quently underwent low-grade metamorphism. Strata contain rare Late Protoliths of the South Fork Mountain schist include ~135 Ma oceanic Cretaceous fossils and have DZ maximum