Magmatic Surge Requires Two-Stage Model for the Laramide Orogeny

Magmatic Surge Requires Two-Stage Model for the Laramide Orogeny | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Magmatic Surge Requires Two-Stage Model for the Laramide Orogeny Joshua Schwartz, Jade Star Lackey, Elena Miranda, Keith Klepeis, and 3 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2327151/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract The beginning of the Laramide orogeny is a pivotal time in the geological development of the western United States, but the driving mechanism responsible for mountain building, basin formation and ore mineralization is controversial. Most prominent models suggest this event was caused by the collision of an oceanic plateau with western North America at ca. 88 Ma which caused the angle of subduction beneath the continent to shallow. This subhorizontal (flat) subduction is thought to have led to shut-down of the arc, crustal cooling, and the formation of deep, basement-involved thrust faults that penetrated far into the continental interior. In contrast to these predictions, we show that the arc experienced a magmatic surge, the lower crust was hot (835-750°C) and partially molten from 90 to 70 Ma, and cooling occurred after 75 Ma. These data contradict plateau underthrusting as the driving mechanism at 90-80 Ma; therefore, the Laramide orogeny cannot have been initiated by flat-slab subduction. We propose that the Laramide orogeny is best explained as a two-stage orogeny consisting of a syn-magmatic phase at 90-75 Ma, and a widespread mountain building phase at 75-50 Ma. Only that latter phase is linked to flat-slab subduction. Earth and environmental sciences/Solid Earth sciences/Tectonics Earth and environmental sciences/Solid Earth sciences/Petrology Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction One of the most important periods in the development of western North America occurred at ca. 90 − 80 million years (m.y.) ago when a series of deeply rooted thrust faults began to uplift and imbricate slices of continental lithosphere located hundreds to thousands of kilometers inland from the coast (Fig. 1 A) 1–4 . This major thick-skinned tectonic event, called the Laramide orogeny, lasted ~ 40 m.y., and resulted in mountain building, the formation of foreland basins, and the development of ore mineralization from Canada to northern Mexico and as far east as the Black Hills of South Dakota 4–6 . Nevertheless, despite its widespread impact on the tectonic development of western North America, the exact mechanisms that caused this major tectonic event remain controversial 3,7–10 . Most widely cited models argue that the cause of the Laramide orogeny was the flat-slab subduction of a thick oceanic plateau beneath the Southern California Batholith (present-day Transverse Ranges in Southern California) at 90 − 80 Ma resulting in shutdown of arc magmatism and cooling of the upper-plate crust 9,11–17 . These ‘amagmatic’ models resemble the present-day central Andean orogen (27–33°S) where a flattened subducted oceanic slab is associated with thick-skin deformation and relative magmatic quiescence in the Sierras Pampeanas 18 . In contrast, other models propose that this tectonic transition was caused by the outboard collision of off-shore arc terranes 19 , or increased lithospheric coupling 7,20 . Important features of these conflicting models are that they make different predictions regarding the timing and duration of magmatism, cooling and uplift during the development of the Laramide orogeny. To resolve these conflicting models, we examined the frontal arc of the Southern California Batholith (SCB) which represents an ~ 500 km-wide, paleo-arc segment of the Mesozoic California arc where prior studies place the initial collision between the conjugate Shatsky plateau and the western North American margin (Fig. 1 B) 14,16 . This arc segment lies between the southern Sierra Nevada batholith (SNB) and northern Peninsular Ranges Batholith (PRB) and is now represented by fault-bounded structural blocks that make up the central and eastern Transverse Ranges and the western Mojave province. This region experienced varying degrees of faulting and rigid block rotation related to development of the San Andreas transform plate boundary beginning in the Miocene 21,22 . We focus on the frontal arc of the Southern California Batholith (SCB) in the Transverse Ranges because of its unique location as the proposed site of initial collision. As such, the frontal arc of the SCB is the key location to test and resolve conflicting models for the structural, magmatic and metamorphic response to tectonic changes that affected continental lithosphere in western North American in the Late Mesozoic. Results Zircon geochronology To test models for the Laramide orogeny, we compiled > 260 Pb/U ages, including 79 new zircon and titanite dates to establish the timing and duration of magmatism, metamorphism and deformation in the Southern California Batholith with the goal of resolving conflicting models. Areal addition rates were calculated from integrating igneous ages with pluton areas determined from digitized geologic maps of Southern California (see Supplementary file). Our compilation and new data encompass all major blocks in the SCB including the San Gabriel, Pine Mountain, Alamo-Frazier Mountain, Little San Bernardino, San Bernardino, and Salinian blocks (Fig. 1 B). Igneous zircon ages reveal 4 discrete pulses of Late Paleozoic to Mesozoic magmatism at 260–210 Ma, 160–140 Ma, 120–118 Ma, and 90–70 Ma (Fig. 2 A). The latter pulse culminated in an arc flare-up event which peaked at 85–75 Ma and was associated with widespread, voluminous plutonism throughout the SCB (Fig. 1 B, 2 B). These Late Cretaceous plutons have typical Cordilleran arc magma geochemistry: most are magnesian, metaluminous to weakly peraluminous, and calc-alkalic with strong crustal affinities that reflect mixtures of Proterozoic crust with juvenile (Mesozoic) sources 23,24 . Although the cause of the 85–75 Ma flare-up remains unclear, magmatism persisted in the frontal arc of the SCB until ca. 65 Ma and our data show that most igneous activity had ceased by ca. 70 Ma (Fig. 2 C; Supplementary file). An analysis of metamorphic zircon and titanite shows that the batholith records high temperatures during the Late Cretaceous transition to thick-skinned, Laramide shortening. The data demonstrate that the arc-flare up event in the SCB was also coeval with high-temperature metamorphism at garnet-granulite to upper amphibolite-facies metamorphism and partial melting in the lower crust of the arc. Evidence for high-temperature metamorphism is preserved in the Cucamonga terrane (eastern San Gabriel Mountains) where metamorphic zircons in gneisses, migmatites and calc-silicates give dates ranging from 86 to 76 Ma at 9 − 7 kbars 25,26 (Supplementary file). Ti-in-zircon analyses on metamorphic rims indicate temperatures of 800 to 713°C and garnet-quartz oxygen isotope thermometry yields similar metamorphic temperatures of 835 to 777°C. These data are consistent with mineral exchange thermometry which give temperatures of 800 − 775°C 26 . In the Coast Ridge Belt (Santa Lucia Mountains, Salinia block), Kidder et al. 27 also report peak metamorphic pressures of 800°C at 7.5 kbars at 81 to 76 Ma. These results are significant because they show that the root of the arc was hot and partially molten through ca. 76 Ma. Our regional mapping of mylonitic ductile-shear zones in the SCB documents that the Late Cretaceous arc flare-up was temporally and spatially associated with syn-plutonic development of a regionally extensive, transpressional shear system. This system includes, from north to south (present-day coordinates): the Nacimiento fault 28 , the Tumamait shear zone (Pine Mountain block), the Alamo Mountain-Piru Creek shear zone, the Black Belt shear zone 25,29 , and the Eastern Peninsular Ranges shear zone 30 . Kinematic indicators from the shear zones generally give oblique top-to-west, sinistral reverse- to thrust-sense motion (present-day geometry). Syn-kinematic, metamorphic titanite dates and Zr-in-titanite temperatures in the Tumamait shear zone range from 77 to 74 Ma at 750°C, titanites in the Black Belt shear zone give an age of 83 Ma, and those in the eastern Peninsular Ranges shear zone give ages of 89–78 Ma at 750°C 31 (Supplementary file). In the Salinian block, Kidder et al. 27 document extensive thickening and high-temperature ductile deformation from 93 − 81 Ma, and Singleton and Cloos 32 show that the juxtaposition of the Salinian block against the Nacimiento block occurred between ca. 75 Ma and 60 Ma along sinistral strike-slip and/or thrust faults. Thus, these dates and temperatures indicate that the frontal arc of the SCB experienced sinistral-reverse, transpressional deformation during the Late Cretaceous flare-up event (Fig. 2 C). Therefore, the collective data show simultaneous magmatism and high-temperature intra-arc shortening during the Late Cretaceous transition to thick-skinned deformation. Implications for Late Cretaceous high-temperature arc processes in the SCB Our compilation of igneous zircon dates from the frontal arc of the SCB document a widespread surge of Late Cretaceous magmatism from 90 − 70 Ma. This surge occurred throughout all major structural blocks which make up the ca. 500-km wide segment of the Late Cretaceous arc system (Fig. 1 B, 2 ). Outside of the frontal arc, coeval magmatism also occurred in the back-arc which is now represented by the adjacent Mojave Desert 33 . The widespread occurrence of plutonic rocks throughout the SCB and their arc-like geochemical features 24,34 suggests that mechanisms for generating large volumes of melt were still active through the Late Cretaceous. Arc flare-ups similar in magnitude and duration also occurred in adjacent sectors of the arc slightly before the SCB event (e.g., southern SNB at 110 − 90 Ma 35 and northern PRB at 99 − 91 Ma 36 (Fig. 2 B). Importantly, our data from the SCB are in direct conflict with existing amagmatic models that invoke underthrusting of the conjugate Shatsky plateau beneath the SCB from 88 − 75 Ma and removal of the lower crust and lithospheric mantle during the beginning of the Laramide orogeny 9,14,16 . Metamorphic ages and thermometry in the Cucamonga and Salinian granulites also demonstrate that the lower crust of the SCB was hot and partially molten through 75 Ma, and these features cannot be explained by existing amagmatic models. The presence of this hot arc root provides further evidence that high-temperature arc processes were operating until 75 − 70 Ma and shut-down of the frontal arc did not occur until after 70 Ma. This observation is illustrated in Fig. 3 which shows a compilation of time-temperature profiles derived from mineral thermochronology from the major structural blocks in the SCB. These data highlight two important features of the SCB: 1) the Late Cretaceous flare-up in the SCB was coeval with intra-arc, oblique sinistral-reverse thrusting and high-temperature metamorphism, and 2) termination of arc magmatism in this region was associated with an abrupt phase of rapid regional cooling of the SCB below 350°C at ca. 75 − 70 Ma (Fig. 3 ). This regionally extensive and rapid cooling event signifies the onset of regional refrigeration of the SCB due to flat-slab subduction involving the cold, conjugate Shatsky plateau and tectonic underplating of trench sediments beneath the SCB after 75 − 70 Ma 37 . Post 75-70 Ma underthrusting of the conjugate Shatsky plateau One of the key results of our work is that flat-slab subduction beneath the SCB post-dates the beginning of Laramide deformation by ~ 15 Myr. Consequently, oceanic plateau underthrusting cannot be called upon as the driver for thick-skin deformation in the western US prior to ca. 75 Ma. However, several existing data sets support a link between Laramide deformation and flat-slab subduction after 75 Ma. For example, the general timing of major thick-skin, basement-cored thrusting and basin development in Utah, Colorado, Wyoming and SW Montana occurred from 70 − 50 Ma 4 which agrees well with underthrusting of the conjugate Shatsky after 75 Ma. In addition, zircon ages in peridotite xenoliths from the Colorado Plateau are consistent with derivation from the lithosphere at the base of the SCB and ~ 500 km of lateral displacement inboard to the Colorado Plateau transition zone after 70 Ma 9 . In the SCB, the presence of underplated schists is commonly cited as evidence for flat-slab subduction 38 , and our geo- and thermochronological results also support a post-75 Ma emplacement model for the schists. Underplated schists in the Transverse Ranges have zircon age distributions with maximum depositional ages ranging from 75 − 68 Ma (Pelona Schist 38,39 ) and amphibole and muscovite 40 Ar/ 39 Ar metamorphic ages from mafic schists are no older than 60 Ma 38,40,41 . Field observations in the Pelona schist also show no evidence for partial melting or intrusion by Cretaceous plutons. These textural and temporal constraints indicate that underplating of schists beneath the SCB took place after the termination of the SCB flare up event after 70 Ma. Therefore, these data are also consistent with flat-slab subduction after 70 Ma. Spatial and temporal trends in sedimentary provenance within California forearc sediments also show a pronounced and sudden influx of continent-derived detritus to the southern California margin at ca. 75 Ma. Sharman et al. 42 argued that this sudden influx reflects the development of a geomorphic breach within the Cretaceous arc and an associated rapid migration of forearc drainages into the continental interior. The timing of this breach is ~ 15 Myr younger than postulated plateau underthrusting in prior models, but is compatible with our model for the arrival of the conjugate Shatsky after 75 − 70 Ma (e.g., Fig. 3 ). These data are also consistent with eastward migration of magmatism away from the coastal arcs after 75 Ma which has been interpreted to reflect shallowing of the subduction angle over time 4,43,44 . We illustrate these features in our model (Fig. 4 ) which shows the tectonomagmatic evolution of the SCB-arc segment from 85 − 50 Ma. A two-stage, model for the Laramide orogeny Data from the SCB provide critical new information that allows us to resolve the debate about the link between upper-plate deformation in the western North American Cordillera and the kinematics and geometry of the down-going plate at the beginning of the Laramide orogeny. Our results show clearly that arc magmatism was robustly active through ca. 70 Ma, and underthrusting of the conjugate Shatsky plateau must have occurred after 75 − 70 Ma. Therefore, flat-slab subduction of the conjugate Shatsky plateau cannot explain the transition from thin- to thick-skin deformation at 90 − 80 Ma. This conclusion is supported by a number of sedimentological and thermochronological studies on Mesozoic sediments in SW Montana which provide evidence for the early onset of Laramide-style deformation well before 80 Ma 10,45,46 . These data are problematic from the standpoint of a single flat-slab event because the timing of basin formation predates the arrival of the conjugate Shatsky plateau in all flat-slab models 9,14,16 . Moreover, the southwest Montana basins are well outside the commonly cited corridor of Laramide deformation caused by flat-slab underthrusting 17 . These relationships coupled with our data from the SCB lead us to the conclusion that the Laramide orogeny cannot have a single driving mechanism. Therefore, we propose that the Laramide orogeny is a composite tectonic event consisting of two distinct stages of paired mountain building and basin formation: 1) an early phase at 90 − 75 Ma, which was active during flare-up activity in the SCB, and 2) a more-widespread phase of basement-involved thrusting and basin formation in the continental interior from 75 − 40 Ma. In this model, the driving mechanism for initial Laramide deformation is not related to flat-slab subduction, but is closely linked to orogen-scale dextral transpression from ca. 100 − 85 Ma along the US Cordillera 19,47,48 . We attribute the second stage to flat-slab subduction of the conjugate Shatsky plateau beneath the SCB following the termination of flare-up magmatism in the SCB. These new data from the SCB show that multiple driving mechanisms are required to explain the diverse and previously conflicting datasets for the development of Laramide orogeny from 90 − 40 Ma. Online Methods Any methods, additional references, Nature Research reporting summaries, source data, statements of data availability, and associated accession codes are available at XXXX. Declarations Acknowledgements We thank Matt Coble, John Wiesenfeld and Zhan Peng for assistance with zircon and titanite petrochronology and Ilya Bindeman for stable isotope thermometry. Gabriel Romero and Ben Conway provided assistance in the field and in the laboratory. John Banacky and Ron Goodman from the Cucamonga Foothill Preservation Alliance and Justin Okin provided tremendous assistance with field logistics. Financial support for this project was provided by the National Science Foundation grant EAR-2138733 (Schwartz and Miranda), EAR 1655152 (Cecil and Schwartz), EAR–0948706 and OCE-1338842 (Lackey), NSF-EAR 2138734 (Klepeis), and Southern California Earthquake Center grants #21140 and #19023 (Miranda and Schwartz). Robles thanks the Geological Society of America for financial assistance. References Dickinson, W. R. & Snyder, W. S. Plate tectonics of the Laramide orogeny. in Laramide Folding Associated with Basement Block Faulting in the Western United States (ed. Matthews, V.) 355–366 (Geological Society of America Memoir 151, 1978). Decelles, P. G. Late Jurassic to Eocene Evolution of the Cordilleran Thrust Belt and Foreland Basin System, Western U.S.A. (2004). English, J. M. & Johnston, S. T. The Laramide Orogeny: What Were the Driving Forces? Int Geol Rev 46 , 833–838 (2004). Yonkee, W. A. & Weil, A. B. Tectonic evolution of the Sevier and Laramide belts within the North American Cordillera orogenic system. Earth Sci Rev 150 , 531–593 (2015). Snoke, A. W. & Chapman, J. B. NORTH AMERICA | Southern Cordillera. in Encyclopedia of Geology (eds. Richard C. Selley, L. Robin M. Cocks & Ian R. Plimer) 48–61 (Elsevier Ltd, 2021). doi:10.1016/B0-12-369396-9/00402-0. Dickinson, W. R. Evolution of the North American Cordillera. Annu Rev Earth Planet Sci 32 , 13–45 (2004). Wells, M. L., Hoisch, T. D., Cruz-Uribe, A. M. & Vervoort, J. D. Geodynamics of synconvergent extension and tectonic mode switching: Constraints from the Sevier-Laramide orogen. Tectonics 31 , (2012). Jackson, W. T. et al. Initial laramide tectonism recorded by upper cretaceous paleoseismites in the northern Bighorn Basin, USA: Field indicators of an applied end load stress. Geology 47 , 1059–1063 (2019). Chapman, A. D., Rautela, O., Shields, J., Ducea, M. N. & Saleeby, J. Fate of the lower lithosphere during shallow-angle subduction: The Laramide example. GSA Today 30 , (2020). Carrapa, B., DeCelles, P. G. & Romero, M. Early Inception of the Laramide Orogeny in Southwestern Montana and Northern Wyoming: Implications for Models of Flat‐Slab Subduction. J Geophys Res Solid Earth 124 , 2102–2123 (2019). Livaccari, R. F., Burke, K. & Şengör, A. M. C. Was the Laramide orogeny related to subduction of an oceanic plateau? Nature 289 , 276–278 (1981). Henderson, L. J., Gordon, R. G. & Engebretson, D. C. Mesozoic aseismic ridges on the Farallon Plate and southward migration of shallow subduction during the Laramide Orogeny. Tectonics 3 , 121–132 (1984). Barth, A. P. & Schneiderman, J. S. A comparison of structures in the andean orogen of northern chile and exhumed midcrustal structures in southern california, usa: An analogy in tectonic style? Int Geol Rev 38 , 1075–1085 (1996). Saleeby, J. Segmentation of the Laramide Slab - Evidence from the southern Sierra Nevada region. Bulletin of the Geological Society of America 115 , 655–668 (2003). Liu, L., Spasojević, S. & Gurnis, M. Reconstructing Farallon Plate Subduction Beneath North America Back to the Late Cretaceous. Science (1979) 322 , 934–938 (2008). Liu, L. et al. The role of oceanic plateau subduction in the Laramide orogeny. Nat Geosci 3 , 353–357 (2010). Axen, G. J., van Wijk, J. W. & Currie, C. A. Basal continental mantle lithosphere displaced by flat-slab subduction. Nat Geosci 11 , 961–964 (2018). Ramos, V. A., Cristallini, E. O. & Perez, D. J. The Pampean Flat-slab of the Central Andes. 15 , 6–8 (2002). Maxson, J. & Tikoff, B. Hit-and-run collision model for the Laramide orogeny, western United States. Geology 24 , 968–972 (1996). Wells, M. L. & Hoisch, T. D. The role of mantle delamination in widespread Late Cretaceous extension and magmatism in the Cordilleran orogen, western United States. Bulletin of the Geological Society of America 120 , 515–530 (2008). Powell, R. E. Balanced palinspastic reconstruction of pre-late Cenozoic paleogeology, southern California: Geologic and kinematic constraints on evolution of the San Andreas fault system. in The San Andreas Fault System: Displacement, Palinspastic Reconstruction, and Geologic Evolution, Geological Society of America Memoir 178 (1993). Dickinson, W. R. Kinematics of Transrotational Tectonism in the California Transverse Ranges and Its Contribution to Cumulative Slip Along the San Andreas Transform Fault System . (Geological Society of America Special Paper Volume 305, 1996). doi:10.1130/SPE305. Barth, A. P., Wooden, J. L., Tosdal, R. M. & Morrison, J. Crustal contamination in the petrogenesis of a calc-alkalic rock series: Josephine Mountain intrusion, California. Geol Soc Am Bull 107 , 201–212 (1995). Barth, A. P. Mid-crustal emplacement of Mesozoic plutons, San Gabriel Mountains, California, and implications for the geologic history of the San Gabriel terrane. in The Nature and Origin of Cordilleran Magmatism (ed. Anderson, J. L.) vol. 174 33–46 (Geological Society of America, 1990). May, D. J. & Walker, N. W. Late Cretaceous juxtaposition of metamorphic terranes in the southeastern San Gabriel Mountains, California. Geol Soc Am Bull 101 , 1246–1267 (1989). Barth, A. P. & May, D. J. Mineralogy and pressure–temperature–time path of Cretaceous granulite gneisses, south‐eastern San Gabriel Mountains, southern California. Journal of Metamorphic Geology 10 , 529–544 (1992). Kidder, S., Ducea, M., Gehrels, G., Patchett, P. J. & Vervoort, J. Tectonic and magmatic development of the Salinian Coast Ridge Belt, California. Tectonics 22 , (2003). William R. Dickinson. Cretaceous Sinistral Strike Slip Along Nacimiento Fault in Coastal California. Am Assoc Pet Geol Bull 67 , (1983). May, D. J. Late Cretaceous intra-arc thrusting in southern California. Tectonics 8 , 1159–1173 (1989). Goodwin, L. B. & Renne, P. R. Contributions to Mineralogy and Petrology Effects of progressive mylonitization on Ar retention in biotites from the Santa Rosa mylonite zone, California, and thermochronologic implications. Contrib Mineral Petrol 108 , 283–97 (1991). Jiang, H., Lee, C. T. A., Morgan, J. K. & Ross, C. H. Geochemistry and thermodynamics of an earthquake: A case study of pseudotachylites within mylonitic granitoid. Earth Planet Sci Lett 430 , 235–248 (2015). Singleton, J. S. & Cloos, M. Kinematic analysis of melange fabrics in the Franciscan complex near San Simeon, California: Evidence for sinistral slip on the Nacimiento fault zone? Lithosphere 5 , 179–188 (2013). Economos, R. C. et al. Testing models of Laramide orogenic initiation by investigation of Late Cretaceous magmatic-tectonic evolution of the central Mojave sector of the California arc. Geosphere 17 , 2042–2061 (2021). Barth, A. P., Wooden, J. L., Mueller, P. A. & Economos, R. C. Granite provenance and intrusion in arcs: Evidence from diverse zircon types in Big Bear Lake Intrusive Suite, USA. Lithos 246–247 , 261–278 (2016). Paterson, S. R., Okaya, D., Memeti, V., Economos, R. & Miller, R. B. Magma addition and flux calculations of incrementally constructed magma chambers in continental margin arcs: Combined field, geochronologic, and thermal modeling studies. Geosphere 7 , 1439–1468 (2011). Premo, W. R., Morton, D. M., Wooden, J. L. & Fanning, C. M. U-Pb zircon geochronology of plutonism in the northern Peninsular Ranges batholith, southern California: Implications for the Late Cretaceous tectonic evolution of southern California. in Peninsular Ranges Batholith, Baja California and Southern California (eds. Morton, D. M. & Miller, F. K.) (Geological Society of America Memoir 211, 2014). doi:10.1130/2014.1211(04). Dumitru, T. A., Gans, P. B., Foster, D. A. & Miller, E. L. Refrigeration of the western Cordilleran lithosphere during Laramide shallow-angle subduction. Geology 19 , 1145–1148 (1991). Jacobson, C. E. et al. Late Cretaceous-early Cenozoic tectonic evolution of the southern California margin inferred from provenance of trench and forearc sediments. Bulletin of the Geological Society of America 123 , 485–506 (2011). Grove, M., Lovera, O. & Harrison, M. Late Cretaceous cooling of the east-central Peninsular Ranges Batholith (33 degrees N); relationship to La Posta Pluton emplacement, Laramide shallow subduction, and forearc sedimentation. in Tectonic evolution of northwestern Mexico and the Southwestern USA (eds. Johnson, S. E. et al.) 355–379 (Geological Society of America Special Paper 374, 2003). doi:10.1130/0-8137-2374-4.355. Xia, H. & Platt, J. P. Structural and rheological evolution of the Laramide subduction channel in southern California. Solid Earth 8 , 379–403 (2017). Jacobson, C. E. The 40Ar/39Ar geochronology of the Pelona schist and related rocks, southern California. J Geophys Res 95 , 509 (1990). Sharman, G. R., Graham, S. A., Grove, M., Kimbrough, D. L. & Wright, J. E. Detrital zircon provenance of the late Cretaceous-Eocene California forearc: Influence of Laramide low-angle subduction on sediment dispersal and paleogeography. Bulletin of the Geological Society of America 127 , 38–60 (2015). Coney, P. J. & Reynolds, S. J. Cordilleran Benioff zones. Nature 270 , 403–406 (1977). Chapman, J. B. et al. The North American Cordilleran Anatectic Belt. Earth-Science Reviews vol. 215 Preprint at https://doi.org/10.1016/j.earscirev.2021.103576 (2021). Garber, K. L., Finzel, E. S. & Pearson, D. M. Provenance of Synorogenic Foreland Basin Strata in Southwestern Montana Requires Revision of Existing Models for Laramide Tectonism: North American Cordillera. Tectonics 39 , (2020). Orme, D. A. New Timing Constraints for the Onset of Laramide Deformation in Southwest Montana Challenge our Understanding of the Development of a Thick‐Skinned Structural Style During Flat‐Slab Subduction. Tectonics 39 , (2020). Wyld, S. J. & Wright, J. New evidence for Cretaceous strike-slip faulting in the United States Cordillera and implications for terrane-displacement, deformation patterns, and plutonism. Am J Sci 301 , 150–181 (2001). Tikoff, B. & de Saint Blanquat, M. Transpressional shearing and strike-slip partitioning in the Late Cretaceous Sierra Nevada magmatic arc, California. Tectonics 16 , 442–459 (1997). Ianno, A. J. Studies of the Late Cretaceous Magmatic Crustal Column at Joshua Tree National Park, California. (University of Southern California, 2015). F. K. Miller & D. M. Morton. Potassium-argon geochronology of the eastern Transverse Ranges and southern Mojave Desert, southern California, Geologic Survey Professional Paper 1152 . (1980). Additional Declarations There is NO Competing Interest. Supplementary Files SupplementaryTables.xlsx Supplementary tables SupplementaryFile.docx Supplementary text file Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-2327151","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":166512985,"identity":"e5f6ad89-129c-4dd2-817a-2d46d7dfddcb","order_by":0,"name":"Joshua Schwartz","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABA0lEQVRIiWNgGAWjYBACxgYGNghLAkLJQSWYidWSwGBMUAsQoGpJbCCkhbm9/dljnhoGe/7ZPYafK3/Upff3nzF7wFBhDdOL6bCeM+bGPMcYEmfcOWMseSaBLXfGjRxzA4Yz6bi1zMhhk+ZhY0gwkMjdINmQwJO7QYLHTIKx7TAeLenPpHn+MdgDtWz+2ZAgkW7Afwao5R8+LQlm0rxtDIwbJHK3AW0xSDBgyAFqacCjpeeMmeTcPonEGTfyv1k2pCUYzriRViaRcCzdGJcWQ2CISbz5ZmPPPyMt+WaDTZ08f//hbRIfaqxlcWqBSEigCSfgUA4C8njkRsEoGAWjYBRAAADHVVFEZwIrEQAAAABJRU5ErkJggg==","orcid":"https://orcid.org/0000-0002-8385-2705","institution":"California State University, Northridge","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Joshua","middleName":"","lastName":"Schwartz","suffix":""},{"id":166512986,"identity":"1dba4fdf-fafe-45de-a91d-d5762f9cbef8","order_by":1,"name":"Jade Star Lackey","email":"","orcid":"","institution":"Pomona College","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jade","middleName":"Star","lastName":"Lackey","suffix":""},{"id":166512987,"identity":"ebe77e1a-a4dc-4bcf-962e-218ece10fe15","order_by":2,"name":"Elena Miranda","email":"","orcid":"","institution":"California State University, Northridge","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Elena","middleName":"","lastName":"Miranda","suffix":""},{"id":166512988,"identity":"1db8d4e1-3ecf-4771-80c3-d99ee9dac2e4","order_by":3,"name":"Keith Klepeis","email":"","orcid":"https://orcid.org/0000-0002-7946-0872","institution":"University of Vermont","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Keith","middleName":"","lastName":"Klepeis","suffix":""},{"id":166512989,"identity":"de0cd5a4-0450-435e-9a7e-64068f1dd5cd","order_by":4,"name":"Gabriela Mora-Klepeis","email":"","orcid":"","institution":"University of Vermont","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Gabriela","middleName":"","lastName":"Mora-Klepeis","suffix":""},{"id":166512990,"identity":"60520a44-8076-4e79-9cfc-043da81d4a8c","order_by":5,"name":"Francine Robles","email":"","orcid":"","institution":"California State University, Northridge","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Francine","middleName":"","lastName":"Robles","suffix":""},{"id":166512991,"identity":"527654c7-cde2-4208-a077-98f49dae9ad9","order_by":6,"name":"Jonathan Bixler","email":"","orcid":"","institution":"California State University, Northridge","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jonathan","middleName":"","lastName":"Bixler","suffix":""}],"badges":[],"createdAt":"2022-11-30 00:05:40","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2327151/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2327151/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":31437371,"identity":"37402676-6e80-4e86-a8cc-60b9d3ca5855","added_by":"auto","created_at":"2023-01-11 16:54:22","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":752097,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA.\u003c/strong\u003e\u0026nbsp;Generalized map of the US sector of the North American Cordillera showing the current distribution of the Mesozoic and present-day magmatic arc, Sevier fold-thrust belt, Laramide foreland belt, and hinterland (after\u003csup\u003e4\u003c/sup\u003e). The distribution of crustally derived granites is after Chapman et al.\u003csup\u003e44\u003c/sup\u003e.\u0026nbsp;\u003cstrong\u003eB.\u003c/strong\u003e\u0026nbsp;Late Cretaceous (ca. 90-70 Ma) tectonic reconstruction of the Cordilleran arc in Southern California (after\u003csup\u003e42\u003c/sup\u003e). The Southern California Batholith (SCB) lies between the northern Peninsular Ranges Batholith and southern Sierra Nevada Batholith. This study focuses on the Late Cretaceous (90-70 Ma) plutonic flare-up in the SCB (yellow rocks), particularly those in the coastal arc in the Transverse Ranges and their relationship to flat-slab subduction models. Our data come from all major structural blocks in the Transverse Ranges (see abbreviations on map). A network of Late Cretaceous, sinistral-reverse shear zones is indicated by purple line. SAF=San Andreas fault; SGF=San Gabriel fault; LSB=Little San Bernardino Mountains; SB=San Bernardino Mountains; MP=Pine Mountain block; SG=San Gabriel Mountains; CM=Cucamonga block.\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-2327151/v1/97d9248c8795aa77f13bdb39.png"},{"id":31436815,"identity":"6637668d-6b98-466c-9a0f-012f9a1b72e1","added_by":"auto","created_at":"2023-01-11 16:46:22","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":233335,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eA.\u003c/strong\u003e\u0026nbsp;Histogram and kernel density estimates for plutons of the Southern California Batholith (SCB).\u0026nbsp;\u003cstrong\u003eB.\u003c/strong\u003e\u0026nbsp;Calculated areal addition rates (km\u003csup\u003e2\u003c/sup\u003e/Ma) versus time for the Mesozoic SCB in 5 m.y. bins. Areal addition rates for the Sierra Nevada Batholith are shown for comparison (not to scale)\u003csup\u003e35\u003c/sup\u003e.\u0026nbsp;\u003cstrong\u003eC.\u003c/strong\u003e\u0026nbsp;Temporal evolution of magmatism deformation, metamorphism, deposition and flat-slab subduction in the SCB. Our new model is compatible with underthrusting of the conjugate Shatsky oceanic plateau after 75-70 Ma, but is inconsistent with earlier amagmatic models. The two stages of the Laramide orogeny are illustrated at the bottom of C. \u0026nbsp;Stage I involved a magmatic flare-up event associated with granulite-facies metamorphism in the SCB, and basement-involved thrusting and basin formation in SW Montana. Stage II involves rapid cooling of the SCB, widespread basement-involved thrusting, and basin formation in Utah, Colorado and Wyoming. We attribute this latter part of the Laramide orogeny to underthrusting of the conjugate Shatsky oceanic plateau beneath the SCB. SCB=Southern California Batholith; SNB=Sierra Nevada Batholith.\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-2327151/v1/41401667e4af228bfd756be6.png"},{"id":31436818,"identity":"100907af-98d7-47e4-8636-b325b16e5cc8","added_by":"auto","created_at":"2023-01-11 16:46:22","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":473591,"visible":true,"origin":"","legend":"\u003cp\u003eTime-temperature cooling curves for the major structural blocks of the Southern California Batholith. Data show that the arc flare-up was associated with sinistral-reverse intra-arc shearing, which was followed by widespread, post-75 Ma cooling below 350°C in all structural blocks. These data support models for regional cooling of the SCB after 75-70 Ma due to underthrusting of the conjugate Shatsky oceanic plateau\u003csup\u003e37\u003c/sup\u003e\u0026nbsp;(Dumitriu et al., 1991). Data compiled from this study and\u0026nbsp;\u003csup\u003e25,27,34,49,50\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-2327151/v1/cad5c82518937220f6b8f161.png"},{"id":31436816,"identity":"9e0932db-afd1-444a-b128-53ebbbc1a6be","added_by":"auto","created_at":"2023-01-11 16:46:22","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":252641,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic models for the two-stage evolution of the Southern California Batholith.\u0026nbsp;\u003cstrong\u003eA.\u003c/strong\u003e\u0026nbsp;Late Cretaceous flare-up occurred from 90-70 Ma in association with sinistral-reverse, intra-arc deformation. Extension in the backarc occurred in the eastern Mojave region and may be related to lithospheric delamination\u003csup\u003e20\u003c/sup\u003e, while shortening occurred in the Laramide thrust belt. B. Cessation of magmatism and rapid cooling after 75-70 Ma in the SCB is linked to flat-slab subduction and underthrusting of the Shatsky conjugate. Eastward (continentward) migration of the arc is associated with basement-involved thrusting and basin formation in the Laramide fold and thrust-belt. Existing mainstream models focus on this stage of the Laramide orogeny and our data show that this event occurred no earlier than 75-70 Ma.\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-2327151/v1/f866e2cad8d4a540328fb628.png"},{"id":31437372,"identity":"91e8e0b0-7f6f-49e6-b778-46689c845312","added_by":"auto","created_at":"2023-01-11 16:54:29","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1884307,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2327151/v1/55c0269b-1651-4a59-ab49-819770876a07.pdf"},{"id":31437370,"identity":"ffbc2f07-b90a-46a7-8fad-ef683d337cff","added_by":"auto","created_at":"2023-01-11 16:54:22","extension":"xlsx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1106517,"visible":true,"origin":"","legend":"Supplementary tables","description":"","filename":"SupplementaryTables.xlsx","url":"https://assets-eu.researchsquare.com/files/rs-2327151/v1/6cc8c1bbea8ced2dddec49d3.xlsx"},{"id":31436819,"identity":"3cfa1dcd-fce4-46fc-8cf7-8634d94cb00c","added_by":"auto","created_at":"2023-01-11 16:46:23","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":4160071,"visible":true,"origin":"","legend":"Supplementary text file","description":"","filename":"SupplementaryFile.docx","url":"https://assets-eu.researchsquare.com/files/rs-2327151/v1/916ebb69afe3126962a4d41a.docx"}],"financialInterests":"There is \u003cb\u003eNO\u003c/b\u003e Competing Interest.","formattedTitle":"Magmatic Surge Requires Two-Stage Model for the Laramide Orogeny","fulltext":[{"header":"Introduction","content":"\u003cp\u003eOne of the most important periods in the development of western North America occurred at ca. 90\u0026thinsp;\u0026minus;\u0026thinsp;80\u0026nbsp;million years (m.y.) ago when a series of deeply rooted thrust faults began to uplift and imbricate slices of continental lithosphere located hundreds to thousands of kilometers inland from the coast (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eA) \u003csup\u003e1\u0026ndash;4\u003c/sup\u003e. This major thick-skinned tectonic event, called the Laramide orogeny, lasted\u0026thinsp;~\u0026thinsp;40 m.y., and resulted in mountain building, the formation of foreland basins, and the development of ore mineralization from Canada to northern Mexico and as far east as the Black Hills of South Dakota\u003csup\u003e4\u0026ndash;6\u003c/sup\u003e. Nevertheless, despite its widespread impact on the tectonic development of western North America, the exact mechanisms that caused this major tectonic event remain controversial\u003csup\u003e3,7\u0026ndash;10\u003c/sup\u003e.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eMost widely cited models argue that the cause of the Laramide orogeny was the flat-slab subduction of a thick oceanic plateau beneath the Southern California Batholith (present-day Transverse Ranges in Southern California) at 90\u0026thinsp;\u0026minus;\u0026thinsp;80 Ma resulting in shutdown of arc magmatism and cooling of the upper-plate crust\u003csup\u003e9,11\u0026ndash;17\u003c/sup\u003e. These \u0026lsquo;amagmatic\u0026rsquo; models resemble the present-day central Andean orogen (27\u0026ndash;33\u0026deg;S) where a flattened subducted oceanic slab is associated with thick-skin deformation and relative magmatic quiescence in the Sierras Pampeanas\u003csup\u003e18\u003c/sup\u003e. In contrast, other models propose that this tectonic transition was caused by the outboard collision of off-shore arc terranes\u003csup\u003e19\u003c/sup\u003e, or increased lithospheric coupling\u003csup\u003e7,20\u003c/sup\u003e. Important features of these conflicting models are that they make different predictions regarding the timing and duration of magmatism, cooling and uplift during the development of the Laramide orogeny.\u003c/p\u003e \u003cp\u003eTo resolve these conflicting models, we examined the frontal arc of the Southern California Batholith (SCB) which represents an ~\u0026thinsp;500 km-wide, paleo-arc segment of the Mesozoic California arc where prior studies place the initial collision between the conjugate Shatsky plateau and the western North American margin (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003eB) \u003csup\u003e14,16\u003c/sup\u003e. This arc segment lies between the southern Sierra Nevada batholith (SNB) and northern Peninsular Ranges Batholith (PRB) and is now represented by fault-bounded structural blocks that make up the central and eastern Transverse Ranges and the western Mojave province. This region experienced varying degrees of faulting and rigid block rotation related to development of the San Andreas transform plate boundary beginning in the Miocene\u003csup\u003e21,22\u003c/sup\u003e. We focus on the frontal arc of the Southern California Batholith (SCB) in the Transverse Ranges because of its unique location as the proposed site of initial collision. As such, the frontal arc of the SCB is the key location to test and resolve conflicting models for the structural, magmatic and metamorphic response to tectonic changes that affected continental lithosphere in western North American in the Late Mesozoic.\u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e\u003cstrong\u003eZircon geochronology\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo test models for the Laramide orogeny, we compiled\u0026thinsp;\u0026gt;\u0026thinsp;260 Pb/U ages, including 79 new zircon and titanite dates to establish the timing and duration of magmatism, metamorphism and deformation in the Southern California Batholith with the goal of resolving conflicting models. Areal addition rates were calculated from integrating igneous ages with pluton areas determined from digitized geologic maps of Southern California (see Supplementary file). Our compilation and new data encompass all major blocks in the SCB including the San Gabriel, Pine Mountain, Alamo-Frazier Mountain, Little San Bernardino, San Bernardino, and Salinian blocks (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eB). Igneous zircon ages reveal 4 discrete pulses of Late Paleozoic to Mesozoic magmatism at 260\u0026ndash;210 Ma, 160\u0026ndash;140 Ma, 120\u0026ndash;118 Ma, and 90\u0026ndash;70 Ma (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA). The latter pulse culminated in an arc flare-up event which peaked at 85\u0026ndash;75 Ma and was associated with widespread, voluminous plutonism throughout the SCB (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eB, \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eB). These Late Cretaceous plutons have typical Cordilleran arc magma geochemistry: most are magnesian, metaluminous to weakly peraluminous, and calc-alkalic with strong crustal affinities that reflect mixtures of Proterozoic crust with juvenile (Mesozoic) sources\u003csup\u003e23,24\u003c/sup\u003e. Although the cause of the 85\u0026ndash;75 Ma flare-up remains unclear, magmatism persisted in the frontal arc of the SCB until ca. 65 Ma and our data show that most igneous activity had ceased by ca. 70 Ma (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eC; Supplementary file).\u003c/p\u003e\n\u003cp\u003eAn analysis of metamorphic zircon and titanite shows that the batholith records high temperatures during the Late Cretaceous transition to thick-skinned, Laramide shortening. The data demonstrate that the arc-flare up event in the SCB was also coeval with high-temperature metamorphism at garnet-granulite to upper amphibolite-facies metamorphism and partial melting in the lower crust of the arc. Evidence for high-temperature metamorphism is preserved in the Cucamonga terrane (eastern San Gabriel Mountains) where metamorphic zircons in gneisses, migmatites and calc-silicates give dates ranging from 86 to 76 Ma at 9\u0026thinsp;\u0026minus;\u0026thinsp;7 kbars\u003csup\u003e25,26\u003c/sup\u003e (Supplementary file). Ti-in-zircon analyses on metamorphic rims indicate temperatures of 800 to 713\u0026deg;C and garnet-quartz oxygen isotope thermometry yields similar metamorphic temperatures of 835 to 777\u0026deg;C. These data are consistent with mineral exchange thermometry which give temperatures of 800\u0026thinsp;\u0026minus;\u0026thinsp;775\u0026deg;C\u003csup\u003e26\u003c/sup\u003e. In the Coast Ridge Belt (Santa Lucia Mountains, Salinia block), Kidder et al.\u003csup\u003e27\u003c/sup\u003e also report peak metamorphic pressures of 800\u0026deg;C at 7.5 kbars at 81 to 76 Ma. These results are significant because they show that the root of the arc was hot and partially molten through ca. 76 Ma.\u003c/p\u003e\n\u003cp\u003eOur regional mapping of mylonitic ductile-shear zones in the SCB documents that the Late Cretaceous arc flare-up was temporally and spatially associated with syn-plutonic development of a regionally extensive, transpressional shear system. This system includes, from north to south (present-day coordinates): the Nacimiento fault\u003csup\u003e28\u003c/sup\u003e, the Tumamait shear zone (Pine Mountain block), the Alamo Mountain-Piru Creek shear zone, the Black Belt shear zone\u003csup\u003e25,29\u003c/sup\u003e, and the Eastern Peninsular Ranges shear zone\u003csup\u003e30\u003c/sup\u003e. Kinematic indicators from the shear zones generally give oblique top-to-west, sinistral reverse- to thrust-sense motion (present-day geometry). Syn-kinematic, metamorphic titanite dates and Zr-in-titanite temperatures in the Tumamait shear zone range from 77 to 74 Ma at 750\u0026deg;C, titanites in the Black Belt shear zone give an age of 83 Ma, and those in the eastern Peninsular Ranges shear zone give ages of 89\u0026ndash;78 Ma at 750\u0026deg;C\u003csup\u003e31\u003c/sup\u003e (Supplementary file). In the Salinian block, Kidder et al.\u003csup\u003e27\u003c/sup\u003e document extensive thickening and high-temperature ductile deformation from 93\u0026thinsp;\u0026minus;\u0026thinsp;81 Ma, and Singleton and Cloos\u003csup\u003e32\u003c/sup\u003e show that the juxtaposition of the Salinian block against the Nacimiento block occurred between ca. 75 Ma and 60 Ma along sinistral strike-slip and/or thrust faults. Thus, these dates and temperatures indicate that the frontal arc of the SCB experienced sinistral-reverse, transpressional deformation during the Late Cretaceous flare-up event (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eC). Therefore, the collective data show simultaneous magmatism and high-temperature intra-arc shortening during the Late Cretaceous transition to thick-skinned deformation.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eImplications for Late Cretaceous high-temperature arc processes in the SCB\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOur compilation of igneous zircon dates from the frontal arc of the SCB document a widespread surge of Late Cretaceous magmatism from 90\u0026thinsp;\u0026minus;\u0026thinsp;70 Ma. This surge occurred throughout all major structural blocks which make up the ca. 500-km wide segment of the Late Cretaceous arc system (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eB, \u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). Outside of the frontal arc, coeval magmatism also occurred in the back-arc which is now represented by the adjacent Mojave Desert\u003csup\u003e33\u003c/sup\u003e. The widespread occurrence of plutonic rocks throughout the SCB and their arc-like geochemical features\u003csup\u003e24,34\u003c/sup\u003e suggests that mechanisms for generating large volumes of melt were still active through the Late Cretaceous. Arc flare-ups similar in magnitude and duration also occurred in adjacent sectors of the arc slightly before the SCB event (e.g., southern SNB at 110\u0026thinsp;\u0026minus;\u0026thinsp;90 Ma\u003csup\u003e35\u003c/sup\u003e and northern PRB at 99\u0026thinsp;\u0026minus;\u0026thinsp;91 Ma\u003csup\u003e36\u003c/sup\u003e (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eB). Importantly, our data from the SCB are in direct conflict with existing amagmatic models that invoke underthrusting of the conjugate Shatsky plateau beneath the SCB from 88\u0026thinsp;\u0026minus;\u0026thinsp;75 Ma and removal of the lower crust and lithospheric mantle during the beginning of the Laramide orogeny\u003csup\u003e9,14,16\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eMetamorphic ages and thermometry in the Cucamonga and Salinian granulites also demonstrate that the lower crust of the SCB was hot and partially molten through 75 Ma, and these features cannot be explained by existing amagmatic models. The presence of this hot arc root provides further evidence that high-temperature arc processes were operating until 75\u0026thinsp;\u0026minus;\u0026thinsp;70 Ma and shut-down of the frontal arc did not occur until after 70 Ma. This observation is illustrated in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e which shows a compilation of time-temperature profiles derived from mineral thermochronology from the major structural blocks in the SCB. These data highlight two important features of the SCB: 1) the Late Cretaceous flare-up in the SCB was coeval with intra-arc, oblique sinistral-reverse thrusting and high-temperature metamorphism, and 2) termination of arc magmatism in this region was associated with an abrupt phase of rapid regional cooling of the SCB below 350\u0026deg;C at ca. 75\u0026thinsp;\u0026minus;\u0026thinsp;70 Ma (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). This regionally extensive and rapid cooling event signifies the onset of regional refrigeration of the SCB due to flat-slab subduction involving the cold, conjugate Shatsky plateau and tectonic underplating of trench sediments beneath the SCB after 75\u0026thinsp;\u0026minus;\u0026thinsp;70 Ma\u003csup\u003e37\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePost 75-70 Ma underthrusting of the conjugate Shatsky plateau\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eOne of the key results of our work is that flat-slab subduction beneath the SCB \u003cspan class=\"ItalicUnderline\"\u003epost-dates\u003c/span\u003e the beginning of Laramide deformation by ~\u0026thinsp;15 Myr. Consequently, oceanic plateau underthrusting cannot be called upon as the driver for thick-skin deformation in the western US prior to ca. 75 Ma. However, several existing data sets support a link between Laramide deformation and flat-slab subduction after 75 Ma. For example, the general timing of major thick-skin, basement-cored thrusting and basin development in Utah, Colorado, Wyoming and SW Montana occurred from 70\u0026thinsp;\u0026minus;\u0026thinsp;50 Ma\u003csup\u003e4\u003c/sup\u003e which agrees well with underthrusting of the conjugate Shatsky after 75 Ma. In addition, zircon ages in peridotite xenoliths from the Colorado Plateau are consistent with derivation from the lithosphere at the base of the SCB and ~\u0026thinsp;500 km of lateral displacement inboard to the Colorado Plateau transition zone after 70 Ma\u003csup\u003e9\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eIn the SCB, the presence of underplated schists is commonly cited as evidence for flat-slab subduction\u003csup\u003e38\u003c/sup\u003e, and our geo- and thermochronological results also support a post-75 Ma emplacement model for the schists. Underplated schists in the Transverse Ranges have zircon age distributions with maximum depositional ages ranging from 75\u0026thinsp;\u0026minus;\u0026thinsp;68 Ma (Pelona Schist\u003csup\u003e38,39\u003c/sup\u003e) and amphibole and muscovite \u003csup\u003e40\u003c/sup\u003eAr/\u003csup\u003e39\u003c/sup\u003eAr metamorphic ages from mafic schists are no older than 60 Ma\u003csup\u003e38,40,41\u003c/sup\u003e. Field observations in the Pelona schist also show no evidence for partial melting or intrusion by Cretaceous plutons. These textural and temporal constraints indicate that underplating of schists beneath the SCB took place after the termination of the SCB flare up event after 70 Ma. Therefore, these data are also consistent with flat-slab subduction after 70 Ma.\u003c/p\u003e\n\u003cp\u003eSpatial and temporal trends in sedimentary provenance within California forearc sediments also show a pronounced and sudden influx of continent-derived detritus to the southern California margin at ca. 75 Ma. Sharman et al.\u003csup\u003e42\u003c/sup\u003e argued that this sudden influx reflects the development of a geomorphic breach within the Cretaceous arc and an associated rapid migration of forearc drainages into the continental interior. The timing of this breach is ~\u0026thinsp;15 Myr younger than postulated plateau underthrusting in prior models, but is compatible with our model for the arrival of the conjugate Shatsky after 75\u0026thinsp;\u0026minus;\u0026thinsp;70 Ma (e.g., Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). These data are also consistent with eastward migration of magmatism away from the coastal arcs after 75 Ma which has been interpreted to reflect shallowing of the subduction angle over time\u003csup\u003e4,43,44\u003c/sup\u003e. We illustrate these features in our model (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) which shows the tectonomagmatic evolution of the SCB-arc segment from 85\u0026thinsp;\u0026minus;\u0026thinsp;50 Ma.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eA two-stage, model for the Laramide orogeny \u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eData from the SCB provide critical new information that allows us to resolve the debate about the link between upper-plate deformation in the western North American Cordillera and the kinematics and geometry of the down-going plate at the beginning of the Laramide orogeny. Our results show clearly that arc magmatism was robustly active through ca. 70 Ma, and underthrusting of the conjugate Shatsky plateau must have occurred after 75\u0026thinsp;\u0026minus;\u0026thinsp;70 Ma. Therefore, flat-slab subduction of the conjugate Shatsky plateau cannot explain the transition from thin- to thick-skin deformation at 90\u0026thinsp;\u0026minus;\u0026thinsp;80 Ma. This conclusion is supported by a number of sedimentological and thermochronological studies on Mesozoic sediments in SW Montana which provide evidence for the early onset of Laramide-style deformation well before 80 Ma\u003csup\u003e10,45,46\u003c/sup\u003e. These data are problematic from the standpoint of a single flat-slab event because the timing of basin formation predates the arrival of the conjugate Shatsky plateau in all flat-slab models\u003csup\u003e9,14,16\u003c/sup\u003e. Moreover, the southwest Montana basins are well outside the commonly cited corridor of Laramide deformation caused by flat-slab underthrusting\u003csup\u003e17\u003c/sup\u003e. These relationships coupled with our data from the SCB lead us to the conclusion that the Laramide orogeny cannot have a single driving mechanism.\u003c/p\u003e\n\u003cp\u003eTherefore, we propose that the Laramide orogeny is a composite tectonic event consisting of two distinct stages of paired mountain building and basin formation: 1) an early phase at 90\u0026thinsp;\u0026minus;\u0026thinsp;75 Ma, which was active during flare-up activity in the SCB, and 2) a more-widespread phase of basement-involved thrusting and basin formation in the continental interior from 75\u0026thinsp;\u0026minus;\u0026thinsp;40 Ma. In this model, the driving mechanism for initial Laramide deformation is not related to flat-slab subduction, but is closely linked to orogen-scale dextral transpression from ca. 100\u0026thinsp;\u0026minus;\u0026thinsp;85 Ma along the US Cordillera\u003csup\u003e19,47,48\u003c/sup\u003e. We attribute the second stage to flat-slab subduction of the conjugate Shatsky plateau beneath the SCB following the termination of flare-up magmatism in the SCB. These new data from the SCB show that multiple driving mechanisms are required to explain the diverse and previously conflicting datasets for the development of Laramide orogeny from 90\u0026thinsp;\u0026minus;\u0026thinsp;40 Ma.\u003c/p\u003e"},{"header":"Online Methods","content":"\u003cp\u003eAny methods, additional references, Nature Research reporting summaries, source data, statements of data availability, and associated accession codes are available at XXXX.\u003c/p\u003e"},{"header":"Declarations","content":"\u003ch2\u003eAcknowledgements\u003c/h2\u003e \u003cp\u003eWe thank Matt Coble, John Wiesenfeld and Zhan Peng for assistance with zircon and titanite petrochronology and Ilya Bindeman for stable isotope thermometry. Gabriel Romero and Ben Conway provided assistance in the field and in the laboratory. John Banacky and Ron Goodman from the Cucamonga Foothill Preservation Alliance and Justin Okin provided tremendous assistance with field logistics. Financial support for this project was provided by the National Science Foundation grant EAR-2138733 (Schwartz and Miranda), EAR 1655152 (Cecil and Schwartz), EAR\u0026ndash;0948706 and OCE-1338842 (Lackey), NSF-EAR 2138734 (Klepeis), and Southern California Earthquake Center grants #21140 and #19023 (Miranda and Schwartz). Robles thanks the Geological Society of America for financial assistance.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eDickinson, W. R. \u0026amp; Snyder, W. S. Plate tectonics of the Laramide orogeny. in \u003cem\u003eLaramide Folding Associated with Basement Block Faulting in the Western United States\u003c/em\u003e (ed. Matthews, V.) 355\u0026ndash;366 (Geological Society of America Memoir 151, 1978).\u003c/li\u003e\n\u003cli\u003eDecelles, P. G. \u003cem\u003eLate Jurassic to Eocene Evolution of the Cordilleran Thrust Belt and Foreland Basin System, Western U.S.A.\u003c/em\u003e (2004).\u003c/li\u003e\n\u003cli\u003eEnglish, J. M. \u0026amp; Johnston, S. T. The Laramide Orogeny: What Were the Driving Forces? \u003cem\u003eInt Geol Rev\u003c/em\u003e \u003cstrong\u003e46\u003c/strong\u003e, 833\u0026ndash;838 (2004).\u003c/li\u003e\n\u003cli\u003eYonkee, W. A. \u0026amp; Weil, A. B. Tectonic evolution of the Sevier and Laramide belts within the North American Cordillera orogenic system. \u003cem\u003eEarth Sci Rev\u003c/em\u003e \u003cstrong\u003e150\u003c/strong\u003e, 531\u0026ndash;593 (2015).\u003c/li\u003e\n\u003cli\u003eSnoke, A. W. \u0026amp; Chapman, J. B. NORTH AMERICA | Southern Cordillera. in \u003cem\u003eEncyclopedia of Geology\u003c/em\u003e (eds. Richard C. Selley, L. Robin M. Cocks \u0026amp; Ian R. Plimer) 48\u0026ndash;61 (Elsevier Ltd, 2021). doi:10.1016/B0-12-369396-9/00402-0.\u003c/li\u003e\n\u003cli\u003eDickinson, W. R. Evolution of the North American Cordillera. \u003cem\u003eAnnu Rev Earth Planet Sci\u003c/em\u003e \u003cstrong\u003e32\u003c/strong\u003e, 13\u0026ndash;45 (2004).\u003c/li\u003e\n\u003cli\u003eWells, M. L., Hoisch, T. D., Cruz-Uribe, A. M. \u0026amp; Vervoort, J. D. Geodynamics of synconvergent extension and tectonic mode switching: Constraints from the Sevier-Laramide orogen. \u003cem\u003eTectonics\u003c/em\u003e \u003cstrong\u003e31\u003c/strong\u003e, (2012).\u003c/li\u003e\n\u003cli\u003eJackson, W. T. \u003cem\u003eet al.\u003c/em\u003e Initial laramide tectonism recorded by upper cretaceous paleoseismites in the northern Bighorn Basin, USA: Field indicators of an applied end load stress. \u003cem\u003eGeology\u003c/em\u003e \u003cstrong\u003e47\u003c/strong\u003e, 1059\u0026ndash;1063 (2019).\u003c/li\u003e\n\u003cli\u003eChapman, A. D., Rautela, O., Shields, J., Ducea, M. N. \u0026amp; Saleeby, J. Fate of the lower lithosphere during shallow-angle subduction: The Laramide example. \u003cem\u003eGSA Today\u003c/em\u003e \u003cstrong\u003e30\u003c/strong\u003e, (2020).\u003c/li\u003e\n\u003cli\u003eCarrapa, B., DeCelles, P. G. \u0026amp; Romero, M. Early Inception of the Laramide Orogeny in Southwestern Montana and Northern Wyoming: Implications for Models of Flat‐Slab Subduction. \u003cem\u003eJ Geophys Res Solid Earth\u003c/em\u003e \u003cstrong\u003e124\u003c/strong\u003e, 2102\u0026ndash;2123 (2019).\u003c/li\u003e\n\u003cli\u003eLivaccari, R. F., Burke, K. \u0026amp; Şeng\u0026ouml;r, A. M. C. Was the Laramide orogeny related to subduction of an oceanic plateau? \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e289\u003c/strong\u003e, 276\u0026ndash;278 (1981).\u003c/li\u003e\n\u003cli\u003eHenderson, L. J., Gordon, R. G. \u0026amp; Engebretson, D. C. Mesozoic aseismic ridges on the Farallon Plate and southward migration of shallow subduction during the Laramide Orogeny. \u003cem\u003eTectonics\u003c/em\u003e \u003cstrong\u003e3\u003c/strong\u003e, 121\u0026ndash;132 (1984).\u003c/li\u003e\n\u003cli\u003eBarth, A. P. \u0026amp; Schneiderman, J. S. A comparison of structures in the andean orogen of northern chile and exhumed midcrustal structures in southern california, usa: An analogy in tectonic style? \u003cem\u003eInt Geol Rev\u003c/em\u003e \u003cstrong\u003e38\u003c/strong\u003e, 1075\u0026ndash;1085 (1996).\u003c/li\u003e\n\u003cli\u003eSaleeby, J. Segmentation of the Laramide Slab - Evidence from the southern Sierra Nevada region. \u003cem\u003eBulletin of the Geological Society of America\u003c/em\u003e \u003cstrong\u003e115\u003c/strong\u003e, 655\u0026ndash;668 (2003).\u003c/li\u003e\n\u003cli\u003eLiu, L., Spasojević, S. \u0026amp; Gurnis, M. Reconstructing Farallon Plate Subduction Beneath North America Back to the Late Cretaceous. \u003cem\u003eScience (1979)\u003c/em\u003e \u003cstrong\u003e322\u003c/strong\u003e, 934\u0026ndash;938 (2008).\u003c/li\u003e\n\u003cli\u003eLiu, L. \u003cem\u003eet al.\u003c/em\u003e The role of oceanic plateau subduction in the Laramide orogeny. \u003cem\u003eNat Geosci\u003c/em\u003e \u003cstrong\u003e3\u003c/strong\u003e, 353\u0026ndash;357 (2010).\u003c/li\u003e\n\u003cli\u003eAxen, G. J., van Wijk, J. W. \u0026amp; Currie, C. A. Basal continental mantle lithosphere displaced by flat-slab subduction. \u003cem\u003eNat Geosci\u003c/em\u003e \u003cstrong\u003e11\u003c/strong\u003e, 961\u0026ndash;964 (2018).\u003c/li\u003e\n\u003cli\u003eRamos, V. A., Cristallini, E. O. \u0026amp; Perez, D. J. The Pampean Flat-slab of the Central Andes. \u003cstrong\u003e15\u003c/strong\u003e, 6\u0026ndash;8 (2002).\u003c/li\u003e\n\u003cli\u003eMaxson, J. \u0026amp; Tikoff, B. Hit-and-run collision model for the Laramide orogeny, western United States. \u003cem\u003eGeology\u003c/em\u003e \u003cstrong\u003e24\u003c/strong\u003e, 968\u0026ndash;972 (1996).\u003c/li\u003e\n\u003cli\u003eWells, M. L. \u0026amp; Hoisch, T. D. The role of mantle delamination in widespread Late Cretaceous extension and magmatism in the Cordilleran orogen, western United States. \u003cem\u003eBulletin of the Geological Society of America\u003c/em\u003e \u003cstrong\u003e120\u003c/strong\u003e, 515\u0026ndash;530 (2008).\u003c/li\u003e\n\u003cli\u003ePowell, R. E. Balanced palinspastic reconstruction of pre-late Cenozoic paleogeology, southern California: Geologic and kinematic constraints on evolution of the San Andreas fault system. in \u003cem\u003eThe San Andreas Fault System: Displacement, Palinspastic Reconstruction, and Geologic Evolution, Geological Society of America Memoir 178\u003c/em\u003e (1993).\u003c/li\u003e\n\u003cli\u003eDickinson, W. R. \u003cem\u003eKinematics of Transrotational Tectonism in the California Transverse Ranges and Its Contribution to Cumulative Slip Along the San Andreas Transform Fault System\u003c/em\u003e. (Geological Society of America Special Paper Volume 305, 1996). doi:10.1130/SPE305.\u003c/li\u003e\n\u003cli\u003eBarth, A. P., Wooden, J. L., Tosdal, R. M. \u0026amp; Morrison, J. Crustal contamination in the petrogenesis of a calc-alkalic rock series: Josephine Mountain intrusion, California. \u003cem\u003eGeol Soc Am Bull\u003c/em\u003e \u003cstrong\u003e107\u003c/strong\u003e, 201\u0026ndash;212 (1995).\u003c/li\u003e\n\u003cli\u003eBarth, A. P. Mid-crustal emplacement of Mesozoic plutons, San Gabriel Mountains, California, and implications for the geologic history of the San Gabriel terrane. in \u003cem\u003eThe Nature and Origin of Cordilleran Magmatism\u003c/em\u003e (ed. Anderson, J. L.) vol. 174 33\u0026ndash;46 (Geological Society of America, 1990).\u003c/li\u003e\n\u003cli\u003eMay, D. J. \u0026amp; Walker, N. W. Late Cretaceous juxtaposition of metamorphic terranes in the southeastern San Gabriel Mountains, California. \u003cem\u003eGeol Soc Am Bull\u003c/em\u003e \u003cstrong\u003e101\u003c/strong\u003e, 1246\u0026ndash;1267 (1989).\u003c/li\u003e\n\u003cli\u003eBarth, A. P. \u0026amp; May, D. J. Mineralogy and pressure\u0026ndash;temperature\u0026ndash;time path of Cretaceous granulite gneisses, south‐eastern San Gabriel Mountains, southern California. \u003cem\u003eJournal of Metamorphic Geology\u003c/em\u003e \u003cstrong\u003e10\u003c/strong\u003e, 529\u0026ndash;544 (1992).\u003c/li\u003e\n\u003cli\u003eKidder, S., Ducea, M., Gehrels, G., Patchett, P. J. \u0026amp; Vervoort, J. Tectonic and magmatic development of the Salinian Coast Ridge Belt, California. \u003cem\u003eTectonics\u003c/em\u003e \u003cstrong\u003e22\u003c/strong\u003e, (2003).\u003c/li\u003e\n\u003cli\u003eWilliam R. Dickinson. Cretaceous Sinistral Strike Slip Along Nacimiento Fault in Coastal California. \u003cem\u003eAm Assoc Pet Geol Bull\u003c/em\u003e \u003cstrong\u003e67\u003c/strong\u003e, (1983).\u003c/li\u003e\n\u003cli\u003eMay, D. J. Late Cretaceous intra-arc thrusting in southern California. \u003cem\u003eTectonics\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e, 1159\u0026ndash;1173 (1989).\u003c/li\u003e\n\u003cli\u003eGoodwin, L. B. \u0026amp; Renne, P. R. Contributions to Mineralogy and Petrology Effects of progressive mylonitization on Ar retention in biotites from the Santa Rosa mylonite zone, California, and thermochronologic implications. \u003cem\u003eContrib Mineral Petrol\u003c/em\u003e \u003cstrong\u003e108\u003c/strong\u003e, 283\u0026ndash;97 (1991).\u003c/li\u003e\n\u003cli\u003eJiang, H., Lee, C. T. A., Morgan, J. K. \u0026amp; Ross, C. H. Geochemistry and thermodynamics of an earthquake: A case study of pseudotachylites within mylonitic granitoid. \u003cem\u003eEarth Planet Sci Lett\u003c/em\u003e \u003cstrong\u003e430\u003c/strong\u003e, 235\u0026ndash;248 (2015).\u003c/li\u003e\n\u003cli\u003eSingleton, J. S. \u0026amp; Cloos, M. Kinematic analysis of melange fabrics in the Franciscan complex near San Simeon, California: Evidence for sinistral slip on the Nacimiento fault zone? \u003cem\u003eLithosphere\u003c/em\u003e \u003cstrong\u003e5\u003c/strong\u003e, 179\u0026ndash;188 (2013).\u003c/li\u003e\n\u003cli\u003eEconomos, R. C. \u003cem\u003eet al.\u003c/em\u003e Testing models of Laramide orogenic initiation by investigation of Late Cretaceous magmatic-tectonic evolution of the central Mojave sector of the California arc. \u003cem\u003eGeosphere\u003c/em\u003e \u003cstrong\u003e17\u003c/strong\u003e, 2042\u0026ndash;2061 (2021).\u003c/li\u003e\n\u003cli\u003eBarth, A. P., Wooden, J. L., Mueller, P. A. \u0026amp; Economos, R. C. Granite provenance and intrusion in arcs: Evidence from diverse zircon types in Big Bear Lake Intrusive Suite, USA. \u003cem\u003eLithos\u003c/em\u003e \u003cstrong\u003e246\u0026ndash;247\u003c/strong\u003e, 261\u0026ndash;278 (2016).\u003c/li\u003e\n\u003cli\u003ePaterson, S. R., Okaya, D., Memeti, V., Economos, R. \u0026amp; Miller, R. B. Magma addition and flux calculations of incrementally constructed magma chambers in continental margin arcs: Combined field, geochronologic, and thermal modeling studies. \u003cem\u003eGeosphere\u003c/em\u003e \u003cstrong\u003e7\u003c/strong\u003e, 1439\u0026ndash;1468 (2011).\u003c/li\u003e\n\u003cli\u003ePremo, W. R., Morton, D. M., Wooden, J. L. \u0026amp; Fanning, C. M. U-Pb zircon geochronology of plutonism in the northern Peninsular Ranges batholith, southern California: Implications for the Late Cretaceous tectonic evolution of southern California. in \u003cem\u003ePeninsular Ranges Batholith, Baja California and Southern California\u003c/em\u003e (eds. Morton, D. M. \u0026amp; Miller, F. K.) (Geological Society of America Memoir 211, 2014). doi:10.1130/2014.1211(04).\u003c/li\u003e\n\u003cli\u003eDumitru, T. A., Gans, P. B., Foster, D. A. \u0026amp; Miller, E. L. Refrigeration of the western Cordilleran lithosphere during Laramide shallow-angle subduction. \u003cem\u003eGeology\u003c/em\u003e \u003cstrong\u003e19\u003c/strong\u003e, 1145\u0026ndash;1148 (1991).\u003c/li\u003e\n\u003cli\u003eJacobson, C. E. \u003cem\u003eet al.\u003c/em\u003e Late Cretaceous-early Cenozoic tectonic evolution of the southern California margin inferred from provenance of trench and forearc sediments. \u003cem\u003eBulletin of the Geological Society of America\u003c/em\u003e \u003cstrong\u003e123\u003c/strong\u003e, 485\u0026ndash;506 (2011).\u003c/li\u003e\n\u003cli\u003eGrove, M., Lovera, O. \u0026amp; Harrison, M. Late Cretaceous cooling of the east-central Peninsular Ranges Batholith (33 degrees N); relationship to La Posta Pluton emplacement, Laramide shallow subduction, and forearc sedimentation. in \u003cem\u003eTectonic evolution of northwestern Mexico and the Southwestern USA\u003c/em\u003e (eds. Johnson, S. E. et al.) 355\u0026ndash;379 (Geological Society of America Special Paper 374, 2003). doi:10.1130/0-8137-2374-4.355.\u003c/li\u003e\n\u003cli\u003eXia, H. \u0026amp; Platt, J. P. Structural and rheological evolution of the Laramide subduction channel in southern California. \u003cem\u003eSolid Earth\u003c/em\u003e \u003cstrong\u003e8\u003c/strong\u003e, 379\u0026ndash;403 (2017).\u003c/li\u003e\n\u003cli\u003eJacobson, C. E. The 40Ar/39Ar geochronology of the Pelona schist and related rocks, southern California. \u003cem\u003eJ Geophys Res\u003c/em\u003e \u003cstrong\u003e95\u003c/strong\u003e, 509 (1990).\u003c/li\u003e\n\u003cli\u003eSharman, G. R., Graham, S. A., Grove, M., Kimbrough, D. L. \u0026amp; Wright, J. E. Detrital zircon provenance of the late Cretaceous-Eocene California forearc: Influence of Laramide low-angle subduction on sediment dispersal and paleogeography. \u003cem\u003eBulletin of the Geological Society of America\u003c/em\u003e \u003cstrong\u003e127\u003c/strong\u003e, 38\u0026ndash;60 (2015).\u003c/li\u003e\n\u003cli\u003eConey, P. J. \u0026amp; Reynolds, S. J. Cordilleran Benioff zones. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e270\u003c/strong\u003e, 403\u0026ndash;406 (1977).\u003c/li\u003e\n\u003cli\u003eChapman, J. B. \u003cem\u003eet al.\u003c/em\u003e The North American Cordilleran Anatectic Belt. \u003cem\u003eEarth-Science Reviews\u003c/em\u003e vol. 215 Preprint at https://doi.org/10.1016/j.earscirev.2021.103576 (2021).\u003c/li\u003e\n\u003cli\u003eGarber, K. L., Finzel, E. S. \u0026amp; Pearson, D. M. Provenance of Synorogenic Foreland Basin Strata in Southwestern Montana Requires Revision of Existing Models for Laramide Tectonism: North American Cordillera. \u003cem\u003eTectonics\u003c/em\u003e \u003cstrong\u003e39\u003c/strong\u003e, (2020).\u003c/li\u003e\n\u003cli\u003eOrme, D. A. New Timing Constraints for the Onset of Laramide Deformation in Southwest Montana Challenge our Understanding of the Development of a Thick‐Skinned Structural Style During Flat‐Slab Subduction. \u003cem\u003eTectonics\u003c/em\u003e \u003cstrong\u003e39\u003c/strong\u003e, (2020).\u003c/li\u003e\n\u003cli\u003eWyld, S. J. \u0026amp; Wright, J. New evidence for Cretaceous strike-slip faulting in the United States Cordillera and implications for terrane-displacement, deformation patterns, and plutonism. \u003cem\u003eAm J Sci\u003c/em\u003e \u003cstrong\u003e301\u003c/strong\u003e, 150\u0026ndash;181 (2001).\u003c/li\u003e\n\u003cli\u003eTikoff, B. \u0026amp; de Saint Blanquat, M. Transpressional shearing and strike-slip partitioning in the Late Cretaceous Sierra Nevada magmatic arc, California. \u003cem\u003eTectonics\u003c/em\u003e \u003cstrong\u003e16\u003c/strong\u003e, 442\u0026ndash;459 (1997).\u003c/li\u003e\n\u003cli\u003eIanno, A. J. Studies of the Late Cretaceous Magmatic Crustal Column at Joshua Tree National Park, California. (University of Southern California, 2015).\u003c/li\u003e\n\u003cli\u003eF. K. Miller \u0026amp; D. M. Morton. \u003cem\u003ePotassium-argon geochronology of the eastern Transverse Ranges and southern Mojave Desert, southern California, Geologic Survey Professional Paper 1152\u003c/em\u003e. (1980).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"nature-portfolio","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"","title":"Nature Portfolio","twitterHandle":"","acdcEnabled":false,"dfaEnabled":false,"editorialSystem":"ejp","reportingPortfolio":"","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-2327151/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2327151/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"The beginning of the Laramide orogeny is a pivotal time in the geological development of the western United States, but the driving mechanism responsible for mountain building, basin formation and ore mineralization is controversial. Most prominent models suggest this event was caused by the collision of an oceanic plateau with western North America at ca. 88 Ma which caused the angle of subduction beneath the continent to shallow. This subhorizontal (flat) subduction is thought to have led to shut-down of the arc, crustal cooling, and the formation of deep, basement-involved thrust faults that penetrated far into the continental interior. In contrast to these predictions, we show that the arc experienced a magmatic surge, the lower crust was hot (835-750°C) and partially molten from 90 to 70 Ma, and cooling occurred after 75 Ma. These data contradict plateau underthrusting as the driving mechanism at 90-80 Ma; therefore, the Laramide orogeny cannot have been initiated by flat-slab subduction. We propose that the Laramide orogeny is best explained as a two-stage orogeny consisting of a syn-magmatic phase at 90-75 Ma, and a widespread mountain building phase at 75-50 Ma. Only that latter phase is linked to flat-slab subduction.","manuscriptTitle":"Magmatic Surge Requires Two-Stage Model for the Laramide Orogeny","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-01-11 16:46:17","doi":"10.21203/rs.3.rs-2327151/v1","editorialEvents":[],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"nature-communications","isNatureJournal":true,"hasQc":false,"allowDirectSubmit":false,"externalIdentity":"NCOMMS","sideBox":"Learn more about [Nature Communications](http://www.nature.com/ncomms/)","snPcode":"","submissionUrl":"https://mts-ncomms.nature.com/","title":"Nature Communications","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"ejp","reportingPortfolio":"Nature Communications","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"e388ae70-efc6-4ebb-aded-1dedcd850250","owner":[],"postedDate":"January 11th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[{"id":18288131,"name":"Earth and environmental sciences/Solid Earth sciences/Tectonics"},{"id":18288132,"name":"Earth and environmental sciences/Solid Earth sciences/Petrology"}],"tags":[],"updatedAt":"2023-06-14T14:02:37+00:00","versionOfRecord":[],"versionCreatedAt":"2023-01-11 16:46:17","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2327151","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2327151","identity":"rs-2327151","version":["v1"]},"buildId":"FbvkV6FR0MCFSLy54lSbu","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}