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A number of metamorphic core complexes (MCCs) developed in the North China Craton and adjacent regions in the Early Cretaceous and were characterized by consistent extensional orientations. These MCCs formed in the continental interior and were conceptually attributed to the retreat of the Palaeo-Pacific (Izanagi) Plate, but the exact physical mechanism remains enigmatic. Here we utilize 2-D thermomechanical simulations to study how mechanical conditions of the continental crust respond to stresses derived from oceanic subduction and their roles in the formation of MCCs. Our results demonstrate that pre-existing weaknesses are key for localized formation within the continental interior. These weaknesses first undergo compression to form thrust faults in response to shallow subduction of the oceanic slab. These thrust faults gradually transform into extensional ones as the oceanic slab starts to retreat, eventually causing the synchronous exhumation of middle-to-lower crustal rocks that form the MCCs. The P-T paths of metamorphic rocks in the core of MCCs reveal a two-stage exhumation, with isothermal decompression followed by rapid isobaric cooling. Sensitivity tests show that (1) stronger upper crust and weaker lower crust favour MCC formation, while lithospheric strength could exert an influence on the formation time of MCCs and (2) when the continental crust is hot (TMoho = 800 °C), a new magmatic dome could form along the continental margin. We suggest that pre-existing weaknesses in the North China Craton played a key role in generating the quasi-simultaneous MCC series in response to the retreating Palaeo-Pacific Plate.

 

Growth of the Andes has been attributed to Cenozoic subduction. Although climatic and tectonic processes have been proposed to be first-order mechanisms, their interaction and respective contributions remain largely unclear. Here, we apply three-dimensional, fully-dynamic subduction models to investigate the effect of trench-axial sediment transport and subduction on Andean growth, a mechanism that involves both climatic and tectonic processes. We find that the thickness of trench-fill sediments, a proxy of plate coupling (with less sediments causing stronger coupling), exerts an important influence on the pattern of crustal shortening along the Andes. The southward migrating Juan Fernandez Ridge acts as a barrier to the northward flowing trench sediments, thus expanding the zone of plate coupling southward through time. Consequently, the predicted history of Andean shortening is consistent with observations. Southward expanding crustal shortening matches the kinematic history of inferred compression. These results demonstrate the importance of climate-tectonic interaction on mountain building.

 

Geoid is a key observable for understanding the dynamics of the deep Earth, but has been considered largely transparent to long‐wavelength shallow density structures, especially those of the cratonic lithosphere. Here, we demonstrate that the observed flat craton‐ocean geoid pattern, traditionally interpreted as reflecting neutrally buoyant cratonic keels, provides critical constraints on both the net buoyancy and the depth‐dependent density distribution of cratonic mantle lithosphere. Using both simple theoretical calculations and quantitative numerical models, we show that the recent seismic data on lithospheric structure require the existence of a dense cratonic mantle lithosphere to explain the observed topography and geoid. In practice, topography reveals the net buoyancy of the cratonic lithosphere, while geoid further delineates the depth‐dependence of excess density. We find that the mantle lithosphere below large cratons bears net negative buoyancy close to that of a pure‐thermal lithosphere, with most of the excess density distributed within the lower half of the lithosphere. Density profiles of small cratons, due to strong edge effects from surrounding orogenic belts, are harder to constrain, except that their mantle lithosphere is also negatively buoyant.

 

The crustal stress field determines continental deformation, including intraplate seismicity and topographic undulations. However, the sources of observed crustal stress patterns remain debated, with proposed mechanisms including lateral variations in gravitational potential energy and mantle flow, the latter of which comprises plate boundary interactions and basal tractions. Here, we present a series of geodynamic models that simultaneously consider lithospheric and mantle dynamics in the same physical framework, based on which we investigate the sources of crustal stress over the conterminous U.S. The data‐oriented nature of these models allows us to systematically explore the relative contributions of different dynamic sources to the three‐dimensional crustal stress field. These models reveal that forces from the plate boundaries play a dominant role in generating the directional pattern of long‐wavelength horizontal crustal stress across the conterminous U.S. In the central U.S., especially regions of high‐topography, lithospheric density heterogeneities locally modify the crustal stress field. Similarly, mantle flow beneath the North American plate modulates crustal stress orientation in the eastern U.S., particularly in regions with thin lithosphere. Furthermore, we find that a denser‐than‐ambient lithospheric mantle beneath the central and eastern U.S. is required to match the observed continental‐scale E‐W topographic contrast.

 

Abstract Transient intraplate sedimentation like the widespread Late Cretaceous Western Interior Seaway, traditionally considered a flexural foreland basin of the Sevier orogeny, is now generally accepted to be a result of dynamic topography due to the viscous force from mantle downwelling. However, the relative contributions of flexural versus dynamic subsidence are poorly understood. Furthermore, both the detailed subsidence history and the underlying physical mechanisms remain largely unconstrained. Here, we considered both Sevier orogenic loading and three different dynamic topography models that correspond to different geodynamic configurations. We used forward landscape evolution simulations to investigate the surface manifestations of these tectonic scenarios on the regional sedimentation history. We found that surface processes alone are unable to explain Western Interior Seaway sedimentation in a purely orogenic loading system, and that sedimentation increases readily inland with the additional presence of dynamic subsidence. The findings suggest that dynamic subsidence was crucial to Western Interior Seaway formation and that the dominant control on sediment distribution in the Western Interior Seaway transitioned from flexural to dynamic subsidence during 90–84 Ma, coinciding with the proposed emplacement of the conjugate Shatsky oceanic plateau. Importantly, the sedimentation records require the underlying dynamic subsidence to have been landward migratory, which implies that the underlying mechanism was the regional-scale mantle downwelling induced by the sinking Farallon flat slab underneath the westward-moving North American plate. The simulated landscape evolution also implies that prominent regional-scale Laramide uplift in the western United States should have occurred no earlier than the latest Cretaceous.