Slab

About: Slab is a research topic. Over the lifetime, 31617 publications have been published within this topic receiving 318693 citations.

Slab geometry of the Cascadia Subduction Zone beneath Washington from earthquake hypocenters and teleseismic converted waves

Abstract: Using earthquake hypocenters obtained from the Washington regional seismograph network and analysis of Ps converted phases from teleseisms at special temporary stations located south of the Olympic Peninsula, we have developed a preliminary model of the structure of the subducted slab beneath western Washington and southern British Columbia. The slab is smoothly arched beneath Puget Sound, subducting at a dip of about 10-12° at the top of the arch. North and south of the arch crest the slab dips 15-20°. Subcrustal earthquakes are localized near the top of the arch. This deformation, from planar slab geometry, is caused by the change in azimuth of the “trench” (or hinge line of the slab) from almost NS south of 47° north latitude, to approximately N30°W north of 48° north. The slab appears to be easily flexed, probably due to small elastic thickness, but its geometry reflects conservation of surface area and minimization of in-plane strain. Crustal seismicity in the Puget Sound basin may result indirectly from the presence of the arch in the underlying Juan de Fuca plate.

The Himalaya in 3D: Slab dynamics controlled mountain building and monsoon intensification

Abstract: Tectonic models for the Oligocene–Miocene development of the Himalaya mountain range are largely focused on crustal-scale processes, and developed along orogen-perpendicular cross sections. Such models assume uniformity along the length of the Himalaya, but significant along-strike tectonic variations occur, highlighting a need for three-dimensional evolutionary models of Himalayan orogenesis. Here we show a strong temporal correlation of southward motion of the Indian slab relative to the overriding Himalayan orogen, lateral migration of slab detachment, and subsequent dynamic rebound with major changes in Himalayan metamorphism, deformation, and exhumation. Slab detachment was also coeval with South Asian monsoon intensification, which leads us to hypothesize their genetic link. We further propose that anchoring of the Indian continental subducted lithosphere from 30 to 25 Ma steepened the dip of the Himalayan sole thrust, resulting in crustal shortening deep within the Himalayan orogenic wedge. During the subsequent ∼13 m.y., slab detachment propagated inward from both Himalayan syntaxes. Resultant dynamic rebound terminated deep crustal shortening and caused a rapid rise of the mountain range. The increased orography intensified the South Asian monsoon. Decreased compressive forces in response to slab detachment may explain an observed ∼25% decrease in the India-Eurasia convergence rate. The asymmetric curvature of the arc, i.e., broadly open, but tighter to the east, suggests faster slab detachment migration from the west than from the east. Published Lu-Hf garnet dates for eclogite facies metamorphism in the east-central Himalaya as old as ca. 38–34 Ma may offer a test that the new model fails, because the model predicts that such metamorphism would be restricted to middle Miocene time. Alternatively, these dates may provide a case study to test suspicions that Lu-Hf garnet dates can exceed actual ages.

Underpinning tectonic reconstructions of the western Mediterranean region with dynamic slab evolution from 3‐D numerical modeling

Abstract: No consensus exists on the tectonic evolution of the western Mediterranean since ~35 Ma. Three disparate tectonic evolution scenarios are identified, each portraying slab rollback as the driving mechanism but with rollback starting from strongly different subduction geometries. As a critical test for the validity of each tectonic scenario we employ thermomechanical modeling of the 3-D subduction evolution. From each tectonic scenario we configure an initial condition for numerical modeling that mimics the perceived subduction geometry at ~35 Ma. We seek to optimize the fit between observed and predicted slab morphology by varying the nonlinear viscoplastic rheology for mantle, slab, and continental margins. From a wide range of experiments we conclude that a tectonic scenario that starts from NW dipping subduction confined to the Balearic margin at ~35 Ma is successful in predicting present-day slab morphology. The other two scenarios (initial subduction from Gibraltar to the Baleares and initial subduction under the African margin) lead to mantle structure much different from what is tomographically imaged. The preferred model predicts slab rotation by more than 180°, east-west lithosphere tearing along the north African margin and a resulting steep east dipping slab under the Gibraltar Strait. The preferred subduction model also meets the first-order temporal constraints corresponding to Mid-Miocene (~16 Ma) thrusting of the Kabylides onto the African margin and nearly stalled subduction under the Rif-Gibraltar-Betic arc since the Tortonian (~8 Ma). Our modeling also provides constraints on the rheological properties of the mantle and slab, and of continental margins in the region.

Migration of dynamic subsidence across the Late Cretaceous United States Western Interior Basin in response to Farallon plate subduction

Abstract: Backstripped cross sections of the Late Cretaceous succession across central Utah, Colorado, and southern Wyoming in the Western Interior Basin, United States, reveal a component of continuously evolving long-wavelength residual subsidence, in addition to subsidence driven by the Sevier thrust belt and associated sediment loads. The loci of maximum rates of this residual subsidence moved eastward from ca. 98 to 74 Ma in phase with the west to east passage of the Farallon slab, as reconstructed from tomography based on quantitative inverse models. These new subsidence data allow testing of existing subduction models and confi rm the dynamic subsidence origin of the Western Interior Basin. Furthermore, regional variations in subsidence rates suggest a possible defi cit of negative buoyancy (mantle loading) inside the slab beneath Colorado, supporting the hypothesis that the thickened slab represents a subducted oceanic plateau. This paper documents how the Cretaceous stratigraphy records the timing, patterns, and position of underlying mantle processes during Farallon slab subduction. The new data also reveal patterns indicative of the commencement of the Laramide orogeny in the western United States.