Effect of plate motion on plume-induced subduction initiation

<p>Subduction zones are key components of plate tectonics and plate tectonics could not begin until the first subduction zone formed. Plume-induced subduction initiation, which has been proposed as triggering the beginning of plate tectonics (Gerya et al., 2015), is one of the few scenarios that can break the lithosphere and recycle a stagnant lid without requiring any pre-existing weak zones. So far, two natural examples of plume-induced subduction initiation have been recognized. The first was found in southern and western margins of the Caribbean Plate (Whattam and Stern 2014). Initiation of the Cascadia subduction zone in Eocene times has been proposed to be the second example of plume-induced subduction initiation (Stern and Dumitru, 2019).</p><p>The focus of previous studies was to inspect plume-lithosphere interaction either for the case of stationary lithosphere (e.g., Gerya et al., 2015) or for moving lithosphere without considering the effect of lithospheric magmatic weakening above the plume head (e.g., Moore et al., 1998). In present study we investigate the response of moving oceanic lithosphere to the arrival of a rising mantle plume head including the effect of magmatic lithospheric weakening. We used 3D numerical thermo-mechanical modeling. Using I3ELVIS code, which is based on finite difference staggered grid and marker-in-cell with an efficient OpenMP multigrid solver (Gerya, 2010), we show that plate motion may affect the plume-induced subduction initiation only if a moderate size plume head (with a radius of 140 km in our experiments) impinges on a young but subductable lithosphere (with the age of 20 Myr). Outcomes indicate that lithospheric strength and plume buoyancy are key parameters in penetration of the plume and subduction initiation and that plate speed has a minor effect. We propose that eastward motion of the Farallon plate in Late Cretaceous time could play a key role in forming new subduction zones along the western and southern margin of the Caribbean plate.</p><p> </p><p>References:</p><p>Gerya, T., 2010, Introduction to Numerical Geodynamic Modelling.. Cambridge University Press.</p><p>Gerya, T.V., Stern, R.J., Baes, M., Sobolev, S.V. and Whattam, S.A., 2015. Plume-induced subduction initiation triggered Plate Tectonics on Earth. Nature, 527, 221–225.</p><p>Moore, W. B., Schubert, G. and Tackley, P., 1998, Three-dimensional simulations of plume-lithosphere interaction at the Hawaiian swell. Science, 279, 1008-1011.</p><p>Stern, R.J., and Dumitru, T.A., 2019, Eocene initiation of the Cascadia subduction zone: A second example of plume-induced subduction initiation? Geosphere, v. 15, 659-681.</p><p>Whattam, S.A. and Stern, R.J., 2014. Late Cretaceous plume-induced subduction initiation along the southern margin of the Caribbean and NW South America: The first documented example with implications for the onset of plate tectonics. Gondwana Research, 27, doi: 10.1016/j.gr.2014.07.011.</p>

Paleomagnetic and structural study of the NEastern Caribbean plate as mean to give paleogeographic constrains for fauna dispersal.

<p>Since the Eocene, the northeastern corner of the Caribbean plate is shaped by the indentation of the buoyant Bahamas platform with the Greater Caribbean Arc, the suture of a portion of the Antillean subduction zone along Cuba and Hispaniola and the subsequent relocation of the plate boundary along the strike slip Cayman Trough. Puzzlingly enough, these major re-arrangements followed a plate motion reorganization (Boschmann et al., 2014). During this kinematic reorganization, the Lesser Antilles trench initiated (or subduction intensified) along the eastern boundary of the Caribbean plate and progressively bent, resulting in an increase of subduction obliquity from south to north (Philippon et al., 2020a). This curvature has been, and still may be, associated with deformation within the Caribbean plate. Interestingly, in the 10-15 Ma following the plate reorganization, a hypothetical, now submerged “landbridge” allowed the dispersion of terrestrial fauna from South America to the Greater Antilles: the GAARlandia landbridge (land of Greater Antilles and Aves Ridge). Although it has been recently shown that Puerto Rico and the Northern Lesser Antilles where connected once forming a land mass called GrANoLA around 33-35 Ma (Philippon et al., 2020b), these rapids and drastics geodynamical changes may have impacted the regional paleogeography, which remains to be constrained. The intraplate deformation in the north-est Caribbean region associated with the plate reorganization, the Bahamas indentation, and the plate boundary curvature likely hold the key to (part of) the evolution of this landbridge.<br>At present day, the N-Eastern border of the Caribbean plate shows parallel to the trench faults dissecting the plate in a sliver-like manner. This “sliver” is cross cutted by perpendicular to the trench faults in four crustal blocks: Gonave, Hispaniola, Puerto Rico and the Northern Lesser Antilles. Present-day and past kinematics of these blocks, and even their existence, are still debated.</p><p>In this study, in the course of the French GAARAnti project, we focus on paleomagnetically determined vertical axis rotations that affected Puerto Rico and the Northern Lesser Antilles blocks since the Eocene, and use these to inform kinematic reconstructions constrained by regional structural analysis and Ar<sup>40</sup>-Ar<sup>39</sup> geochronology. These reconstructions will be used to refine the paleogeographic evolution of the NEastern edge of the Caribbean plate since the Eocene in order test the GAARlandia hypothesis.</p><p>A new set of paleomagnetic data (180 Oligo-Miocene specimens of sediments sampled in 18 sites) indicates that the Puerto Rico block underwent an early to mid-Miocene 10° counterclockwise (CCW) rotation. This result clearly differs from those of Reid et al., 1991 who concluded a Late Miocene 25° CCW rotation and that is currently used by the community to interpret the tectonic history of the northeastern Caribbean plate. The use of a larger dataset, that geographically covers the entire island, and of a more recent reference frame explain the difference observed between the two results. This new result will lead to a re-interpretation of the tectonic evolution of the region that will be integrated in a regional kinematic reconstruction.</p>

The Septentrional–Oriente strike-slip Fault Zone: polyphase deformation and fault strand switching in the Northern Caribbean plate boundary (Windward Passage)

<p>The northern border of the Caribbean plate is characterized by the oblique collision between the Caribbean and North American tectonic plates. Increasing obliquity of the collision between these two plates lead to complex strike-slip fault zones, which successively jump southward to accommodate the eastward escape of the Caribbean plate and the collisional indentation against the Bahama carbonate platform. The present-day Septentrional–Oriente Fault zone (SOFZ) defines the northern limit of the Caribbean plate, accommodating much of the obliquity of the convergence. Since its inception, at the end of the Oligocene, the current active style of the strike-slip boundary evolves over time. We focus our study on the Windward Passage area between the south-east of Cuba and the north-west of Haiti coast. Currently crossed by the SOFZ, the tectono-sedimentary framework of this large strait displays critical evidences to constrain the Neogene evolution of the northern boundary of the Caribbean plate. Based on seismic reflection and swath-bathymetric dataset we shed light on the structure and tectonic pattern of the Windward Passage. Our study provides structural and stratigraphic insights into relative timing of deformation along the Windward Passage and new elements to constrain the southeastward shift of the north Caribbean plate boundary until its present-day position. Contrasts in patterns of deformation on the Windward Passage area reveal a polyphase tectonic history of dominant strike-slip faulting impacted by the rate and obliquity variations of the convergence. Deformation phases recorded by the offshore sedimentary cover in the Windward Passage correlate well with the major paleogeographic reorganization episodes described onland (Late Eocene, Late Oligocene, Middle Miocene and Late Pliocene). A left-lateral shift of at least ~80 km is demonstrated by the restoration of the offset of the seismic units, estimating a Pliocene age for the onset of the SOFZ segments activity in this area.</p>