We present four companion digital models of the age, age uncertainty, spreading rates, and spreading asymmetries of the world's ocean basins as geographic and Mercator grids with 2 arc min resolution. The grids include data from all the major ocean basins as well as detailed reconstructions of back-arc basins. The age, spreading rate, and asymmetry at each grid node are determined by linear interpolation between adjacent seafloor isochrons in the direction of spreading. Ages for ocean floor between the oldest identified magnetic anomalies and continental crust are interpolated by geological estimates of the ages of passive continental margin segments. The age uncertainties for grid cells coinciding with marine magnetic anomaly identifications, observed or rotated to their conjugate ridge flanks, are based on the difference between gridded age and observed age. The uncertainties are also a function of the distance of a given grid cell to the nearest age observation and the proximity to fracture zones or other age discontinuities. Asymmetries in crustal accretion appear to be frequently related to asthenospheric flow from mantle plumes to spreading ridges, resulting in ridge jumps toward hot spots. We also use the new age grid to compute global residual basement depth grids from the difference between observed oceanic basement depth and predicted depth using three alternative age-depth relationships. The new set of grids helps to investigate prominent negative depth anomalies, which may be alternatively related to subducted slab material descending in the mantle or to asthenospheric flow. A combination of our digital grids and the associated relative and absolute plate motion model with seismic tomography and mantle convection model outputs represents a valuable set of tools to investigate geodynamic problems.

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Age, spreading rates, and spreading asymmetry of the world's ocean crust

/pdf/global-continental-and-ocean-basin-reconstructions-since-200-huopwd2ldv.pdf

Global continental and ocean basin reconstructions since 200 Ma

Sea levels have been determined for most of the Paleozoic Era (542 to 251 million years ago), but an integrated history of sea levels has remained unrealized. We reconstructed a history of sea-level fluctuations for the entire Paleozoic by using stratigraphic sections from pericratonic and cratonic basins. Evaluation of the timing and amplitude of individual sea-level events reveals that the magnitude of change is the most problematic to estimate accurately. The long-term sea level shows a gradual rise through the Cambrian, reaching a zenith in the Late Ordovician, then a short-lived but prominent withdrawal in response to Hirnantian glaciation. Subsequent but decreasingly substantial eustatic highs occurred in the mid-Silurian, near the Middle/Late Devonian boundary, and in the latest Carboniferous. Eustatic lows are recorded in the early Devonian, near the Mississippian/Pennsylvanian boundary, and in the Late Permian. One hundred and seventy-two eustatic events are documented for the Paleozoic, varying in magnitude from a few tens of meters to ∼125 meters.

https://science.sciencemag.org/content/sci/322/5898/64.full.pdf

A chronology of Paleozoic sea-level changes.

Cretaceous eustasy revisited

Late Jurassic–Cenozoic reconstructions of the Indonesian region and the Indian Ocean

Earth9s long-term sea-level history is characterized by widespread continental flooding in the Cretaceous period (∼145 to 65 million years ago), followed by gradual regression of inland seas. However, published estimates of the Late Cretaceous sea-level high differ by half an order of magnitude, from ∼40 to ∼250 meters above the present level. The low estimate is based on the stratigraphy of the New Jersey margin. By assimilating marine geophysical data into reconstructions of ancient ocean basins, we model a Late Cretaceous sea level that is 170 (85 to 270) meters higher than it is today. We use a mantle convection model to suggest that New Jersey subsided by 105 to 180 meters in the past 70 million years because of North America9s westward passage over the subducted Farallon plate. This mechanism reconciles New Jersey margin–based sea-level estimates with ocean basin reconstructions.

https://science.sciencemag.org/content/sci/319/5868/1357.full.pdf

Long-Term Sea-Level Fluctuations Driven by Ocean Basin Dynamics

Catastrophic initiation of subduction following forced convergence across fracture zones

The relationship between subduction and back-arc spreading has been well known since the early days of plate tectonics. However, the reasons why back-arc basins are associated with some subduction systems but not all has remained elusive. We examine the kinematic controls on subduction and back-arc basins for both the present-day and Cenozoic to differentiate between the major competing hypotheses for back-arc basin formation and to explain their temporal and spatial distribution. Our new data set of subduction and back-arc basin parameters uses a new set of paleo-oceanic age grids (Muller et al., 2005) associated with a moving Atlantic-Indian Ocean hot spot reference frame (O'Neill et al., 2005). The plate model includes detailed reconstructed spreading histories of back-arc basins based on marine geophysical and satellite gravity data. Our combined rotation and oceanic paleo-age model provides the age distribution of subducting lithosphere through space and time, convergence rates, and the absolute motion of the downgoing and overriding plates. We find that back-arc basins develop when the age of subducting normal oceanic lithosphere is greater than 55 million years. Additionally, we establish an age-dip relationship showing that the intermediate dip angle of the subducting slab is always greater than 30° with back-arc spreading. Our results suggest that back-arc basin formation is always preceded by an absolute motion of the overriding plate away from the subduction hinge, thereby creating accommodation space between the overriding and subducting plates. Once back-arc extension is established, it continues regardless of overriding plate motion, indicating back-arc spreading is not a simple consequence of overriding plate behaviour. The landward migration of the overriding plate as a precursor to back-arc extension may indicate that extension on the overriding plate is influenced by the oceanward lateral flow of the mantle. However, once back-arc extension is established, rollback of the subduction hinge appears to be the primary force responsible for the continued creation of accommodation space. Our analysis indicates the driving mechanism for back-arc extension is a combination of surface kinematics, properties of the downgoing slab, the effect of lateral mantle flow on the slab, and mantle wedge dynamics.

Controls on back-arc basin formation

A marked bend in the Hawaiian-Emperor seamount chain supposedly resulted from a recent major reorganization of the plate-mantle system there 50 million years ago. Although alternative mantle-driven and plate-shifting hypotheses have been proposed, no contemporaneous circum-Pacific plate events have been identified. We report reconstructions for Australia and Antarctica that reveal a major plate reorganization between 50 and 53 million years ago. Revised Pacific Ocean sea-floor reconstructions suggest that subduction of the Pacific-Izanagi spreading ridge and subsequent Marianas/Tonga-Kermadec subduction initiation may have been the ultimate causes of these events. Thus, these plate reconstructions solve long-standing continental fit problems and improve constraints on the motion between East and West Antarctica and global plate circuit closure.

https://science.sciencemag.org/content/sci/318/5847/83.full.pdf

M. Sdrolias

Papers

Age, spreading rates, and spreading asymmetry of the world's ocean crust

Long-Term Sea-Level Fluctuations Driven by Ocean Basin Dynamics

Catastrophic initiation of subduction following forced convergence across fracture zones

Controls on back-arc basin formation

Major Australian-Antarctic Plate Reorganization at Hawaiian-Emperor Bend Time