Characteristics of extinct spreading centers and the relationship between spreading ridges, hotspots and deep mantle structure

Abstract

Oceanic spreading ridges and mantle plumes represent the vehicles through which heat is lost from the deep Earth and govern the distribution of most basic volcanism at Earth’s surface. Despite numerous hotspots located in close proximity to spreading ridges, generally, hotspots are seen to be independent of them. This study catalogues extinct spreading ridges and their physical and spreading characteristics to understand ridge evolution. Variability of ridges related to tectonic subtype is described and compared with active ridges. Uncertain extinct spreading ridges are compared with ‘characteristic’ extinct ridges and a number of possible new ridges are identified. The spatial correlation of hotspots with active plate boundaries through time is assessed, including reorganizations of spreading ridges at times of major ridge jumps. This evaluation determines that over the last 100 m.y. spreading ridges have been closer to hotspots than expected by random distribution, as they are at present-day. After ridge jumps, spreading ridges are more often located closer to a hotspot, particularly when microcontinents are formed. In contrast, subduction zones are generally further from hotspots than expected by a random distribution over the last 100 m.y., particularly those likely to have a deep mantle origin. To explore relationships of plumes and deep mantle structure with surface tectonics spherical geodynamic models are evaluated, using different tectonic reconstructions for boundary conditions. First order behavior and motion of modelled hotspots are compared with observations of present-day hotspots and their trails. Evolution of large-scale modelled anomalous dense structures in the deep mantle are quantified. The direction and rate of boundary retreat or advance for the African, Pacific and ‘Perm’ anomalies are described and overlap with large low-shear wave seismic provinces evaluated. Insight is gained on behavior of plumes and deformation of deep mantle structures.