A global review and digital database of large-scale extinct spreading centers

Abstract

Extinct mid-ocean ridges record past plate boundary reorganizations, andidentifying their locations is crucial to developing a better understanding ofthe drivers of plate tectonics and oceanic crustal accretion. Frequently, extinctridges cannot be easily identified within existing geophysical data sets, andthere are many controversial examples that are poorly constrained. We analyzethe axial morphology and gravity signal of 29 well-constrained, global,large-scale extinct ridges that are digitized from global data sets, to describetheir key characteristics. Additionally, the characteristics of a representativecollection of active spreading centers are analyzed to review the present-dayvariation in the bathymetry and gravity signal of ridges in different tectonicsettings such as backarc basin ridges, microplate ridges, and large-scale plateboundaries with varied spreading rates. Uncertain extinct ridge-like structuresare evaluated in comparison with the signals of well-defined extinct ridges,and we assess whether their morphology and gravity signals are within therange seen at extinct (or active) ridges. There is significant variability in extinctridge morphology; yet we find that the majority of well-defined extinctridges have a trough form and a negative free-air gravity anomaly. We compileavailable data on the spreading characteristics of extinct ridges prior tocessation, such as their spreading rates and duration of spreading, and findsignificant differences between ridge subtypes and between oceans. Largescaleextinct mid-ocean ridges persist much longer than extinct microplatespreading ridges and extinct backarc basin spreading ridges before cessation.Extinct fragmented plate and microplate spreading centers have the highestpre-extinction spreading rates, and they have greater median relief at theiraxial segments, suggesting that different crustal accretion styles could leadto different morphology after spreading cessation. Backarc basin ridges havemore pronounced relief when they have been active for longer before cessation,which supports theories of reduced magmatic supply as the basin widthincreases. Extinct ridges in the Atlantic Ocean have the lowest spreading ratesprior to cessation and tend to persist for twice as long as those in the Pacificbefore extinction. There are a larger number of extinct ridges preserved withinmarginal basins than expected for their combined area; these ridges may relateto the complexity of the plate boundaries in these regions. Our reviewof a large number of controversial extinct ridge locations offers some insightinto which proposed locations are more likely to have been former spreadingcenters, and our analysis further leads to the discovery of several previouslyunidentified structures in the south of the West Philippine Basin that likelyrepresent extinct ridges and a possible extinct ridge in the western South Atlantic.We make available our global compilation of data and analyses of individualridges in a global extinct ridge data set at the GPlates Portal webpage.