Extinct mid-ocean ridges record past plate boundary reorganizations, and identifying their locations is crucial to developing a better understanding of the drivers of plate tectonics and oceanic crustal accretion. Frequently, extinct ridges cannot be easily identified within existing geophysical data sets, and there are many controversial examples that are poorly constrained. We analyze the axial morphology and gravity signal of 29 well-constrained, global, large-scale extinct ridges (classed as Primary Tier ridges) that are digitized from global data sets, to describe their key characteristics. Additionally, the characteristics of a representative collection of active spreading centers are analyzed to review the present-day variation in the bathymetry and gravity signal of ridges in different tectonic settings such as backarc basin ridges, microplate ridges, and large-scale plate boundaries with varied spreading rates. Uncertain extinct ridge-like structures (classed as Secondary Tier ridges or Excluded from analysis) are evaluated in comparison with the signals of well-defined extinct ridges, and we assess whether their morphology and gravity signals are within the range seen at extinct (or active) ridges. Our review of a large number of controversial extinct ridge locations offers some insight into which proposed locations are more likely to have been former spreading centers, and our analysis further leads to the discovery of several previously unidentified structures in the south of the West Philippine Basin that likely represent extinct ridges and a possible extinct ridge in the western South Atlantic. The global compilation of data and alayses of individual ridges is presented within this GPlates Portal page.
The linked summary pages below provide a detailed catalogue of extinct spreading centres that have been reported within present-day oceanic crust. This catalogue improves access to the data that have been collected at extinct spreading centres over many years of research that have not previously been synthesized. Key details from published studies are briefly summarized, including existing hypotheses for cessation of spreading, tectonic influences at the time of extinction and cessation style. This information, however, is not readily available for all of the extinct ridges included here, and therefore the depth of discussion varies significantly between regions. Some key references are provided, rather than an exhaustive list of all previous studies at individual centres. We adopt the timescale of Gee and Kent (2007) when referring to the timing of spreading cessation.
Maps are provided for each location where an extinct spreading centres has been suggested in previous studies or where an identification could reasonably be made from the seafloor bathymetric or gravity signature. The maps show the inferred position of axial segments in relation to:
A) Regional bathymetry (Weatherall et al., 2015, GEBCO_2014_1D, version 20141103)
B) Gridded vertical gravity gradient (Sandwell et al., 2014, V. 23.1)
C) Free-air gravity grids (Sandwell et al., 2014, V. 23.1)
D) Magnetic anomaly identifications contained within the online database hosted by the University of Hawaii (Seton et al., 2014) and the gridded magnetic anomaly map (WDMAM, Maus et al., 2007).
Profiles across the inferred extinct ridge axial segments are shown, that have sampled a global bathymetry dataset (Weatherall et al., 2015, GEBCO_2014_1D, version 20141103) and the global free-air gravity grid (Sandwell et al., 2014, V23.1). Individual digitized segments from each spreading system are shown, with segment numbers listed above the profiles. The grey shaded area encloses the envelope of the median absolute deviation. The black-solid line is the median stacked profile and the coloured line shows the ‘representative profile’ that was chosen to calculate the characteristics of the ridge axis for that segment. The minimum (white filled circle) and maximum (red filled circle) values are shown and the distances between them are shown, as explained in Figure 3 (MacLeod et al., 2017). The colour of the representative profile corresponds to the colours of segment on maps in S3.
Note that some of the locations shown in the 'Secondary' and 'Excluded' classes are controversial and may not in fact represent a former axis of spreading.
The ridge names and identification numbers (ID#-##) listed below can be cross-referenced with Table 1A - 1D in the manuscript. These summaries form part of the Supplemental Materials for the manuscript: MacLeod, S. J., Williams, S. E., Matthews, K. J., Müller, R. D. and Qing, Xiaodong, 2017 (in press), Global review and digital database of large-scale extinct spreading centers, Geosphere, v. 13, doi:10.1130/GES01379.1.