Types And Regional Distribution And Frequency Of...

i. Abstract Numerous extinct spreading centres are found within the world’s ocean basins and these record instances of spreading cessation or migration that provide valuable insights into the mechanism of heat-loss from the mantle and plate tectonic behaviour. This study presents the first comprehensive review of all reported extinct ridges and investigates their characteristics and regional distribution and frequency of occurrence over the last ~170 Myr as recorded in present-day preserved oceanic crust. The axial morphology, gravity signal and crustal structure of extinct ridges are evaluated by generating across-axis profiles through global datasets (IHO - IOC 2014; Sandwell et al. 2014) for individual ridge segments. Information on the spreading-rates, time of cessation and duration of spreading prior to cessation was collating information from previous studies. The potential geodynamic influences on the lifespan and activity of mid-ocean ridges were investigated by evaluating the rel ationship of extinct ridges to hotspots at their time of extinction using GPlates (Boyden et al. 2011) and a global reconstruction (Seton et al. 2012). Global examples are investigated to assess similarities or differences and to determine the ‘characteristic’ signal of extinct ridges. Ridges were classified according to the quality of constraints into a primary, secondary or tertiary tier that dictated their inclusion in the quantitative analysis undertaken. Spreading centre subtype is