Regional Variations in the Spreading‐Rate Dependence of Abyssal Hill Roughness as Indicators of Mantle Heterogeneity.

Abyssal hills are potential proxy records of mid‐ocean ridge faulting and volcanism, as well as the spreading rates and mantle properties that influence these processes. Satellite gravity‐based global prediction of abyssal hill root‐mean‐square (RMS) heights could provide such a proxy, but are broadly influenced off‐axis by pelagic sediment cover, which can lower their values by preferentially filling lows. Here I formulate a sediment‐corrected RMS height prediction by estimating an empirical relationship between mean RMS and sediment thickness as a function of spreading rate. I utilize these values to investigate regional variations in the spreading‐rate dependence of mean RMS across eight regions world‐wide, focusing on half spreading rates <40 mm/yr where spreading rate dependence is strongest. I find that regional variations in this relationship are significant, likely indicating heterogeneity in mantle properties between the different regions. Plain Language Summary: Abyssal hills are formed by faults and lavas at the mid‐ocean ridges, where tectonic plates spread apart, and cover much of the ocean floor. We can use their heights to infer the history and spatial pattern of the spreading process. Here I do an analysis with a global map of abyssal hill heights, applying corrections to account for the effect of sediment cover. I look at the relationship between spreading rate and height in eight different regions in the Atlantic, Pacific and Indian Oceans. Abyssal hills are typically larger where spreading rates are slower. However, changes in this trend can provide clues about differences in Earth properties beneath spreading ridges. My results did show important trend differences across these regions. I conclude that the Earth's properties below the mid‐ocean ridges change significantly from one region to the next. Key Points: Global predicted abyssal hill root‐mean square (RMS) heights can be corrected for sediment thickness using empirical relationships dependent on spreading rateSignificant regional variations are observed in the relationship between mean abyssal hill RMS height and spreading rateGeographic variations in abyssal hill roughness, independent of spreading rate, are likely indicative of heterogeneity in mantle properties [ABSTRACT FROM AUTHOR]