Discrete characterization of abyssal hills: Unraveling temporal variations in crustal accretion processes at the 10°30′N segment, East Pacific Rise

Abstract

The morphology of abyssal hills provides important information on the crustal accretion processes acting at mid ocean ridges. Discretely characterizing abyssal-hill shape is challenging, and therefore, the study of abyssal-hill morphology is often approached by examining the average properties of relatively wide regions containing multiple hills. However, this averaging process removes any spatial trends in abyssal-hill shape that may reflect temporal variations in crustal accretion processes. Here we present an automated approach for analyzing the shape of individual abyssal hills, which we detect using the ridgelet transform method of Downey and Clayton (2007). We first analyze seafloor morphologies, as revealed in multibeam bathymetry surveys, across 16 mid-ocean ridge segments with varying spreading rates. The results of this analysis display the known negative correlation between the width and height of abyssal hills and the spreading rate, thus validating our approach. Our results also show that the fraction of inward-facing abyssal hills exhibits a simple linear trend across all spreading rates, suggesting a property that could be used to determine the spreading rate at which the seafloor formed. We then apply our technique to study a flow line transect collected across the fast-spreading 10°30′N segment of the northern East Pacific Rise, revealing temporal changes in the shape of the abyssal hills formed during the last 3.8 Myr. The youngest part of the flow line coincides with a location where basaltic glasses were previously sampled. The abyssal-hill morphology and MgO content of the glass samples share mutual trends (over 105-106 yrs), suggesting that abyssal-hill morphology is sensitive to the rate at which magma is supplied to the ridge axis. Finally, a ∼1 Myr cyclic variation in seafloor morphology is observed. This periodicity is attributed to temporal changes in magma supply at the ridge axis, possibly related to upper mantle dynamics or the presence of chemical heterogeneities.