Carlsberg Ridge and Mid-Atlantic Ridge: Comparison of slow spreading centre analogues

Bramley J Murton,Peter A Rona

doi:10.1016/j.dsr2.2015.04.021

Bramley J Murton, Peter A Rona

Open Access

https://doi.org/10.1016/j.dsr2.2015.04.021

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Abstract

Eighty per cent of all mid-ocean spreading centres are slow. Using a mixture of global bathymetry data and ship-board multibeam echosounder data, we explore the morphology of global mid-ocean ridges and compare two slow spreading analogues: the Carlsberg Ridge in the north-west Indian Ocean between 57°E and 60°E, and the Kane to Atlantis super-segment of the Mid-Atlantic Ridge between 21°N and 31°N. At a global scale, mid-ocean spreading centres show an inverse correlation between segment length and spreading rate with segmentation frequency. Within this context, both the Mid-Atlantic Ridge super-segment and Carlsberg Ridge are similar: spreading at 22 and 26mm/yr full rates respectively, being devoid of major transform faults, and being segmented by dextral, non-transform, second-order discontinuities. For these and other slow spreading ridges, we show that segmentation frequency varies inversely with flank height and ridge axis depth. Segments on both the Mid-Atlantic Ridge super-segment and Carlsberg Ridge range in aspect ratio (ridge flank height/axis width), depth and symmetry. Segments with high aspect ratios and deeper axial floors often have asymmetric rift flanks and are associated with indicators of lower degrees of melt flux. Segments with low aspect ratios have shallower axial floors, symmetric rift flanks, and evidence of robust melt supply. The relationship between segmentation, spreading rate, ridge depth and morphology, at both a global and local scale, is evidence that rates of melting of the underlying mantle and melt delivery to the crust play a significant role in determining the structure and morphology of slow spreading mid-ocean ridges.

Highlights

Introduction1.1 BackgroundSlow spreading centres (spreading at a half-rate of less than 18mm/yr) comprise 80% of the total length of the global mid-ocean ridge (MOR) system
1.1 BackgroundSlow spreading centres comprise 80% of the total length of the global mid-ocean ridge (MOR) system
1.2 Aims and objectives: Here, we examine the relationships between second order MOR segmentation, spreading rate, segment morphology, ridge depth and mantle melting for two slow spreading mid-ocean ridge analogues: the well known Kane to Atlantic super-segment (KA-MAR) of the Mid-Atlantic Ridge between 21°N and 31°N spreading at a half-rate of 11 mm/yr, and the lesser known Carlsberg Ridge (CR) in the north-west Indian Ocean between 57°E and 60°E, spreading at a half-rate of 13 mm/yr, (Figure 1)

Summary

Introduction

1.1 BackgroundSlow spreading centres (spreading at a half-rate of less than 18mm/yr) comprise 80% of the total length of the global mid-ocean ridge (MOR) system. Most of our knowledge of these types of spreading centre is derived from one type example, the central northern Mid-Atlantic Ridge, which is the best-known and most intensively studied slow spreading centre on Earth. Our knowledge of slow spreading centres elsewhere comes largely from incomplete multibeam bathymetry coverage, satellite and ship-derived gravity and derivative (predicted) bathymetry, some magnetic lines, sporadic rock-dredge sampling, and a few hydrothermal plume surveys. Despite this relative paucity of data, a number of general characteristic features are recognised for slow spreading centres

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