Gravity and Magnetic Signatures of Different Types of Spreading at the
Mid-Atlantic Ridge
Abstract
In recent years it has been recognised that parts of slow spreading
ridges such as the Mid-Atlantic Ridge (MAR) are characterised by typical
magmatic spreading, while other parts are characterised by the formation
of detachment faults and Oceanic Core Complexes (OCC). These different
spreading modes can be clearly identified in the near-ridge environment
in the bathymetry, with magmatic mode crust characterised by linear
fault-bounded ridges, and detachment mode crust by more chaotic
bathymetric signatures. The aim of this project is to characterise the
magnetic and gravity signatures of lithosphere created by different
modes of spreading, with the aim of using these signatures to identify
if the structures still remain in ocean-continent transitions, where
they have been covered by sediments coming from the continental crust.
We first characterise different modes of spreading using available
high-resolution bathymetry data of the MAR up to 20 My of age. The
identified characteristics are then related to the corresponding
ship-borne gravity and magnetic data in the same area. From the gravity
anomalies, thinner crust is observed where the OCCs are in place. This
allows the mantle to be exhumed to the sea-floor. As for the magnetic
anomalies, it is found that in places where OCCs are present, the
anomalies are not as symmetrical as those found in magmatic mode
regions. We present a range of parameters extracted from the data that
characterise different spreading modes, and use these to test whether
transitions between detachment and magmatic mode crust identified in the
bathymetry can be readily identified in gravity and magnetic data.