Magma Transport Along a Single Slow-Spreading Segment of the Mid-Atlantic Ridge at 14°N

Abstract:

The distribution of volcanism is highly variable along slow spreading mid-ocean ridges (MORs), with thicker basaltic crust at segment centers compared to segment ends. This has resulted in two end-member models for magma transport along slow spreading segments: 1) a focused model where magma upwelling focuses and pools in the center of the segment and migrates towards the segment ends via lateral diking in the shallow crust and 2) a distributed model where magma vertically upwells along the entire segment but is enhanced at the segment center. Both models are supported by the bathymetric and geophysical observations, but have different implications for magma transport and the chemical compositions of erupted lavas.

To evaluate lava chemistry variability along a slow-spreading MOR, we systematically mapped and sampled a segment of the Mid-Atlantic Ridge (MAR) at ~14°N over the course of two research expeditions aboard the R/V Atlantis (AT 33-03 & AT 40-02). Lavas were collected from 6 regions spanning the magmatically robust segment center to a sparsely magmatic non-transform offset adjacent to an extinct oceanic core complex. Systematic sampling along this segment allows us to evaluate the two end member models. Major elements were analyzed for 382 basaltic glasses, 162 of which were also analyzed for trace element contents. Results show that there is greater geochemical variability near the non-transform offset than in the magmatically robust region of the segment. For example, K/Ti varies from 0.24 to 0.46 and La/Sm varies from 2.58 to 3.59 at the segment center, whereas the sparsely magmatic region’s K/Ti values range from 0.06 to 0.42, and La/Sm varies from 1.06 to 3.42. In contrast to the magmatically robust segment center, fractional crystallization models show that the sparsely magmatic region requires multiple parents and/or pressures and lower extents of crystallization (~35% less crystallization), suggesting less storage and mixing within the shallow crust. We will present numerical models that evaluate how mantle source contents and extents of melting vary along the ridge axis and suggest a hybridized model of magma transport along this single slow spreading MOR segment.