Influence of magma flux on magma storage depths along the Reykjanes Ridge

Abstract

Quantitative thermomechanical models of mid-ocean ridge magmatic systems focus on spreading rate variations as the principal control on crustal thermal structure and the distribution of melt storage. The Reykjanes Ridge (RR), a slow-spreading portion of the Mid-Atlantic Ridge, has a near-constant spreading rate, but crustal thickness varies by a factor of two. Therefore, magma flux to the ridge varies independently of spreading rate. Here, we investigate the role of magma flux on storage depths along mid-ocean ridges (MORs) and constrain the roles of mantle melt generation rate and spreading rate on oceanic crustal magmatic systems.Using pyOPAM, an open-source Python script written to carry out olivine–plagioclase– augite–melt (OPAM) thermobarometry, with an uncertainty of 1.2 kbar and 9.7°C, samples between 64°N and 52.5°N are compared. The distribution of median OPAM pressure and temperature estimates are compared with calculated magma flux rates across the area of interest.The section of the RR immediately south of the subaerial Reykjanes Peninsula has a median OPAM pressure of 3.7 kbar, and estimated magma flux of 8.82 × 10−6 km3 km−2 y−1. The southern end of the RR has a median storage pressure of 4.8 kbar, and magma flux of 4.58 × 10−6 km3 km−2 y−1. In comparison, The Charlie-Gibbs Fracture Zone to the south has a median OPAM estimate of 6.3 kbar and calculated magma flux of 2.71 × 10−6 km3 km−2 y−1. Despite important local variation, median final magma storage depths and temperatures before eruption increase southwards along the RR. This finding indicates that magma storage depths at mid-ocean ridges are controlled predominantly by magma flux rather than spreading rate alone. Increasing magma flux drives the shallowing of cooler, final magma storage depths, and decreasing magma flux increases magma storage depths and temperature.