Photo credit: NSF and NOAA

by Brendan

Today, Nature published an article by two RSES researchers, Hugh O’Neill and Fran Jenner (now at the Carnegie Institution of Washington) that presents a fundamental change in our understanding of how the chemical composition of ocean floor basalts is controlled.

All of this is based upon what happens inside the magma chambers below the mid-ocean ridges and how this effects the so-called ‘incompatible elements‘, which are elements that much prefer to stay in the melt rather than become part of the minerals, as such their concentration in most minerals is very low. So how did a laser help work this out? Well, one of our major analytical instruments is known as a laser ablation-inductively coupled-plasma-mass spectrometer, which fires a laser at a sample of rock, vaporising the material, allowing us to then analyse in and determine the concentration of most elements at very low concentrations. This work involved Fran spending days to analyse hundreds of samples from all over the ocean floor for 30-odd trace elements (those elements present at low concentrations) and then combining this with previous work looking at the major element concentrations of the same samples. Suffice to say this is a painstaking process that requires significant effort to get good data and also putting up with the constant ticking caused by the pulses of the laser.

The main finding from this work is that all most magma chambers that produce ocean floor basalts are in a constant steady-state where magma is removed (forming the ocean floor) whilst also being recharged and that variation in trace elements happens at different stages of this process, with most extreme variations representing the newest and oldest chambers.

Feel free to check out the Nature paper (subscription required) along with corresponding comment.

ANU Media also has an article about the paper