B is potentially a key element to study in mid-ocean ridge mantle-derived rocks, because it is thought to behave similarly to volatile species in the Earth's mantle (ie water) during subduction and recycling. The majority of studies of boron therefore have been carried out in convergent plate boundaries. The geochemical behavior and concentration of boron in the mid-ocean ridge upper mantle however, are not directly constrained. Boron is considered a moderately to highly incompatible element. Our knowledge of its mantle concentration and partitioning is largely derived from studies of basalt. Its concentration in the non-arc upper mantle is estimated to be 0.1ppm. MORB glasses average 0.34-0.72 ppm and 0.54-1.54 ppm for N-MORB and E-MORB respectively. Literature measurements on mantle minerals from orogenic peridotites show clinopyroxene to have the greatest affinity for B. We have measured concentrations of B, Li and Be on mantle minerals from abyssal peridotites and basalt glasses from Gakkel Ridge, Arctic Ocean. Preliminary data acquired using both quadrupole and sector field LA-ICP-MS seem to contradict many of the previously held assumptions about the concentration and behavior of B in the mid-ocean ridge upper mantle. Higher than expected bulk rock B concentrations of at least 5.6 ppm for the abyssal peridotites were estimated based on the B concentration in mantle silicates and their modal percentage in peridotites. Slightly higher than expected average B concentrations of 3.3 ppm in basalt glasses may be due to the relatively enriched nature of Gakkel Ridge. On both instruments B was also found to be more compatible in olivine than in clinopyroxene. Although these results agree with each other, measurements on additional samples and new data reduction methods will be tested to determine their validity.
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- 1032 Mid-oceanic ridge processes (3614;
- 3035 Midocean ridge processes;
- 8150 Plate boundary: general (3040);
- 8416 Mid-oceanic ridge processes (1032;