Near mantle solidus trace element partitioning at pressures up to 3.4 GPa

摘要: [1] We present new experimental partitioning data for a range of petrogenetically important elements at pressures up to 3.4 GPa. The experiments are designed mimic low degrees anhydrous melting beneath mid-ocean ridges. available indicate that the partition coefficients pressure, temperature, and composition dependent. Therefore behavior over appropriate must be quantified, in order model continuous extraction melt during adiabatic rise mantle material. For this purpose, we have parameterized REE, Hf, Zr, U, Th based on simple thermodynamic model. Although these parameterizations cannot used retrieving constants yet, they do yield accurate descriptions useful modeling decompression melting. Our show trace is strongly dependent Ca Al-content clinopyroxene (cpx) REE always incompatible cpx peridotite solidus garnet heavy decrease with increasing pressure. also indicates Pb more than Ce clinopyroxene; similar garnet. presence residual phase high required produce near-constant Ce/Pb ratios MORB OIB. Sulfides most likely buffer content melt. Except small porosities (<0.3%), unable fractionate U from significantly (15% 230Th-excess), whereas can effectively 1%. if 230Th-excesses ridge basalts phenomena, then compatible physical observations upwelling rate New calculations include compositional predicted characteristics (depth extent melting, rate, porosity) regime Lu/Hf, Sm/Nd, U-Th systems.