Experimental reactions between olivine and orthopyroxene with phonolite melt: implications for the origins of hydrous amphibole + phlogopite + diopside bearing metasomatic veins

摘要: Amphibole + phlogopite + diopside bearing veins are observed in a large number of upper mantle xenoliths, but the composition melt that forms them is poorly constrained. Recent data from Heldburg Phonolite, Central Germany, has shown phonolite will react with olivine and orthopyroxene xenocrysts to form reaction rims amphibole + phlogopite + diopside at mid-lower crustal pressures. This first example where reacted peridotite mineralogy metasomatic veins. It therefore necessary explore whether could be parent Experimental reactions between single crystals were conducted conditions 1.0–1.5 GPa 900–1,000 °C. Melt water contents varied anhydrous >12 wt. H2O. Olivine reacts phlogopite overgrowths diopside 1,000 °C. Orthopyroxene amphibole epitaxial <1,000 °C. No when bulk H2O lower than ~3.8 wt%. Pressure little effect over small range tested. These experiments reproduce on suggest relatively narrow temperatures required for rim formation. The compositions amphibole, have very similar those do not match Phenocrysts veins, suggesting potentially if vein formation dominated by crystallization rather replacement wall rock phases.