Magmatic Na-rich phlogopite in a suite of gabbroic crustal xenoliths from Volcán San Pedro, Chilean Andes: Evidence for a solvus relation between phlogopite and aspidolite

摘要: Magmatic Na-rich phlogopite (1–5 wt% Na 2 O) is present as a late-crystallizing mineral in two groups of texturally and mineralogically distinct gabbroic xenoliths at Volcan San Pedro (36°S, Chile), an Andean arc volcano. Phlogopites are characterized by high 100·Mg/(Mg + Fe) (up to 83) Cr O 3 contents 0.4 wt%), they always found surrounding variably resorbed olivine, pyroxenes, Cr-spinel, some cases, plagioclase. We interpret these micas the result open-system processes involving infiltration water-rich evolved melts [with Na/(Na K)] reaction with refractory minerals. The highest 100·Na/(Na K) (~70) concentrations (~5 wt%) appear require liquids unrealistically if no other factor considered. This, together observation that phlogopites consist alternating Na-poor cleavage-parallel bands, can be best interpreted presence solvus between aspidolite (Na) (K) end-members. proportions 15 vol%) different suggest it might more common abundant than has been previously recognized, may used indicator processes.