Time-dependent geochemistry of clinopyroxene from the Alban Hills (Central Italy): Clues to the source and evolution of ultrapotassic magmas

摘要: Abstract We investigated chemical and isotopic compositions of clinopyroxene crystals from well age-constrained juvenile scoria clasts, lava flows, hypoabyssal magmatic ejecta representative the whole eruptive history Alban Hills Volcanic District. The is a Quaternary ultra-potassic district that was emplaced into thick limestone units along Tyrrhenian margin Italy. volcanic products, even most differentiated, are characterised by low SiO2 content. suggest silica activity in evolving magmas can be ultimately due to decarbonation process occurring at magma/limestone interface. According liquid line descent we propose, differentiation driven crystallisation clinopyroxene + leucite ± apatite ± magnetite coupled with assimilation small amount calcite and/or interaction crustal CO2. By combining age, data, strontium oxygen compositions, REE content clinopyroxene, give insights evolution primitive ultrapotassic District over an elapsed period about 600 kyr. Geochemical features crystals, consistent data coming other Italian magmas, indicate primary were generated metasomatized lithospheric mantle source. In addition, our study shows 87Sr / 86Sr LREE/HREE continuously diminished during 600–35 ka time interval history, possibly reflecting progressive depletion source magmas.