Paleozoic metasomatism at the origin of Mediterranean ultrapotassic magmas: Constraints from time-dependent geochemistry of Colli Albani volcanic products (Central Italy)

Abstract

The major processes that control the genesis of potassic volcanic rocks, like the timing of multi-stage mantle metasomatism, remain largely unclear. In an attempt to clarify the timing of the metasomatic process, a detailed geochronologic and geochemical study has been conducted on the ultrapotassic rocks of the Colli Albani Volcanic District (Central Italy). New 40Ar/39Ar data coupled with literature and newly performed 87Sr/86Sr, 143Nd/144Nd and chemical data allow us to precisely delineate the time-dependent geochemical variations of the magmas erupted at the Colli Albani Volcanic District and to better define mantle source processes responsible for their genesis. The temporal geochemical variations observed in the Colli Albani magmas indicate that: i) the ultrapotassic magmas originated from a metasomatized mantle source in which phlogopite is the potassium-bearing phase; ii) the partial melting of the mantle source involved mainly phlogopite and clinopyroxene (±olivine), whereas the role of accessory phases was less significant; and iii) the metasomatic process that led to the formation of the phlogopite in the mantle can be reasonably related to events that have occurred during the Paleozoic Era