Mineralogical evidence for lamproite magma mixing and storage at mantle depths: Socovos fault lamproites, SE Spain

Abstract

Detailed textural and mineral chemistry characterisation of lamproites from the Socovos fault zone, SE Spain Neogene Volcanic Province (NVP) combining X-ray element maps and LA-ICP-MS spot analyses has provided valuable information about mantle depth ultrapotassic magma mixing processes. Despite having similar whole-rock compositions, rocks emplaced in the Socovos fault are mineralogically varied: including type-A olivine-phlogopite lamproites; and type-B clinopyroxene-phlogopite lamproites. The Ol-lacking type-B predates Ol-bearing type-A by c. 2 million years. We propose that the mineralogical variations, which are representative of lamproites in the NVP as a whole, indicate mantle source heterogeneities. Major and trace element compositions of mineral phases suggest both metasomatised harzburgite and veined pyroxenite sources that were most likely closely spatially related. Thin section scale textural and compositional variations in mineral phases reveal heterogeneous mantle- and primitive magma-derived crystals. The variety of crystals points to interaction and mingling-mixing of ultrapotassic magma batches at mantle depths prior crustal emplacement. The mixing apparently occurred in a mantle melting zone with a channelised flow regime and localised magma chambers- reservoirs. Magma interaction was interrupted when the Socovos and other lithosphere-scale faults tore down to the mantle source region, triggering rapid ascent of the heterogeneous lamproite magma