Geochemistry of the volcano-sedimentary complex of the Algarve Basin (Silves-Ayamonte, SW Iberia)

Abstract The Volcano-Sedimentary Complex of the Algarve basin (south of the Iberian Peninsula) belongs to the Large Igneous Province of the Central Atlantic Magmatic Province (CAMP), which developed c.200 Ma following the start of the breakup of Pangaea, and preceding the opening of the Atlantic Ocean. This volcanic complex was emplaced in a short period of time in the Lower Jurassic (Hettangian-Sinemurian). It includes subaerial lava flows, pyroclastic deposits and peperites, and contemporaneous sedimentation. We present new field evidence and geochemical data of mafic rock suites within a > 150 km long transect across the volcanic belt. The rocks have a subalkaline geochemical affinity and low TiO 2 contents. They are moderately evolved (Mg# 53–76) and have quartz-hypersthene-normative associations, classifying as low-Ti tholeiites (TiO 2 = 1.2–1.5 wt%). They have slight yet variable enrichment in light ion lithophile and light rare erath elements [(La/Yb) N = 2.55–3.40] and a negative Ta-Nb anomalies. The mafic rocks have enriched MORB compositions, compatible with low-Ti tholeiitic CAMP suites. A trait of CAMP basaltic flows is their compositional homogeneity. Distinct volcanic rocks are only described in the Algarve basin, and have relatively lower SiO 2 and high CaO contents than typical CAMP rocks. Our data suggest that the subset of volcanic rocks with lower SiO 2 and high CaO are linked to contamination-assimilation of ascending magmas with carbonate-evaporite material from Silves marl-carbonated-evaporitic complex, immediately underlying the CAMP sequences.