ALBERT

Description: 〈h3〉Abstract〈/h3〉 〈p〉Late Proterozoic–Early Cambrian magmatic rocks that range in composition from mafic to felsic have intruded into the Hour region of the central Iranian micro-continent. The Hour lamprophyres are alkaline, being characterized by low contents of 〈span〉 〈span〉\(\hbox {SiO}_{2}\)〈/span〉 〈/span〉 and high 〈span〉 〈span〉\(\hbox {TiO}_{2}\)〈/span〉 〈/span〉, Mg# values, high contents of compatible elements, and are enriched in LREE and LILE but depleted in HFSE. Mineral chemistry studies reveal that the lamprophyres formed within a temperature range of 〈span〉 〈span〉\(\sim \)〈/span〉 〈/span〉1200〈span〉 〈span〉\(^{\circ }\)〈/span〉 〈/span〉 to 〈span〉 〈span〉\(1300^{\circ }\hbox {C}\)〈/span〉 〈/span〉 and relatively moderate pressure in subvolcanic levels. The Hour lamprophyres have experienced weak fractional crystallization and insignificant crustal contamination with more primitive mantle signatures. They were derived from low degree partial melting (1–5%) of the enriched mantle characterized by phlogopite/amphibole bearing lherzolite in the spinel-garnet transition zone at 75–85 km depth, and with an addition of the asthenospheric mantle materials. We infer the Hour lamprophyres to be part of the alkaline rock spectrum of the Tabas block and their emplacement, together with that of other alkaline complexes in the central Iran, was strongly controlled by pre-existing crustal weakness followed by the asthenosphere-lithospheric mantle interaction during the Early Cambrian.〈/p〉