Late Paleozoic basaltic magmatismof Tarom- Masuleh area (western Alborz): whole-rock chemical characteristics and tectonic implications

The Tarom- Masuleh area (western Alborz) exposes considerable Late Paleozoic volcanic rocks. Stratigraphic relationships indicate that the igneous units are of Carboniferous- Permian age. Based on whole- rock chemical data, the samples are compositionally basic (SiO2= 45.3- 50.7 wt.%) and alkaline (TiO2= 1.1- 4.4 wt.%; Nb/Y=0.9- 2.3). Furthermore, these rocks are characterized by nearly primitive to evolved compositions (MgO= 14.5- 2.5 wt.%). Major and trace elements data show that chemical variations were predominantly controlled by crystal fractionation and, mantle source processes or crustal contamination was not so effective. Trace element theoretical modeling of crystallization process also shows that fractional crystallization of olivine + clinopyroxene has played a major role in the chemical evolution of the melt. The chemical characteristics of the samples in terms of HFSE enrichment and elevated LREE/HREE ratio ((La/Yb)N= 4.8- 17.5) are identical to those of oceanic island basalts (OIB). Thus, the Late Paleozoic magmatism of the Tarom-Masouleh region took place in an intraplate setting (passive continental margin) influenced by the extensional tectonic regime. Coeval magmatism in other parts of Iran, including Central Iran, Sanandaj- Sirjan and Azerbaijan, as well as other areas of the northern margin of Gondwana (Oman, North Africa) and China, similarly represent intraplate magmatic signature attributed to the mantle plume and/or hot spot activity or extensional tectonics and rifting concurrent with the early stages of the appearance of the Neotethys Ocean.