The Central Alborz Permian basaltic magmatism: an evidence of southern passive continental margin of Paleo- Tethys

Abstract

The study area is located in the Central Alborz (northeast of Baladeh). The Permianmagmatism in this area occurs as a basaltic unit between Ruteh-Nessen Formation.Petrographically, the rocks are plagioclase phyric and geochemically, display alkalinesodic nature. Chondrite- normalized rare earth element (REE) patterns are extremely LREE- enriched similar to those of oceanic island basalts (OIB) with (La/Sm)N,(Sm/Yb)N and (La/Yb)N in the ranges of 1.95- 4.62, 4.23- 5.45 and 8.30- 20.52,respectively. Furthermore, primitive mantle normalized multi element diagramsrepresent OIB characteristics. Modeling based on trace element values and the contentof some major elements reveal low degree partial melting (< 10%) of a deep (~110 km)garnet-bearing mantle source. In addition, variation of some trace element ratios such asNb/Rb, K/La, La/Nb, Ba/Nb, Th/Nb and K/Nb suggests a HIMU mantle origin. As thesamples geochemically show intra-plate tectonomagmatic setting without subductionzone signatures. Thus, during the Permian (and earlier times), Alborz has been as apassive continental margin in the southern border of Paleo-Tethys and its magmatism was more probably affected by extensional tectonism or mantle plume activity related toearlier stages of Neo-Tethys ocean development.

Keywords

• alkaline basalt
• intra-plate
• Permian
• Central Alborz