THE PERMIAN VOLCANICS OF CENTRAL ALBORZ: IMPLICATIONS FOR PASSIVE CONTINENTAL MARGIN ALONG THE SOUTHERN BORDER OF PALEOTETHYS

Morteza Delavari, Asghar Dolati, Ali Mohammadi, Farzaneh Rostami

Abstract


The Permian volcanics of Central Alborz (PVCA) crop out between the Ruteh and Nesen Formations in the Baladeh-Siahbisheh area. The volcanics are predominantly basaltic and plagioclase-phyric. Ferromagnesian minerals such as clinopyroxene and olivine are not modally abundant and sometimes are totally altered. Chemical composition of clinopyroxene is characterized by high TiO2 contents (4.9-7.2 wt.%). Based on whole rock geochemistry, the samples display sodic alkaline nature (Na2O = 3.7 to 7.8 wt.%). Chondrite-normalized rare earth element (REE) patterns are extremely LREE-enriched with (La/Yb)N of 8.3-20.5. Both normalized REE and multi-element diagrams represent ocean island basalt (OIB) characteristics. Modeling based on trace element values, and the content of some major elements reveal low partial melting degree (< 10%) of a deep garnet-bearing mantle source. As the samples geochemically show an intra-plate tectonomagmatic setting without subduction zone signatures, during the Permian (and earlier times), the Alborz area was possibly a passive continental margin along the southern border of Paleotethys. As a result, the Alborz Permian magmatism could have  been reasonably induced by an extensional tectonic regime along the northward-moving Cimmerian terranes during the early stages of Neotethys development.

Keywords


Alkaline basalt; intra-plate volcanism; Permian; Central Alborz

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DOI: https://doi.org/10.4454/ofioliti.v41i2.44