Petrology of the post-Eocene volcanic rocks in the north Naybandan, Lut block

Executor of project: Dr. Morteza Khalatbari Jafari 

2018 

 The studied area located in north of Naybandan village, in Kerman main road, west of Lut block.  In the Lut region, Tertiary volcanism is extended. The volcanic rocks in the studied area could be distinguished in two categories: Oligocene and Neogene which erupted in an aqueous to aerial environments.  The Oligocence volcanic lavas, including andesite, trachyandesite, trachydacite, dacite and rhyolite.  These lavas have porphyric texture with abundance amphibole. They recorded evidences of magma mixing and mingling. In the geochemical diagrams they display calc alkaline trend.  In the normalized REE patterns and spider-diagrams, they display enrichment of LILE in relative to HREE, with clear depletion of HFSE, like as the characteristics of post-collision volcanism. The Neogene volcanic products comprise of tuff, breccia and acidic lava at the base. The Neogene products gradually change to andesitic, trachyandesitic and dacitic lavas at passing upwards. In the petrography investigations, they have aphyric-porphyric textures with vitric, hyalomicrolitic and microlitic groundmass. They recorded disequilibrium features including sieve texture in plagioclase phenocrysts and heterogeneous groundmass. As like as Oligocene lavas they display calk-alkaline magmatic trend. In the normalized REE patterns and spider diagrams they display enrichment of LREE and LILE in relative to HREE with clear depletion of HFSE.  These geochemical characteristics indicate that both Oligocene and Neogene lavas have similar peridotitic source which have been previously enriched by fluids and melts release from subducted slab.  Regarding to these geochemical evidences, it seems that the studied lavas produced from partial melting of lithospheric mantle which had previously been enriched by subduction fluids.  It seems that after collision and ticking of lithosphere in the Eocene, the continental lithosphere is thin in the Oligocene and Neogene periods.  Consequently of these processes were calc-alkaline and moderately intermediate volcanism in relative to Eocene shoshonitic and more acidic volcanism. These processes consequently occur probably by asthenosphere upwelling and lithospheric delamination which have been occurred in post-collision orogeny belt.