Petrology of Eocene volcanic rocks in west of Se-Changi

Executor of project: Dr. Morteza Khalatbari Jafari 

2018 

In this thesis results of field, petrography and geochemical data from the Eocene volcanic rocks of the western Se-Changi in Block Lut were discussed. Most part of the study area formed lavas and volcanoclastic rocks with basalte, basaltic andesite, andesite, thrachyandesite, trachydacite, dacite, rhyolite-ignimbrite, lithictuff, vitriccrystaltuff and volcanic breccia in composition. The Eocene volcanic rocks consist of lava and pyroclastic rocks which flare up over the conglomerate, sandstone, marl including Nummulite-bearing limestone. It seems that the Eocene volcanic series covered by Oligocene and Neogene volcanoclastic and lavas. The volcanic rocks of the study area, erupted in four stages in aqueous to subaerial environments.
The intermediate-acidic volcanic rocks recorded envidences of magma mixing and mingling including dark-colored and mafic enclaves inside acidic groundmass with lobbed contact, alternations of rhyolitic flames with andesitic flames, plagioclase phenocrysts which display sieve texture, oscillatory zoning and dissolution margin.
In geochemical discrimination magmatic diagrams, the lavas display shoshonitic, calc-alkaline and high-Kcalc-alkaline magmatic trends. In the tectonomagmatic diagrams, they plot in the active continental margin and subduction zone. In REE patterns and spider diagrams, they show enrichment of LILEs and LREEs in relative to HREEand depletion in HFSE. The geochemical evidences indicate that the source of the basic-intermediate lavas produced from partial melting of a sub continental lithospheric mantle, which have been previously enriched by subduction components (melt, fluids). It seems that the primary and basic magma emplaced into the continental crust and caused partial melting of it. These evidences indicate that the Eocene volcanism in the studied area occurs in a collision-extension to post-collision environment. Therefore, it seems that the volcanic rocks studied in this thesis are the result of the subduction of the oceanic Makran crust or the result of subduction towards the west of the oceanic remains of the eastern Sistan.