Petrology and geochemistry of the volcanic rocks in NW Sechangi, Lut block

The Eocene volcanic rocks which exposed in the NW Sechangi Lut block, including pyroclastic deposits and lavas.  The volcanic rocks in the study area are basalt-basaltic andesite-trachyandesite, trachydacite, dacite and rhyolite-ignimbrite in compositions. Based on the field observations the volcanic rocks erupted in four stages in the aquous to the aerial environments.  The volcanic rocks in this area exposed as alternation of acidic and basic-intermediate rocks like as bimodale volcanism.  Under the petrography investigations the acidic rocks including pyroxenite microenclaves probably the remains of sub continental lithospheric mantle.  In the discriminating magmatic diagrams the volcanic lavas show shoshonitic to high-K calck-alkaline trends.  In the normalized REE patterns and spider diagrams they display enrichments of LREE and LILE in relative to HFSE comparable with subduction related volcanism.  In the tectonic-magmatic diagrams they cluster in continental margins field.  The interpretation of the geochemical diagrams indicate that the basic-intermediate volcanic rocks produced from partial melting of lithospheric mantle which have previously enriched by the subduction components (fluids-melt) which cannot distinguish from the crustal effects.  The acidic rocks rcords some crustal elemnts which indicating the involving of the crust in the generation of the acidic rocks.  It seams that after the collision of the Neo-Tethys branchs in Late Cretaceous and subsequence lithospheric thickening in the Lut block, the Eocene volcanic rocks in the Sechangi area formed in an extentional-collisional environment.