S Younesi; M.R Hosseinzadeh; M Moayyed; A Maghsoudi
Abstract
The study area is located at the center of the Lut area and the southern part of the Eocene- Oligocene Lut volcano-plutonic belt. The main exposed igneous rocks include widespread and thick units of Middle Eocene volcanic (basaltic andesite, andesiteand trachy-andesite) and Eocene-Oligocene volcanic-subvolcanic ...
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The study area is located at the center of the Lut area and the southern part of the Eocene- Oligocene Lut volcano-plutonic belt. The main exposed igneous rocks include widespread and thick units of Middle Eocene volcanic (basaltic andesite, andesiteand trachy-andesite) and Eocene-Oligocene volcanic-subvolcanic (dacite and rhyodacite) with related tuffs, intruded by microdioritic stock and dykes of Oligocene with gabbrodiorite to quartzdiorite compositions. Texture is dominantly porphyritic and the main minerals are plagioclase, clinopyroxene, hornblende, K-feldspar, quartz and minor amounts of biotite with apatite, zircon, rutile and opaque minerals as accessory phases. These rocks with predominant K-high calc-alkaline to shoshonitic affinities, are I type and metaluminous and are characterized by LILE, LREE and Th enrichment relative to HFSE, depletion in Nb,Ti,Ta and weak depletion in HREE and Y. These features are characteristic of the post-collisional calc-alkaline rocks along with a continental active margin tectonic setting. In spite of the low ratios of Nb/U, Nb/La and Ce/Pb, the Sm/Yb (1.6-2.1) ratio reveals low contamination of magmas with relatively thin crust which is in accordance with low crustal thickness in this area (36-38Km). According to geochemistry of trace elements and REEs, the main cause of magmatism in Mahour was melting of a metasomatized lithospheric mantle (E-MORB like) with spinel lherzolite composition accompanied by very small amount of garnet in the presence of phlogopite. On the basis of the phenocrysts assemblage, REE pattern with negative Eu anomaly (Eu/Eu*= 0.63- 0.9) and also La/Yb calibration to crustal thickness, magmas have undergone relatively dry crystallization in the magma chamber at shallow depths (
