فهرست مطالب لیلا محمودآبادی

The Eocene volcanic rocks in the SW Jandaq that outcrop in the south of Doruneh fault constitute a part of the Central Iran zone. The predominant rocks consist of basalt andesite، trachyandesite and dacite that porphyritic، microlitic porphyritic and hyaloporphyritic textures are common. The essential minerals are represented by intermediate plagioclase، diopside، augite، phlogopite and magnesiohastingsite and the secondary minerals are Fe -oxide and chlorite. Based on geochemical data، these rocks belong to high-K calc-alkaline and shoshonitic series which with K2O، Ta/Yb، Th/Yb and Ce/Yb. Lava eruption in subduction setting can be demonstrated by highly negative Nb and Ti anomalies، and also by comparison with mantle normalized trace element trend with that of the volcanic arc. In addition، the discrimination diagrams (TiO2/Al2O3 and Zr/Y) display a continental volcanic arc setting for these rocks. The REE patterns (chondorite normalized) and their ratios plus positive Pb anomaly، point to the effective role of low grade partial melting of a metasomatized mantle and garnet amphibolites source accompanied by crustal contamination in the course of formation these rocks.

In the south west of Jandaq area, the Eocene volcanic rocks crop out, near the Doruneh Fault in a large area. These rocks are composed predominantly of basalt, quartz andesite, andesite, dacite and latitewith porphyritic, microliticporphyritic and hyaloporphyric textures. The main constituents are plagioclase, amphibole, clinopyroxene, quartz, minor alkali feldspar and biotite and opaque minerals as accessory minerals. The secondary minerals are opaque, sericite, calcite and chlorite. The composition of the plagioclase ranges from andesine to labradorite, the clinopyroxene is diopside-augite and the amphiboles are magnesio-hastingsite some plagioclase phenocrysts show oscillatory zoning. The study of chemical composition of clinopyroxenes classifies these rocks as sub-alkaline series and volcanic arc. The geothermometry of clinopyroxene reveal the temperature of 941-959 ºC for pressure of 1-10 kbars. Clinopyroxenes barometry point to their formation in defferent depths during their ascending. The Hlb-Plg thermometry shows the temperature of 858-941 ºC for pressure of 1-10 kbars. The high volume of water in the crystalization environment of the pyroxenes as well as variations on AlIV+Na/ AlIV+2Ti+Cr diagram indicate the high oxygen fugacity of the environment. Field observations and some petrographic evidences demonstrate traces of hydrothermal alteration.