فهرست مطالب a. ahmadi khalaji

The south of Bavanat area is located in the high Zagros zone and it is considered a part of the Neyriz ophiolite. In this area, the ophiolitic complex is small coloured melanges include radiolarite cherts and serpentinites. The serpentinites composed of serpentine, spinel, opaque (as residual minerals from protholith), amphibole, rarely olivine and pyroxene. Olivines have been highly altered to serpentine and pyroxenes to bastite. Low values of Al2O3 and very low TiO2 against high values MgO, Cr, Ni and V in these serpentinites indicate the protholith of harzburgite- dunite tectonites. Also, very low values of CaO in these serpentinites indicate the low amount of clinopyroxene in the protholith and its harzburgite-dunite type. Based on the chemistry of the major, minor and rare elements, the primary peridotites that make up these rocks are formed in the suprasubduction-fore arc zone from a mantle affected by the reaction with the melt (melt-rock reaction) resulting from the subducted plate.

Bitumen is a mixture of oxidized hydrocarbons with color, hardness, specific gravity and various metamaterials that are in solid or semi-solid forms and can be dissolved in Carbon disulfide (CS2). To evaluate the physical and chemical characteristics of bituminous deposits in Lorestan sedimentary basin (a part of the Folded Zagros zone), 6 fresh and non-weathered bitumen samples were collected from the veins and inside the mines of three areas with high potential of bitumen, including the northern region of Kohdasht, western Poldokhtar and southeastern Sepiddasht. The surface studies of above mentioned area, indicates the appearance of bitumen (tar mats) occurred in Amiran Formation. According to the analysis, the average amount of oxygen, nitrogen and carbon in the studied samples is 6.30%, less than 1% and 74.47% respectively, the average percentage of mineral ash and moisture of the samples is 6.4% and 0.8 percent respectively which indicates the very favorable quality of the studied bitumens .The solubility of studied bitumens in CS2, benzene and ethanol solvents shows that most of these bitumens have compounds with high molecular weight (asphaltene molecules) and low amounts of hydrogen (average 6.02). This example is also consistent with this conclusion. X-ray fluorescence analysis (XRF) on 6 bitumen samples from the studied area shows that Al2O3, SiO2 and Fe2O3 oxides are more abundant than other oxides. This issue can be due to the formation of this mineral in the host rock of the Amiran shale formation, which is rich in the mentioned elements. The values of CaO and K2O in the analyzed bituminous samples can be due to the formation of this mineral from the underlying formations (Ilam and Gurpi) which have found their way into the Amiran formation after formation and migration. The ratio of Ni vs V of the samples of the studied area is low (Ni/V <1) and has an average of 0.57%, so their rock of origin was somewhat carbonate-shale. The current studies reveal that, the origin of the studied bitumen started from deeper and older shale sediments (Ilam and Gurpi Formations), in which the deeper bitumen has migrated upward and washed the younger hydrocarbons to shallower formations and earth surface accumulation.

Sahneh, Harsin-Nourabad ophiolits (Kermanshah Provience) located in outer Zagros ophiolitic zone and are parts of the Cretaceous ophiolitic belt, as remnants of southern branch of the Neo-Tethys Ocean obducted over the Arabic–Tauric platform from Oman to northwestern Syria, Cyprus and Antalya. Calculation of Fe/Mg separation coefficient of olivine indicates the mantle origin of this mineral. Textural evidence of ultramafic rocks displays clear evidence of cooling with decompression, partial melting and melt-rock reactions. Tectonomagmatic discrimination diagrams show that peridotite samples are located in olivine- spinel mantle array and SSZ peridotite field. Based on geothermobarometry calibration the temperature and pressure of crystallization of harzburgite and lherzolite rocks were 1100 to 1500 ° C and 12 to 18 Kbar and the wehrlite sample was 1200 to 1500 ° C and 21 to 23 Kbar, which corresponds to the SSZ tectonic environment.

The Pillow lava and diabase dykes of the southwestern region of Aleshtar are host different species of zeolites and secondary minerals. Zeolites are formed by the cavities and veins and decomposed from primary minerals. Based on field studies, X-ray diffraction (XRD) and Electron Microprobe Analysis (EPMA), natrolite zeolites (most abundant zeolites), mesolite, scolecite and analcime have been identified in the pillow lava and diabase dykes in the study area. The average Si/Al ratios for natrolite, mesolite, scolecite and analcim are 1.46, 1.49, 1.62 and 2.29, respectively. These zeolites are formed during two stages of metamorphic hydrothermal fluids, during fractures and in the cavities of host rocks and at temperatures below 250 °C. The investigation of the geochemical properties of zeolites host rocks, shows that their magmatic series is calc-alkaline to tholeiitic and their tectonic environment depends on the mid-ocean ridges (MORB).

The Geysour area is located east of Gonabad and is a part of the northern Lut block. The rocks in this area include granitoid and metamorphic rocks. Based on field and mineralogical evidence, the protolith of amphibolite rocks are calc-silicate. The metamorphic rocks of this region are divided into metapelites and amphibolites. Textures, such as post-tectonic garnet and random amphiboles, are indicative of contact metamorphism in amphibolites. Garnets behave from ideal to non-ideal. The end members of the garnet are varied in these rocks and include Al-schorlomite, uvarovite, spessartine, pyrope, almandine, grossular, andradite, morimotoite, and majorite, but their profile patterns are flat. The amphibole is of the ferrohornblende type to the ferrochermakite and chermakite, and has zoning. Biotite has converted to chlorite. The presence of titanite, hematite and epidote are an indication of the effect of oxygen fugacity. Temperature and pressure were calculated in the range of 534-609 oC and 2-<4 Kbar, respectively.  Geysour amphibolites have progressed to the mid-amphibolite facies in the metamorphic aureole. Also, these rocks were undergone a retrograde metamorphism where the temperature and pressure were 489oC and 2.8 kbar, respectively, and the chloritizied biotites exhibit temperatures below 150 oC.

The volcanic rocks in the north of Kaboudarahang consist of andesite-tracky andesite with the Eocene age have been exposed in the Uromieh-Dokhtar zone. These andesite are scattered as prasmatic columns. Petrographic studies show that these rocks consist of amphibole and plagioclase with porphyritic, glomoroporphyritic and microlitic tetures. Geochemical studies show that these rocks belong to the calc alkaline magmatic series. In terms of tectonic environment, they are located in the active continental margin associated with subduction zone. Trace element patern shows the enrichment of LREE to HREE. Amphibole mineral chemistry shows that they are belonging to the calcic group of magnesium hornblend and chermackit types. These amphiboles belong to active continental margin that consistent with the results of host andesite. Based on thermobarometric methods, these amphiboles are formed at a temperature of 815.5 ° C and a pressure of 6.35 kbar. The high fugacity obtained for these rocks indicates the oxidant conditions in the formation of these rocks and evidence of their formation at the boundary of convergent plates.

The studied area is a small portion of Sanandaj – Sirjan zone. Metasomatism at the contact of intrusive body studied and penetration of Al-rich rocks caused tourmalinization to stratiform tourmalinite in pelitic hornfels. In addition, hydrothermal fluids crystallized tourmaline nodules in monzogranite surface. The Fe/ (Fe + Mg) ratio in varied between 0.4-0.76 in stratiform tourmaline and 0.83-0.96 in tourmaline nodules respectively. The tourmaline composition is schorlite- dravite. Chemical zoning in this mineral show that system is open and crystallization is unequilibrium. The flat trace end rare earth elements imply to mobility of LREE induced to alteration that this phenomena occur to increasing HREE/ LREE in this type tourmalines.