morteza khalatbari jafari

The study area is located in the north of the Yusef -Kandi village, north of Lahrud, Ardabil Province (northwestern Iran). This area comprises portions of the Alborz-Azarbaijan structural zone, which together with the Little Caucasus and the highlands of southeastern Turkey have evolved due to the convergence of the Arabian and Eurasian plates during the Alpine-Himalayan orogeny. The study area includes outcrops of Eocene volcanic and volcano-sedimentary sequences which were deposited in marine to continental environments. The volcanic portion of these sequences consists of volcanoclastic rocks as well as lava flows. A few acidic volcanic rocks and ignimbrite are locally exposed in this area. The petrographic studies show that the Yusef-Khan-Kandi volcanic rocks include picrobasalt, basalt, tephrite, basanite, trachybasalt, basaltic trachyandesite, phenotephrite, tephrophenolite, trachyandesite and trachyte compositions. Phyric texture is common within the volcanic lavas. The majority of the samples show transitional to potassic trends, with only a few samples exhibiting sodic trends. The transitional trend observed in a significant number of the studied samples probably has resulted from the mingling of the sodic and potassic magmas. The Harker binary variation diagrams indicate trends that are consistent with fractional crystallization. The chondrite-normalized REE patterns and primitive mantle-normalized spider diagrams show high LREE/HREE ratios which could be explained by partial melting of an enriched mantle (including asthenospheric) or a metasomatized mantle in collisional to continental arc environments. Most of the studied volcanic rocks plot in the active continental arc or within plate domains. It seems that following the convergence between the Arabian and Eurasian plates in the Late Cretaceous, the northward subducting Neotethyan slab in the Eocene, triggered partial melting of the metasomatized subcontinental lithospheric mantle. Therefore, we suggest that the Yusef-Khan-Kandi Eocene volcanic rocks were erupted in a post-collision extensional environment.

The Sabalan is one of the Pliocene-Quaternary volcanoes in northwestern Iran. Based on the activity history, the Sabalan volcanic rocks can be classified into two rock groups: Paleo- and Neo- Sabalan volcanic rocks. Paleo-Sabalan was constructed during the Pliocene-Pleistocene inmultiple eruptions between 4.5 and 1.3Ma, whereas Neo-Sabalan activity initiated after a series of violent explosive eruptions during the middle to late Pleistocene (545 to 149 ka; Ghalamghash et al, 2016). The Paleo-Sabalan volcanic rocks are trachy-andesitic to andesitic and rarely trachy-dacitic and Neo-Sabalan volcanic rocks are generally dacitic to andesitic.

Field investigation and sampling, petrography and mineral geochemistry are different part of our studies during this project. Mineral chemistry have been performed on two thin-polished sections of Paleo-Sabalan olivine basalt and Neo-Sabalan trachyandesite in Iran Mineral Processing Research Center. In this center, a Micro-probe model EPMA Sx100 model made by Cameca company with a voltage of 15 kV (Kv: 15 Kev), current intensity of 20 nm (nA), a diameter of 5 um and a detection limit of 500 ppm for microscopy and point chemical analysis Used. Sample preparation for microprobe studies has also been done in Iran Mineral Processing Research Center using carbon coating device.

Plagioclase composition in the Paleo-Sabalan volcanic rocks in the oligoclase to andesine range, and in the Neo-Sabalan volcanic rocks in the range of oligoclase, to andesine. K-feldspars are sanidine and orthoclase. The Olivine and pyroxenes of the Paleo-Sabalan volcanic rocks have chrysotile and diopside-augite compositions, respectively. The most of the mica in Neo-Sabalan lava are Biotite. The most amphibole of Neo-Sabalan lavas are Magnesiohornblende, and rarely are edenite. Based on the mineral chemistry diagrams of Sabalan volacic rocks have a sub-alkaline and calc-alkaline nature that have formed in the orogenic environment. Paleo-Sabalan clinopyroxenes have crystallized at 5 to 10 kbar pressure (equal 17.5 to 35 Km depth). The amphibole phenocrysts have crystallized at a pressure of 1 to 3 kbar (equal 3.5 to 10.5 Km depth) and a temperature of about 725 to 750 °C.

Considering the crystallization temperature of amphibole (725 to 750° C) and biotite modeling with FMQ buffer oxygen fugacity at the time of biotite crystallization was estimated to be -16 to -16.50. Probably, high oxygen fugacity and the presence of aqueous minerals indicate the effect of water-rich old subduction environment on the source of primary magma of Sabalan volcano.

The sediments are generally limestone and marl. The lower boundary with the loer red Formation is disconfomity and the upper boundary with the equivalent formatin of Bakhtiari Firmation is paraconformity. The total number of fossils found in this section is 69 species, 72 genera and 46 families. These sediments are formed in an open shelf and under the open sea and lagon environment. The variety and abundance of bentic foraminifer’s forms and the low presence of plagic forms testify to the shallow basin in this section, which is also confirmed by the study of other fossils. One of the Markable features of this section is the presence of Ammonia species, especially Ammonia parkinsonia. This section has a complete sequence of members of Qom Formation. This species are profe of shallow water and continental shelf for this carbonates. This section consist all of members of Qom Formation and based on identified foraminifera comparable to assemblage zone 1 & 2 introduced by Adams & Bourgeois (1967). These zones that inclod: 1-Borealis Melo Group- Meandropsin; 2- Miogypsinoides- Archaias- Valvulinid. Based on index foraminifer's species and their stratigraphic distribution the age of this section is Chatian- Burdigalian (Upper Oligocene-Lower Miocene)

The Ebrahim-Abad iron deposit, consisting of Paleozoic metamorphic rocks, Mesozoic plutonic bodies and metasomatic rocks, occurred in the northwest of Divandere and the Sanandaj- Sirjan structural zone.The metamorphic rocks including micaschist and marble are cut by plutonic intrusive rocks (granodiorite to milonitic and cataclastic granite). Mica schist and associated detrital sediments have been changed in the low- grade greenschist facies. Marbles and plutonic rocks have also undergone cataclastic metamorphism along shear zones. Metasomatic rocks are garnet- amphibolite to garnititic skarn composition crosscutting by magnetic veins. Iron mineralization as magnetite, chiefly occurred as lenses, veins and veinlets as well as dissimented grains. Massive, dissiminated, replacement, and network textures are the main textures of this deposit. Magnetite developed as amorphous, fine (less than 1 mm), or dissiminated. Chlorite, trermolite- actinolite, epidote, garnet, and quartz with minor clay minerals and calcite are the gangue minerals of the studied ore deposit. Iron oxide grade varies from 14 to 47 FeO%. Fe shows a negative correlation with S, and Si, Al, Mg, Mn, Ca, K oxides but positive correlation with Cr and Co. Ti/Ni+Cr and Ni/Cr diagrams point to the hydrothermal origin of the iron ore under study. The variations in the cobalt, nickel, vanadium, and titanium contents indicate that the skarn- hydrothermal origin of the Ebrahim- Abad iron deposit. It seems that the iron oxide remobilized by hot hydrothermal fluids originated from intrusive bodies and redeposited in marble, mica schist, greenschist, and skarn.

The Neogene volcanic rocks are exposed in south Arab abad, Lut block. The studied volcanic rocks covered Eocene and Oligocene volcanic lavas and Neogene evaporitic deposits. The base of the Neogene volcanic sequence made of breccia and tuff gradually covered by andesite, trachyandesite and dacitic lavas. These lavas have aphyric-phyric textures and microlitic to hyalomicrolitice in matrix. These lavas show calck alkaline magmatic trend. REE patterns and spider diagrams display enrichement in LREE and LILE relative to HREE and depletion in HFSE which like as subduction zone magmatism. In the tectonomagmatic diagrams they plot of subduction and post-collisions fields. Interpretation of the geochemical data indicates that the studied lavas probably produced from partial melting of lithospheric mantle which had previously enriched by subduction components (fluids and melt). Partial melting of crust, probably involved in generation of acidic lavas. It seems that in the Neogene period, lithosphere thinning induced partial melting of heterogeneous Sub Continental Lithospheric Mantle (SCLM). These processes consequently occurred by lithospheric delamination and asthenospheric upwelling.

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.

Mantle peridotites exposed in south Jazmourian comprise of lherzolite and porphyroclastic Cpx-bearing harzburgite in the lower part with chromitite lenses in the upper parts. Petrography and microprobe studies shows evidence of melt-peridotite interactions; post melting processes and subsolidus interactions, which has been associated with appearance of two generations of deformed primary pyroxene-olivine and fine-grained pyroxene-olivine-amphibole neoblasts. Second generation of minerals formed as inclusion, interstitial and fine-grain. These two groups of minerals have different geochemical characteristics, So that, the first group are comparable with abyssal peridotites and second group are comparable to suprasubduction (SSZ) peridotites. Thus, the chemical compositions of different generations minerals show different petrogenesis for ultramafic rocks in south Jazmourian. Whole rock chemical data indicate south Jazmourian peridotites have a depleted MORB mantle source which undergoing 10-20% partial melting. Thus this peridotites have experienced multistage evolution and show characteristics of the abyssal environment to suprasubduction zone. We are belived that peridotites transition from the abyssal environment to suprasubduction and affected by fluids derived from the subducted slab.