نشریه پترولوژی
پیاپی 44 (زمستان 1399)

In Tighanab area at southeast of Sarbisheh, the intrusion of quartzdioritic subvolcanic bodies into the Paleocene- Eocene limestone and sandstone led to the skarn formation. Plagioclase, hornblende (magnesiohornblende) and quartz are the main minerals in the subvolcanic rocks. Base on microprobe analyses, the composition of plagioclases with 15-45% anorthite content varies from andesine to oligoclase. The pressure during mineral crystallization of the Tighanab quartzdiorite porphyry is about 5.27kbar and its average temperature, on the basis of thermometry with coexisting hornblende and plagioclase, was obtained about788ºC. The Tighanab exo- skarn are characterized by the presence of garnet, epidote, pyroxene (diopside), calcite, chlorite, quartz, magnetite, pyrite, hematite and gypsum. The studied garnets belong to the calcic category and are of the andradite- grossular solid solution type. The composition of andradite varies slightly whereas the grossular constituents, to some extent, are uniform. The occurrence of andradite as well as its compositional changes represents high oxygen fugacity and Fe3+/Al ratio changes respectively, during the garnet crystallization. The presence of andradite, diopside- rich pyroxene and the over abundance of garnet relative to pyroxene in the studied skarn indicates oxidant conditions and correspond with the results of amphibole chemistry study in generating skarn quartz diorite porphyry. The lack of wollastonite in exo- skarn can be indication of garnet clinopyroxene crystallization at temperatures below 550 °C by metasomatizing solutions.

The Seghin metamorphic complex of ophiolitic mélange from the north Soghan, composed of metamorphic suites varying in protolith and metamorphic grade. The rock units of this complex have been metamorphosed under PT conditions of pumpellyite- actinolite, greenschist- Ep amphibolite and blueschist facies enclosed by a serpentinitic mélange. The pumpellyite- actinolite and greenschist- Ep amphibolite facies rocks display overprinted metamorphic evidences of blueschist facies as glaucophane overgrowth around actinolite and magnesiohornblende crystals. The average temperature and pressure calculated by thermocalc software and petrogenetic grids is 6- 7, 290- 350 and 11 Kb, 350 ˚C for pumpellyite- actinolite schist and blueschist samples, respectively. The relations of minerals transformation, thermobarometry calculations and the lawsonite preservation are in accordance with counter- clockwise metamorphic path. Generally, the metamorphic blocks of serpentinitic mélange with counter- clockwise PT path like Seghin complex are characteristics of long- lived subduction systems. During the onset of subduction event and attaining to blueschis facies, metamorphic path of down- going slab has passed through greenschist- Ep amphibolite facies. Then, the prograde metamorphic path extending across Pmp- Act subfacies owing to decreasing of geothermal gradient during maturity of subduction setting. Consequently, hairpin- like PT path is governed that is characteristic of Franciscan- type accretionary prisms.

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 Ghezelhesar alkali olivine basalt flows as dark horizontal flows with about 20 m thickness covered the Quaternary deposits, 2 km southwest of Ghezelhesar village, 60 km northeast of Hamedan and in the Sanandaj-Sirjan geological and tectonic zone. The phenocrysts of these rocks are olivine and clinopyroxene often as euhedral crystals and common porphyritic, vitrophyritic and glomeroporphyric textures. The matrix of the rocks studied formed from volcanic glass, leucite, nepheline and microliths of pyroxene. The Ghezelhesar basalts, with continental within plate alkaline nature, are silica-under saturated and characterized by normative minerals of Diopside, Hematite, Anorthite, Albite, Orthoclase, ±Hypersthene, ±Olivine, ±Nepheline, and ±Quartz. REE normalized patterns show enrichment in LREEs rather than HREEs and fractionation between LREE and HREE is relatively high (LaN/YbN = 37.05–43.43). A negative anomaly in High Field Strength Elements (Nb, Ta, Zr, Ti, P, and Rb) and positive anomaly in Large Ion Lithophile Elements (i.e. Ba, Pb) and elements such as Th, La, Ce, Nd, and Sm are remarkable geochemical features of the rocks under study. These criteria along with parameters of their trace elements such as the ∆Nb indicate that the parent magma of the rocks under investigation derived from the low-grade degree partial melting of an enriched garnet-mantle, and the fractional crystallization has affected their chemical properties.

Tashina area, as a part of the Sanandaj- Sirjan magmatic- metamorphic Zone, located 10 kilometers north of Serkan city and on the southern slope of Kuhe- Gavbar. The most important geological unit is the porphyroid granite belonging to the Middle Jurassic. Tourmaline is observed as massive in pegmatites and as quartz tourmaline veins within the host granodiorite. The massive tourmalines are spherical, elliptical, elongated, and radial, and sometimes it is so abundant that it can be as the tourmalinite type. Optically, the massive tourmalines show brown- green in color, sometimes very intense intefrance whereas the tourmaline veins are brown- green and blue (indicolite). Indicolite related to the tourmaline delayed phase and is newer than brown- green tourmalines.The studied tourmalines are Fe- rich and schorl type, base on EPMA data as well as several diagrams. The tourmaline in the quartz- tourmaline veins are the vacancy type while the second type is often alkaline with tendency to this group.  Euhedral forms and the lack of chemical zoning, with high Al and Fe/Fe+Mg contents, deficiency in X sites, and plentiful tourmaline in host granitic rock which is Li poor are all indicative of  the magmatic origin of tourmaline enriched in B. The presence of Ba, Eu, Nb, and Sr negative anomalies in the studied samples and the separation of plagioclase and K- feldspar can be accounted as important factors in magmatic evolution of the studeid rocks.  Overall, the results of petrographic studies are well in accordant with trace and REE geochemistry data.

The monzonitic-syenitic Gowdal intrusive body located in the north of Ahar, East- Azerbaidjan province is a member of the Shivardagh batholithic body and a part of the Alborz- Azerbaidjan- Lesser Caucasus magmatic belt related to the Meso-Tethys (Sevan- Akera- Ghareh Dagh) Ocean. Fe- Cu and Mo skarn mineralization (magnetite, specularite, pyrite, chalcopyrite, and molybdenite) occurred at the contact of the Gowdal intrusive body with limestone- marly limestone units. The supergene copper and iron minerals (malachite, azurite, secondary hematite, and Fe-hydroxides) are superimposed on the hypogene skarn mineralization assemblages. Based upon diagrams of major elements versus SiO2, with mean values, ratios of trace elements, and diagrams of trace elements, the Gowdal intrusive body formed from relatively evolved magma and compositionally lies within the range of intrusive bodies affiliated with copper and to some extent zinc skarns. On the other hand, distribution patterns of trace elements of the Gowdal intrusive body normalized to N-MORB shows considerable similarity to known zinc and to some extent copper skarn-related intrusive bodies. Consequently, despite having dominant iron mineralization at the current level, the Gowdal intrusive body displays the utmost similarity with the bodies associated with copper skarns.