نشریه پترولوژی
پیاپی 48 (زمستان 1400)

Zarrin granitoid, with mostly metaluminous to slightly peraluminous, and I-type composition, outcropped in Yazd block, Central Iran. The U-Pb SHRIMP zircon age from Zarrin granitoid yields 557-567 Ma age consistent with the Late Neoproterozoic-Early Cambrian ‘Cadomian’ plutonism at northern margin of Gondwana supercontinent. The chondrite and primitive mantle normalized trace elements patterns show light rare earth elements (LREE) enrichment relative to heavy rare earth elements (HREE) and enrichment of large ion lithophile elements (LILE) relative to high field strength elements (HFSE), accompanied by negative anomalies in Nb, Ti, and Eu consistent with arc-related magmatism, associated with subduction of Proto-Tethys oceanic crust beneath the northern margin of Gondwana. Geochronological and geochemical data including inherited zircon age suggest the  Zarrin granitoid originated from partial melting of relatively younger mafic crust and point to the existence of hidden Paleoproterozoic-Mesoproterozoic rocks in the lower continental crust of Iran.

The volcanic complex of North Khour  located in southern Khorasan province, 90 km northwest of Birjand in the Eastern of  Iran. The rocks under study are basaltic andesite, andesite and trachyandesite, latite, dacite to rhyodacite with tuff and breccia as pyroclastic rocks. The volcanic rocks are predominantly calc-alkaline nature with some tholeiitic affinity and porphyry texture. Iron mineralization developed as magnetite, hematite and small amount of goethite with magmatic origin, on the base of field observations. Bornite as the only and the primary Cu ore occurred as a small body. The presence of minor amounts of bornite and pyrite as the sulfide phases as well as the absence of the other Cu primary sulfide ores in the area along with secondary Cu mineralization phases reflect a hydrothermal solution with high oxidation degree which has passed the latest magmatic differentiation and gave rise to form surface Cu ores as chalcocite in supergene zone. The thermobarometry of fluid inclusions studies from Ghar Kaftar and Hoze Sabz, yield temperature range of 178 -324 C for Cu mineralization. Therefore, it seems that Cu mineralization is related to epithermal to mesothermal conditions.

Several outcrops of migmatitic rocks (metatexite to diatexite) developed in the northern part of the Sanandaj-Sirjan zone (Hamedan, Touyserkan and Boroujerd). Two types of inherited zircons (2590 to 190 Ma) and metamorphic zircons (180 to 160 Ma) are found in the mesosome of migmatites. As the cathodoluminescence images display, inherited zircons are euhedral to subhedral with oscillatory zoning, and are jagged their margins in some cases. Metamorphic zircons as thick form grains are characterized by the lack of magmatic zoning and the presence of ghost texture, growing on the margins of the inherited zircons as a thin sheath.  In some cases, metamorphic zircons are found as single crystals without any inherited nuclei. As the structural evidence suggests the process of recrystallization formed metamorphic zircons and their elements were moved under sub-solidus conditions. During migmatization, on one hand, the presence of fluid phase due to partial melting, gave rise to the formation of metamorphic zircons showing oscillating zoning and on the other hand, it has precluded the deformation due to shearing in the internal structure of these phases.  Metamorphic zircons, belonging to 180 Ma, and younger are possibly nucleated through the Jurassic period thermal-dynamic metamorphism.

The Sargaz Cu–Zn volcanogenic massive sulfide deposit, in the southern Sanandaj–Sirjan Zone, composed of felsic and mafic volcanoclastic, volcanic rocks, with sandstone, limestone and calcareous tuff and NW-SE trending. The basaltic host rocks with mostly tholeiitic to transitional affinity host the massive sulfide mineralization. The alteration zones related to mineralization system representing the channels of ascending hydrothermal solutions existing within a footwall alteration pipe, with a central siliceous and quartz–sericite core giving rise to zones of quartz–chlorite, chlorite–quartz, and finally chlorite–sericite (stringer envelope zone) on the margins. Pervasive alteration started with the development of chlorite–sericite subsequently overprinted by chlorite, sericite, and finally quartz as hydrothermal activity intensified in the center of the alteration zone. Despite intense alteration of the volcanic rocks, immobile elements (i.e. Ti, Zr) have remained essentially immobile, which allows identification of the precursors and calculation of mass changes. Mass changes calculated for mafic footwall rocks indicating most of the volcanic rocks in the mine area are strongly depleted in Na2O and CaO, and highly enriched in MgO, Si2O and K2O. The Si content is the largest within 5–10 m of the massive sulfide lenses. Intensely silicified footwall basaltic rocks underlie the massive sulfide lens in Sargaz deposit were characterized by white to grey, microcrystalline silica. Mass change analysis of altered footwall basaltic rocks immediately below the massive sulphide zone shows the SiO2 content increases to about 90%. The chloritic and chlorite–sericite alteration zones were enriched in Fe, Mg, with only small amount of K in the chlorite–sericite zone but depleted in Na and Ca most likely due to the alteration of clinopyroxene, plagioclase, and volcanic glass. The change from chloritization to silicification and sericitization must be accompanied by a reduction in pH during silicification and sericitization. Identification of such alteration patterns can be used as an exploration key in other massive sulfide mineral exploration.

This study presents the results of mineral chemistry data of Early–Cenozoic volcanic rocks in the south of the Tarom-Hashtjin magmatic zone. The Uchbolaq lavas in the north of Zanjan are a part of Oligocene eruptions within Turkish- the Iranian plateau. Based on microprobe analysis of the andesite-trachyandesites’ samples of this area, show that these rocks are composed of, labradorite (An55-66), augite (Wo44 En44 Fs12), mg-hastangsite ((Na+K) A≥0.50 and Alvi<Fe3+), and mg-biotite (Fe2+/(Fe2++Mg)>0.3). Geothermometric calculations suggest that the range of crystallization temperatures for amphiboles is between 985 to 941 ºC, and biotite’s temperature ranges are between 770 to 758 ºC. Based on geobarometric calculations, amphiboles are indicated a pressure range between 5.3 to 6.5 kb, and biotite’s pressures are shown from 0.9 to1.9 kb. The results of the amphibole and biotite's mineral chemistry data suggest that these rocks are derived from a calk-alkaline magma with approximately high ƒO2, in a volcanic arc related to subduction zone and orogenic setting suites.

This study focuses on quantitative calculations on the texture of metamorphic rocks. For this purpose, a variety of garnet-bearing metamorphic rocks were selected from West Azerbaijan province, and then related measurements were performed. Regardless of the whole rock chemistry or the type of metamorphism and even with the interference of directional pressures, the results of the shape analysis show that the w/l of garnet crystals has 0.9 and is produced an equant shape. Studying the CSD of garnet crystals in metamorphic rocks reveals that the J/G was always several times higher indicating the considerable degree of overstepping in the early stages of crystallization. It is also possible to notice the annealing of smaller crystals and the sudden change in the slope of the pattern and the existence of two statistical populations due to crystallization during two phases of metamorphism on the rocks. The slope of the patterns (-1/Gt) indicates that the growth rate of garnet crystal per unit time (Gt) is independent of the type of metamorphism and its conditions and is more a function of the appropriate combination available as well as the number of nuclei. The distance to the nearest neighbor is used to achieve the SDP in these rocks. By calculating the Big-R values against the sum of other phases, the SDP of crystals has been evaluated from random to regular type, which indicates uniform heat transfer and homogeneous crystallization.