PETROLOGY
Year:2017 | Volume:7 | Issue:28 |Papers Count:10

In this research, zircon Hf isotopic ratios from Sungun, Sar Cheshmeh, Meiduk, Darreh Zar and Bondar Hoza porphyry mineralized intrusions has been studied. The Hf isotopic ratios in the studied porphyry intrusions are similar and the average of zircon Hf values from Sar Cheshmeh, Meiduk, Darreh Zar, Bondar Hanza and Sungun porphyry intrusions are+8.2, +9.3, +9.2, +10 and+8.6, respectively. Also, the averages of zircon TDMC ages from the Sar Cheshmeh, Sungun, Meiduk, Darreh Zar and Bondar Hanza porphyry intrusions are 573, 550, 502, 510 and 464, respectively. The positive and restricted Hf values in the studied porphyry intrusion zircons along with the lack of inherited zircons shows continental crust did not contribute in the evolution of the porphyry magmas. The Hf in the studied zircons is between depleted mantle and lower crust values with a tendency towards the depleted mantle. According to adakitic nature of studied porphyry intrusions, post collisional tectonomagmatic setting and their zircon Hf values, the primary magma has been likely originated from a juvenile metamorphosed mafic lower crust with an impressive contribution of depleted mantle.

The Alvand Intrusive Complex (AIC) is located in an area between Hamedan and Tuyserkan cities, and crops out over an area 400 km2 intruding the Sanandaj-Sirjan plutono-metamorphic belt. The emplacement age of the AIC is constrained to Upper to Middle Jurassic, based on U–Pb zircon geochronogic data. Lanthanide tetrad effects are often observed in REE patterns in the granites of the Alvand. The degree of the tetrad effect (TE1, 3) is estimated and plotted vs. K/Rb, Sr/Eu, Eu/Eu*, Y/Ho, and Zr/Hf. The diagrams reveal that the tetrad effect develops parallel to granite evolution, and significant tetrad effects are strictly confined to highly differentiated samples. The strong decrease of Eu concentrations in highly evolved rocks suggests that Eu fractionates between the residual melt and a coexisting aqueous high-temperature fluid.

Andesitic and andesitic-basaltic lavas are widespread over most of the ground surface of the Gurgur area altered mostly by the hydrothermal solutions. The main rock forming minerals in these rocks are plagioclase, pyroxene and olivine affected by the hydrothermal solutions. The altered rocks do contain minerals including calcite, sericite and chlorite. Given the results obtained and the mineral chemistry studies, the clinopyroxenes formed in the area are, chemically, calkalkaline and of diopside-augite type formed in subvolcanic to near surface levels contemporaneous with magma ascending. Plagioclase minerals show zoning textures and lie within the two andesine and albite-oligoclase fields. These units, in terms of total rock chemistry, are classified as the calk-alkaline volcanic rocks formed in the continental arcs. On the other hand, on the trace elements chondrite-normalized diagrams and enriched mantle-normalized multi- element diagrams, the LREE enrichment relative to the HREE is observed. The LILE (i.e. Rb, K and Th) and the LREE (e.g. La, Ce and Nd) show an enrichment in comparison to the HFSE (Zr, Hf, Nb, Yb, Y and Sm). Given the Nd/Th (1.42-1.15), Zr/Nb (12.27-21.22), Ba/La (18.64-29.77) as well as LILE enrichment associated with depletion in Nb, Ta and Ti, an environment related to the subduction zones can be proposed for the area under study. Moreover, the similarity between the REE distribution pattern and the incompatible elements point to the genetic relationship between these rocks. Finally, on the base of the obtained data, it can be concluded that the volcanic rocks in the Gurgur Mountain were likely formed during the extended magmatism of the Urumieh-Dokhtar in the Cenozoic.

The Sadrabad iron deposit is located 28 km west of Sadrabad village (west of Yazd) at the Urumieh-Dokhtar magmatic arc. The Upper Triassic-lower Jurassic sedimentary rocks (dolomitic limestone, sandstone, shale and marl), the Cenozoic granite to dioritic intrusive bodies and the Quaternary unconsolidated deposits outcrop in the study area. The intrusive bodies are of I-type calc-alkaline series formed in syn-collision to post collision settings of continental margin subduction zone. The later quartz monzodiorite intrusions played a significant role in iron mineralization. The location of mineralization controlled by NW-SE and NE-SW fault systems. Olivine, clinopyroxene, garnet, tremolite-actinolite, epidote, serpentine, talc, phlogopite, calcite, dolomite, brucite and hydromagnesite are the main skarn minerals. The ore bodies consist mainly of magnetite with minor pyrite, chalcopyrite and pyrhotite which occur as massive, vein-veinlets, brecciate and disseminated magnetite. Skarn formation occurs in two prograde and retrograde stages. Olivine, clinopyroxene and garnet formed in prograde and the remaining minerals in retrograde stages. The temperature and salinity of fluid inclusions in quartz veins associated with serpentine (in retrograde stage) range from 217 to 280oc and 8 to 16 (wt %) NaCl respectively, indicating the mixing of magmatic and meteoric water in retrograde stage. The Mg-bearing silicates such as serpentine, phlogopite, diopside and talc in the Sadrabad skarn, point to the mineralization of magnesian type.

The Dalli porphyry Cu-Au deposit is located in Delijan city, Markazi province, Iran. The deposit, structurally, is placed in the central part of the Urumieh-Dokhtar magmatic arc (UDMA) and consists of two parts, the South Part and the North Part with andesite to andesite basalt wall-rock intruded by granitoids (diorite, quartz diorite and monzodiorite). The aim of this study is the investigation of geologic, mineralogic and geochemical characteristics of the Dalli deposit in order to understand the mineralization factors effective in productive parts. For this purposes, in addition to field observations as well as mineralogical investigations, sampling was done from unaltered, mineralized and less-altered portions for geochemical studies using LA-ICP-MS. Mineralogical and geological evidences indicate that the presence of phyllic, argillic and supergene alterations with more abundance of hornblende, biotite and magnetite in the South Part are effective parameters in increasing the mineralization potential of the Southern Part. As the presence of hornblende, magnetite and lesser abundance of plagioclase indicate high ƒH2O and ƒO2 during magma evolutions and the phyllic and supergene alterations provide conditions for copper precipitation by creating heat loss and copper solution, respectively. This is also supported by high Eu/Eu*, [Dy/Yb] n, [La/Sm] n values and REEs trend with a upward concavity for the South Part.

Sahl area, in the south of Shahrood, is a part of the northern portion of the Central Iran Structural Zone. The area is dominated by a thick sequence of the Paleocene to the middle Eocene volcanic and volcano-sedimentary rocks. Hypabyssal igneous rocks as dome, dike and sill with trachybasaltic andesite and trachyandesite composition intruded the sequence. Various enclaves with amphibolitic, gneissic, hornblenditic, pyroxenitic, tonalitic, gabbroic, tuffaceous sandstone and siltstone nature with different sizes and shapes are present in the rocks studied which can be taken as an evidence of contamination and magma mixing processes. With respect to geochemical characteristics, the studied rocks are belonging to low silica adakites, with calc-alkaline to high potassium calc-alkaline affinity, enriched in LREE and LILE and depleted in HREE and HSFE. Overall, the mentioned adakites resulted from crystallization of melts originated from partial melting of metasomatized or modified mantle wedge, above the subduction zone of the Neotethys oceanic slab (Sabzevar - Daruneh branch).

The young basalts in East Azerbaijan are placed in West Alborz – Azerbaijan zone. Volcanic activities have extended from the Pliocene to the Quaternary by eruption from fracture systems and faults. Rocks under study are olivine-basalt and trachybasalts. The main minerals are olivine, pyroxene, plagioclase set in glassy or microcrystalline matrix and olivine are present as phenocryst. The textures in the studied rocks are mainly hyaloporphyric, hyalomicrolitic and porphyritic. Trace elements and rare earth elements on spider diagrams have high LREE/HREE ratio. Rare earth elements on diagram display negative slope indicating alkaline nature for the basalts under study. As it may be observed, on tectonic diagrams, the Marand basalts are placed on Island Arc basalt (IAB) field, whereas the Ahar, Heris, Kalaibar and Miyaneh basalts are classified as Ocean Island Basalts (OIB) and finally the basalts of Sohrol area are plotted on continental rift Basalt (CRB) field. The Marand and Sohrol basalts were likely originated from lithospheric - astenospheric mantle with 2 to 5 % partial melting whereas, the Ahar, Heris and Kalaibar basalts having same source experienced 1-2% partial melting rate and the Miyaneh basalts possibly produced from lithospheric mantle with 10-20% partial melting rate pointing to shallow depth of mantle and the higher rate of melting. Based on tectonic setting diagrams, all the rocks studied are plotted in post collisional environments.

Kharaju mafic intrusions (south Azarshahr; East Azarbaijan) are gabbro in composition. The rocks with Eocene age intruded the northwest part of Urumieh -Dokhtar magmatic belt with a trend of NW-SE. These rocks contain mostly of minerals such as plagioclase, quartz, pyroxene, titanite, apatite and magnetite. The rocks are moderate to high calc-alkaline. The gabbros were produced as a result of the partial melting of mantle wedge with spinel lherzolite and after emplacement into the crustal magma chamber underwent fractional crystallization. Injection of the Kharaju intrusions is in relation to the last stages of Neotethys subduction activity under Central Iran. Negative anomaly in the high ionic strength elements (HFSE) like, Nb, Ta, P, Hf and Zr and mild positive anomalies of Eu and Sr with moderate increases in values of K, Sr, Rb, Ba, Pb and U show oblique subduction beneath Central Iran might be willing to make the appropriate space on the edge of central Iran and as a result, partial melting in the mantle wedge occurred due to reduce the pressure as decompression.

The Khunik area is located in the south of Birjand, Khorasan province, in the eastern margin of Lut block. Tertiary volcanic rocks have andesite to trachy-andesite composition. Dating analyzing by Rb-Sr method on plagioclase and hornblende as well as whole-rock isochron method was performed on pyroxene-hornblende andesite rock unit. On this basis the emplacement age is Upper Paleocene (58±11 Ma). These rocks have initial87Sr/86Sr and εNd 0.7046-0.7049 and 2.16-3.12, respectively. According to isotopic data, volcanic rocks originated from depleted mantle and have the least crust contamination while it was fractionated. Geochemically, Khunik volcanic rocks have features typical of calk-alkaline to shoshonite and are metaluminous. Enrichment in LILEs and typical negative anomalies of Nb and Ti are evidences that the volcanic rocks formed in a subduction zone and active continental margin. Modeling suggests that these rocks were derived dominantly from 1–5% partial melting of a mainly spinel garnet lherzolite mantle source that is metasomatized by slab-derived fluid.

Asalem metamorphic complex consists mostly of metabasite, metapelite and serpentinite. Metabasites display metamorphic features of greenschist and blueschist facies. Greenschist facies rocks that found as both foliated and massive types contain mineralogical assemblage of actinolite, chlorite, albite and epidote. Blueschists contain mineralogical assemblage of sodic amphibole, epidote and phengite. Whole rock analyses of the metabasites indicate basaltic to andesitic composition with mainly calcalkaline nature of their protolith. According to the discrimination diagrams of tectonomagmatic setting, the protolith of investigated metabasites has been islands arc and somewhat mid ocean ridge. The patterns of rare earth elements and spider diagrams of the Asalem metabasites resemble to the basic and intermediate magmatism of islands arc or suprasubduction setting as well. Greenschists and blueschists facies rocks of the Asalem metamorphic complex have been probably equivalent to islands arc or young and hot oceanic crust of suprasubduction zone setting. This portion of oceanic basin unlike the subducted even and thick oceanic lithosphere of Paleotethys during accretion in the shallower levels of accretionary prisms, have underwent metamorphic conditions of blueschist and green schist facies and finally gave rise to the formation of the metabasites of the Asalem metamorphic complex.