PETROLOGY
Year:2018 | Volume:9 | Issue:33 |Papers Count:10

The Jalal Abad region lies within the southern sector of Posht Badam block near to Jalal Abad, Najaf Abad iron deposits. In this region, several mafic intrusions and associated dyke and sills were intruded within the volcano-sedimentary unit of Rizu series and magnetite veins producing a narrow contact metamorphic aureole and overlain by Desu Series dolomites. These intrusion massives include irregular coarse- grained gabbrodiorites stocks and several NW-SE-trending basaltic dykes and sills. Petrographical and geochemical studies on the Jalal Abad mafic units reveal that they are alkaline in nature and based on the tectonic discrimination diagrams are grouped in alkaline basalts field of the intra-continental rift setting. They display LREE enrichment and HREE depletion, and significant enrichment in LILE in comparison to HFSE and HREE. Compositionally, they resemble modern OIB and the Hawaiian alkaline basalts. Magmas of these OIB-type and alkaline rock associations formed from partial melting of garnet- lherzolite facieses in the plume source, during the rift-drift and seafloor spreading evolution of the Proto-Tethys oceanic lithosphere during the Ordovician through Silurian periods.

In the southwest of the Qorveh area, north of the Sanandaj-Sirjan zone, there are outcrops of acidic and intermediate rocks including monzogranite, granodiorite, tonalite and diorite. According to petrographical studies, plagioclase, alkali-feldspar, quartz, amphibole, clinopyroxene and biotite. Geochemical and mineralogical studies indicate that these rocks are metaluminous to some peraluminous, belonging to calc-alkaline magma series and having I-type characteristics. The REE normalized chondrite pattern of the samples show the M-type tetrad effect and relatively negative Eu anomalies. All of petrography and geochemistry data show fractionation crystallization REE-enriched minerals e.g. feldspar, amphibole, apatite and titanite followed by magma-fluids reaction in late crystallization phenomena are the most important factors for the formation of tetrad effect in these rocks. Lanthanides tetrad effects are recognizable in REE patterns of the samples and they change versus Y/Ho, K/Rb, Zr/Hf, Sr/Eu and Eu/Eu* ratios in accordance with evolution trend of granitoid. These rocks are enriched in LILE (i.e. U, Rb, K, Th) and LREE and show some depletion in Nb, Hf, Ti, Ta, Ba, Zr and P. LILE and LREE enrichment and HSFE depletion of the samples are indication of their formation in subduction zone.

The Tannurjeh porphyry Au-Cu prospect area is located in the northeastern Kashmar, the Khorasan Razavi province, and central of the Khaf-Kashmar-Bardaskan magmatic belt. Geologically, the area is dominated by the Tertiary rhyolitic-rhyodacitic volcanic rocks, which are intruded by monzonitic to dioritic subvolcanic intrusive rocks. The texture in the most of the study igneous rocks is porphyry with fine groundmass and the main minerals are plagioclase, alkali feldspar, quartz, biotite, hornblende and magnetite. The monzonitic intrusions are the source of widespred mineralization and alteration, whereas the diorite is the later phase, which is devoid of mineralization. Using zircon UPb method, the age of monzonitic intrusive was determined at 39.8 Ma (Middle Eocene), geochemically as well as mineralogically, the igneous rocks of the area are calc-alkaline granitoids belonging to magnetite series (I-type) which were developed in subduction tectonic setting. The LREE enrichment relative to HREE and enrichment in K, Rb, Cs, Th, and U in comparison to Ti and Nb elements are observed in all of the samples studied. Eu negative anomalies and low Sr/Y ratios can be attributed to the presence of residual plagioclase in the source. (87Sr/86Sr) i (0.705673 and 0.705158), (143Nd/144Nd) i (0.512524 and 0.512570), and eNdi (-1.22 and -0.32) values indicate magma is derived from mantle wedge above subducted slab, which is assimilated with upper crust. Finally, the Eocene is an important metallogenic episode, particuarly for Au and Cu, in NE of Iran.

The Eocene volcanic rocks in Jirande area are dominated by basalt, andesite, trachyt and trachyandesite, which range from basic to intermediate rocks. Plagioclase as major mineral in igneous rocks makes up the largest percentage mineral in these rocks. Clinopyroxene and olivine in basaltic rocks and amphibole in acidic rocks are the prevalent minerals. In petrological studies, the existence of glomeroporphyry, sieve, corrosion gulf, skeletal, and also reaction rims confirm the role of crustal contamination and fractional crystallization in the evolution of the study rocks. Also, variation diagrams of trace elements, spider diagrams together with AFC modeling and ratio-ratio diagrams of trace elements, highlights the role of crustal contamination and magmatic fractionation in the genesis of the rocks studied. The parent magma of these rocks, have a composition like as the melts derived from enriched mantle, and plots in the field of 10-20 percent partial melting of a garnet-spinel lherzolitic source in the depth of 90 to 110 km.

The Cretaceous volcanic rocks (Andesite and basaltic andesite) in the northwest of Iran, south - southwest of the Germi city (Ardabil province), have considerable outcrops with northwest - southeast trend. The textures in the studied rocks are porphyry, hyalomicrolitic and glomeroporphyry and the main mineral is plagioclase with pyroxene, brown amphibole and biotite as accessory minerals. The rocks under study have calc-alkaline nature and have been crystallized from a magma experienced fractional crystallization. In the primitive mantle normalized spider and chonderite normalized rare earth elements diagrams. The studied rocks are characterized by LREE and LILE enrichment and depletion in HFSE as well as spikes in Pb and Eu. The overall features are compatible with subduction-related. The Cretaceous volcanic rocks under study have been generated in an active continental margin.

The Oligo-Miocene Qazan granitoid body caused contact metamorphic of surrounding rocks and skarn formation in the wall limestone. The main intrusive rocks are essentially granite to diorite in composition. Two different types of skarn, exo and endoskarn have been developed. On the base of microprobe data, the northern skarn are characterized by zoning and the amounts of andradite and grossular changes oscillatory. While garnets from the southwestern skarn is predominantly andradite in composition.Using Fe/Ti vs. Al/ (Al+Fe+Mn) diagram that were calculated based on the mole percent of the used elements, it is estimated that about less than 50 percent hydrothermal waters were involved for the northern skarn whereas it was over this amount for the southwestern skarn. This leds to difference in garnet composition. The composition of clinopyroxene in both skarns is the same (diopside). As a result, hydrothermal fluids have not had much influence on pyroxene genesis. With regards to the occurrence of mineral assemblage and the presence of wollastonite in the skarns under study, these rocks have evolved in temperature above 500oC and O2 fugacity in the range of 10-17 to 10-15.

The volcanic rocks of the Kojid area (south of Lahijan) crop out in northern Alborz. They show mainly pillow structure with numerous crosscutting dykes. Based on lithostratigraphic relationships and interpillow pelagic limestones, the volcanics are Late Cretaceous in age. The volcanics of the Kojid area are predominantly basic in composition (olivine basalt and basalt) and minor more evolved suites such as trachyandesite and dacite. Olivine phenocrysts display forsterite (Fo) content of 63 to 83%. The phenocrystic and interstitial clinopyroxene crystals are augite to diopside in composition, with Na2O, Al2O3 and TiO2 contents of 0.24-0.68, 2.3-6.53 and 1-5.1 wt.%, respectively. Furthermore, the plagioclase is labradorite (An%=51-68). The results of various geothermobarometric methods of the clinopyroxene, the plagioclase and the olivine indicate good correlation with each other. Different thermometric calculations yielded temperatures in the range of 1100 to 1250oC, which are compatible with temperatures of basic melts. Moreover, the clinopyroxene and the plagioclase barometry of the phenocrysts (4 to 8 Kb) and interstitial phases (<5 Kb) correlates with mid- to lower and upper crustal depths, respectively. On the basis of the clinopyroxene chemistry, the composition of the melts is alkaline basalts formed in an intra-plate (intra- continental rift) tectonomagmatic setting. The high volume of Late- Cretaceous volcanics of northern Alborz is probably related to a significant mantle thermal perturbation associated with asthenosphere upwelling and hot spot/plume activity.

In the Hamedan region, migmatitic rocks occur with various structures. In the Simin area (South Hamedan) stromatic and in the Darreh-Omar (Toyserkan) area ophtalmitic structures are abundant. Migmatites have been developed in a poly-metamorphic region. At least one regional metamorphism and two contact metamorphism by mafic and felsic intrusions occurred in the area. It seems that in the Darreh-Omar area contact metamorphism of mafic body leading to migmatization, But in the Simin area previous regional metamorphism and development of shear zones followed by contact metamorphism by felsic body. Therefore, in some areas, such as the Simin area, the migmatization may have occurred in more than one stage. These are consistent with recent geochronological studies of the Alvand plutonic body and surrounding metamorphic rocks. Index minerals of metapelites such as garnet (almandine), biotite (siderophyllite), staurolite, andalusite, sillimanite, kyanite, fibrolite, cordierite, plagioclase (andesine) and spinel (hercynite) are existing in these rocks. Field geology, petrographic and geochemical evidences suggest that different generations of staurolite, biotite and cordierite exist in metamorphic rocks of different grades in the Hamadan area. These minerals sometimes have been formed by progressive reactions and some other times from retrogressive reactions. A number of these phases have been formed at the peak of metamorphism and some others in later time. Based on thermometric cation-exchange method of garnet-biotite pair, using different calibrations, the obtained temperature using first-generation of biotites is 655oC and temperature range of 529oC for second-generation biotites. Cordierite-garnet thermometry indicates a temperature of 637oC for related migmatitic rocks. In barometry with GPBQ system, calculated pressure for first-generation biotite is estimated to be about 3.9 kbar and for the second-generation biotite around 3.6 kbar.

The Eocene volcanic sequence in NE of the Zanjan and in the Alborz-Azarbaijan zone is mostly intermediate in composition and is accompanied with pyroclastic tuff and breccia. Petrographic studies reveal that these volcanic rocks are andesite and trachyandesite. The common textures are porphyritic and glomeroporphyritic and the phenocrysts are composed of plagioclase, pyroxene and amphibole minerals. Also, calcite, quartz, chlorite and epidote are the secondary phases. According to geochemical classification, Theses rocks are plotted on the fields of andesite and trachy-andesite. Geochemically, the study rocks are enriched in LREEs and LILEs relative to HFSEs. Petrographical observations along with geochemistry of rare earth and trace elements suggest calc-alkaline affinity of the rocks under discussion as well as crustal assimilation, fractional crystallization and derivation from a subducted-related environment. Accordingly, the studied rocks are analogous with tectonic features of active continental margin arc settings.

Khanchay-Aliabad area as a part of Tarom magmatic belt contains some shallow depth intrusions which are intruded the Eocene volcanic- sedimentary rocks and have very close association with Cu mineralization. The Eocene volcanic- sedimentary rocks include alternation of basalt, basaltic andesite and andesite, various kinds of tuff, tuffaceous sandstone, sandstone, siltstone and occasionally shale. Petrographical studies demonstrate that intrusions are pyroxene quartz monzonite and olivine gabbro in composition. The Khanchay pyroxene quartz monzonite have porphyritic to porphyroidic, hetero-granular to sereitic, ophitic and sub- ophitic textures and composed of plagioclase, clinopyroxene, hornblende, quartz, K-feldspar and biotite. The Aliabad pyroxene quartz monzonite shows porphyritic to porphyroidic textures composing of plagioclase, clinopyroxene and hornblende in the quartz- feldspatic matrix. The Khanchay olivine gabbro is characterized by the presence of coarse grained granular, ophitic and sub- ophitic textures as well as the occurrence of plagioclase, clinopyroxene and olivine. Geochemical studies indicate that the Khanchay- Aliabad pyroxene quartz monzonitic intrusions have SiO2 content varying from 59.58 to 61.34 %. These intrusions have high- K calc- alkaline nature and are classified as I-type metaluminous granitoids. Their similar patterns on spider diagrams are indication of genetic relation of these intrusions. On these diagrams LILEs (Ba, K, Th and Pb) enrichment along with negative anomalies of HFSEs (Nb and Ti) are observed. Moreover, the Chondrite normalized REE patterns demonstrate LREE enrichment with high ratio of LREE/HREE and Lan/Ybn ratio ranging from 3.08 to 3.72. The overall field investigation, petrological and geochemical studies as well as tectonic setting discrimination diagrams confirm that the Khanchay- Aliabad high-K intrusions were formed from a subduction related metasomatized lithospheric mantle in a postcollisional setting.