PETROLOGY
Year:2016 | Volume:7 | Issue:27 |Papers Count:10

The Mangavai and Ganjnameh pegmatitic rocks are part of the Alvand granitoid pluton in the Sanandaj-Sirjan zone. The composition of tourmaline in Mangavi is Schorl and that of the Ganjnameh lies in the Schorl- foitite fields. The amounts of aluminum and X-vacancy in the Ganjnameh tourmalines are more than those of Mangavi. But commonly, the main substitution of both types of tourmaline is proton production and Al increase types that Al increase; X-vacancy and Fe reduce occurred. During these substitutions, olenite and foitite, Al-tourmaline and X-vacancy have been formed, respectively. The absence of dravite and the Fe # value over 0.8 in analyzed samples indicate that the tourmalines in pegmatites are related to magmatic types. In addition, the substitution of X-vacancy and Na+Al (olenite) type of tourmaline point to its magmatic nature and so, the required elements (i.e. boron, iron, sodium and aluminum) provided by magmatic fluids. The HREE amount of the Mangavi tourmalines due to accompanied garnet are very low but in the absence of garnet, the Ganjnameh tourmaline have high levels of these elements. Although tourmalines have the extensive substitutions but do not have a tendency to absorb all rare earth elements and the greatest impact on the control of these elements in tourmaline related to paragenesis minerals.

The Mahour 2 lead mineralization area is located, about 145 km west of Nehbandan and 2 km northwest of Mahour polymetal deposit and in the eastern part of Lut Block. The area comprises of volcanic and pyroclastic rocks (Eocene) intruded by several intrusive rocks mainly as dioritic dykes and stocks. Mineralization as veins and filling the space, occurred in altered andesitic rocks. Supergene zone is characterized by azurite, malachite, linarite and iron oxides (hematite and limonite) whereas, galena, pyrite, chalcopyrite and magnetite are the main minerals of hypogene zone. And, quartz and calcite are main gangue. The area is dominated by four types of alteration including silicic, sericitic, propylitic, and argillic. Fluid inclusions study on quartz mineral sections polished reveals the presence of 1.0 to 5.6 percent salt and homogeneous temperature between 278 to 570oC. The high temperature with low salinity zone mineralization in this area is likely related to another generation of mineralization in the area. The results of fluid inclusions show that the mineralization is probably a mixture of magmatic fluid and atmospheric, although there is doubt. Several similar criteria including form of deposit, primary ore deposit, alteration facies, tectonic environment and magmatic series document that there should be a correlation between the origin of the studied mineralization area and that of the Mahour polymetal deposit.

The spilli volcanic rocks suite consisting of Basalt- Trachyte- Rhyolite with upper Cretaceous, outcrop in the northern part of Alborz and south of Siahkal area (east of the Guilan province). Based on geochemical data, the studied suite attributed to transitional to alkali series. Negative correlation of Al2O3, CaO, P2O5 and positive correlation of Rb and Th versus SiO2 reveal the occurrence of fractional crystallization process. Also, the negative correlation of Sr versus Y, Sr/Zr versus Sr and CaO/Al2O3 versus SiO2 show that fractionation of plagioclase has played an important role in petrogenesis of the spilli Suite. The hypotheses is supported by the negative anomalies of Eu, Ba and Sr. The overall geochemical evidences indicate that the basic rocks belong to intra-continental rift zone whereas the felsic rocks are classified as A1 type derived from parent basaltic magmas via fractional crystallization in an anorogenic setting. The studied magmatism share many similarities with bimodal magmatism in continental rift zones.

In the northern ranges of Guilan in Degarmankesh, alkali gabbroic bodies have been outcropped. Based on petrographic studies, the essential minerals are plagioclase, pyroxene and ± Olivine. Chlorite, termolite-actinolite, serpentine, sosorite are secondary and opaque is accessory mineral of the rocks studied. Based on geochemistry data, the rocks studied are plotted on gabbro domain. Normalized trace element patterns relative to MORB and primitive mantle show LREE enriched and HREE depleted. K, Th, Rb positive anomaly as well as negative anomaly of Ta, Nb and Ti point to continental crust contaminated by the rocks under discussion. In terms of tectonic setting, the studied rocks lie in continental intraplate and continental arc environment. The parent magma generated by 5% to 14% partial melting of garnet lehrzolite mantle source possibly at the depth of approximately 80 km. The overall petrographic and geochemical criteria indicate that the studied gabrros originated from magmatism related to Paleogene pull apart basin, in the course of partial melting of asthenosphere arisen under continental lithosphere and contaminated with derived subducted fluids in supraduction zone.

The studied area is located in the east of Nabar village and southwest of Kashan, a part of the Urumieh– Dokhtar magmatic arc. The volcanic rocks belonging to Eocene age, are composed of pyroxene andesites, andesites, dacites and rhyolites. Porphyritic, glomeroporphyric, microlitic, and sieved textures are the most common textures of these rocks. Plagioclase, clinopyroxene and amphibole are the predominant minerals in the pyroxene andesites and andesites, whereas dacites and rhyolites are characterized by the presence of plagioclase, amphibole, quartz, biotite, and K-feldspar. Inequilibrium textures including embayed plagioclases and quartz with rounded margins, and oscillatory zoning in the plagioclases, sieved texture, and dusty rims are evidences of magma mixing. The enrichment in LREE and LILE and the HREE and HFSE depletion in the chondrite and primitive mantle normalized diagrams point to calc-alkaline nature of the rocks studied and they are related to volcanic arcs setting. High ratio of La/Nb (2-4.36) and negative Ti and Nb anomalies in spider diagrams can support crustal contamination hypotheses of these rocks. Also, low ratio of Nb/La (0.23-0.5) and high ratio of Sr/Ce (8.4-19) indicate contamination of parental magma with crustal materials. The rocks studied are formed from magma which is derived from enriched-mantle with 1-5 percent partial melting of spinel-lehrzolite.

In north and northwest of Garmsar in Semnan province, some basic igneous rocks with the Oligocene age outcropped as dyke, sill and very small stocks in the Lower Red Formation. These rocks have basic composition and alkaline nature. They show various textures such as porphyric, glomeroporphyric, ophitic, subophitic, intergranular and granular. Plagioclase and clinopyroxene as the main minerals, olivine, opaque (magnetite, titanomagnetite), apatite and phelogopite as the minor minerals and chlorite, prehnite, epidote, serpentine sericite and calcite are the secondary minerals in these rocks. Primitive mantle and chondrite normalized diagrams of these rocks show strong enrichments in light rare earth elements (LREEs) and relative depletions in heavy rare earth elements (HREEs). Also, parallel trends of the samples in these diagrams indicate a common source for these rocks and the role of the differentiation crystallization in their genesis. Investigated rocks are plotted in back-arc basin setting field in discrimination tectonic diagrams. Geochemical studies show magma forming of these rocks have been formed from 11- 16% partial melting of an enriched modified garnet lherzolitic mantle source in 90-100 km depths. This magma intruded via deep fractures and faults in the incipient extensional back-arc basin resulted from northward subduction of Arabian plate beneath the Central Iran in the Oligocene-Miocene time.

Khur area is located in east of Iran and northwest of Birjand. The area comprises outcrops of Eocene to Oligocene volcanics with basaltic andesite to rhyolite composition, which were intruded by subvolcanic and intrusive bodies of granodiorite to gabbro. In the present work, petrogenesis of volcanic units in Cheshmeh Khuri and Shekasteh Sabz areas was studied, which are located in Khur area and these volcanics have most widespread in them. Rhyolite, dacite, andesite, trachyandesite and basaltic andesite units in Cheshmeh Khuri and trachyandesite unit in Shekasteh Sabz were identified. The main textures of these units are porphyritic, hialoporphyritic and microlitic and plagioclase, pyroxene, K-feldspar, hornblende, biotite and quartz are the main minerals. Volcanic units of Cheshmeh Khuri have characteristic of high-K Calc-alkaline. Enrichment of LREE relative to HREE and LILE to HFSE are important evidences that magma was formed in a magmatic belt of a subduction zone. Based on the initial 87Sr/86Sr of andesite and dacite, their magma has originated from partial melting of an enriched mantle and contaminated with the crust through its differentiation. Trachyandesites of Shekaste Sabz have characteristic of shoshonitic nature. These units are characterized by high FeOt/FeOt+MgO, K2O/Na2O and Zr>360 ppm, Y>39 ppm, and Ce>100 ppm. Also, they are enrichment in REE particularly in LREE, depletion of Eu, strong enrichment in HFSE, and depletion in Ba and Sr. Therefore, trachyandesites of Shekaste Sabz belong to post collision volcanics.

The Dehe Bala pluton is exposed approximately 45 km south-west of Boein Zahra town, Qazvin province. This Pluton which intruded the Eocene volcano-sedimentary rocks of the Urumieh- Dokhtar Magmatic assemblage (UDMA), is mainly composed of granodiorite and produced narrow thermal metamorphic contact aureoles surrounding the intrusion. The body is characterized by SiO2 content ranging from 64.2 to 66.9 wt%, high-k calc-alkaline nature and metaluminous character (A/CNK<1.1). On the primitive mantle-normalized trace element spider diagram, the intrusive rocks have similar trace element patterns with pronounced enrichment in Cs, Th, U, K, Zr and P, Ti, Nb and Ba depletion. Chondrite-normalized rare earth elements (REEs) patterns display moderate negative Eu anomalies, enrichment of LREES relative to HREES and moderate fractionated REES pattern. The granodiorites under discussion, based on geochemical features, belong to I-type granitoids. Their low TiO2 and P2O5 contents and high Th/Ta=6.23-9.35 ratios are characteristic of subduction-related magmatism. The Dehe Bala granodiorites display geochemical characteristics typical of magmatic arc intrusions related to an active continental margin. These criteria include their calc-alkaline nature, pronounced negative Nb anomaly, light-REE-enriched patterns and weak fractionation of MREE and HREE. Enrichment of incompatible elements such as La, Ce, Rb, Th, K and Nd coupled with negative anomalies of Ti, Ba, Eu, Nb and P suggest that the parent magma originated by partial melting of lower crust. The presence of mafic microgranular enclaves (MMES) in granodiorites along with disequilibrium textures in plagioclase phenocrysts and also the attendance of plagioclase phenocrysts between host granodiorites and the MME across the boundary point to mixing of crustal magma with mantle-derived mafic magma.

The Sarab-3 intrusive body is located in the NW of Iran, in Sanandaj-Sirjan zone and in the east of Takab city. Based on field observations as well as petrographic features, the lithologic composition of intrusion (Miocene age) ranges within the diorite-leucodiorite, monzodiorite, quartz monzodiorite, granodiorite and granite. In terms of geochemical characteristics, the rocks studied, are I-type, with calc-alkaline affinity and meta-aluminous character. Enrichment of LILE (K, U, Sr, Ce, Th, Pb, Ba) and LREE relative to HFSE (Zr, Y, Ti, P, Nb) and HREE, low Ce/Pb and Nb/U ratios and high Ba/Nb reveal that the rocks under study were originated in an active continental margin subduction-related tectonic setting. The negative anomalies of Ti, Nb and P on the spider diagram also confirm this fact. Low ratios of (Na2O+K2O / (FeOt+MgO+TiO2) and (Al2O3 / FeOt+MgO+TiO2) along with low Rb/Sr concentration (<0.6) propose that the Sarab-3 intrusive rock is derived from a meta-basaltic source.

The Aderba leucogranite in the Golpayegan metamorphic core complex (GMC), a part of Sanandaj-Sirjan zone, host lentiform small (2*4 cm) (Type 1) and large (7*14 cm) (Type 2) tourmaline nodules. In terms of mineralogical features, the core of these two types tourmaline nodules is different. The Type 1 composed of small blue-green tourmaline, quartz, K-feldspar (microcline) and apatite while the Type 2 is characterized by tourmaline coarse crystals accompanied by quartz. Based on major and trace elements data the tourmalines under discussion are classified as alkaline, schorl (Type 1) and schorl-dravite (Type 2). The mean REE values displays a negative slope and a negative (Type 1) and positive (Type 2) Eu anomalies. The overall petrographic observations and geochemical results indicate that the Type 1 is likely influenced by two mechanisms of liquid immiscibility in the evolved melt followed by biotite breakdown in the final stages of tourmaline crystallization to complete consumption of B (closed system). For nodules, Type 2, breakdown of biotite in equilibrium with the external fluid (open system) is proposed.