PETROLOGY
Year:2016 | Volume:7 | Issue:26|Papers Count:10

Nakhilab igneous complex is located in 145 km northwest of Zahedan and is geologically situated between Lut block and the Sistan-suture zone. Rock units in the area range from Cretaceous to Quaternary and consist of sedimentary and igneous types. The igneous rocks occur as intrusive and extrusive in the Nakhilab. The extrusive rocks occur as lava and pyroclastic and consist of basalt, basaltic andesite, andesite and rhyolite. The intrusive rocks occur as stock and dyke and consist of gabbro, diorite and granodiorite. These rocks are porphyry and granular in texture. In these rocks, plagioclase, pyroxene, hornblende, biotite and quartz are the main minerals and apatite, sphene and magnetite are the accessory minerals. The intrusive rocks that were altered by hypogene and supergene processes are associated with Cu mineralization in the central part. The igneous rocks in the Nakhilab are metaluminus and calcalkaline. Patterns of minor and rare earth elements normalized to MORB and Chonderit show that LREE and LILE contents are sharply higher than HREE and HFSE contents, respectively. Higher contents of LREE and LILE compared to HREE and HFSE, respectively, negative anomalies of Zr, Ti, P and positive anomalies of K, Rb, Sr, suggest that the study samples may belong to an active continental margin. The studied igneous rocks were probably solidified from a basaltic magma by AFC processes that derived from partial melting a subducting oceanic crust and it`s above mantle wedge.

The Kolah Ghazi granitoid is one of the main upper Jurassic intrusion in the Sanandaj-Sirjanzone which intruded Jurassic shale and overlaid by Lower Cretaceous strata’s. The intrusion consists of the monzogranites, granodiorites, Syenogranites, aplitic dykes associate with several tourmaline veins in three separated outcrops. Based on petrographic studies quartz, plagioclase, biotite and alkali feldspar are present as the major minerals and andalusite, sphene, tourmaline, garnet, sillimanite, spinel, kyanites constitute minor mineral phases. Geochemical results show high-K calc-alkaline and peraluminous affinities and S-type. The Kolah Ghazi granitoid belong to subduction-related volcanic arc magmatism, which related to middle Cimmerian compression movement which derived from Partial melting of metapelites in the upper crust materials and emplaced at depths (about 20-30 Km) under low water-vapor pressure (0.5-1 Kbar) and temperature range (in 750°C).

Aliabad-Daman granitoid body with NW-SE trend is located in northeastern of the Rashtkhar city (about 15 km) with an area of approximately 10 km2. This body with probably age of middle Jurassic is located above Darouneh fault and is part of Sabzevar zone. This pluton consists of alkali feldspar granite, syenogranite and monzogranite. In the discriminant diagrams of micas, biotites plot in the field of syderophyllite and are generated from the crystallization of magma. The plagioclase is in the field of albite to oligoclase and orthoclase resemble to anortoclase due to its micro-perthitic occurrence. Chlorite located in the field of repidolite and brensovigite which indicate its iron-rich composition. Based on petrographic and geochemiscal studies Aliabad- Daman granitic pluton resemble with A2-type granites with slightly peraluminous nature. Negative Ba, Nb, Ti, Sr and P anomalies in discrimination tectonic setting diagrams indicate that they are generated in a volcanic arc setting. Extensional environment in a continental arc has provided conditions for generation of these granitic rocks.

Tarom plutonic complex is located in northeast of Zanjan and in the Alborz-Azerbaijan zone with northwest-southeast trending. The Eocene Tarom plutons include Zanjan (quartz monzodiorite), Zaker (quartz monzonite), Morvarid (monzogranite to syenogranite) and Kuh Tabar (porphyry microquartz diorite) which intruded within the volcanic and volcanoclastic rocks of Karaj Formation. The EPMA analyses of plagioclase, alkali feldspar, pyroxene and chlorite indicate that the core of plagioclase crystals is more calcic than their rim suggesting normal zoning in these minerals. The pyroxenes are mostly clinopyroxene with minor amount of orthopyroxene that belongs to Fe-Mg-Ca pyroxenes. The pyroxenes of these plutons show augite-diopside composition. The chlorites are Mg-bearing chlorite and classified as the picnochlorite, diabanite and talc chlorite. Based on the composition of pyroxenes, the Tarom plutonic complex crystallized from sub-alkaline magmas which formed in a subduction tectonic setting. Barometric studies exhibit that the clinopyroxenes crystallized in pressures lower than 5 Kbar. Pyroxene thermometry in these plutons indicate that the pyroxenes crystallized in temperatures ranging of 700-850oC in the quartz monzodioritic, 600-700oC in the quartz monzonitic pluton and 800-900oC in the porphyry micro quartz dioritic pluton. Moreover, plagioclase thermometry shows that the crystallization temperatures of plagioclases in the Tarom area range from 550 to 900oC.

The southwest of Sorkh-kuh area is located in 120 km SW of Birjand city and it is a portion of the Tertiary volcanic-plutonic rocks in the west of the Lut block. Geology of this area comprising andesitic and basaltic volcanic rocks, which have intruded by intrusive rocks, at different stage, such as hornblende diorite, hornblende micro diorite, hornblende diorite porphyry, hornblende quartz diorite porphyry and biotite quartz monzonite caused extensively alteration in volcanic rocks. The texture of intrusive rocks is porphyritic, granular and poikilitic. Hornblende and plagioclase are two common minerals in these intrusive rocks and biotite and quartz are common in biotite quartz monzonite. Composition of intrusive rocks show metaluminous to low peraluminous nature with calc-alkaline and sometimes tholeiitic affinities in diorites. These intrusive rocks belong to volcanic granite arc and magnetite (or I) series granitoids. Enrichment of LILE (Ba, K, Cs and Sr), depleted of HFSE (Nb, P, Ti) and enrichment of LREE versus HREE indicated that magma formed in subduction zone environment. The high ratios of Eu/Eu* (0.8-0.9 in all diorite rocks and 1.5 in biotite quartz monzonite) and also enrichment of Sr especially in biotite quartz monzonite (900 ppm) shows there were no plagioclase in the source of magma. Depletion of Nb and high amount of Zr/Nb show low contamination of crust in magma. The (LaN/YbN) is low between 5-9. The magmatic source of intrusive rocks had been generated from 1 to 5% of partial melting of garnet-spinel lherzolite (low garnet) and in 60 km asthenosphere depth.

The Nabijan gabbroic and dioritic plutons outcropped at the southwest Kaleybar town. According to the field studies the diorite is younger than gabbro and crosscut the gabbroic pluton. Geochemical data reveal clear geochemical difference between the Nabijan gabbroic and dioritic compositions. Variations of major oxides versus SiO2 and Mg# and trace element ratios indicate that the composition of Nabijan intrusive bodies were modified by fractional crystallization and crustal contamination (AFC) processes. However the geochemical characteristics of the Nabijan plutons suggest a same source for them. According to mineralogical and geochemical data, fractionation and/ or accumulation of olivine, orthopyroxene, clinopyroxene and Ca-rich plagioclase at the first stage has formed the gabbroic body. Due to fractionation of the above mentioned minerals, the composition of the remained magma has enriched by fluids and incompatible elements. At the final stage the Nabijan diorites has formed by crystallization of amphibole, biotite, Na-rich plagioclase accompanied with minor amounts of clinopyroxene. The fractionation/accumulation of the mentioned mineral associations has caused to possess tholeiitic and calc-alkaline character for the Nabijan gabbroic and diorites, respectively. The geochemical features of the Nabijan intrusive rocks show hybrid characteristics among active continental margin and within plate tectonic settings. These features can visible in continental post-collision settings.

The mylonitic granitoids of Gole Gohar, south east of Sirjan, are located in a key area which their study is important for understanding the history of Precambrian basement of Sanandaj- Sirjan zone and its metamorphic and magmatic evolution during the subduction of Neo- Tethys. Field studies show that these granitoids are located in the basement of the metamorphic rocks such as metapelite, calc schist and amphibolite. In this Study the granitoidic intrusions are classified in two types based on lithology and their geochemistry. Type I is garnet- biotite granitoid and type II is hastingsite granitoid. Both of these granites show some evidence of mylonitic fabric, which is more clear in garnet- biotite granitoid. These plutons are Meta aluminous, I Type granitoid and have high K calc-alkaline nature. Based on U-Pb dating of zircon, the age of all granitoids is between 538.6–580.7 Ma (Late Precambrian- Early Cambrian). Based on the results of this study, despite the mineralogical and geochemical differences, all granitoidic intrusions formed in the Precambrian during the Pan African orogeny. The old age of the granitoids is similar to those introduced in other parts of Sanandaj-Sirjan zone that may indicate the presence of Precambrian basement in almost the entire Sanandaj-Sirjan zone.

Precambrian basement of Central Iran in Lakh Bargheshi area from SW Bardaskan mainly consists of metapelite, metabasite and mylonitic gneiss and has been invaded by Lakh Bargheshi granitic body with the age of Ediacaran-Cambrian. Metapelites mostly are Garnet schist type and encompass mineralogical paragenesis of garnet+biotite+muscovite+quartz+feldspar. Metabasites contain of garnet amphibolite and garnet-epidote amphibolite and show mineralogical paragenesis of amphibole+feldspar+garnet± quartz ± epidote ± whitemica ±rutile ± sphene ±ilmenite. Metamorphic conditions that obtained by Thermocalc software, petrogenetic grids and conventional thermobarometries are compatible for both metapelitic and metabasitic units and include pressure between 7.1 until 12.3 Kb and temperature between 482 until 661°C that nearly are equivalent of high pressure amphibolite and epidote amphibolite facieses that are dominant in the lower continental crust. Epidote and garnet-bearing granitic body of Lakh Bargheshi and host metapelites and metabasites probably representing thickened continental arc induced by Prototethys subduction beneath Iran plate.