جستجوی مقالات مرتبط با کلیدواژه « فرورانش » در نشریات گروه « زمین شناسی »

The Astaneh Plutonic body is located at SW of Arak city in the Sanandaj – Sirjan belt . It is composed of granodiorite and tonalite and minor monzogranite. The enclaves in this body consist of mafic microgranular enclaves, hornfelsic enclaves, andalusite xenocrysts and tourmaline nodules. Variations in major and trace elements of microgranular mafic enclave and host rock are the same. The variety of enclaves in the Astaneh plutonic body is less in comparison to enclaves of the Qorveh, Alvand (Hamedan), Malayer and Aligoudarz plutonic bodies. The origin of the enclaves is often magma mixing, with the exception of Aligoudarz, that enclaves are chilled margin of the magma reservoir, which were broken off in later stages and dispersed within the host rock. The nature of the shape and size of the enclaves in these bodies are nearly similar but the border of the enclaves with the host rock in the Astaneh body is sharp, but in other bodies, there are also gradual to ambiguous boundaries. Intergranular and poikilitic textures, and presence of zoned and sericitic plagioclase and mafic nature of enclaves in contrast to their hosts is the same in bodies. The shape of the enclaves of the Astaneh body vary from roughly angular to rounded. According to the chondrite normalized diagrams which show negative anomalies of niobium, phosphorus and titanium. The geotectonic setting of the enclaves is often related to the subduction zones according to the chemistry of biotite, plagioclase, amphibole, tourmaline and chlorite minerals.

The granitoides of west Ardakan are outcropped in the middle part of the Central Iran zone. Quartz, orthoclase and plagioclase are the main minerals and amphibole, biotite, sphene, zircon and apatite are secondary minerals. The dominant textures are medium to fine grain granular, granophyry and myrmikite[r1] . According to mineral chemistry data, calcic amphiboles of magnesiohornblende to actinolite nature have crystallized at temperatures of 530-890 ºC. Oligoclase to andesine plagioclased crystallized at 700-800 ºC. Magnesium biotites was crystallized at 650-730 ºC. On the basis of the oxidant conditions, magnetite are formed as opaque. The chemical analysis of all these minerals show the mantle nature of the magma. Magma seems to suffer produced these minerals, moderate to severe crustal contamination during its ascent. These granitoides are I type and calc-alkaline and were formed in the subduction setting related to the active continental margin.

The studied area is located in the high Zagros zone and it is considered a part of the Neyriz ophiolite. In this area, the ophiolitic complex is small coloured melanges include radiolarite cherts and serpentinized ultrabasic rocks. The main lithological unit is serpentinized ultrabasic rocks, which have a variety of colors from dark to light brown and dark to light green. These ultrabasic rocks have composed of olivine, pyroxene, amphibole, opaque, serpentine and spinel. Olivines have been highly altered to serpentine and pyroxenes to bastite. Based on whole rock chemistry, the studied rocks are basic and ultrabasic cumulates type (lherzolite-harzburgite) with a composition close to the average composition of the mid-ocean ridge basalt (MAR). Based on mineral chemistry, pyroxenes are calcic type and in the range of diopside and augite, and amphiboles are calcic and actinolite type. Pyroxenes have crystallized under conditions of low oxygen fugacity, temperature higher than 910 °C (1100 - 1200 °C) and pressure more than 2 kbar (2 to 10 kbar). Amphiboles have crystallized at a temperature below 700 °C and a pressure less than 1 kbar. Based on the geochemical characteristics and mineral chemistry, the ultrabasic rocks in the Koopan area were formed in a subduction zone.

Andesitic-dacitic subvolcanic domes of Nudeh Enghelab and Kuh Kamartang are located in the northern domains of the Sabzevar ophiolitic belt, and in the northeast part of the Central Iran structural zone. Geochemically, the studied rocks exhibit a metaluminous, calc-alkaline to high k-calc-alkaline nature, and are enriched in LILE and LREE and depleted in HFSE, HREE and negative anomaly in TNT elements, and have formed in an environment related to subduction zone. With attention to their other geochemical characteristics, such as a silica content (SiO2>61wt%), Al2O3>15wt%, MgO<2.2wt%, Na2O>3.3wt%, Sr/Y>24, La/Yb>8, can be classified these rocks as high silica adakites. The petrographical, geochemical and isotopic ((87Sr/86Sr)i=0.7047-0.7045, ƐNdi=6.02-6.10) characteristics display that the studied high silica adakites have been originated from partial melting of subducted oceanic slab of Neo-Tethys (Sabzevar sea/ocean sub-branch) under the Turan plate in amphibolite to garnet amphibolite facies and during the ascent to high levels, they show very little assimilation and contamination with continental crust.

The subduction and closure of the vast Neo-Tethys ocean between the Arabian and Eurasian plates has left numerous ophiolitic traces, the unique position of Iran in its central part is noticeable. The lack of information, right on the border of Iran with Iraq and Turkey, due to security considerations, has so far prevented the overview of this suture zone in the northwestern border of Iran. Adding Gysian ophiolite in southern Urmia as a missing link in this stretch can partially cover this lack of information. A comparative study of whole rock chemistry of serpentinites in the central part of the Neo-Tethys ophiolites, considering several sectors from Iran (Kamyaran, Marivan and Gysian), Iraq (Penjwin and Mawat) and Turkey (Guleman and Osmanie) in this article, indicates that they belong to subducted serpentinites, whether they were originally formed in the fore-arc environment or the at abyssal oceanic environment. Composition of the serpentinites of the central part of the suture zone is similar to the average global serpentinites which have mostly lizardite/chrysotile. All of them show depletion of Mg resulting sea floor alteration during serpentinization. The mentioned point may be caused to data deviation from abyssal peridotites field. Considering that the transition metals contents the confirmed the above setting. Almost all of the studied serpentinites are from subducted type which indicates refertilization of LILE evidences as a result of rock/fluid interaction through serpentinization.

The study area is located in the south of Damghan, 160 km south of Shahrood, and 17 to 30 km south of Torud village. The area geologically, lies in the Cenozoic magmatic belt, a part of the Alpine-Himalayan belt, in the north of the structural zone of Central Iran (Aghanabati, 2004). The Cenozoic magmatic belt has been studied by many researchers (e.g., Ghorbani, 2005; Khajehzadeh, 2009; Mardani-Beldaji, 2011; Tayefi, 2014; Yousefi, 2017). The volcanic rocks in the southern part of the Torud area have not been comprehensively studied. Therefore, it requires a detailed study. So, for the purpose of this study attempt has been made to investigate and to study the nature of magma, tectonic setting, and the petrogenesis of the volcanic rocks using the geochemical data of the whole rock. Also, the results of this study have been compared with some areas belonging to the Cenozoic Era located in the north of the structural zone of Central Iran.

Regional Geology:

The area under study in the Torud-Moalleman magmatic belt belongs to the Chah-Shirin-Sabzevar-Khaf magmatic complex, located in the western part of this magmatic complex. In this magmatic belt, the Eocene volcanic rocks, including the main volume of igneous rocks are basic to acidic in composition. The predominant rocks are basaltic to intermediate rocks. The Torud-Moalleman magmatic belt is mainly composed of volcanic rocks with a lithological composition consisting of olivine-basalt, basalt, andesite, and dacite rocks and their pyroclastic equivalents, as well as plastic and limestone interlayers.

During field surveying, 50 samples of the volcanic rocks with the least alteration were collected. From these samples, 30 thin sections were prepared for microscopic studies and 11 samples were selected for ICP-MS geochemical analyses for minor elements and XRF for major elements and were sent to ACME Laboratory in Vancouver (Canada). GCDkit, Excel, and Corel Draw software were used to check the results obtained from the whole rock chemistry analyses and drawing diagrams.

Petrography:

The study rocks include volcanic rocks ranging from andesite to basalt. The basalts are dark gray to black in color with glomeroporphyritic, microlithic, sieve, and trachytic textures containing plagioclase and clinopyroxene as the main minerals. These minerals along with olivine and magnetite can also be seen in the form of microcrystals in the background of the rock, and their accumulation have created the glomeroporphyritic texture in these rocks. Secondary minerals are chlorite, iron oxide, zeolite (natrolite and analcime), calcite, and gypsum, filling the holes.The andesites are light gray to slightly dark with porphyritic and glomeroporphyritic textures and are dominated by amphibole (green and brown hornblende), plagioclase, and clinopyroxene as the main, biotite, iron oxide, sphene, and zircon. as the minor, as well as sericite, chlorite, calcite, and epidote as the secondary minerals.

Whole Rocks Chemistry :

The data obtained from the whole rock geochemical analyses display that the volcanic samples of the Torud area are classified as the andesite and basalt, placed mostly in the range of calc-alkaline series (medium potassium). LREE and LILE enrichment, HREE and HFSE depletion and Nb, Ta, and Ti negative anomalies of these rocks point to their formation in subduction zones. Also, as the tectonic diagrams display the rocks belong to the active continental margin. The rocks under study have mostly mantle origin and are derived from an enriched lithospheric mantle. The flat HREE patterns also show that melting occurred in the mantle, above the stability field of garnet. Therefore, the parent magmas were formed by the melting of spinel lherzolite at a depth of 80 to 100 km and evolved due to fractional crystallization as well as contamination caused by subducted sediments and the continental crust.

The rare elements pattern of the study rocks in spider diagrams show the cogenesis of these rocks and the role of differential crystallization as the main mechanism of their formation. Based on geochemical data, the study samples and compared volcanic rocks share similar characteristics. Therefore, the normalized REE patterns with chondrite (Nakamura, 1974) NMORB (Sun and McDonough, 1989) and MORB (Pearce, 1983), indicate the enrichment of LREEs (such as La, Ce) and LILEs (e.g., Ba, K, U, Pb, Cs) compared to HREEs and HFSEs (i.e. Nb, Ta, Ti, P) indicating that the rocks under study were formed in the active continental arc margin. The samples have no negative anomaly of Eu. Volcanic rocks with the age of late Eocene and Oligo-Miocene and basaltic to trachy-basaltic composition range from alkaline to sub-alkaline rocks and volcanic rocks with the age of middle Eocene with andesite to trachy-andesite composition have the nature of calc-alkaline.

The volcanic rocks in the south of Torud, with calc-alkaline and medium potassium nature, are mainly composed of basalt and andesite characterized by LREE enrichment, negative Nb-Ta-Ti anomaly, and the high ratio of LILE/HFSE. These characteristics point to the formation of these rocks in the subduction zones.The rocks under investigation have low SiO2 content, high amounts of Sr, no significant Eu anomaly, and Mg# content greater than 40. These geochemical features indicate a mantle source for the studied volcanic rocks. The changes of Rb/Y versus Nb/Y show the enrichment by subduction components or crustal contamination in the magmatic evolution of these rocks. Based on the geochemical investigations, the productive magma originated from a spinel lherzolitic source at a depth of about 80 to 100 km; during the ascent of magma, as a result of fractional crystallization and contamination, the magma derived from the mantle has been enriched and gave rise to lithological diversity.

This study presents a 3-D model of the shear wave velocity (Vs) for SE Iran, containing the Makran subduction zone and termination of the Zagros collision zone. The model is developed using surface wave tomography and the associated local dispersion curves that were inverted to the Vs velocity maps. Our findings provide insights into the tectonics of the SE Iran region and the geometry of the subducting lithosphere. To obtain Rayleigh waveforms, we extracted data from 458 teleseismic earthquakes recorded by 58 seismic stations in the Makran region between June 2016 and May 2019. Events with magnitudes greater than 5.5, epicentral distances between 30º and 120º, and depths shallower than 50 km were considered for two-plane wave tomography. This resulted in phase velocity maps at nine periods ranging between 25 s and 125 s. Our results suggest the presence of a high-velocity anomaly at the northern coast of the Gulf of Oman extending ~100 km northward up to the Qasr-e Qand fault and the southern edge of the Jaz Murian depression as it was observed at shorter periods of 25-40 s. Further west of Makran and north of the Strait of Hormuz, there is also a high-velocity anomaly at the southwest of the Zendan-Minab-Palami fault at periods of 25-40 s. At periods of 50-125 s, this anomaly is observed at the northern latitudes beneath the Sanandaj-Sirjan zone at the termination of the Zagros collision zone. Our analysis suggests that this anomaly reveals underthrusting of the Arabian lithosphere under Sanandaj-Sirjan zone and Urumieh-Dokhtar magmatic arc. Additionally, we detected a low-velocity anomaly at periods of 25-33 s showing a crustal root potentially generated by underthrusting of the Arabian lithosphere in this region. At the second inversion step, we employed a nonlinear inversion of the local dispersion curves to construct a 3-D Vs model. Our results indicate that there is a flat high-velocity anomaly in the middle of the study region (in the western Makran and under the depression of Jaz Murian), indicating a horizontal oceanic lithosphere, potentially remaining from a truncated oceanic lithosphere between the collision and subduction zones. Furthermore, our findings suggest the presence of a near-horizontal oceanic lithosphere in the eastern part of the study area, extending at a low angle underneath the northern edge of the Jaz Murian depression and subsequently subducting beneath the volcanic arc with a steep angle. Finally, we identified a low Vs anomaly at the crustal-scale in the Sistan suture zone, which stretches towards the north-northwest and is limited by the large N-S directed strike-slip faults.

The regional and  contact metamorphic rocks of the studied area are located in the west of Hamedan city and Alvand plutonic body as a part of the northern part of the Sanandaj-Sirjan belt. This metamorphic complex consists of slate, garnet mica schist, amphibole schist and tremolitite in regional metamorphic rocks and spotted schists, mica hornfels, epidote amphibole hornfels and cordierite hornfels in contact metamorphic rocks. The analyzed minerals in these rocks include biotite, garnet, staurolite, amphibole and cordierite. EMP chemical analyses indicate that the composition of garnet is almandine, the composition of biotite is siderophyllite and amphibole is actinolite. Staurolite has iron-rich composition and cordierite has intermediate composition (iron-magnesian). Thermometric calculations based on biotite in garnet staurolite schists show a temperature of about 555°C, and the temperature of about 511°C was determined by the garnet-biotite pair method. Due to the presence of staurolite and the absence of kyanite and other medium and high pressure minerals, the pressure of 3 to 4 kilobars is possible. The type of metamorphism of the study area is suggested to be related to a  subduction tectonic environment. The stability of the garnet + staurolite assemblage requires the presence of water in the environment.

Hassanabad-Shojaabad region is located in Urmia-Dokhtar magmatic belt. Regarding the formation of this area, two theories of rifting and subduction have been proposed. In this article, data obtained from desert, petrography, geochemical and magmatic tectonic studies were combined and analyzed. Using several geochemical and magmatic tectonic charts, the type of rocks in the region and the magmatic series of intrusive and volcanic rocks were determined. The intrusive and volcanic rocks in Hassan Abad region are of calc-alkaline type and the result of subtraction of basic magma with the origin of lithospheric mantle, these rocks belong to the subduction tectonic environment in the final stages of expansion of Komani Island. Volcanic rocks and intrusive masses in Shujaabad area are of shoshonite type and are the result of tonalitic melting of the lower crust, these rocks belong to the tectonic environment of the continental arc margin. Therefore, the area under study has been inclined to pressure at the edge of subduction and back arc areas, where Hassan Abad is located in the area of the edge of subduction and Shoja Abad is located in the back arc area.

Volcanic rocks with adakitic nature, are outcropped, in the south of Rudbar city as a part of the Alborz magmatic zone and the northern part of the Alborz zone. Most of the rock units in this area are volcanic and pyroclastic belonging to the Tertiary age and specifically Middle Eocene. For this study, we present new data to understand the origin and tectonic setting of the adakitic early Cenozoic magmatism in the southern part of the western Alborz orogenic belt.

Regional Geology:

Based on the 1:100,000 Guilan geological map (Nazari and Salamati, 1998), the predominant geological units of the region include the Paleozoic, Mesozoic, and Cenozoic stratigraphic units. The volcanic activity resulting from the subduction of an oceanic crust beneath the active continental margin of Alborz began in Paleocene and its peak is attributed to the Lutsin period (Nazari and Salamati, 1998).

Following microscopic studies, 11 samples were analyzed at Actlabs Lab in Canada by ICP-MS method. IGPET and GCDKIT software were applied to draw diagrams and interpret the data. Petrography and Whole rocks chemistry The studied lavas consist mainly of dacite to trachy-dacite, rhyodacite, and rarely rhyolite. Abundant plagioclase as phenocrysts and microlites and rare amphibole, biotite, and quartz with hyaloporphyritic, microlithic porphyry to felsitic porphyry and microfelsitic textures are the dominant petrographic features of these rocks. Geochemically, they are characterized by mean value of 61.87 wt%< SiO2<66.54, 1.1 wt%<MgO<2.8 wt%,10 ppm<Y<14 ppm, 1.4 ppm<Yb<1.7 ppm, 450 ppm<Sr<1887 ppm as well as the average amounts of Sr/Y: 103.8, 10.5<(La/Yb)N<14.09 and 5.1<Yb/Lu<6.5. Thus, the overall geochemical data point to HAS characteristics of the rocks under study.  On normalized spider diagram to chondrite, MORB, and primitive mantle, all rocks demonstrate subparallel trend, linear and homogeneous REE profiles with LILE and LREE enrichment together Ta, Nb, and Ti negative anomalies. As the tectonic diagrams display, all the studied samples are plotted in an arc volcanic granite field formed in a subduction environment in an active continental margin. Moreover, all the obtained geochemical data point to a high silica adakitic magma as the parent magma.

The studied area lies in Alborz Mountain, which owing to the collision of two Eurasian and Arabian plates, where a Neo-Tethyan oceanic lithosphere (Southern Caspian Sea Ocean or SCO)” is subducted beneath the Central Iranian continental lithosphere (Salavati et al, 2013), is an active deformation zone. The studied rocks formed in arc and subduction zones setting. Adakitic rocks in the arc setting can be produced by partial melting of a hot and young subducted oceanic slab and subduction of a very young oceanic crust (<5Ma) at depths of about 25 to 90 km is required to produce adakitic magma in the arc setting (Thorkelsona and Breitsprecher, 2005). In the north of the investigated area and south part of the Caspian Sea, an Alpian oceanic belonging late Cretaceous age was reported and named “Southern Caspian Sea Ocean (Salavati et al., 2013), which was subducted toward the south. Adakitic activity and not-adakitic magmatism continued to migrate toward the trench supporting a slab window model. The proposed tectonomagmatic model "Ridge-Trench", indicates that the studied lavas were generated in the Neothetyan supra-subduction zone. Based on this model, in the south of Guilan Province, SCO oceanic crust (and likely its ridge) has subducted towards the south the first because of a pressure change that might be caused by the extension and thinning of the overlying crust. A slab window was formed therefore in the source region, and partial melting occurred by asthenospheric upwelling. It looks like the adakitic rocks imply a deep source with a low magma source melting degree.

The overall petrological and geochemical features of the studied lavas gave rise to the following conclusions A new group of extrusive rocks, with remarkable geochemical characteristics of adakitic rocks, is outcropped in the south of Guilan Province .These rocks are characterized by HFSE and HREE depletion relative to LILE and LREE and negative Nb, Ta, and Ti anomalies, suggesting the parent magmas were affected by subduction-related geochemical processes. On tectonic diagrams, the studied adakitic rocks plotted on an Active Continental Margin setting and they show HAS characteristics produced by 5% to 10% partial melting of an amphibolite garnet source from a hot and young Cenozoic slab subduction. All the geological and geochemical data indicate that the early Cenozoic adakitic magmas in the south of Guilan Province were generated in an extensional tectonic setting (Slab window setting) when the active spreading center of the Neo-Tethys oceanic (Southern Caspian Sea Ocean) subducted toward the south and produced a slab window. According to the proposed model, the active spreading center of the Neo-Tethys oceanic crust (Southern Caspian Sea Ocean) subducted toward the south and produced a slab window in the subducted oceanic lithosphere.

In this research, geochemical data from 314 samples of volcanic and intrusive rocks with adakitic or adakite-like affinity reported from eastern Iran have been studied, these rocks are often known with Sr>400 g/ton and Y<18 g/ton. By comparing and analyzing the characteristics of these adakites, it is concluded that: (1) The adakite rocks of eastern Iran are mainly high silica adakites; (2) High-silica adakitic rocks in northeastern Iran have lower MgO, Th, and Th/Ce and relatively higher Cr, Ni, and SiO2 contents than other adakites in eastern Iran, indicating their connection with the subduction zone and melting of the oceanic crust, while the adakitic rocks of southeastern Iran with lower SiO2 content and higher MgO, Sr, and Th/Ce are categorized as post-collision adakites mainly formed from melting of the thickened lower crust; (3) Most of the adakites in the central parts (eastern Iran) were formed from the melting of the thickened lower crust after the collision, from an amphibolite garnet source, and the ratios of Sr/Nb, Ba/Nb and La/Nb of adakites decreases towards the northeast in this section; 4) The analyzed data and the results presented in this research show that the adakites of eastern Iran have characteristics associated with mineralization and often have the necessary potential to play a role in the formation of valuable reserves.

The term adakite refers to volcanic and intrusive rocks that have more than 56% SiO2, more than 15% Al2O3, and usually less than 3% MgO by weight, high Na2O content (3.5-7.5 %), and low ratio of Drummond et al., 1996K2O/Na2O (<0.5) (Defant and Drummond, 1990;; Martin, 1999; Martin et al., 2005; Condie, 2005; Castillo, 2012). Adakites are divided into (1) a high- SiO2 adakite (HSA) and (2) a low- SiO2 adakite (LSA). The HAS have >60 wt.% SiO2, low MgO (0.5–4 wt.%), CaO + Na2O contents <11 wt.% and Sr abundances <1100 ppm. In contrast, the LSA have <60 wt.% SiO2, higher MgO (4–9 wt.%), CaO + Na2O contents >10 wt.% and Sr contents 1000–3000 ppm (Martin et al., 2005).
The studied area in the eastern part of Iran (Figure 1-A) includes a large part of the structural zones in the south and east, including the Lut block, Makran arc, the Sistan suture and Binaloud. This region is a part of the extensive magmatism that has spread from Turkey to Pakistan and had numerous magmatic activities over time, especially from the Cretaceous to the Quaternary.
Adakitic series have received special attention in recent years in Iran and some articles have been published by various researchers. The main goal of this research is to review the published articles and documents related to the geochemical and isotopic characteristics of adakites in eastern Iran, in order to open a window for a better understanding of the relationship between adakite magmatism and magmatic-tectonic evolution and porphyry copper ± gold mineralization in the east of Iran.

Geochemical data of 314 samples of volcanic and intrusive rocks with adakitic nature were collected from eastern Iran. The location of the studied areas and a summary of data and references is presented in Figure 1 and Table 1. In this study, acidic and intermediate rocks (volcanic and intrusive) with adakitic characteristics were studied and mafic rocks such as basalt and samples with high LOI (above 3) were not considered in the database (Figure 2-A, B).

Volcanic and sub-volcanic adakitic rocks have been reported from Sabzevar, Neishabur and Quchan regions (Table 1, Figure 1-B). These rocks are mainly dacite to trachyandesite and andesite with calc-alkaline to high K- calc-alkaline affinity. Rocks with adakitic nature in central part of eastern Iran are reported from the areas of Garjagan, Khosuf, Shurab, Fadeshk, Pironj, Gurung, Shah Suleiman Ali, Sang-Rahuzag, Shadan, and Tighnab (Figure 1-C and Table 1). According to the chemical classification diagram (Middlemost, 1994), the composition of volcanic rocks is mainly dacite, rhyodacite, andesite and trachyandesite and intrusive rocks are mainly diorite, granodiorite and granite (Figure 2-A, B). They are mostly calc-alkaline to high-K calc-alkaline, sometimes shoshonite (Figure 5-A) and meta-aluminous affinity.
Southern part include adakitic rocks from Lar, Malek Siah Kuh, Lakhshak, Chah Serbi, Shaheswaran, Taftan and Karvander areas (Table 1 and Figure 1-D). The volcanic rocks of the southern part are mainly dacite to andesite (Figure 2-A) and the intrusive rocks are mainly diorite and gabbrodiorite (Figure 2-B). These rocks have the characteristics of calc-alkaline with high-K to and meta-aluminous affinity.

Based on the data presented in this study, it is clear that the adakite rocks of eastern Iran are mainly high silica adakites. These rocks in northeastern Iran have lower MgO, Th, Th/Ce and relatively higher Cr, Ni, and SiO2 contents than other adakites in eastern Iran, which indicate their connection with the subduction zone and melting of the oceanic crust.
The adakitic rocks of southeastern Iran with lower SiO2 content and more MgO, Sr, and Th/Ce are in the range of post-collision adakites, which are mainly formed from melting of the thickened lower crust.
Most of the adakites in the central parts (eastern Iran) were formed from the melting of the thickened lower crust after the collision, from an amphibolite garnet source.
Temporal-spatial relationship between adakites and porphyry copper deposits and/or epithermal gold-copper deposits is studied in many researches (e.g., Thiéblemont et al., 1997; Sajona and Maury, 1998; Li et al., 2011; Richards et al., 2012; Zhang et al., 2021). Porphyry mineralization in Iran mainly took place during the evolution of the branches of the Neo-Tethys Ocean and its final closure. The results presented in this research illustrate the adakites of eastern Iran have characteristics associated with mineralization and often have the necessary potential to play a role in the formation of valuable reserves. Changes in La/Sm and Dy/Yb ratios in adakites are considered as a geochemical sign for mineralization potential. The ratios of (LaN/SmN) and (DyN/YbN) help to determine the fertile magmatism (with the participation of amphibole) from the barren (without amphibole) (Richards et al., 2012). Amphibole-dominated adakites are clearly associated with economic porphyry copper mineralization (e.g., Kheirkhah et al., 2020). In the studied adakites, the changes of LaN/SmN and DyN/YbN ratios are 1.7 to 10.7 (average 4.5) and 0.7 to 2.5 (average 1.2), respectively. Based on these ratios, most of the studied adakites, except for some adakites that show changes in LaN/SmN ratios of less than 4 and DyN/YbN less than 1.1, have mineralization potential.
The analyzed data and the results presented in this research yields that the adakites of eastern Iran have characteristics associated with mineralization and often have the necessary potential to play a role in the formation of valuable deposits. The distribution of copper-gold indices, and the outcrops of adakites along with magnetic anomalies (Figure 10-A), and crust thickness variations in eastern Iran (Figure 10-B), emphasize the importance of focusing on future prospecting, drilling and isotopic studies in this area.

According to the outcrops of volcanic and intrusive rocks with different compositions and ages in the northwest of Iran, the magmatism of the northwest of Iran has been introduced under the titles of Talash and Arsbaran tectonomagmatic zone (Berberian, 1981; Aghazadeh et al, 2010, 2011; Castro et al, 2013). The Talash zone in the east of the Western Alborz-Azerbaijan zone, like the rest of Azerbaijan and Urmia-Dakhtar magmatism, has experienced the peak of magmatism in the Eocene to Oligomiocene (Vincent et al, 2005; Shafaii Moghadam and Shahbazi Shiran, 2010). Volcanic rocks in the northeast of Lahrud are andesitic, basaltic eruptive outcrops and plutonic internal alkaline, calc-alkaline and Shoshonitic masses (Vincent et al, 2005), which continue to spread significantly beyond the borders of the country. Eocene volcanic rocks are seen in the 1:100,000 maps of Lahrud with a northwest-southeast trend. In this research, the lithological, geochemical and petrogenesis characteristics of volcanic rocks in the north of Lahrood in the Khanali Daresi section have been evaluated.
Volcanic rock outcrops in the study area were first evaluated in the field and 45 samples were taken from different parts and then 20 thin sections were prepared from the samples for petrographically studies by using an Olympus type polarizing microscope. Then 11 fresh samples were sent to MS Analytical Laboratory in Canada by Zaminriz Kavan company for chemical analysis and determining the main oxides of whole rock.
Eocene- trachy-andesite and trachy andesy basaltic rocks in northwestern Iran, north of Lahroud (Ardabil province), Extruded with northwest-southeast trend. These rocks have hyalomicrolith porphyritic textures and have plagioclase as major minerals with minor amphibole, pyroxene, biotite and opaque minerals and alkali feldspar minerals. The productive magmas of these rocks are of potassic and shoshonitic nature of Roman type. The parent magma of these volcanic rocks is affected by the fractional crystallization process and Eu / Eu * ≤ values (0.83 to 1.08) indicate plagioclase separation in the magmatic reservoir. Negative anomaly of Ta Ti, Nb in the spider diagrams and enrichment of the LILE and LREE index indicate the effect of subduction environments component in generation of g these rocks. Ba / Nb ratios of 45 to 131, La / Sm ratios of N above 2 and Th / Ce ratios of 0.13 to 0.2 indicate enrichment correlations with melting of subducted sediments during subduction. Also, low Ba / Rb ratios from 0.10 to 15.2 and Rb / Sr ratios from 0.07 to 0.1 indicate melting of phlogopitic bearing source with shoshonitic nature in genesis of these rocks. primary magmas of these rocks form from partial melting of less than 10% matosomatized phlegopolite bearing spinel- lherzolite source and melting of magmatic subduction sediments during subduction in the post-Collisional setting.
 
The geochemical characteristics of the studied samples indicate their enrichment and formation in connection with the subduction environment. This indicates a continental volcanic arc in the experimental diagrams of determining the tectonic environment. The primary magma of volcanic rocks consists of the melting of less than 10% of spinel-phlogopite mantle and metasomatized with subduction factors and associated sediments.

Anomaly 21A, as a part of Bafq iron-apatite ore metallogenic district, is located in Central Iran, and encompasses wide spectrume of igneous, sedimentary and metamorphic rocks. The igneous rocks that show narrow geochemical variations and dominantly plot in the monzonite to monzodiorite fields, are plotted in the calc-alkaline and high-K calc-alkaline affinities. Geochemical data are characterized by enrichment LILE and LREE as compare to HFSE and HREE, respectively, and depletions in Nb-Ta-Ti imply the mantle-derived melts modified by subduction components. The isotopic signatures of Anomaly 21A samples, e.g., (87Sr/86Sr)i, εNd(t)=, imply the dominant mantle signature. Their initial Pb isotopic composition of study rocks are 18.87 to 20.32 for (206Pb/204Pb), 15.72 to 15.84 for (207Pb/204Pb), and 40.74 to 42.32 for (208Pb/204Pb). The isotopic modellings show less than 4% incorporation of melt-derived subducted sediment into the mantle wedge or variable degrees of contamination by upper continental crust. We suggest partial melting of a sub-arc mantle melt that has been metasomatized by slab-derived sediments and interacted with continental crust en-route the shallower surface as the premise of the geodynamic of Central Iran.

Geoid determination using Stokes’ integral requires that all masses above geoid (topography + atmosphere) to be removed. Using 2nd Helmert condensation model, the topographical masses were replaced by a surface layer on the geoid. This replacement caused changes in gravity and equipotential surfaces which are so-called direct topographical effect (DTE) and indirect topographical effect (ITE), respectively. There are two different methods to formulate the Helmert topographical effects: Moritz-Pellinen and Vanicek-Martinec methods. In the Moritz-Pellinen method, the DTE is defined as the gradient difference of topographic potential of topography at the terrain and the potential of the condensation layer at the geoid surface, while in Vanicek-Martinec method both real and condensation potential refer to terrain surface. In study of Jekeli and Serpas (2003) both methods were applied on 1'×1' gravity data and 30''×30'' grids of height to geoid determination of different regions of the USA. The results indicated that the Moritz-Pellinen method is clearly superior to Vanicek-Martinec method. However, in this study, our goal is not to evaluate the effectiveness of these two methods. The subject of this study is the propagation of DEM error in the direct and indirect topographical effects in geoid using the planar approximation of the Moritz-Pellinen method. The integral formulas of standard deviation of the topographical effects were obtained in terms of DEM standard deviation error and error covariance function.    To increase performance, all numerical calculations of all derived integrals were performed by FFT. Numerical investigations of this study are done over the central Alborz mountainous area, as this area is the most rugged terrain in Iran. Two global DEMs, the SRTM and the AW3D30, were freely available with a spatial resolution of one arc second (approximately 30 meters) in the test region. The mean and standard deviation of differences between two DEMs are about 2 and 3 meters, respectively, which produce 0.1 mGal and 1 mm differences in DTE and ITE.Estimation of DTE and ITE error requires the global average error (standard deviation) of the DEM as well as the parameter of correlation length for evaluation of correlated error. Accurate estimation of these parameters needs high-resolution ground control points that were not available in this study. Therefore, using an overall accuracy and a correlation length based on the previous studies, the estimated standard deviation for direct and indirect topographical effects varied from 0 to 0.6 mGal and 0 to 17 mm in the test region, respectively.    The influence of DTE error on the geoid error can be computed by applying the error propagation law on the Stokes’ integral. Our calculations show that the error of SRTM DEM on geoid in central Alborz can exceed from 1 cm, but the values are about 1-2 mm in the flat areas. Therefore, geoid determination with 1 cm accuracy in mountainous areas in Iran requires DEM with better average accuracy than the current available models. Various previous studies indicate that the error of DEMs decreases in mountainous areas.

The study area is located 12 km south of Zahedan city, Sistan and Baluchistan province. Rock units in this area include a series of slightly altered flysch facies units with Eocene age, subvolcanic rocks and basic to intermediate dikes with probably Oligocene-Miocene age. Subvolcanic rocks in the form of stocks and domes intruded into the flysch unit and were cut by intermediate dykes in the later stages. The subvolcanic units of the region have two main compositions diorite-monzodiorite and quartzdiorite-quartzmonzodiorite with porphyry texture. The subvolcanic units of this area are in the range of metalalumin to slightly peralumin and I-type. This is consistent with the evidence such as the widespread presence of hornblende, apatite and sphene in the studied subvolcanic units, which indicates the oxidic conditions and high oxygen fugacity for these rocks at the time of formation. Spider diagrams drawn for trace and rare earth elements show the single origin and the role of fractional crystallization in the formation of these rocks. Based on the spider diagram of rare earth elements, the studied subvolcanic units of LREE elements show a enrichment toward to HREE elements, which is one of the prominent characteristics of calc-alkaline rocks in the subduction zones of the continental margin. These rocks are placed in the tectonomagmic environment diagrams in the adakitic range and in the category of shoshonite and high potassium calc-alkaline rocks, related to subduction environments.

One of the main products of caldera collapses is ignimbrite, and there is a direct relationship between the volume of ignimbrite and caldera dimensions. During caldera collapse, a large volume of magma is explosively discharged as products and pyroclastic flows (Druitt and Sparks, 1984). Lava domes and cones are placed along or inside the caldera rim structures after the collapse (Aguirre-Díaz, 1996). The studied area, in the northwest of Takestan, is a part of the Alborz and Western Alborz magmatic arcs, which consisting of some granitoid rocks, volcanic units, dacitic and rhyolitic domes as well as pyroclastic units. The presence of ignimbrite and dacitic and rhyolitic domes along with mafic volcanic rocks and intrusive rocks show the occurrence of the caldera in the region.In the Alborz and Urumieh-Dokhtar belts, extensive volcanic eruptions occurred in the Eocene. The studied area lies in the western Alborz zone. The first studies of stratigraphy and classification of the Paleogene volcanic and intrusive rocks in western Alborz are related to Taleghan and Qazvin regions (Annells et al., 1975). The dominant feature in the northwest of Takestan is pyroclastic deposits, lava flows, and intrusive and sub-volcanic rocks. Volcanic rocks and lava flows are placed on the tuffs with a more limited expansion. Sub-volcanic rocks are in the form of dacitic and rhyolitic domes and intrusive rocks intruded the tuffs.

Method of study:

In this research, about 120 samples of different volcanic, intrusive, and pyroclastic rocks are gathered, then 56 thin sections were prepared and studied. To measure the main and rare elements, 29 suitable samples including 16 fresh samples of intrusive rocks and 13 volcanic samples were selected and analyzed using ICP-OES and ICP-MS at Zarazma Minerals Studies Laboratory in Tehran.

Volcanic rocks are rhyolite, dacite, andesite, trachyandesite, basaltic andesite, and basalt, with porphyry texture and a glassy or microlitic groundmass. Evidences such as the presence of ocelli quartz, plagioclases with sieve texture and the formation of a thin layer of fine pyroxenes at the edge of some pyroxenes show that the basaltic and basaltic andesitic rocks are contaminated with crustal compounds or mixed with crustal melts. The intrusive rocks are alkaline granite, granite, quartz monzonite, quartz monzodiorite, and monzodiorite, which often have a granular texture. The absence of muscovite and hypersolvus feldspars in alkaline granites and quartz monzonites confirms that these granites are anorogenic (Kleemann and Twist, 1989).

Whole rocks chemistry:

Basic to felsic members are seen in both intrusive and volcanic groups. The range of SiO2 changes from 53.52-75.23% for intrusive rocks and 51.11-74.8% for volcanic rocks. MgO is 0.19-4.66% for intrusive rocks and 0.24-4.18% for volcanic rocks, and Al2O3 is 10.22 and 17.2% for intrusive rocks and 10.24 and 16.66% for volcanic rocks. According to Irvine and Baragar (1971) diagram, volcanic samples and most of the intrusive samples are sub-alkaline. In AFM ternary diagram, volcanic and intrusive samples have a calc-alkaline trend.

 Petrogenesis Trace elements variation diagrams show two groups with two separate trends in the volcanic rocks. The first group (rhyolites and some dacites) show the fractional crystallization trend, but the second group (andesite basalts and andesites and some dacites) demonstrate the partial melting trend. This phenomenon can also indicate the different origins of these rocks. Intrusive rocks are also divided into two groups with a parallel trend, which have a dominant trend of fractional crystallization trend, and probably these two groups also have different origins. The spider diagrams show that all the samples are enriched concerning the primary mantle. Some of the anomalies observed in these diagrams indicate that these rocks originated in subduction zone. Crustal contamination or extensive melting of crustal materials occurred in the region. Genetic classification of granitoids and tectonic setting Discrimination diagrams show that the samples of monzodiorite and quartz monzonites are I-type and alkaline granites are A-type (subgroup A2). According to the tectonic setting diagrams, except for some alkaline granites, the other samples are in the field of volcanic arc setting rocks. Alkaline granites and rhyolites are related to the post-orogenic setting, quartz monzonitic samples are related to the late orogenic setting, and granites are located in the range between these two groups. The dacitic samples are located in the syn-collision to late orogeny environments. Acidic volcanic and intrusive samples are the melting results of amphibolites (some dacites and quartz monzonites) and some others are probably melting result of the metagraywakes (rhyolites, some dacites, and alkali granites). Basalt, basaltic andesite, and monzodiorite to monzogabbro, are product of mantle melting in the volcanic arc and rhyolite, dacite, alkali granite, and quartz monzonite, are the result of crustal melting.

Caldera formation:

The presence of ignimbrite units, dacitic and rhyolitic domes with a semi-circular arrangement in the east of the intrusive rocks, and co-ignimbrite breccias, reveal the possibility of caldera formation in the region. Considering the relatively less amount of ignimbrites, the dimensions of the formed caldera were probably small. The presence of dacitic and rhyolitic domes on one side of the intrusive rocks shows that the type of caldera is trap-door type.

The aim of this study is to simulate stress variations and deformation of the continental plate in the subduction process. The main concept considered is that trench retreat during the subduction process can lead to the creation of an extensional stress regime in the overriding continental plate, and subsequent extension tectonics, and the thinning of the continental crust. The Iranian plate experienced distributed extension in the Eocene. One of the scenarios regarding this event considers the roll-back of the Neo-Tethys slab at that time as the cause of the extensional stress regime. Through numerical simulations to solve the conservation equations governing the flow and deformation in the crust and mantle, the role of rheology, thickness and age of the continental plate in the above-mentioned developments have been investigated. The results show that trench retreat can occur for a large range of physical parameters. Prolonged trench retreat can lead to a localized extensional tectonic regime near the edge of the continental plate above the subduction zone, 7 to 12 million years after the initiation of subduction. For a lithosphere with strong rheology, this tectonic regime results in negligible thinning, too small to be observable in the geological record. In contrast, for weaker continental plate, as well as a thin lithosphere, a wide-range of extensional deformations can occur, some of them comparable in terms of amplitude and time-scale with the events of the Eocene in central Iran.

The Daraloo ore deposit area, structurally located in the Central Iran and Urumieh Dokhtar magmatic belt, is situated in the south of Kerman Province. In this region, Eocene andesitic flows and pyroclastic rocks have been invaded by Oligo-Miocene hypabyssal intrusive bodies. Most of the intrusive samples are granodiorite porphyry to monzogranite porphyry with a microgranular groundmass and affected by severe phyllic alteration. Mineralogical and geochemical evidence show that Daraloo granitic rocks are calc-alkaline, metaluminous to slightly peraluminous and I-type in nature. Clear negative Nb-Ti anomalies in most samples can be explained by the fractionation of titanium-containing phases such as titanite and titanomagnetite. Also, obvious enrichment in the large ion lithophile elements (LILEs such as K, Rb, Ba and Cs) and light rare earth elements (LREEs) compared to high field strength elements (HFSEs such as Ta, Nb, Ti and Zr) and heavy rare earth elements (HREEs), all clearly show a geochemical feature of magmas generated in subduction environments. So, it can be concluded that Daraloo granitic rocks must be formed in an active continental margin environment as a result of subduction of the Neotethys oceanic crust beneath the Central Iranian microcontinent during the Tertiary time.

Intrusive masses are exposed in the Bostanabad-Mianeh axis with the northwest-southeast trend. The rocks are known as granite in general geological maps. Detailed studies in this study have also shown the presence of syenites which their petrology was considered in order to investigate the Zagros orogeny development in northwestern of Iran. The magmatic rocks of the region are the result of magmatism of the Uromieh-Dokhtar magmatic belt and include intrusive, volcanic and pyroclastic rocks with sedimentary units. Syenites of the Bostanabad-Mianeh axis are along with large volume of granites. Syenites provides important information about the interaction of the crust-lithosphere mantle, magma evolution processes, tectonics and crustal growth. In this study, syenites are divided from granitic rocks and their geochemical properties have been investigated to determine their tectono-magmatic and Petro-genetic conditions.

During field study, samples from the syenite and granite outcrops were collected for petrography, geochemistry and determining magmatic series and the magma origin. For geochemical studies, 13 samples of intrusive rocks with the lowest degree of alteration were chemically analyzed by ICP-MS and ICP-OES methods in the Act Lab Ontario Canada.

The Bostanabad-Mianeh axis in northwestern of Iran and in the East Azerbaijan province is part of the Cenozoic magmatism of the Lesser Caucasus towards southeastern Iran. Magmatism is related to the subduction of the northern ocean of Neotethys during the collision of the Arabian Plateau with Eurasia and its subsequent events. The presence of arc-type magmatism in the regions of Azerbaijan, the Alborz Mountains, Talesh and the Lesser Caucasus all indicate the subduction of the Neotethys branch with the Eurasian plate. Due to the LILE and LREE enrichment and the HREE depletion, the source of the magmas for the studied syenites are originated from an enriched mantle source in the continental lithosphere in the subduction zone belonging to post orogenic extension events. Consequently, the formation of the intrusions is related to mantle melting which is enriched and fed by fluids and melts and finally contaminated with crustal material during the ascent.

In the north of Oshnavieh, Western Azerbaijan Province, Cenozoic (Eocene) trachy-dacite and rhyolite rocks formed a part of the Oshnavieh Mountains. In Iranchr('39')s structural- sedimentary division, these igneous rocks are located in the Sanandaj-Sirjan zone. The common texture in these rocks is porphyritic with microlithic matrix, and in some samples, porphyritic textures with hyaline matrix. In terms of mineral accumulation, they have plagioclase, alkali feldspar, quartz, and biotite minerals. These rocks are high-k Calc-Alkaline series and are among the Peraluminous rocks. In terms of tectonomagmatic position, the studied samples have evolved in the range of associated volcanic arc and in a syn-collisional environment. Due to the depletion of Nb, magma is formed in the subduction zone (active continental margin). Also enriched values of Rb and K reveals contamination of magmas with upper continental crust or magma transformation.