جستجوی مقالات مرتبط با کلیدواژه "زون فرورانش" در نشریات گروه "زمین شناسی"

Balazard prospecting area is located in eastern Iran, about 120 km south-west of Nehbandan in the Central part of Lut Block. This area consists of exposed Eocene volcanic rocks, intruded by several diorite and monzodiorite dykes and stocks. These intrusive rocks display porphyritic textures with mm-sized phenocrysts, most commonly of plagioclase, clinopyroxene and hornblende, embedded in a fine-grained groundmass with variable amounts of plagioclase, quartz, and opaque minerals. The assessment of geochemical properties of the major elements showed that these granitoids are metaluminous and of high-K calc-alkaline variety. The patterns of trace elements are identical, denoting enrichments in the light REE (LREE) to heavy REE (HREE). Moreover, LILE enrichment relative to HFSE and Nb, Ti, and P show negative anomalies. The Eu/Eu* ratios range from 0.96 to 0.76, which means that the plagioclase is a slag remnant in the origin of magma. The (87Sr/86Sr)i values of the assessed intrusive rocks range from 0.706 to 0.707, assuming an Oligocene age, while the εNdi values are between -1.9 to -3.2. These results manifest that the magmas were contaminated by continental crust. The contamination has probably occurred over the ascent of magma to crustal levels, and geochemical data verifies the preposition that the investigated intrusions were intruded in a volcanic belt resting on a subduction zone. Early magmas were created through the melting of mantle wedge peridotite, occasioning magma differentiation through crystal fractionation and crust contamination as they ascended to crustal levels.

Shotorsang iron skarn is located in 60 km northwest of Neyshabour (Khorasan Razavi, Iran) in Quchan-Sabzevar magmatic belt. Subvolcanic intrusion rocks have intruded into Cretaceous limestones and created skarnization. These rocks are divided into syenite porphyry and granodiorite porphyry based on their geochemical characteristics. They are I type oxidizing, metaluminous, and tectonic. Setting of the subvolcanic rocks are the subduction zone of the continental margin (VAG). Comparing the mineralization potential of the subvolcanic rocks of this area based on the use of the graph of SiO2 against K2O, MgO, Na2O+K2O, and Ni-V shows that they are fertile in terms of the formation of Fe and Cu skarn. Syenite porphyry is the origin of this mineralization, and magnesium in skarn is taken from hydrothermal fluid. The diagram of Eu/Eu*, Ce/Ce*, (Pr/Yb)n ratios also confirms the presence of meteoric water in the formation of the skarn zone. The primary fluid, which has a positive anomaly of Ce/Ce* and Eu/Eu* had acidic and oxidant conditions and high temperature, and formed pyroxene skarn. A part of magnetite mineralization is formed in this zone, and in this condition, the highest amount of REE entered the pyroxene skarn zone and diluted the fluid in terms of REE. This issue has led to a sharp decrease in the amount of REE in the mineralization zone. Negative Ce/Ce* and Eu/Eu* anomalies indicate alkaline conditions with less concentrated REE content, consistent with chlorite skarn. The highest amount of Fe mineralization is formed in this zone.

The Chore-Nab iron deposit is located in the northwest of the Zanjan-Zaker district. The deposit was formed in quartz monzonite, syenogranite, and granodiorite bodies introded into Lower Cambrian volcanic (andesite) and sedimentary units (siltstone, tuff, and ignimbrite) in the Tarom-Hashtjin metallogenic province. Iron mineralization occurs as brecciated, massive, disseminated, and vein-veinlet types. Major alteration minerals include actinolite, albite, magnetite, epidote, phlogopite, k-feldspar, and biotite. The main sulfide minerals are pyrite, chalcopyrite, and bornite. Based on field and mineralogical studies, sodic-calcic, potassic, propylitic, sericitic, siliceous, and argillic alterations have been identified in the deposit. Sodic-calcic alteration (albite-actinolite-magnetite), characterized by massive and brecciated magnetite in the depth, calcic (actinolite) and potassic (secondary biotite) alteration in the middle levels associated with vein-veinlet sulfide mineralization and finally propylitic alteration (chlorite-epidote) in the shallow levels are observed. Based on the results of chemical analyses, the clinopyroxenes in the alteration zones (mainly sodic-calcic) are mostly augite and less commonly diopside. Plagioclase has a range of albite compositions. Amphiboles are calcic and often tremolite and magnesio-hornblende. Finally, the absence of Cl in the composition of the amphiboles of the Chore-Nab deposit and the presence of at least two Cl-rich amphiboles in all the IOCG deposits of the Carajas mineral province can be attributed to the lack of influence of replacement mechanisms generated by Cl-rich hydrothermal fluids during sodic-calcic alteration.

This study has focused on the result of seismic data. The first stage of basin formation is the opening of Neo- Tethys Sea which is Simultaneous with Dashtak, Kangan and Khaneh kat Formation and after that on the early to middle Triassic sediments an unconformity that can be named as an expansion of sedimentary basin in the upper Triassic happened. This stage of basin opening caused the formation of big faults and probably basement faults in the area that studying on this faults and their movements is the main goal of this study. The next stage of evolution of basin starts when the basin began to closure and still there is disagreement about the exact time; but the obvious thing is the four compressional events: first, from Cenomanian- Turonian up to Masstrichtian; second, Late Paleocene- Early Eocene; third, Late Oligocene-Miocene and the forth, Miocene up to Quaternary. All events caused to obduction of Ophiolite and sedimentation of Gurpi with partly erosion and Pabdeh with regional erosion, then disappearing formations such as Asmari and Gachsaran and at the end, the late Zagros orogenic phase which is the compression that is continues to this day.

Abstract In the west and south-west part of Salafchegan near Zavarian village in Iran (In central Iranian volcano plotonic belt) there are some Plutonic rocks. Based on petrography and geochemistry findings these Plutonic rocks are Diorite, Monzonite and less Quartz monzonite. The main texture in Dioritic rocks is intergranular and in Monzonite is Porphyritic. Based on TAS diagram Samples located in Diorite, granodiorite and gabbrodiorite. Tectono-magmatic diagram Y Versus Zr shows the magmatic arc setting and Zr/TiO2 Versus Ce/P2O5 diagram contrasts postcolligenal magmatic arcs. Based on Chondrite and primitive mantle Spider diagrams, LREE have enriched to HREE in this area that makes the overal slope of these diagrams declined from left to right and this consident with the overal pattern of subduction zone. The results of petrography, geochemistry and tectonic setting studies in this area, indicate that neogene magmatism occurred in post colligenal tectonic setting - subduction of Neo-thetise ocean under central Iranian plate in neogen era.

The Noorabad ophiolite is a part of Eastern Mediterranean-Zagros-Oman Tethyan ophiolites, cropping out in south-southwest of the Main Zagros Thrust fault. In this sequence of the ophiolite rocks, diabase dikes and basaltic lavas are widespread. The chemical composition of these rocks comprise sub-alkaline basalts, andesitic basalt and andesite. According to normalized REE diagrams to the chondrite and trace elements normalized to the primitive mantle, these rocks show calc-alkaline series, the enrichment of LREE and LILE and depletion of HFSE elements. The characteristics of these ophiolites are similar to other exposed Tethyan ophiolites along Bitlis-Zagros suture zone, and their formation is associated with supra-subduction zones.

Baft ophiolitic melange, as a part of ophiolitic melange belt of the Central Iran, is adjacent to Urumieh-Dokhtar magmatic assemblage in the north and Sanandaj-Sirjan metamorphic zone in the south. The ophiolitic complex has been emplaced in the Late Cretaceous time as a result of closure of Nain-Baft oceanic basin. The gabbros are the main constituent of the complex and occur as large intrusive bodies showing isotropic and rarely layered structures with hypidiomorphic granular to pegmatitic textures. The color index varies from melanocratic to lesser extent mesocratic and leucocratic. Geochemical studies reveal that gabbros are tholeiitic to calc-alkaline, low-Ti in nature and show similarity to N-MORB. The chondrite-normalized rare earth elements patterns are almost flat with slight enrichment in LREEs relative to HREEs which indicates a similarity in their origin. It seems that gabbros were derived from a depleted refractory mantle source in a subduction zone setting.

Hornblende-bearing gabbroic rocks are quite common in subduction-related magmatic suites and considered to represent magmatic differentiation process in arc magmas (Heliker، 1995; Hickey-Vargas et al.، 1995; Mandal and Ray، 2012). The presence of hornblende as an important mineral phase in gabbroic rocks of subduction zone has been considered either as an early crystallizing mineral from water-bearing mafic magmas (Beard and Borgia 1989; Mandal and Ray، 2012) or as a product of reaction of early crystallized minerals (olivine، pyroxene and plagioclase) and water-rich evolved melt/aqueous fluid (Costa et al.، 2002; Mandal and Ray، 2012). The careful study of petrology and geochemistry of hornblende-bearing gabbroic rocks from Chahak area، of Neoproterozoic age، can provide important information about their petrogenesis. Because of the special characteristics of Chahak hornblende gabbros according to their age and their situation in the main structural units of Iran، their study can present critical keys for the knowledge of geological history of Iran specially central Iran zone. This study carried out in two parts including field and laboratory works. Sampling and structural studies were carried out during field work. Geological map for the study area was also prepared. 65 thin and polished thin sections for petrographical purpose were studied. Major oxides، rare earth elements and trace elements were analyzed for 4 samples (92P-1، 92P-3، B1and B6) from hornblende gabbros on the basis of 4AB1 method using ICP-MS of ACME Laboratory from Canada. In addition، major oxides of three hornblende gabbro samples (89P-62، 89P-59 and 89P-46) were used from Partovifar (Partovifar، 2012). Fariman metamorphic terrains، of Proterozoic age، consist of metamorphosed sedimentary and igneous (plutonic and volcanic) rocks. Hornblende gabbros of the study area include plagioclase، hornblende، biotite pyroxene and olivine as major minerals and apatite، ilmenite and magnetite as minor minerals. In many examples، hornblende and biotite can be seen as corona textures around plagioclase، pyroxene and olivine، while plagioclase، pyroxene and olivine show obviously corrosion features. This can be considered to be formed by the reaction of early formed crystals with aqueous fluid/evolved melt. In some cases، amphiboles show rhythmic overgrowths. The rhythmic amphibole overgrowths represent deep-seated crystallization in a volatile-rich magma under conditions of high but varying gas pressure. In the study area، the most dominant texture of the hornblende gabbros is hypidiomorphic granular، but intergranular and porphyric textures are common too. Based on geochemical data from major and minor elements، studied rocks belong to tholeiite series with meta–aluminous nature. The geochemical behavior of main elements of the studied rocks reveals the normal trend of differentiation in their magma. Chondrite-normalized REE diagram of hornblende gabbros indicates an obvious enrichment of LREE in compare with HREE. MORB-normalized spider diagrams indicate variable enrichment in LILE and depletion in high field strength elements (HFSE). Primitive mantle-normalized spider diagram show negative anomaly for Nb and Zr. Gabbros from southeast of Fariman have an island arc tholeiite nature and based on trace element diagrams، they formed as a result of 3 to 10% partial melting of a garnet lherzolite source. The mineralogy، texture and geochemistry of the studied rocks show striking similarities with gabbroic rocks of subduction zone developed in supra subduction zone of arc-marginal basin setting.

The Baft ophiolitic mélange, covering an area approximately 150 Km2, is located in the Esfandaghe-Khamrood melange belt. The main part of intrusive rocks in the Baft ophiolitic mélange consists of gabbros, mostly isotropic and occasionally as pegmatitic rocks. Plagiogranites, as veins and small outcrops, are common along with gabbros and doleritic dikes through the area. Plagiogranites consist of trondhjemite, albite granite and granophyre. Based on geochemical studies, gabbros and plagiogranites are belonging to tholeiitic-calc-alkaline magmatic series. Plagiogranites are metaluminous to slightly peraluminous and typologically show characteristics between oceanic ridge (OR) and I-type granites which is consistent with their formation in a supra-subduction zone environment. Chonderite normalized REE patterns of plagiogranites show slight enrichment in LREEs along with flat HREE patterns. Chonderite normalized REE pattern of gabbros are relatively flat with slight enrichment in LREEs compare to HREEs. The derivation of an acidic melt from a gabbroic phase through either fractional crystallization and/or partial melting is less likely. It appears that the origin of Baft ophiolitic melange plagiogranites must be related to doleritic phase, although partial melting of hornblend gabbro and/or amphibolite can be also considered for at least one of the samples.

Basalts, andesites, trachyandesites and latites with shoshonitic affinity are the main volcanic rocks of Eocene age in the Lahrud region (Ardabil). Plagioclase, K-feldspar, biotite and amphibole associated with clinopyroxene are the main constituents of trachyandesites (shoshonites) while clinopyroxene, plagioclase and biotite are the rock-forming minerals of basalts (absarokites). The Lahrud volcanic rocks show enrichment in LREE and are characterized by enrichment in LILE and depletion in HFSE. Petrographical observations along with geochemistry of rare earth and trace elements of these lavas suggest shoshonitic affinity and derivation from a subduction zone. The geochemical behavior of the Lahrud lavas reveals the role of the trench sediments in the source region and genesis of these volcanic rocks. These lavas exhibit low degree of partial melting from a garnet-spinel lherzolite source. The comparison between the Lahrud volcanic rocks with Plio-Quaternary lavas of Sabalan and Eocene lavas of Hashtjin region highlights the different mantle source and degree of partial melting for the genesis of these volcanic rocks. The formation of these lavas is linked to slab steepening and breakoff in a post subduction collision zone.

The Siah-Cheshmeh ophiolites at the north-northwest part of the Khoy ophiolites show a dismembered pile of metamorphic units, mantle sequence, and basaltic-andesitic lavas associated with Late Cretaceous pelagic limestones and cherts. The basaltic-andesitic lavas can be divided into alkaline and calc-alkaline varieties. The presence of Ti-rich amphibole prisms and Ti-bearing clinopyroxenes is characteristic of these lavas. The calc-alkaline lavas are characterized by enrichment in LREE and depletion in HFSE while the alkaline lavas display positive LREE and HFSE anomalies. The interaction between mantle plumes with a spreading center can be considered for generation of alkaline basalts while a subduction zone is responsible for the genesis of calc-alkaline basalts.

South Kahrizak volcanic rocks with Eocene age are located in the north part of Central Iran. These rocks are mainly composed of pyroclastics (tuff and ignimbrites) and lava flows (rhyolite, trachyandesite, basaltic trachyandesite and basalt). Petrographic evidence such as: zoning, sieve texture and rounded crystals in plagioclase and pyroxene phenocrysts show the non-equilibrium conditions between melt and crystals during magma cooling. Geochemical characteristics indicate that these rocks locate in the subalkaline to alkaline domain. The highly enrichment of LREE compared to HREE, high content of LILE relative to HFSE and significant anomalies of Nb, Ta and Ti reveal the characteristics of a subduction - related volcanism. Whereas, the alkaline affinity of rocks shows that they may have formed in an extentional region, most probably a back-arc basin.

The upper Jurassic to lower Cretaceous volcano-sedimentary rocks of Deh-Sard are located in southern part of Sanandaj-Sirjan zone in the south of Kerman. They consist of intermittent lava flows (mainly basalt, basaltic-andesite and trachy-basaltic-andesite), pyroclastics (various types of tuffs and bereccias) and sedimentary rocks (limestones and shales). The Deh-Sard basalts composed essentially of plagioclase and clinopyroxene microphenocrysts, set in a matrix of the same mineralogy associated with opaque minerals and apatite as accessory phases. The existence of disequilibrium textures in Deh-Sard basalts reveals the rapid changes in the pressure of rising magma.The pyroclastic rocks are less common in the area and consist mainly of crystal litic tuffs, in which crystals are mainly plagioclases and lithic fragments mainly basaltic-andesites and trachy-basalt-andesites. The sedimentary rocks were formed in a shallow marine environment. The Deh-sard basalts shows a selective enrichment of elements with low ionic potential (eg., K, Rb, Sr, Ba,+ Th) and a depletion in elements having high ionic potential (eg., Nb, Ce, P, Y, Cr)compared to N-type MORB. Based on the geochemical data, trace and REE element diagrams, the Deh-Sard basalts show characteristics of transitional tholeiitic basalt. MORB and chonderitic normalized trace element patterns are believed to reflect that the Deh-Sard basalts have affinities toward subduction and within-plate basalts. A rift environment formed on transitional continental-oceanic crust “off-axis” from the spreading center is suggested for the formation of Deh-Sard basaltic rocks. In this case, off-axis magmas do not represent the same range of chemical variation as magmas delivered to the axial system, but they show similarity with seamount-type volcanism. The occurrence of intermittent limestones and lava flows may suggest that Deh-Sard basalts might have formed in a rift environment on transitional continental-oceanic crust “off-axis” from the spreading center.