جستجوی مقالات مرتبط با کلیدواژه « enclave » 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 Alvand plutonic complex is located in Sanandaj- Sirjan Zone in south and west of Hamedan. Petrographic studies indicate that this body is composed of mafic intrusive rocks, porphyry granitoids and leoucocratic granitoids with various enclaves such as surmicaceous, mafic microgranular and felsic microgranular enclaves. Field, petrography and geochemical studies show that the enclaves, the host and the mafic rocks have calc-alkaline affinity and aluminum saturation index of the host rock is peraluminous and mafic microgranular enclaves and mafic rocks are metaluminous and in the boundary between metaluminous and peraluminous fields. On the base of spider diagrams, all rocks are depleted in HFSE and enriched in LILE, which is particular of rocks of the subdution zones. The complexity of the morphology of the enclaves (fractal dimension) confirms the importance of magma mixing in this body. Fractal dimensions of the enclaves vary between 1.08 to 1.21 and the frequency of Dbox=1.1 is the highest one in histogram. According to the fractal dimensions of enclaves, the logarithm of viscosity ratio of the host rock and the enclave ranges from 0.48 to 0.74 with most values clustering around 0.51. The different forms of the studied microgranular mafic enclaves suggest that the effect of magma mingling (mechanical mixing) on the enclaves and the host have been various in different parts of the Alvand body so that from the border of mafic body to the center of granitoid body enclaves become smaller, fewer; and their fractal dimensions decrease.

The Tekieh intrusive complex is located in S-Qorveh in northern parts of the Sanandaj-Sirjan Zone. In this collection, the granite inclusions located in the granite host compound have a diorite composition and the inclusions located in the monzonite host compound have a gabbroic composition. The enclaves are scattered in rounded and elliptical shapes in the host rocks. Generally, they have a sudden contact with the host rock and are composed of igneous minerals. Amphiboles are calcic-type, and their composition is magnesio-hornblende and actinolite. The plagioclases have a range of composition from oligoclase to andesine and oligoclase to bytownite for host rock and enclaves samples, respectively. Based on geothermobarometry studies on amphiboles and also amphibole-plagioclase pairs, the temperatures of 660-5540C and 742-5920C with pressure ranges of 0.3 to 3.62 and 0.21 to 1.8 Kbar were estimated for host rock and diorite enclaves samples, respectively. Oxygen fugacity was high in magma that is consistent with calc-alkaline nature and the formation of rocks in its subduction setting.

Alvand plutonic body is one of the largest intrusive plutons in northern part of Sanandaj-Sirjan zone which is located in south of Hamadan city. It is composed of porphyroid and leucocratic granitoids, basic intrusive rocks, and abundant enclaves in various sizes and in a variety of forms. Biotites of porphyroid monzogranite, diorite, felsic microgranular enclave, mafic microgranular enclave and surmicaceous enclaves are located in magnesian biotites and biotites of norites in phlogopite field. Orthopyroxenes of norite are clinoenstatite and orthopyroxenes of mafic microgranular enclaves are clinofrosilite. Based on the Ti-in-biotite thermometer, temperature of monzogranite porphyroid is 662 to 734 oC, norite is 688 to 776 oC, diorite is 598 to 724 oC, surmicaceous enclaves temperature is 662 to 687 oC, felsic microgranular enclaves is 694 to 712 oC and mafic microgranolar enclaves is 635 to 737 oC. the enclaves of the Alvand plutonic body and their host rocks are located in the field of calc-alkaline suite. Orthopyroxenes in the norite and mafic microgranular enclaves indicate that rocks of the Alvand intrusive complex are located in the field of high oxygen fugacity rocks. It is in accordance with calc-alkaline property of rocks and is consistent with the subduction-related tectono-magmatic environment.

Geysour area is located in the east of Gonabad city and is part of the north of the Lut Block. The rocks in this area include granitoid rocks and high temperature - low pressure metamorphic rocks. Granitoid rocks are composed of granodiorite, enclave (metamorphic and igneous) and microgranites. These rocks belong to medium to high potassium calc-alkaline series, low temperature I type granite and are poorly peraluminous. The Chondrite-normalized REE patterns show that the rocks are enriched incompatible elements, with negative anomalies in Nb, Ta, Sr, P, Ti and Ba and strong enrichment in Rb, K and Th. These patterns are in perfect harmony in granodiorite, microgranular enclave (MME) and microgranite specimens. This harmony also has in upper, middle continental crust and greywackes. Positive anomalies in Rb, Th, Sm and negative anomalies in Ba are prominent in the composition of the crust. Based on the integration of these patterns with the pattern of upper continental crust (UCC) elements and greywackes and adaptation to laboratory work, the Geysour granitoid originated from crustal materials and a little mantle component. The temperature of granitoid formation was estimated based on the Zircon saturation temperature of 748-790 C. Microgranular enclaves have rounded and oval shapes, mixed areole around them, fine grained texture, quartz and plagioclase eyes, bladed biotite, needled apatite, oxide phases in biotite, and the presence of a simple mixed - hyperbolic curve between MME and granodiorite. Field, petrography and geochemistry of the major and rare earth elements data suggest mixing/ mingling (partial melting) processes for the origin of enclaves and the rare earth elements patterns indicates the relationship between Geysour granitoid with the subduction system. Analysing its data, based on logarithmic ratios, show collision tectonic environment. Also, the tectonic-chemical distinctive diagrams suggest a syn-collision to post-collision tectonic type that is interpreted in connection with the collision of the Afghan Block with the Lut Block.

The Ghikhlar area is located at the NW Marand town, East Azarbaidjan. The wide range of Plio-Quaternary volcanic activites with volcanic and associated volcano-clastic rocks having compositions mainly as andesite to silica-undersaturated rocks (leucite basanite, leucite-tephrite and tephrite) have been covered mostly the rock units prior to the Cenozoic. The phenocrysts in andesites are amphibole, plagioclase and clinopyroxene which occurred in microcrystalline and microlithic matrix. The main characteristic of these rocks is bearing various enclaves as autholiths and xenoliths. The clinopyroxenes in the host andesite and cumulative enclaves are diopside to augite. The autholithic andesitic and dioritic enclaves indicates compositions as augite and dipside, respectively. Investigation of mineral chemistry and magmatic features for the host andesitic rocks and their enclaves are the main goal of this research. Variety of magmatic enclaves are including homogenic, cumulative and gabbroic ones. They all show similar mineralogy with host andesitic rocks whereas they are different texturally. Homogenic and gabbroic enclaves are more fine and coarse grained than host andesite, respectively. Cumulative enclave has been formed as aggregation of coarse grained ferromagnesian crystals similar with phenocrysts of andesite. On the basis of mineral chemistry data, composition of the host andesite as well as homogenic and cumulative enclaves are subalkaline with arc magmatic tectonic setting feature. However gabbroic enclave with alkaline characteristic corresponds to interior plate tectonic setting. Considering mineralogy, textural evidence and mineral chemistry data from the host andesite and their magmatic enclaves it can be concluded that the homogenic and cumulative enclaves are autoliths. The homogenic enclave corresponds to chilled margin of magma reservoir which disjoined during upward ascending of andesitic magma and their falling into magma chamber. Cumulative enclave resulted from aggregation of magmatic minerals in the magma chamber. About genesis of the gabbroic enclave it seems that gabbroic enclave has exotic genesis. Gabbroic rocks fall into andesitic magma during magma passing upward.

Sahl area, in the south of Shahrood, is a part of the northern portion of the Central Iran Structural Zone. The area is dominated by a thick sequence of the Paleocene to the middle Eocene volcanic and volcano-sedimentary rocks. Hypabyssal igneous rocks as dome, dike and sill with trachybasaltic andesite and trachyandesite composition intruded the sequence. Various enclaves with amphibolitic, gneissic, hornblenditic, pyroxenitic, tonalitic, gabbroic, tuffaceous sandstone and siltstone nature with different sizes and shapes are present in the rocks studied which can be taken as an evidence of contamination and magma mixing processes. With respect to geochemical characteristics, the studied rocks are belonging to low silica adakites , with calc-alkaline to high potassium calc-alkaline affinity, enriched in LREE and LILE and depleted in HREE and HSFE. Overall, the mentioned adakites resulted from crystallization of melts originated from partial melting of metasomatized or modified mantle wedge, above the subduction zone of the Neotethys oceanic slab (Sabzevar - Daruneh branch).

Zargoli intrusive pluton is located in the North West of Zahedan city and along Zahedan-Saravan granitoidic band. Main litology of the pluton is I-type granodiorite rocks and nature of their magma is a calc-alkaline granitic magma which formed in orogenic subduction invironment and partially contaminated with sedimentary rocks of the upper crust. Notable feature of this granodiorites, is abundance presence of metasedimentry enclaves in them. There is not amphibole mineral in granodiorite rocks of Zargoli intrusive pluton but it is observed as major mafic mineral in metasedimentry enclaves and diorite dikes which presence in the pluton. Respectively, amphiboles analyzed from diorite dikes and metasedimentry enclaves of Zargoli pluton are tschermakite and magnesio-hornblende which sometimes have been alterated into actinolite. Amphiboles of diorite dikes formed at higher pressure and temperature then amphiboles of metasedimentry enclaves. Amphiboles analyzed from metasedimentry enclaves have been crystallized at 770oC temperature and about 2Kbar pressure while amphiboles analyzed from diorite dikes formed in the temperature range 750 to 775oC and relatively wide pressure of 4 to 7Kbar. Calculated pressure for amphiboles analyzed from metasedimentry enclave is indicator emplacement pressure of the intrusive pluton, after possibly Zargoli intrusive pluton has been emplacement at about 2Kbar pressure and 7 kilometer depth.

Darreh-Bagh granitoidic pluton in the northwest of Aligoodarz composed of two felsic and mafic parts، with lithological composition range from diorite to quartzdiorite، and granodiorite to leucogranite respectively. Felsic rocks have calc-alkaline and peraluminous affinity and belong to S-type and continental arc granitoids (CAG). The most significant characterizes of felsic part are as follows: presence of the metapelitic andalusite bearing enclaves، silica (quartz fragments which inherited from quartz vein with metamorphic origin)، surmicaceous and metapasamitic enclaves and also andalusitic xenocrysts through out of the felsic part. Mafic rocks have calc-alkaline and metaluminous affinity and belong to I-type and continental arc granitoids (CAG). Based on the field observations، petrographical and geochemical characterictics، penetration of basic-intermediate magmas into late Triassic - lower Jurassic metapelites and metagraywackes caused to rise temperature up to produce a large scale contact metamorphism including andalusite hornfels and sillimanite hornfels. Intersecting the temperature of melting point of metapelites and metagraywackes resulted in producing melts with suitable composition for forming of S – type granitoid plutons. Then، the produced magma ascended to the higher levels in the upper crust and emplaced in it. Granitoid magmas emplacement are associated with low-extent contact metamorphism up to cordierite hornfels facies.

The Ghohroud intrusion is a part of the Orumieh-Dokhtar magmatic belt. This pluton with probably Oligo-Miocene age، occurred due to intensive volcanic activity during the Alpine orogenic which is composed of granodiorite to tonalite rocks. The pluton is mainly composed of felsic minerals، such as quartz، plagioclase and alkali feldspar. Ferromagnesian minerals are biotite، amphibole and clinopyroxene. Dioritic enclaves are common in the pluton which vary extensively in diameters. Mineral chemistry of the pyroxenes from the diorite enclaves indicate augite - diopside composition that locally have undergone oralitic alteration. Chemical composition of the clinopyroxenes confirmed a subduction geological setting، the pressure of 6-15 kbars and the temperature of 1250-1300 °C as well as the presence of high percent water content in the magma. High oxygen fugacity and water content increment during magmatic evolution could represent that the clinopyroxenes were crystallized during magma ascent and within different pressures.

Sefidkuh Granitoid is located west of Nehbandan (South Khorasan Province) east of Lut Block. Compositionally, this granitoid ranges from granite (monzo and synogranite), to granodiorite and tonalite. It has microgranular felsic enclaves with minerals similar to the host body. Major minerals are quartz, plagioclase, microcline, orthoclase, and biotite which were analyzed using electron probe micro-analyzer (EPMA) for thermometry and mineral chemistry studies. Plagioclases in granites are mainly andesine and sometimes albite and in enclaves they are andesine. Anortite content in plagioclase decreases from core to rim, which shows normal zoning of plagioclase. Alkali feldspars in enclaves are sanidine compared to orthoclase in granite. Biotites in granite are primary ferroan and formed in low fo2 and under, reduced condition while biotites in enclaves are primery magnesian and formed in high fo2 and oxidized conditions. Thermometry based on feldspar and biotite compositions yielded about 500-750 ˚C for granite and 650-950 ˚C for enclaves. Mineral chemistry studies indicate that granite (peraluminous magma) and enclaves are derived from a calc-alkaline magma belonging to active continental margin setting.

The Ghaidou monzogranite in the southeast of Khomein constitute a part of rock complex from the northern part of the Sanandaj-Sirjan zone. This body intruded into the Jurassic micaschists and created a metamorphic aureole. Also، aplitic veins، tourmaline bearing pegmatitic dikes، felsic microgranular enclaves and surmicaeous enclaves are observed in this area. The predominant minerals of these rocks are K-feldspar (orthoclase and microcline)، Na-plagioclase (Albite- oligoclase in the monzogranite and oligoclase in the felsic microgranular enclaves)، quartz and black mica (Annite) -as the main minerals- with minor amount of tourmaline (schorle)، garnet، white mica (phengite)، sillimanite، kyanite، zircon، apatite and ilmenite. On the basis of biotites mineral chemistry، these phases are enriched in FeO and Al2O3 and relatively low in TiO2. These minerals are magmatic and primary and thermometry results yielded 660-690 ºC. According to the chemical composition of primary igneous biotites in the enclaves and monzogranites، these rocks have calc-alkaline، peraluminous and an orogenic continental collision affinity characteristics of S-type granites. Also، the biotite composition and the presence of ilmenite point to low oxygen fugacity and redox conditions during magma crystallization. Based on the available data، the generation of these rocks can be related to Arabian-Eurasia collision zone.

The Aligoudarz granitoid occurs in the central part of the Sanandaj-Sirjan Zone, western Iran. It comprises three distinct facies mainly of tonalite, granodiorite and granite composition. Magmatic microgranular enclaves (ME) extensively occur in granodiorite. Field, textural, whole rock and mineral chemistry data of the ME and the host rocks does not support magma mixing as the ME-forming mechanism. Major and trace elements variation diagrams, similarities in spider diagrams and geochemical modeling indicate the cogenetic relation of the ME and host rock. Fractional crystallization is the main process in the geneses of ME. Rapidly-cooled borders of the magma chamber can best explain formation of the ME. ME are the result of later fragmentation and dispersal of the rapidly-cooled borders in the host magma. These enclaves recorded the least degree of chemical exchange with the host. Biotite and amphibole crystallize with more rapid nucleation rates in rapid cooling zones. This process can explain different chemical behavior of the ME and the host rock.

Astaneh granitoid body with middle cretaceous age is located in south west of Arak and Sanandaj - Sirjan structural zone. This body is composed quartz diorite, granodiorite, tonalite and monzo granite dikes and intruded into regional metamorphic rocks (S.S.B). Correlated enrichment in LILEs compare to HFSEs and high Yb La, (5) Yb Th reveal volcanic arc granites and existence enclave (Andalusite) and ratio of 0 71044 86 87 (). I Sr Sr show high crustal contamination the partial of mantle wedge, subducted oceanic crust by lower continental crust, according probably this magmatism related to volcanic arc environment and is the result of the subduction of Neo-Tethys oceanic plate below the Iranian continental crust.

The composition of Kuh-e- Barandeh volcanic dome is andesite, dacitic andesite and dacite of calc-alkaline affinity. A prominent feature of this dome is the presence of various types of enclaves with different composition, shape and size. Detailed field and laboratory investigation proved that they are of xenolith and autolith types. The xenoliths are of pelitic and basic protoliths. Xenoliths show two distinct metamorphic events: (1) Regional dynamomorphic event justified by clear preferred orientation and foliation. (2) Thermal metamorphism producing andalusite, sillimanite, cordierite and spinel at the expense of former minerals like biotite, muscovite etc in pelitic rock and green hornblend at the expense of brown hornblend in basic rock. T. P measurement shows that these xenoliths have suffered a range of T.P 768- 830 mC and 5-7 Kb) during regional metamorphism and a retrograde contact metamorphism (747- 821 mC and 3.6-6.7 Kb).

The study area is located in the southern part of Qorveh granitoid complex. Investigation of textural and mineral chemistry evidence in granitoid host with composition of granodiorite, granite, qtz-monzonite, and mafic microgranular enclave (MME) with composition of qtz-diorite to meladiorite, are focused in this paper. Microscopic study and data of microprobe analyses in host and enclave rocks reveal disequilibrium textures and compositional (such as, tabular plagioclase with inclusions, sieved, zoned and resorbed plagioclases, needles of apatite, overgrowth of felspars and zoned amphiboles) in the granitoid host and mafic microgranular enclave. Because of agreement between the textural and mineralogical evidence, we accept the Elburg theory that globules (drops) of mafic magma and host granitoid rock have mixed and effective process in formation of enclave is a simple mechanical magma mixing (magma mingling), ceased by mafic magma stopping in a felsic magma chamber. This fact is linked to geochemical conditions and tectonic setting of the complex in Sanandaj-Sirjan Zone, as a remained zone of subduction setting.

Granitic rocks of Malayer plutonic complex contain varieties of enclaves with different shapes, sizes, mineralogy and chemical composition. The interpretation of bivariant geochemical diagrams of major oxides and trace elements with respect to higher values of some of oxides such as MnO, TiO2, MgO, CaO & FeOt than host rocks in one groups of enclaves and moreover linear trend of these oxides and some of trace elements such as Ni, Cr, V indicate to different nature and mafic source of these enclaves (Mafic type) than host rocks and other enclaves (Felsic type).The study of chemical composition of this enclaves by using of univariant and bivariant statistical methods (bivariant regression analysis, correlation coefficients, cluster analysis and principle component analysis) indicate clear chemical contrast between mafic enclaves with felsic enclaves and granitic host rocks and in other side chemical affinity of felsic enclaves and their host rocks. Distinctive distribution of the majority of oxides and trace elements of mafic enclaves and host rocks and low values for R2 in regression analysis, low value of correlation coefficient of major element oxides and trace elements between enclaves and their host rocks, separate position of samples in cluster pattern and special direction of variants and samples of vectors in bivariant diagram of principle component analysis (PCA) are outputs of different geochemical characteristics of enclaves and host rocks. Moreover this correlates with different trends of each major oxides and trace elements in bivariant geochemical diagram (Harker diagram).

The polyphase Nevis granitoid pluton extends 70 km2, is located in Urmieh-Dokhtar zone, shows variation which in terms of emplacement depth is related to epizonal to mesozonal environments [16], and in range of acidic to basic including tonalite, granodiorite, granite, monzonite, diorite and gabbro. The mentioned pluton is intruded to different units of volcano-sediments (according to the 1:250000 Geological Survey map) of Eocene sequences (E1, E2, E3, E4,E5, E6) and has imposed a contact metamorphism in Eocene 3]. Existance of mafic enclaves in the main body could confirm the initial basic-intermediate magma replacement. According to the coarse granular texture of these basic-intermediate rocks can be said that they have been replaced in crust middle depths (mesozonal) and in later stages, a large size of tonalitic magma intruded to the region shows variation in texture. Part of this tonalitic magma get to higher levels and show porphyry textures. Then they involved in mylonitic textures under tectonic stresses. Stress effects produced subgrain minerals and undulose extinction. The final phase of plutonism was made up leucocratic micro-granite and granophyres, comparing to tonalite they have limited volume and they are the most shallow plutonism in the area. Another pervasive process had been the effects of heat and fluid (hydrothermal process) caused by successive injections which had different influences on the rocks, and created secondary mineral paragenesis of greenschist facies including epidote, chlorite, calcite, albite, sphene and opaque minerals, represent the geothermal system activities in different phases and the formation history of polyphase Nevis pluton. Based on field surveys, lithology and geochemical, granitoids are I-type. These rocks are calc alkaline and metaluminous.