Petrology
Seyevahid Shahrokhi
Abstract
The Dalayon granitoid is located in the south of Borujerd and, is part of the Sanandaj-Sirjan zone. The lithological composition includes granodiorite, granite, pegmatite-granite, tonalite, quartz diorite, tourmaline-bearing pegmatite, and quartz-tourmaline veins intruded into volcanic and metamorphic ...
Read More
The Dalayon granitoid is located in the south of Borujerd and, is part of the Sanandaj-Sirjan zone. The lithological composition includes granodiorite, granite, pegmatite-granite, tonalite, quartz diorite, tourmaline-bearing pegmatite, and quartz-tourmaline veins intruded into volcanic and metamorphic rocks. The minerals set of granodiorite mass with color leucocratic to mesocratic index mainly minerals quartz, plagioclase, orthose and microcline and secondary minerals biotite, muscovite, zircon, garnet, apatite, rutile, leucoxene, and sphene. The indicator mineral of ferromagnesian in these rocks is biotite, which has a primary nature rich in magnesium and poor in chlorine in composition. The value of Fe/Fe+Mg ratio shows an average 0.44(apfu), that indicates that the studied micas are placed in the range of biotite and between siderophiles and anite poles. The average crystallization temperature of biotites is 681ºC and the average formation pressure is 2.95kb based on the total aluminum of biotites, which indicates formation at a shallow depth. Based on the proportions of MgO- FeO-Al2O3 in biotites, the magma that produced this mineral is of the calc-alkaline type. The existence of relatively high fugacity of oxygen and oxidant environment indicates magma of mantle-crust origin and host rock of magnetite granitoid series and I-type granitic rock for biotites.
Leili Fathiyan; farhad aliani; ali akbar baharifar; mohamad hossein zarinkoub
Abstract
Granitoid bodies of west of Zanjan with Precambrian age are located in northwest of central Iranian structural zone. Based on field observations and microscopic studies, these bodies contain tonalite, granodiorite and monzogranite. Tonalite are I-type, calc-alkaline, and peraluminous (206Pb/238U age ...
Read More
Granitoid bodies of west of Zanjan with Precambrian age are located in northwest of central Iranian structural zone. Based on field observations and microscopic studies, these bodies contain tonalite, granodiorite and monzogranite. Tonalite are I-type, calc-alkaline, and peraluminous (206Pb/238U age of 576±13 Ma) which base on isotopic studies (87Sr/86Sr (i) and εNd (i) values equal to 0.710544, -7.01), and geochemistry of major and trace elements, can concluded that they were resulted from melting of amphibolitic crust that generated from thickened mafic crust or under plate basalts (with presence of plagioclase in source area) in low pressures and depth in an active continental margin. Monzogranites are S-type, peraluminous and calc-alkaline, which is plotted in collision zone. These rocks were generated from melting of crustal rocks (melt derived from pelitic rocks with high plagioclase). Granodiorite are I-type, calc-alkaline and Weakly peraluminous (206Pb/238U age of 548±27 Ma). They have value of 87Sr/86Sr (i) more than 0.705, negative value of εNd (i), and geochemical data, which is generated from partial melting of lower to middle crust, because of thickening and shortening due to continental- continental collision. With respect of geographical location of granitoid bodies of Mahneshan and age of their units, it seems that these granitoid rocks have formed in an active continental margin during convergence of Central Iran and Alborz-Azarbayjan with Arabian platform during Precambrian
N. Sarhaddi; A. Ahmadi; Z. Firoozkoohi; M. Jami
Abstract
The Lakhshak granodiorite body with Oligo-Miocene age crops out in flysch sediments of northwest of Zahedan. This body has been intruded by dykes with variable color indices ranging from mesocratic to melanocratic, and NE-SW trend. Based on field observations, , melanocratic dykes have cut mesocratic ...
Read More
The Lakhshak granodiorite body with Oligo-Miocene age crops out in flysch sediments of northwest of Zahedan. This body has been intruded by dykes with variable color indices ranging from mesocratic to melanocratic, and NE-SW trend. Based on field observations, , melanocratic dykes have cut mesocratic dykes in some parts.This indicates that mesocratic dykes are younger than the melanocratic types. Different thickness (2 to 12m) of dykes shows the effect of tectonic activities and magama injection into structural joints, and the formation of dykes during tectonic activity. In terms of lithology, the Lakhshak body is composed of granodiorite, dacitic mesocratic dykes and melanocratic dykes of microdioritic and andesitic types. The granodiorite body and the two types of dykes are of I type nature, and are calc-alkaline, high-K calc-alkaline and metaluminous. Based on the geochemical characteristics, dykes and granodiorite show enrichment in LILE, LREE such as Ba, Cs, Rb, Eu and Pb, and depletion in HFSE, HREE such as Nb, Ti and Ta, which are related to index characteristics of the volcanic arc setting of an active continental margin. Pb positive anomaly may demonstrate continental crust assimilation by magma associated with mantle metasomatism. Based on field observation and petrogenesis, the Lakhshak granodiorite and mesocratic-melanocratic dykes originated from magmatic activity of subducted oceanic crust (Sistan plate) beneath the continental plate (Afghan block). The parental magma of the Lakhshak granitoid was originated from melts resulted from amphibolite melting, and dykes are the late derivative of magma recrystallization granodiorite.
A. Ansari; S. J. Sheikh Zakariaee; S. Dargahi; M. Arvin
Abstract
The Chargonbad batholith is located close to Sirjan and southeast of Urumieh-Dokhtar magmatic zone . This batholith is acidic to intermediate in composition and intruded into the Eocene volcanic rocks. The main volume of these rocks consisted of granodiorite and monzogranite, but it also consists of ...
Read More
The Chargonbad batholith is located close to Sirjan and southeast of Urumieh-Dokhtar magmatic zone . This batholith is acidic to intermediate in composition and intruded into the Eocene volcanic rocks. The main volume of these rocks consisted of granodiorite and monzogranite, but it also consists of quartzdiorite, tonalite and syenogranite. Their contacts are gradational. They have allotrimorphic granular texture with subordinate porphyritic texture. Their enclaves consist of xenoliths enclaves, microgranular mafic enclaves (diorite to quartzdiorite in composition) and autolith enclaves(tonalite, granodiorite and monzogranite in composition).The Chargonbad batholith rocks are also cut by different types of dykes which are mainly consisted of dykes and veins of pegmatitic stage, microgranular dykes (andesite and andesite basaltic in composition) and microgranular dykes that are similar to mafic enclaves. Evidenc show that the samples represent properties of I-type granitoids. Chargonbad granitoid has magnesium nature and shows cordellarian granites features. Based on the tectonomagmatic environment diagrams, all samples from the Chahargonbad plot in the island arc setting of a subduction zone and show active continental margin setting characteristics .
Petrology
Z. Gharamohammadi; A. Kananian; M. Eliassi
Abstract
The Dehe Bala pluton is exposed approximately 45 km south-west of Boein Zahra town, Qazvin province. This pluton includes several mafic microgranular enclaves (MMES) with ellipsoidal and rounded shapes and varying sizes (from a few centimeters up to 30 cm). The MMEs are composed of diorite, monzodiorite ...
Read More
The Dehe Bala pluton is exposed approximately 45 km south-west of Boein Zahra town, Qazvin province. This pluton includes several mafic microgranular enclaves (MMES) with ellipsoidal and rounded shapes and varying sizes (from a few centimeters up to 30 cm). The MMEs are composed of diorite, monzodiorite and diorite-gabbro while the host rocks comprise mainly granodiorite. The presence of disequilibrium textures in enclaves, such as plagioclase phenocrysts with repeated resorption surfaces and sieve texture, quartz ocelli and acicular apatite, suggest a varity of magma mixing processes affecting the Dehe Bala pluton. The distribution of major, trace and rare earth elements apparently reflect exchange between the MMEs and the felsic host rocks. Unusual REE enrichment of the enclaves compared to the country rocks can be attributed to significant differences in their parent magma compositions. The complexity of the morphology of the enclaves (fractal dimension) caused by magma mixing processes. Fractal dimensions of the enclaves vary between 1.14 to 1.29. The frequencies of Dbox = 1.29 is the highest frequency in histogram. According to the fractal dimensions of enclaves, the logarithm of the viscosity ratio between the host granodiorite and the enclave ranges between 0.56 to0.96 with most values clustering around 0.96. The most of enclaves in the Dehe Bala pluton characterized by silica content around 56 w% and a high fractal dimension. These evidence confirmed the occurrence of slight hybridization between the mafic enclave magma and surrounding felsic magma, causing increasing of viscosity difference between the host granodiorite and the enclave magmas.
Gh Ghadami; A Moradiane Shahre Babaki; S.M Mortazavi
Abstract
More than 20 tonalitic to granodioritic plutonic domes, Oligo-Miocene in age, have intruded into the older volcanic rocks, in southeast of Urumieh- Dokhtar Magmatic Belt, northwest of Shahr-e-Babak. These rocks have granoporphyritic texture and consist of Phenocrysts of plagioclase, amphiboles and biotites. ...
Read More
More than 20 tonalitic to granodioritic plutonic domes, Oligo-Miocene in age, have intruded into the older volcanic rocks, in southeast of Urumieh- Dokhtar Magmatic Belt, northwest of Shahr-e-Babak. These rocks have granoporphyritic texture and consist of Phenocrysts of plagioclase, amphiboles and biotites. The geochemical data show calc-alkaline affinities of these rocks , which formed in volcanic arc (I type) of an active continental margin. These data also show LILE and LREE enriched normalized multi-element patterns, and depleted of HFSE (Nb, Ta and Ti). Primitive mantle-normalized REE patterns display a dramatic decrease from LREE to HREE without any Eu anomaly. They have higher SiO2, Al2O3 and Sr content and Sr/Y and La/Yb ratios and lower MgO, Y and Yb contents than the normal calc-alkaline rocks, which reveal their adakitic characteristics. The high content of Sr, LREE enrichments, absente of Eu anomaly, HREE depletion, Y and Yb depletion pattern suggest the existence of garnet, amphibole and absence of plagioclase in the source rocks. Our data suggest that the plutons produced by partial melting of amphibole-eclogite or garnet-amphibolite, due to the subduction of Neotethys oceanic slab under the Central Iran continent.
A. Kananian; M. Rezaei-Kahkhaei; D. Esmaeili
Abstract
The Lakhshak granitoid pluton which is located at 10 km northwest of Zahedan, has intruded into the Eocene flysch sediments with an elliptical shape and NW-SE direction. This pluton after emplacement has been cut by numerous dykes with NE-SW trend. These dykes comprised about ...
Read More
The Lakhshak granitoid pluton which is located at 10 km northwest of Zahedan, has intruded into the Eocene flysch sediments with an elliptical shape and NW-SE direction. This pluton after emplacement has been cut by numerous dykes with NE-SW trend. These dykes comprised about 20-30% of the Pluton with various compositions, ranging from granodiorite to monzodiorite in composition.
The Lakhshak plutonic rocks are mainly metaluminous, calc-alkaline and belong to I type granites based on the P2O5 and Th content versus SiO2. Regarding TiO2 content these rocks resemble the continental margin granites. The MgO, Na2O, Ni, Cr content as well as Mg# and depletion in Y, these plutonic rocks are similar to the adakite, a rock type produced by partial melting of young oceanic crust. The low Ba/La content of the studied samples may suggest that subducted slab suffered dehydration prior to partial melting.
These rocks are enriched in LIL, LREE, however, they are depleted in HREE and Y. In addition, they show negative anomalies of Nb, Ta, P and Ti, and positive anomaly of Pb. The negative anomalies of Nb and Ta may indicate the effect of mantle wedge metasomatism by oceanic crust. The positive anomaly of Pb may demonstrate continental crust assimilation by magma associated with mantle metasomatism.
It seems that Lakshak pluton has been formed by subduction of Sistan young oceanic crust under the Afghan Block. Moreover, the low content of HREE and Y besides a decreased ratio of Yb versus SiO2, Y<15.13, Yb<1.2 and existence of amphibolite enxenoliths in these rocks may suggest partial melting of amphibolites. The latter is formed during the oceanic crust subduction in depth more than 35 km.
