جستجوی مقالات مرتبط با کلیدواژه "crustal contamination" در نشریات گروه "زمین شناسی"

The Taftan volcano hosts an extensive volcanic activity during Late Miocene to Quaternary where took place over Makran-Chagai subduction zone. Taftan rocks are mainly basaltic andesite, andesite, trachyandesite, and dacite that occur as lavas and pyroclastic rocks. They are characterized by basic-intermediate inclusions enclosed by acidic groundmass, and disequilibrium textures in plagioclase phenocrysts including sieve texture, zoning, and dissolution margin, which may reflect magma mixing. These rocks record high-K calc-alkaline to calc-alkaline affinity with enrichment in LREE and LILE relative to HREE and HFSE, respectively. These features, coupled with the clear depletion in HFSE (such as Nb, Ta, and Ti) are consistent with typical subduction-related volcanic arcs. Taftan primary melts might have been produced by ~15% partial melting of spinel lherzolite mantle. The normalized multi-element patterns which mimic the upper continental crust values, and enrichment in Pb, Th, U, and Rb agree well with magma evolution by assimilation and fractional crystallization (AFC). The available isotopic geochronology dataset reveal that the youngest volcanoes of the Makran-Chagai magmatic arc are Bazman and Kuh-e-Sultan volcanoes. A geochemical comparison of these volcanoes highlights that magmatism in the Taftan where the crust is thick, underwent a higher degree of crustal assimilation en route to the surface.

The study area in north of Iran is located between 49 °, 30' and 50 °, 00' longitudes and 36 °, 30' to 37 °, 00' latitudes and in the 1.100000 sheet of Jirandeh. This area is considered as part of the structural zone of Iran in Alborz zone and is part of Tertiary zone. In this paper, with the help of geochemical evidence in Rudbar region, as part of Paleogene magmatism in Alborz, an attempt has been made to comment on the tectonic petrogenetic of the region.

After field studies, considering lithological varieties of the volcanic units in the region, 100 samples were collected and thin sections were prepared and studied in terms of petrography using polarizing microscope. Then, among the mentioned samples, 22 samples with the lowest weathering and most lithological variety were selected to analyze the major elements using XRF method and the trace and REE elements by ICP-MS method at SGS laboratory in Toronto. In order to analyze data, the software Igpet 2007 and GCDkit are used.

The studied area is located in the sheet of Jirande at a scale of 1:100000 ,that are outcrops of volcanic and pyroclastic rocks of Paleogene age. Based on petrographic studies carried out on the lavas’ units, three rock units were distinguished: a) olivine basalts, b) andesitic basaltic and basaltic andesite, c) hornblende pyroxene andesites and andesites. In most investigated rocks, there are different types of xenoliths and xenocrysts. Xenoliths are composed of gabbro, diorite and sometimes basalt. These xenoliths and xenocrysts are petrographic evidence for magmatic contamination.   The positive correlation of Na2O and K2O and the negative correlation of Fe2O3, MgO, CaO oxides with the increasing of SiO2 evidence, indicates fractional crystallization in the magma evolution trend of rocks in the area. The constant trends are also maintained through series, which were exposed to the AFC process and assimilation with fractional crystallization.
Comparing the pattern process of incompatible rare elements to crust values in mafic and intermediate terms indicates crustal contamination of mafic rocks to the lower crust and contamination of intermediate rocks towards upper crust. Linear correlation between the ratio of Y/Nb compared to Zr/Nb indicates the origination of magmas from MORB source mantle which were somewhat contaminated with the continental crust rocks.

Geochemical studies represent original relationship between all the studied rocks. This relationship indicates the crystal fractionation in the magma that forms these rocks. Investigations of the ratios of incompatible trace elements, suggest that the mafic samples of the region are close to MORB asthenosphereic mantle source. Also, the trends between primary and evolved samples indicate a linear arrangement between the MORB source mantle and the continental crust, representing an interaction of the MORB mantle-derived magmas with continental crust. All geochemical evidence indicates that the volcanic rocks in the area were originated from melting of a MORB asthenosphere mantle source with spinel facies, which was contaminated with the continental crust rocks to some degree.
The crustal contamination of these basalts has caused, firstly, these rocks to follow exactly the elemental processes of the crust, and secondly misleadingly show the geochemical characteristics of rocks in subduction zones. This means generating magmas from mantle MORB source with crustal contamination are commonly seen in within-plate continental rift magmatisms.

The plutonic bodies occurring in Sursat complex are some parts of plutonic rocks of Sanandaj- Sirjan Zone. Based on the field observations and microscopic studies, rocks of the study area are consist of hornblende gabbro, quartz diorite, monzodiorite, granodiorite and tonalite. The EPMA analyses of minerals such as amphiboles (in granodiorite and monzodiorite), plagioclases and alkali feldspars indicate that amphiboles are magnesiohornblende, plagioclases are albite and oligoclase and alkali feldspares are orthoclase. Geochemical studies indicate that monzodiorite unit (Turke Dare and Khangholi bodies) are metaluminous I-type and calc-alkaline in nature. They are plotted in volcanic arc granite (VAG) region with 87Sr/86Sr and εNd values equal to 0.70448 and -0.12. All evidence represent that the monzodiorite were generated from a magma which was derived from mantle affected by assimilation and contamination processes. Granodiorite unit (Pichaghci, Hamzeh Ghasem and Northeast Khangholi bodies) represents I-type, metaluminous to peraluminous and calc-alkaline characteristics and is plotted in VGA field of magmatic arc. The 87Sr/86Sr and εNd values are equal to 0.70529 and -2.82 respectively. So these granodiorites were generated through mixing processes of a mantle magma with crustal sources. Tonalite–trondhjemites group are I-type, tholeiitic, peraluminous according to the low value of Mg# (2.9-11.6), Cr (20-46 ppm) and Ni (1-2.4 ppm) contents. They are also low in LA/Yb, Sr/Y, and Nb/Ta. The slight negative anomaly in fractionated patterns of the rare earth elements (REE) and very low depletion in Eu, indicate that these rocks were resulted from amphibolitic crustal source that were previousely generated from thickened mafic crust or from basaltic plate in low pressures at shallow depth in the presence of abundant plagioclase.

The study area is a part of the Sanandaj-Sirjan zone which is mainly composed of metamorphic rocks, a variety of igneous basic rocks and sediments. the metamorphic rocks studied at Bahram Gur area (west of Kheyrabad, Northwestern of Gol-e Gohar mine) in Sirjan, Kerman Province are slate, phyllite, schist (garnet schist, amphibole schist, micaschist, kyanite schists), epidote amphibolite, amphibolite, gneiss, quartzite and marble. Amphibolite facies is the highest metamorphic grade in the region experienced by the rocks. Protolith of amphibolites is basic to intermediate igneous rocks with chemical composition of tholeiitic to calc-alkaline. . Based on Zr / P2O5 against Nb / Y diagram amphibolite protolith is from oceanic crust. Based on Ti against V diagram, amphibolites of the study area belong to mid-ocean ridges (MOR) and Volcanic arc tectonic environments in relation to Neotethys ocean. Primary magma of igneous rocks that are protholite amphibolite is derived from the spinel-peridotite. The negative anomaly of Nb and low Nb/U ratio indicates the contamination of this magma during rising.

The study area is located northwest of Gol-e Gohar mine (Bahram Gur Protected Zone) in Sirjan, the Kerman Province, a part of the Sanandaj-Sirjan zone. The area is mainly dominated by metamorphic rocks with their basic igneous origin and sedimentary including slate, phyllite, schist (garnet schist, amphibole schist, mica schist, kyanite schist), epidote amphibolite, amphibolite, gneiss, quartzite and marble. Among the study rocks, amphibolites with different minerals paragenesis, have been experienced the highest metamorphic grade to amphibolite facies. The basic igneous rocks ranging in composition from tholeiitic to calc-alkaline are the source rocks of the studied amphibolites and the oceanic crust is their protolith. As the discrimination geochemical diagrams display the amphibolites of the study area probably belong to back arc tectonic environments, which are very similar to mid-ocean ridges (MORB). The primary magma of the igneous rocks and the protolith of amphibolites were derived from spinel-peridotite. Furthermore, on the geochemical diagrams which were used for the purpose of this study, the positive Ba and negative Nb anomalies along with low Nb/U ratio show that the magma of the protolith has been subjected to crustal contamination during rising to the surface. All the geochemical data indicate that the magma has emplaced in a supra-subduction environment related to Neotethys Ocean.

Pyroclastic rocks in the Badam area (E-Mahabad, west Azarbaijan Province), are located at the most extreme northern part of the Sanandaj-Sirjan zone. Petrographic studies revealed that they are basanitic in composition and have porphyric and microlithic porphyric textures. Olivine and clinopyroxne occur as phenocrysts and clinopyroxene and nepheline as microliths. Opaque minerals and glass have occupied the space between different minerals. In classification diagram, they have basanitic composition. Geochemical features such as enrichment in LILE, high LREE concentrations and negative anomalies in Nb, Ta and Y, with positives anomalies in Ba, Pb and Th and enrichment in Th/Yb, all suggest that these rocks have mantle source that are enriched by melt/fluids from the metasomatized subducted oceanic slab. These features are inherited from mantle source and they are not caused by crustal contamination. Regarding MREE and HREE ratios, these basanites originated from 1 % partial melting of a garnet lherzolite source in the garnet stability field (85 Km). Melting trigger in this area is not clear, but old theories such as lithosphere delamination or slab break up are not applicable any more. There is three suggestions about melting in these are: 1) break up of hydrated phases by depth increase, 2) changing and turbulence in convection follows, 3) subduction and dehydration of Arabic passive margin

The study area includes Alam Baghi, Vashaghan, Sar Band and Ghermez Cheshmeh and is located in the northeast of Farmahin and the southwest of Tafresh. Based on the structural subdivisions of Iran, the mentioned area is a part of Central Iran and the Urumieh-Dokhtar magmatic belt (Hajian, 1970).
The studied volcanic rocks consist of trachybasalt, trachyandesite, basaltic andesite, andesite, dacite, rhyodacite, rhyolite, ignimbrite, tuff and tuffit in composition and in terms of age they belong to the middle and upper Eocene. It seems that the volcanic activities are related to folding and faulting in the studied area. On the other hand, in addition to causing orogenic activity, at the middle and upper Eocene (Ghasemi and Talbot, 2006), locally extensional regime has played a main role in volcanic eruption. Similar to this scenario happened in other areas such as Taft and Khizrabad in Central Iran (Zarei Sahamieh et al., 2008). Porphyritic, microlite porphyritic and microlitic are the main textures in these rocks. Mineralogically, they contain plagioclase, clinopyroxene, amphibole, quartz and biotite as the main minerals and zircon, apatite, and opaque minerals as accessories.
The major and trace elements of mineral composition are determined by electron probe micro-analysis (EPMA) using a Cameca SX100 instrument in the Iran Mineral Processing Research Center (IMPRC). Moreover, the whole-rock major and some trace elements analyses for a few samples were obtained by X-ray fluorescence (XRF), using an ARL Advant-XP automated X-ray spectrometer.
Based on EPMA analyses, plagioclase mineral in basaltic andesite and trachybasalt samples range from labradorite to bytownite in andesite and trachyandesite has oligoclase- andesine and in dacite, rhyodacite, rhyolite has an albite-oligoclase composition. In the Wo-En-Fs diagram, all clinopyroxenes show augitic and a lessor amount of clinoenstatite composition and in the Q-J diagram located in the Mg-Fe-Ca (Quad) field and in the 2Tiિ肕 vs. Naɒ diagram (Morimoto et al., 1988) located above on the Fe3=0 line that indicate high oxygen fugacity during crystallization. Microscopic study on these rocks such as oscillatory zoning, resorption rims in plagioclase and the presence of basic inclusions suggest the occurrence of magmatic contamination on the parent magma. The presence of oxidized amfibool rims (in hornbelende as oxy hornbelende) indicate the high temperature of the magma at the time of eruption.
According to the classification diagrams such as total alkaline vs. SiO2 (Irvine and Baragar, 1971) TAS (Le Bas et al., 1986) and tectonic discrimination diagrams (Pearce et al., 1984) samples are plotted in sub-alkaline, basaltic-andesite, andesite, dacite and rhyodacite, subduction and volcanic arc fields, respectively.
The geochemical diagrams such as AFM are used for the identification of magma series and show that the studied rocks are calc-alkaline and A/NK vs. The A/CNK diagram shows the metaluminous to peraluminous nature. Incompatible and LIL elements such as Ba, K and Rb enrichment show that the contamination of magma with continental crust has occurred. The similarity between the REE patterns in all of the collected samples in Alam Baghi, Vashaghan, Sarban and Ghermez Cheshmeh areas suggest the same source for all of the volcanic rocks.
The tectonic setting diagrams show that these rocks belong to the continental margin which has been involved in a subduction zone.
The position of the samples on the major elements vs. SiO2 diagrams indicate that magma differentiation has occurred. Spider diagrams show a positive anomalous in Rb and a negative anomalous in Nb and Ti This phenomenon shows a contamination between the magma and the crustal rocks (Rollinson, 1993). Also, MORB-normalized incompatible element patterns of the Farmahin area show that the parent magma has been contaminated. It appears that assimilation and fractional crystallization (AFC) were the dominant processes in the genesis of the studied volcanic rocks.
As a conclusion and according to field evidence and geochemical characteristics presented in this article, the studied area is composed of lava flows and pyroclastic rocks such as andesite, dacite, rhyodacite, ignimbrite, tuff and tuffits that cross cut by younger dykes and belong to the middle to late Eocene age (middle to upper Lutetien). According to Sm/Yb vs. Sm diagram (Aldanmaz et al., 2000), all the studied samples in terms of composition are similar to enriched mantle-derived melts that are generated by varying degrees of partial melting (10% - 20%) from a spinel lherzolite to spinel-garnet lherzolite source.
Considering the evidences, all rocks in the studied area belong to the subduction zone and the parent magma originated from mantle and was contaminated with continental crust during eruption and rising.
Acknowledgments: The authors wish to thank the Journal Manager and reviewers who critically reviewed the manuscript and made valuable suggestions for its improvement.

The Eocene volcanic rocks in Jirande area are dominated by basalt, andesite, trachyt and trachyandesite, which range from basic to intermediate rocks. Plagioclase as major mineral in igneous rocks makes up the largest percentage mineral in these rocks. Clinopyroxene and olivine in basaltic rocks and amphibole in acidic rocks are the prevalent minerals. In petrological studies, the existence of glomeroporphyry, sieve, corrosion gulf, skeletal, and also reaction rims confirm the role of crustal contamination and fractional crystallization in the evolution of the study rocks. Also, variation diagrams of trace elements, spider diagrams together with AFC modeling and ratio-ratio diagrams of trace elements, highlights the role of crustal contamination and magmatic fractionation in the genesis of the rocks studied. The parent magma of these rocks, have a composition like as the melts derived from enriched mantle, and plots in the field of 10-20 percent partial melting of a garnet-spinel lherzolitic source in the depth of 90 to 110 km.

In the Ahmadabad Khartouran region located at 175 Km southeast of Shahrood, a considerable number of adakitic domes crop out, which are intruded into the Paleocene- Eocene volcanosedimentary rocks. Lithological compositions of these domes include andesite, trachyandesite and dacite. Pyroxene (augite), green hornblende and plagioclase are typical mafic and felsic rock forming minerals. With respect to low HREE and high LREE along with other characteristic such as silica content (58.91- 63.41), Na2O more than 3%, Al2O3 more than16%, Yb less than 1.8 ppm, Y less than 18 ppm and K2O/Na2O ratio between 0.98- 2.3, these rocks can be classified as high silica adakite. Enrichment of LREE relative to the HREE and depletion of Nb, Ti, and high concentration of Rb, Ba, K and Th, imply crustal contamination of the mentioned adakitic domes. Enclaves with different sizes and compositions were seen in these domes which indicate contamination and magma mixing with continental crust. Petrographic and geochemical evidence show that the magma forming these rocks originated melting of subducted metamorphosed Neotethys oceanic slab (Sabzevar – Darouneh branch) at the Peak-T conditions of amphibolite facies.

Kuh-Bubak and Sikh-kuh volcanic cones are located in Southeast of South Khorasan province, north and Southwest Nehbandan city. Based on structural geology classification of Iran, these volcanos are belonging to Lut zone. These cones are composed mainly of Thrachybasalte and Thrachyandesite composition rocks and they are dominant porphyric texture. These rocks have plagioclase, pyroxene, olivine, hornblende and biotite as main minerals and quartze, sericite, epidote, zeolite and calcite is secondary minerals. Twelve fresh rock samples are selected for chemical analysis and then send to the Zrazmay Mahan laboratory were analyzed major and trace elements with XRF and ICP methods respectively. Geochemical characteristics of these rocks show that the primary magma formed these rocks have changes from Calk-alkaline to alkaline. In spider diagrams observed that LREE enrichment and HREE depletion, similar pattern can be seen in parallel and indicated their origin is the same. In addition, enrichment in LILE, and Pb, ratio elements of Nb/U and Ce/Pb indicates that they are contamination with crustal rocks. On the other hand, geochemical diagrams La/Yb versus La and Zr versus TiO2 indicating fractional crystallization process are happen in these rocks. Geochemical various diagrams show that fractionation and crustal contamination has affected on the primary magma. Nb and Ti negative anomalies and geochemical properties indicating that these volcanoes are belonging to subduction zone.

In the northeastern part of Kurdistan province، there are many volcanic cones that are basaltic in composition. Petrographic investigations reveal these rocks are dominated by clinopyroxene and olivine phenocrysts and plagioclase and pyroxene micro crystals، while space between them is filled by opaque mineral and brown glass. The presence of zoned pyroxenes and sieve texture in these rocks are evidences of crustal contamination and magmatic unequilibrium. The studied rocks with 5-14% normative nepheline are alkaline nature. On Harker diagrams fractional crystallization is indicated by MgO decreasing while CaO، FeO، Ni، TiO2 and Cr and SiO2 increase. On discriminated diagrams the tectonic environment of the samples is inter continental extensional zone. Geochemical characteristics such as LILE، LREE enrichment، Nb، Ta and Y negative anomalies، positive anomalies of Ba، Pb، Th and Th/Yb enrichment suggest that the basaltic lavas studied derived from lithospheric mantle that contaminated by subduction fluids. Also، Zr/Hf and Hf/La ratios are evidence for upper crustal contamination. High (Th/Yb) N، (La/Yb) N and high Nb anomaly (0. 37-0. 98) show that the magma generated from a garnet lherzolitic source.

The Cheheltan Mountain is located at south west of Bardsir, Kerman Province. It represents a part of the Eocene Hezar volcanic complex (Urumiyeh-Dokhtar volcanic belt) and consists of lava flows, pyroclastics, epiclastics and numerous intrusions. The lava flows comprise of basaltic-andesites and basalts and contain plagioclase and pyroxene phenocrysts that set in a vitreous or fine-grained matrix. Geochemical studies show that the lava flows belong to the calcalkaline and high-K calcalkaline magmatic series, and in the variation diagrams, they show continuous chemical trends, which can be formed due to fractional crystallization of minerals such as olivine. These rocks show negative anomalies of Nb, Ti, Ta, HFSE and HREE, and positive anomalies of Ba, Rb, Th, LREE and Sr in the spider diagrams, resembling the subduction related magmas. These evidences show that the parental magmas may have been affected by crustal contamination processes. According to the petrogenetic studies, these magmas belong to the active continental margin setting, and all of them have the same source. The present work shows that the parental magmas of the studied rocks, probably originated by partial melting of metasomatized mantle sources in a subduction zone environment.

Felsic volcanic rocks embrace a portion of the volcanic succession in Kajan area of Urumieh-Dokhtar magmatic assemblage. Based on trace elemental abundances and patterns, the felsic rocks might be attributed to two distinct series. In one series, normalized trace and REE patterns are rather flat (La/Yb<17) but display negative Ti, P, Sr and Eu anomalies. This series, which is called normal calc alkaline series, is comparable to the felsic melts evolved by differentiation of mantle-derived basic partial melts in subduction zones. In the second series, which is here called adakitic series, trace and REE patterns are steep (La/Yb>28) and positive Sr anomaly. Origin of the magmas that generated the latter series is likely to be the Neotethyan slab partial melts under high pressure (amphibole eclogite mineralogy).

Quaternary volcanic rocks are widely developed in NW of Ahar, NW Iran. Based on geochemical data, these rocks mainly consist of alkali basalts, trachybasalts, basaltic trachyandesites and trachyandesites. The major- and trace-element chemistry indicates that the lavas are dominantly alkaline in character. The studied rocks display microlithic porphyritic texture with phenocrysts of olivine, clinopyroxene, and plagioclase ± amphibole ± biotite. Major and trace element abundances vary along continuous trends of increasing SiO2, Al2O3, K2O, Na2O, Ba and Rb decreasing CaO, Fe2O3 * and Cr with decreasing MgO.The volcanic rocks in this area are characterized by the LILE and LREE enrichments and negative HFSE anomalies. The Sr and Nd isotopic ratios vary from 0.704463 to 0.704921 and from 0.512649 to 0.512774, respectively. CaO/Al2O3 ratios versus MgO, La/Sm ratios versus Rb and Ba and Zr versus Th suggest that that fractional crystallization was a major process during the evolution of magmas. AFC modeling and isotopic data as well as microscopic evidence, clearly indicate that crustal contamination accompanied by the fractional crystallization played an important role in petrogenesis of the trachyandesites. Also, geochemical and isotopic compositions indicate that magma mixing was not essential process in the evolution of Ahar magmas. Alkali basaltswith high 143Nd/144Nd ratio, low 87Sr/86Sr ratio and high MgO, Ni and Cr contents indicate that they crystallized from relatively primitive magmas. REE modelling and Trace element ratios indicate that the alkali baslats were derived by small degrees (1-3%) of partial melting from the spinel lherzolite.

The Nash''s Tertiary volcanic rocks in the Alborz Mountains in the east of Roudbar (North of Iran) show a compositional range from olivine basalt، basaltic andesite، pyroxene-andesite to andesite. From petrographical point of view، the diversity of xenoliths and xenocrysts are evidences for crustal contamination. The positive correlation of CaO/Al2O3 vs. MgO and Al2O3/CaO vs. SiO2 are signatures of differentiation of olivine and clinopyroxene in magmatic evolution. The positive correlations of K2O/P2O5 vs. SiO2 and La/Sm vs. K2O/P2O5 indicate the contamination of magma with continental crust. The incompatible elements patterns and their comparison with those of continental crust point to the contamination of volcanic rocks with lower and upper continental crust. The linear trends on Zr/Y vs. Nb/Y diagram، indicate two different sources for the studied rocks. The MORB-mantle source and the continental crust. The variations of Zr/Nb vs. Y/Nb and Rb/Y vs. Nb/Y display the crustal contamination of magmas which are derived from MORB-mantle source. Geochemical studies show that the studied rocks were originated from 15% melting of a MORB source in spinel facies in continental within-plate.

The studied area is located about 35 KM north-west of Rafsanjan (Kerman Province) and belongs to Hezar volcanic complex (in Uromieh-Dokhtar volcanic belt) and consists of Eocene folded lava flows (basalt, basaltic andesite, andesite) and pyroclastic rocks. Plagioclase phenocrysts show evidences of disequilibrium textures such as sieve texture, resorption and oscillatory zoning. These features can be formed by magma mingling, PH2O variations and decompression, as magma rises to the surface. Geochemical Studies indicate that lava flows belong to calc-alkaline magmatic series and their parent magmas have not extensively fractionated. The highly enrichment of LREE compared to HREE, high contents of LILE to HFSE and significant anomalies of Nb, Ti and P suggest a subduction-related volcanism. Chemical composition and phenocryst assemblages of these rocks indicate that these magmas probably derived from mantle, and then, have been erupted in a form of continental volcanic and they have passed some stages of their crystallization´s history in the crustal reservoirs During these stages, crustal contamination affected them.

Gandom Berian area is a basaltic messa composed of dark flows covering about 480 km2 of the western part of Lut desert in the northeast of Kerman. In this area، the fault system follows a north-south trend and، basaltic lavas have flowed along this trend. It seems that in Gandom Berian area، the activity of Nayband fault has created a tensional tectonic regime leading to the creation of open fractures in the crust which have conducted the flow of magma to the surface. Comparing maps of the lineation index factor of Nayband fault and also the related maps to situation of volcanic cones admit the role of fault in formation of Gandom Berian basaltic magma. The presence of coarse euhedral olivine crystals along with coarse crystals of clinopyroxenes and the absence of magmatic quartz، all reveal a fast deep ascending magma through fractures system and deep faults. The deep fracturing of Nayband fault has prevented the mixing of magma with crustal contamination. The high La/Nb value (with average 1. 7) along with low ratio of Ce/Pb and Pb/Nd indicate low mixing of magma in the studied area. Also، none scattering compatible element plots show negligible magma mixing. Uniformity in crystal size distribution (CSD) plots and its constant slope indicate the low impact of physical processes such as magma mixing in basaltic magma which effects the crystallization of plagioclase microlites during its ascent to the surface. The main cause of steepness in CSD is the rapid quenching of basaltic magma during upwelling which leads to plagioclase fine microliths. The presence of olivine and clinopyroxene phenocrysts indicates that in the primary magma، crystallization had occurred before ascent and eruption. Based on Dy/Yb versus La/Yb plot the Gandom Beryian basalts were formed by 8 to 10% partial melting of a garnet-lehrzolite parental rock. In general، lower partial melting of upper mantle (less than 10%) leads to the creation of alkaline basaltic magma. On the other hand، Gandom Beryian basaltic magma has characteristics similar to a high magnesium parental magma with low degree of evolution.

The Paleogene volcanic rocks of Damash have a considerable outcrops in Alborz structural zone in Guilan Province. These volcanic rocks show a compositional range from olivine basalt, basaltic andesite, pyroxene andesite to andesite. The petrographical and geochemical studies indicate that the fractional crystallization of clinopyroxene and olivine play an important role in lithological varieties of the Damash volcanic rocks. The positive correlation of Hf and Nb v.s Zr, CaO/Al2O3 v.s MgO and Al2O3/CaO v.s SiO2 are geochemical signatures of differentiation of clinopyroxene and olivine. The depletion in elements such as Nb, Ta, Zr, Hf, P, Ti and high ratios of Ba/Nb, La/Nb and Rb/Y, and low ratios of Zr/Nb and Y/Nb are geochemical evidences of crustal contamination of these volcanic rocks.The range of the incompatible elements and comparison with the crustal data range show that these volcanic rocks have a clear elemental equilibrium with continental crust and have been contaminated with it.

The Cretaceous gabbros located in Javaherdasht area in the northern part of Alborz Mountains, south of Guilan province. These gabbros show layered structure at the bottom and the isotropic structure at the top. From the mineralogical point of view, they have plagioclase, augite, olivine, biotite and magnetite. Geochemically, they belong to transitional magmatic series. Positive anomaly of Pb, K, Th, Rb and negative anomaly of Ba, Zr, Nb and P indicate contamination with continental crust. Tectonic setting diagrams of these gabbros suggest a continental intraplate environment, also the value of (Nb/Nb*)pm ~0.89 in the studied gabbros is similar to intra-continental rift basalts with crustal contamination. The REE pattern of the studied gabbros is also similar to transitional-sub alkalic intracontinental rift basalts and the values of (Ce/Yb)N ~3.9 and (Dy/Yb)N ~1.3 indicate the presence of spinel in their mantle source. The high ratio of Th/Nb and Nb>0 prove that the magma is derived from MORB mantle plumes (P-MORB) which has been contaminated with continental crust.