Search published articles


Showing 34 results for Basalt

, , ,
Volume 15, Issue 1 (4-2007)
Abstract

Mafic rocks including basalts and gabbros are the main constituents of Birjand ophiolites. They are found in several places and show low grade metamorphism in the field and under the microscope. Chondrite-normalized REE patterns for basalts and gabbros indicate that these rocks are transitional-enriched to depleted mid-oceanic ridge basalts respectively. Otherwise, N-MORB normalized trace elements patterns for basalts and gabbros are considered to be enriched in some LIL elements. Depletion in Ti and also in Nb (in gabbros) is other characteristic of these rocks. Therefore an incomplete short-lived subduction regime for generation of those heterogeneities can be suggested. The primary mantle-normalized trace elements pattern for Birjand harzburgite also confirms some LIL enrichments.


, , ,
Volume 16, Issue 2 (7-2008)
Abstract

Acidic and basic volcanic and intrusive rocks of Harzandat-Divan Daghy as individual masses, are located in North and Northwest of Marand (Harzandat) and South of Jolfa (Ghareh Gose-Divan Daghy) trending NW-SE.These rocks are located under Permian progressive deposits, which are covered by an igneous sole unconformity. Lithological composition of the acidic volcanic rocks ranges from dacite, rhyodacite to rhyolite, and basic volcanic rocks range from basalt to basaltic-andesite, where as plutonic rocks are of quartz-syenite. Major minerals of the acidic volcanic rocks and acidic intrusive bodies are quartz, plagioclase and K-feldspar and of the basic volcanic rocks are plagioclase, pyroxene and olivine. Minor minerals of these rocks are biotite, amphibole, sodic pyroxene, apatite, titanite and zircon. Emplacement of intrusions was in shallow depths as dyke, sill and small stocks and are of A-type. Studies show that acidic volcanic rocks are cognate to intrusive bodies and these rocks are A1 type. Basic volcanic rocks plot in two field on the discriminant diagrams for basalts: oceanic basalts and within plate basalts, therefore two possibilities may reinforced:1) either these basalts are the remanents of early Paleo-Tethys oceanic-crust or 2) these basalts were erupted in post collision and within plate environments perior to acidic eruptions and intruding of acidic masses. With respect to shoshonitic characteristics of these basalts which have been determined on the basis of immobile elements, and considering absence of shoshonitic rocks in oceanic environments the latter idea seems to be more acceptable.                                    


, , , , ,
Volume 16, Issue 2 (7-2008)
Abstract

The Plio–Quaternary volcanic eruptions have made basaltic lavas in NW Iran and Azerbaijan. Basaltic lavas with prismatic structure cover the Plio-Pliostocene volcano-sedimentary or Quaternary alluviums. The studied regions are situated in Azerbaijan provinces in areas of Monnavar, Herris, Ahar, Kaleibar, Mahabad, Salmas, Maku, Marand, Sarab and Zunuz. The studied sample rocks are olivine basalt, trachy basalt and basaltic andesite. These rocks have microlithic porphyritic vesicular, hyallo microlithic vesicular porphery and doleritic textures in thin sections. On the basis of chemical analysis, magma that has formed the rocks had alkaline nature with a Na2O/K2O>1 ratio. The tectonic environment for the samples in discriminate diagrams is post collisional volcanic arc setting. The study of Rare earth elements patterns in diagrams show that, common dip of variations have descending trend and indicate basaltic rocks enriched in LREE and depleted in HREE. Other features of the diagrams are small negative anomaly for Eu, Ta, Nb and distinct positive anomaly for U, Th, La, Rb, Ba, and Cs. The study of rare earth elements patterns display that magma originated from an enriched asthenospheric mantle with garnet in source.


, , ,
Volume 16, Issue 3 (10-2008)
Abstract

The submarine volcanic rocks of Totmaj volcano-sedimentary sequence, located at 25 Km southeast of Kashan city, have suffered extensive non-uniform propylitization. Based on field and petrographical studies, the volcanic rocks can be classified into three alteration zones: chlorite-epidote zone, epidote zone and hematite zone. The secondary hydrothermal minerals formed in the volcanic rocks include epidote-chlorite, calcite and hematite. These minerals have pseudomorphly replaced the primary phenocrysts (e.g. plagioclase, amphibole, and pyroxene) or have filled veins and vesicles. Stable carbon and oxygen isotope analysis of the hydrothermal calcite indicate that the δ18O and δ13C values range from -9.2 to -11.3 and -2.02 to -6.02 per mil respectively. Thus, seawater has been a source for hydrothermal fluid which by circulation into the hot submarine lavas, caused to leaching of some elements such as Fe and Mg from the altered rocks with the exception of epidote-chlorite zone. Also, the seawater circulation leads to an increase in Na ratio in the rocks. Geothermometrical studies on hydrothermal chlorite showed that these minerals have formed at a temperature between 240 to 300˚C. Furthermore, the ranges of temperature stability of coexisting secondary minerals in the volcanic rocks are compatible with those of the green schist facies.


, , ,
Volume 16, Issue 4 (1-2009)
Abstract

Diabases, pillow lavas and basaltic flows in the Nain-Dehshir ophiolites are marked with flat to slightly depleted pattern in REE chondrite-normalized diagram and are characterized by depletion in HFSE and enrichment in LILE. This geochemical behavior can be considered for lavas erupted in arc-related environments. Clinopyroxene in these rocks shows low content of TiO2 and resemble those found in island-arc tholeiites. These characteristics are consistent with back-arc formation during middle to upper Cretaceous, due to the oblique subduction of Neotethyan Ocean along the active continental margin of the central Iranian block.


, ,
Volume 17, Issue 1 (4-2009)
Abstract

Eocene volcanic rocks in south of Asad Abad (north-east of Koohpayeh, Isfahan Province) experienced very low-grade metamorphism (hydrothermal metamorphism), resulting in prehnite, malachite, azurite, zeolite, quartz and calcite crystallization in cavities and fractures. Chlorite (brunsvigite) and amphibole (ferro-actinolite) appear on secondary phases. Augite and labradorite are two main minerals based on electron microprobe analyses and petrography evidence. Composition of minerals in these volcanic rocks and xenoliths are similar. Field and microscopic evidence show that an alternation of acidic and basic magmatism has occurred in the study area. Very low-grade metamorphic minerals formed in neutral to slightly alkaline PH, low CO2, at temperature of 200-400oC and pressure lower than 3 Kbars. Based on calculations, clinopyroxene and plagioclase phenocrysts in basaltstic magma in the study area have formed at temperature of 1100oC and pressure of 3.17 Kbars corresponding to a depth of 11 Km. Chemistry of volcanic minerals and open space fillings minerals is close, both are rich in Ca, Si and Al and relatively poor in Fe, Na, K and Mn. This shows that the volcanites chemistry had important role in composition of metamorphic minerals. On the basis of the geochemical studies and tectonic setting patterns, these rocks are volcanic arc basalts. These basalts belong to the calc-alkaline magmatic series.

Keywords: Basalt, Eocene volcanism, Very low-grade metamorphism, Koohpayeh


, ,
Volume 17, Issue 2 (7-2009)
Abstract

The Javaherdasht Basalts show compositional range from olivine basalts to quartz basaltic andesites. Petrographic studies indicate that the differentiation of clinopyroxene and olivine minerals has main role for lithologic variety of the basalts.The corosion golf, crenated margins and lack of the same colour in the clinopyroxene phenochrysts margins with matrix Pyroxene grains express a nonequilibrium and are petrographic features for crustal contamination of the basalts.The positive correlation CaO,CaO/Al2O3 and Cr with Mg# and CaO/Al2O3 with Sc and the negative correlation Al2O3 with Mg# are geochemical  characters for the differentiation of clinopyroxene and olivine in the magmatic evolution of the area.The high ratios of Ba/Zr and Pb/Nd and low ratio of Ce/Pb and positive correlation of SiO2 and Rb with 87Sr/86Sr and negative correlation of Nd-Sr isotopes display the contamination of these basalts with continental crust.


, , ,
Volume 18, Issue 2 (7-2010)
Abstract

Post-Eocene volcanic rocks of Alborz tectonic zone located in the NE of Qazvin, composed of rhyolite, trchydacite, trachyandesite, andesite, trachybasalt and basalt with porphyritic textures, pyroclastic rocks and volcanic red breccia which are settled alternatively on Eocene pyroclastics and tuffs. The volcanic rocks are enriched in LIL and depleted in HFS elements which may indicate a calc-alkaline volcanic arc. However negative Ti and Nb anomalies as well as enrichment in LILE implied in generation of these rocks by a low grade partial melting of an enriched mantle on a subduction zone. The presence of a negative Ba anomaly in rhyolitic to andesitic rocks is a common characteristic for the upper continental crust and is a typical feature for high-K suite which reveals the role of upper crust contamination.


, , , ,
Volume 18, Issue 4 (1-2011)
Abstract

Plio-Quaternary volcanic eruptions in southeast of Nehbandan are composed of basic rocks, overlying the Late Cretaceous flysch-type and younger alluvium deposits. Petrographically, these rocks are basalt, basaltic andesite and andesite. These lavas are characterized by porphyritic, microlitic-porphyry, trachytic and glomeropophyritic textures. They contain plagioclase, clinopyroxene (augite), olivine and amphibole (hornblende) phenocrysts and fine-grained plagioclase-clinopyroxene microlite in groundmass. Geochemically, these rocks are calc-alkaline and represented by 47.8 - 57 wt. %. SiO2 and about 17 wt. % Al2O3. In chondrite-normalized REE diagram, these rocks show enrichment in LREEs and depletion in HREEs. In primitive-mantle normalized trace elements diagram, they are characterized by Nb (and P, Ti, Zr) negative anomalies and positive anomalies in Pb, K, Ba and Sr. These chemical characteristics of Nehbandan Plio-Quaternary lavas associated with high LILE/HFSE and LREE/HREE ratios are consistent with derivation from a subduction environment. Y/Zr ratio of these rocks is similar to that of continental arc lavas. Discrimination tectono-magmatic diagrams suggest an active continental margin for the formation of Nehbandan Plio-Quaternary lavas.


, , , ,
Volume 20, Issue 3 (10-2012)
Abstract

The study area is located in the central part of the Siahrood geological map, Kharvanagh of Ahar town, in the East Azerbaijan Province. The volcanic rocks of the Kharvanagh area include trachybasalt, trachy-andesi-basalt and trachy-andesite. The main minerals in the rocks are plagioclase, pyroxene, olivine and hornblende and the main textures are microlitic-porphyry. At the contact between the volcanic rocks and Miocene sandstones, epidote and calcite are formed due to thermal effect. Based on the geochemical data of major and trace elements, these rocks belong to High K alkaline to shoshonitic magmatic series. The absence of distinct Eu anomaly and relatively enrichment in LILE (Ba, Rb, and K) and LREE in these rocks indicate a back arc tectonic setting. Also enrichment of incompatible elements can be related to mantle metasomatism or contamination by continental crust. The chemistry of back arc rocks is relatively complicated and the geochemical features depend on the degrees of partial melting, heterogeneity in the sources mantle, etc. Considering the geological features and the Miocene age of the rocks, it can be concluded that the parental magma belongs to extensional basins magmatism, which produced from partial melting of the garnet lherzolite mantle.


, , ,
Volume 20, Issue 3 (10-2012)
Abstract

In southeast of Bardsir (Kerman Province), there is a volcanic complex belongs to Uromieh-Dokhtar volcanic belt.This complex mainly contains basaltic-andesite and basalt lava flows with the Eocene age, alternative with pyroclastic rocks. Petrographic evidences include zoning, sieve texture and rounded crystal in plagioclase and pyroxene phenocrysts disequilibrium conditions between crystals and host melts during crystalization. Geochemical characteristics indicate that these rocks belong to calcalkaline domain. The highly enrichment of LREE compared to HREE, high contents of LILE relative to HFSE and significant anomalies of Nb, Ti and P suggest a subduction-related volcanism. These features indicate that these rocks have probably been generated in an enriched mantle with a low degree of partial melting in a subduction zone. Mineralogical, textural and geochemical investigations on volcanic successtions in this area show that systematic chemical changes have been occurred in shallow magma chamber and these changes have been affected on mineralogy, texture and chemistry of related lava flows.


, ,
Volume 21, Issue 2 (7-2013)
Abstract

Outcrops of the Upper Ordovician igneous rocks, as basaltic lava and microgabbroic dyke and sill, present within the Abarsej and Ghelli formations in north and southwest of Shahrood. These rocks have basaltic, trachybasaltic and basaltic trachyandesitic composition with alkaline nature. Their parallel patterns on the primitive mantle and chondrite normalized spider diagrams indicate the common source of these rocks and the role of fractional crystallization in their generation. These rocks plot on the field of alkali basalts related to intracontinental rift on various discrimination tectonic setting diagrams. This tectonic setting corresponds to paleogeography of the Alborz during early Paleozoic (occurrence of Turan intracontinental Paleotethys rift) in Ordovician- Silurian times. Geochemical investigations indicate the magma forming of these basaltic rocks generated from 14-16% partial melting of an enriched garnet peridotitic astenospheric mantle source in 100-110 km depths. This magma has not contaminated by continental crust during ascending to the earth surface.


, , , ,
Volume 22, Issue 2 (7-2014)
Abstract

The studied volcanic and pluton rocks are located in west of Nir city in the Ardebil Province and south of Sabalan volcano. Volcanic rocks in the studied area are display basaltic to trachy-andesite composition with microlitic porphyry texture. The main minerals of basalt to trachyandesite rocks are plagioclase, pyroxene and olivine. Bordering to volcanic units, pluton of microgabbroic to microdioritic is exposed. These rocks have a granular texture with essential minerals of plagioclase; pyroxene, olivine and biotite. Multi-element diagrams, normalized to chondrite and primitive mantle, indicates LREE and LILE enrichment and HREE and HFSE depletion such as Ti, Nb and Ta in the studies samples. Based on trace elements ratios diagrams La/Sm vs. La and Zr/Nb vs. La/Yb, parental magmas may have been generated from low degree partial melting of subcontinental mantle source with garnet-lherzolite composition. Post-collisional geotectonic environment of the studied samples and trace element geochemical evidence indicate that produced magma formed from a metasomatic mantle due to ancient subduction.


, ,
Volume 22, Issue 4 (1-2015)
Abstract

The Plio- Quaternary volcanoes are located in the NE-Qorveh (Kurdistan) in the Qorveh-Takab volcanic belt, in the Hamedan-Tabriz Zone (HTZ). The volcanic rocks consist of basalt to olivine-basalt. The electron microprobe (EMP) analyses of pyroxenes show occurrence of one type of clinopyroxene, as diopside (Fs 2.65-6.42 En 40.44-50.47 Wo45.97-53.14) with Mg # = 84-98. The compositions of the pyroxenes suggest that rocks belong to alkaline-subalkaline magmatic series.  Considering different methods of geothermometry of clinopyroxene, the temperature of  crystallization stage for pyroxene was 800-1300°C. Distribution of Al in octahedral and tetrahedral sites of pyroxenes displays that this mineral is crystallized from a magma with ˂ 10% water contents, in low-medium pressure which is in accordance with their formation the depth of 18-30 km. Fe+3 content of clinopyroxenes  implies crystallization in high oxygen fugacity condition.


, , ,
Volume 23, Issue 2 (7-2015)
Abstract

Soltan Maidan Basaltic Complex consists of a thick succession of basaltic lavas associated with some thin sedimentary interlayers that are exposed in the northwest to northeast of Shahrood. Soltan Maidan basaltic rocks has been generated from magma with transitional to mildly alkaline nature and derived by 14-20 percent partial melting of an enriched garnet peridotitic mantle source in an intra-continental rift setting during Late Ordovician to early Late Silurian. These basaltic rocks are relatively uniform in mineralogical composition and they have undergone moderate to high degrees of alteration. Labradorite plagioclase and augite clinopyroxene are major minerals, and Fe-Ti oxides as titanomagnetite and ilmenite form accessory minerals in these rocks. Thermobarometry results on the clinopyroxenes indicate that they have crystallized in temperatures between about 1100oC to 1200oC, with pressures less than 6 kbar and show that they have crystallized in magma chamber/chambers located at depths less than 23 kilometers.


Barzgari, Ghasemi, Rezaei-Kahkhaei,
Volume 26, Issue 1 (4-2018)
Abstract

The Kahak- Abbasabad Eocene magmatic belt is situated in the northeast edge of Central Iran Zone and extended from Davarzan in the west of Sabzevar to Mayamey in the east of Shahrood. Rock units of the study area include an alternation of basic- intermediate volcanic rocks (olivine basalt, basalt, Trachybasalt, trachyandesitic basalt, trchyandesite and andesite) and pyroclastic–sedimentary rocks (varieties of tuffs, breccia, agglomerate, sandstone, shale, conglomerate, nummolitic limestone and tuffuceous limestone), which belong to Upper-Middle Eocene, and sedimentary rocks of Oligocene and Quaternary. The volcanic rocks of this belt form a continuous fractional series, originated from a same parental basaltic magma. Hence, the basaltic-andesitic lava flows are pyroxene porphyry, plagioclase porphyry and pyroxene-plagioclase porphyry; they are favorable for Crystal Size Distribution (CSD) studies. According to calculations of this research, plagioclase and pyroxene phenocrysts of the volcanic rocks have been grown in magmatic chamber in time range of 86.20 to 118.01 years with nucleation rates from 1.48×10-10 to 1.56×10-10 mms-1and in time range of 3.21 ×104 to 6.34×104 years with nucleation rates from 0.55×10-3 to 2×10-5mms-1, respectively.
Azad Karimi, Ali Ahmadi, Abdolreza Partabian,
Volume 26, Issue 4 (1-2019)
Abstract

One of the most prominent cases of the study of alteration processes and their effect on geochemistry is the ophiolite investigation. The Marivan-Palangan ophiolite (MPO) complex is a part of the Neotethyan ophiolites, which situated in the Kurdistan Province, western Iran. The studied samples reveal the occurrence of the secondary minerals such as epidote group, chlorite, zeolites, and less calcite and iron hydroxides in the form of veins, vesicles and fractures infilling, and replacement phases. The element concentration variation versus Loss on ignition (LOI), normalization of the samples as to fresh sample in the study area and standard sample, and immobile element modeling indicate that element contents changes vary depending on the degree of alteration so that the concentration of Large-Ion Lithophile Elements (LILE) such as Rb, Cs, K, Ba, and Na shown a significant increase. CaO and FeO oxides are relatively depleted. Light Rare Earth Elements (LREE) display slight enrichment, while Middle Rare Earth Elements (MREE) and Heavy Rare Earth Elements (HREE) are almost constant. Therefore, in evaluation of the geochemical characteristics of extrusive section of the MPO complex, the effect of alteration on the changes in the concentration of elements, in particular LILEs, CaO, FeO and also LREEs should be considered.
Maryam Yazdani,
Volume 26, Issue 4 (1-2019)
Abstract

The Piranshahr ophiolitic complex is located in NW Iran, and at north west of the Piranshahr town. Tectonically, the NW Piranshahr ophiolitic complex is severely mélanged and the boundary of different units in this complex is undistinguishable. Piranshahr ophiolite includes ultramafic, mafic, sedimentary and metamorphic rocks. Mafic rocks with basalt and diabase compositions are exposed in several parts of the region. In this paper, clinopyroxene geochemistry of basaltic rocks are studied and compared with the similar rocks from other supra-subduction zone-type of Eastern Mediterranean ophiolites. Clinopyroxenes display diopsitic compositions within the range of (En0.39-0.59 Fs0.01-0.05 WO0.50-0.57), calc-alkaline nature with low Ti and high Mg content. High-Mg and low-Ti magma suggest a supra-subduction zone setting for the formation of the Piranshahr ophiolitic basalts. According to the distribution of aluminum in clinopyroxenes, these minerals have formed at high oxygen fugacity and water content about 10 percent. The clinopyroxenes of the Piranshahr Ophiolite have similar chemical compositions to those of the other supra-subduction zone-type Eastern Mediterranean ophiolites (e.g., Troodos, Varinous, Pindos and Oman ophiolites) that show arc affinity.
Seyed Mohammad Hosseini, Alireza Davoudian Dehkordi, Nahid Shabanian Borojeni, Hosain Azizi,
Volume 27, Issue 1 (4-2019)
Abstract

Amphibolite rocks with mylonitic texture exposed in the NE of Yan- Cheshmeh village (SE of Zayandeh-Rud Lake). Mineralogy of rocks include amphibole, plagioclase, quartz, rutile, clinozoesite, chlorite, titanite, biotite and opaque. Amphiboles are seen as fish. Basic igneous rocks are protolith of the amphibolites that have subalkaline nature. Ni (299-370 ppm), Cr (1169-1900 ppm) and SiO2 (44.91-49.20 %Wt) contents highly resemble to unfractionation magmas. Chondrite normalized REE patterns exhibit pronounced LREE enrichment relative to HREE without Eu anomaly. Low TiO2, Zr, P2O5 and Nb/Y contents with enrichment of LREE and negative Nb anomaly are pronounced characters of continental flood tholeiitic basalt within plate magmatism. Tholeiitic affinities, low values of alkali elements, high MgO, FeO, Cr and Ni contents suggest high partial melting in an extensional setting of continental within-plate with rapid decrease in pressure, resulting in high rate of partial melting and quick uplift which are effective factors for the formation of basaltic protolith of the amphibolites.   
Mahnaz Khodami, Behnaz Bakhtiari,
Volume 27, Issue 3 (10-2019)
Abstract

Plagioclase is the most abundant mineral in basaltic andesites in the north Gavkhouni. Olivine and pyroxene are the other rock forming mineral there. In their 3-dimensional shapes, they are unequal and varies between bladed to prolate. Plagioclase sometimes exhibit dusty texture, oscillatory zoning and sinusoid growth. Based on crystal size distribution data, the rate of crystal nucleation of plagioclase varies between 2.77*10-8-3.07*10-8 mm-3s-1 in 71.78 - 17.77 years. The results indicate the higher nucleation rate, rapid cooling and a short crystal residence time in the magma chamber. The crystal size distribution diagrams show the high frequency of smaller crystals and the coarsening of the average crystals. However, the presence of two populations of plagioclase indicates the interfering of new magma with the same chemical composition and new crystal population into the magma chamber. This event can increase the volume of the magma chamber pressure and eruption of the magma.

Page 1 from 2    
First
Previous
1
 

© 2025 CC BY-NC 4.0 | Iranian Journal of Crystallography and Mineralogy

Designed & Developed by : Yektaweb