جستجوی مقالات مرتبط با کلیدواژه "whole rock chemistry" در نشریات گروه "زمین شناسی"

Makran amphibolites are exposed in different locations in the northern Makran ophiolitic belt. Based on lithological studies and mineral assemblages in these rocks, they are containing ordinary amphibolite (oriented and massive), garnet-pyroxene amphibolite, epidote-garnet amphibolite and marble. The minerals that made up ordinary amphibolites (oriented and massive) include amphibole, plagioclase, zircon apatite, quartz and sphene. In addition to these minerals, garnet and pyroxene are found in garnet-pyroxene amphibolites. In addition, epidote, garnet and pyroxene are found in epidote-garnet amphibolites. Also, marbles are containing calcite with a distinct cleavage, quartz and amphibole. Geochemistry of amphibolites shows that these amphibolites are of igneous origin with basaltic protolith that originate from an enriched mantle. Amphibolite samples of the region have relatively similar composition based on the diagrams of changes of normalized rare earth elements to chondrite and N-MORB and are also similar to mid-oceanic ridge basalts (MORB) as well as within plate volcanic zone (WPVZ) basalts in terms of geochemical properties.

Dorojin area in the Southwest of Ardestan city is part of the Urmia-Dokhtar magmatic zone. In the area of study, the intrusion of the Early Miocene granodiorite into the Middle-late Eocene sedimentary-volcanic complex caused the formation of hydrothermal propylitic alteration zones with green color. The vlcanics range in composition from basalt-andesite, trachyandesite, andesite, to rhyolite. These rocks under study are characterized by LREE and LILE enrichment compared to HFSE, calc-alkaline nature, and meta-aluminous composition related to the subduction zone. The most abundant mineral in the alteration zones is epidote formed by saussuritization of plagioclase. Average Pstacite [Fe3+/(Fe3++Al)×100] composition is 22% (PS22). Comb and radial textures are its remarkable textural features. Calcite is the second most abundant mineral in alteration zones. The nodules tourmaline is chemically dravite and alkaline. They have FeO/ (FeO+MgO)<0.6 and lower Al amount, high Mg, and low X site vacancy. Dravite composition and the Mg abundant reflect their alteration origin. Hence, they are regarded as hydrothermal tourmalines.  Titanite with CaO<25wt%, Al2O3<2wt% as well as Al2O3+TiO2 versus CaO, and Al/Fe on variation diagrams are indication of hydrothermal alteration. Ore mineral potential in the region points to the effect of hydrothermal fluids.

The amphibolites of east Salmas, as one of the widest units of the metamorphic complex, are located in the northwest of Sanandaj-Sirjan zone, which according to field studies are mainly oriented and foliated amphibolites. Based on microscopic studies, amphibolites include amphibolites, biotite-amphibolites, epidote-amphibolite, biotite-epidote-amphibolite, tremolite-actinolite-amphibolite, and biotite-clinopyroxene-amphibolite. Amphibolite specimens of the region have maximum parallel pattern based on the variation diagrams of rare earth elements normalized to chondrite, EMORB and primary mantle and are similar to intra-plate basalts in terms of geochemical properties. According to the results of whole rock chemistry, the study amphibolites are mainly ortho-amphibolites with a basaltic protolith and calc-alkaline magmatic series, which are located in the intra-plate tectonic position.

East Salmas gneisses are located in the northernmost parts of the Sanandaj-Sirjan zone and are seen in banded and deformed with the 6 different groups of lithological diversity. Their protolith is of paragneiss type with arkosic sedimentary rock type.Texturally, they are immature. Based on this study, chemical maturation trend of protolith of the present investigated gneisses are in the arid to semi-arid boundary climatic conditions with average granite composition and chemical alteration index of about 55%. The linear trend in the diagrams of major oxides variations of the parent gneisses in the region confirms the partial melting and granitization of the genesis in these rocks. According to the pattern of normalized diagrams, these rocks show good agreement with typical paragneiss diagrams of the world. Investigating the various diagrams reveals that the tectonic setting of the gneisses is mainly of continental margin type with passive sedimentary trend.

The purpose of this study is to explore the influence of whole rock chemistry of metamorphic protolith on the crystal size distribution curve of garnet in metapelites. With this aim, perfect mosaical photograph from two groups of metapelites have been prepared: regional (Shahindezh schists) and contact (Dorbeh Oshnavieh aureole) metamorphic rocks image processed and their patterns illustrated. They show that the nuclei numbers in the hornfelses are one fourth of schists, but when they start to grow, it is more than 40 times. These content in addition to high degree of overstepping during regional poly-phase metamorphism, show the important role of effective water fluid presence at the contact aureole and inhibitor role of it at nucleation which help ion transportation on the nucleation sites. Considering the similar composition of garnet in two groups (almanden), it is the symptom of suitable whole rock composition of hornfelses per schists to garnet grew.

The Anarak ophiolite, with E-W trending, located at north of Anarak. In addition to the gabbros in Anarak ophiolite sequence, intrusion of metasomatized gabbros injected into the ophiolite of Anarak in the form of stocks and dykes. metasomatized gabbros are younger than Anarak ophiolite and older than Anarak metamorphic assemblage and contain diopside, augite, actinolitic hornblende, actinolite, tremolite, phlogopite, albite, oligoclase, pycnochlorite, penninite, epidote, garnet, sphene, prehnite, calcite and opaque minerals. Penetration of seawater into the lower crust and upper mantle led to high temperature matasomatism in the gabbros. Positive Pb anomaly and negative Ta,Nb and Ti anomalies in whole rock and minerals chemistry of clinopyroxene and amphibole are markers of volcanic arc tectonic environments and association with subduction zones. Crystallization temperatures of diopside, phlogopite, actinolitic hornblende, actinolite and chlorite are 1150-1200 °C, 750 °C, 600 °C, 450 °C and 360-540 °C respectively.

Asalem metamorphic complex consists mostly of metabasite, metapelite and serpentinite. Metabasites display metamorphic features of greenschist and blueschist facies. Greenschist facies rocks that found as both foliated and massive types contain mineralogical assemblage of actinolite, chlorite, albite and epidote. Blueschists contain mineralogical assemblage of sodic amphibole, epidote and phengite. Whole rock analyses of the metabasites indicate basaltic to andesitic composition with mainly calcalkaline nature of their protolith. According to the discrimination diagrams of tectonomagmatic setting, the protolith of investigated metabasites has been islands arc and somewhat mid ocean ridge. The patterns of rare earth elements and spider diagrams of the Asalem metabasites resemble to the basic and intermediate magmatism of islands arc or suprasubduction setting as well. Greenschists and blueschists facies rocks of the Asalem metamorphic complex have been probably equivalent to islands arc or young and hot oceanic crust of suprasubduction zone setting. This portion of oceanic basin unlike the subducted even and thick oceanic lithosphere of Paleotethys during accretion in the shallower levels of accretionary prisms, have underwent metamorphic conditions of blueschist and greenschist facies and finally gave rise to the formation of the metabasites of the Asalem metamorphic complex.

Gasht metamorphic complex is situated in the Talesh mountains of western Alborz range. This metamorphic complex consists mainly of metapelite and metabasite. Metabasites display metamorphic conditions of amphibolite and greenschist facies. Mineralogical paragenesis of greenschists are amphibole, feldspar and epidot and clinopyroxene occures as accessory minerals. The amphibolites of Gasht metamorphic complex are both granular and foliated types. Rock forming minerals are andesin and magnesiohornblende and accessory minerals contain sphene, ilmenite and clinopyroxene. Biotite formed as a result of amphibole altration. Thermobarometry results, that calculated by different thermobarometry methods, show temperature rangs between 550 to 750°C and pressure between 6 to 8 Kb that are nearly equivalent to geothermal gradient of 30°C/Km. These metamorphic conditions and geothermal gradient are resemble to the adjacent metapelites. Whole rock chemistry of metabasites from Gasht metamorphic complex display geochemical characteristics of subduction setting basic magmas. Probably, greenschists and amphibolites of Gasht metamorphic complex are indicative of basic magmatic arc products that resulted of Paleotethys oceanic basin subduction beneath edge of  the Turan plate and has experienced continental active margin or collision metamorphism.