جستجوی مقالات مرتبط با کلیدواژه « دیوپسید » در نشریات گروه « زمین شناسی »

Dokhan region is located in the west of Nobaran (Saveh), between Urumieh-Dokhtar and Sanandaj-Sirjan zones. In this study, the geochemistry of whole rock and the chemistry of clinopyroxene, olivine and nepheline minerals in Dokhan Quaternary volcanic rocks have been studied. From Petrographic aspect, the studied rocks are mostly melanephelinite and olivine melanephelinite. The chemical composition of rocks include foidite, tephrite and basanite. These rocks are relatively rich in CaO and MgO and poor in SiO2 and Al2O3. Their olivine is chrysolite and clinopyroxene is diopside. The parent magma of these rocks is derived from a metasomatized garnet lherzolite mantle that is somewhat contaminated with the continental lithosphere. Temperature-pressure measurement of these rocks using the composition of minerals shows the temperature of 1200° C to 1250 ° C and pressure of 5 to 10 Kb. These rocks are probably formed in the intercontinental environment after the subduction of Neotethys and the collision of the Africa-Arabia and Eurasian continents.

Saray volcano is an extinct volcano and is located in the east of Urmia Lake. This volcano mainly consists of Leucititic lava flows and their related pyroclastic materials forming a Sequence which repeated more than five times. Leucite phonolitic dykes, Lamprophyric (Minette, Monchiquite and Spessartite) lavas and dykes, Trachytic domes and dykes, Syenitic dykes and a small syenitic stock are other rock types of Saray volcano. Since clinopyroxene is present in all rock types of this volcano, mineral chemistry study of clinopyroxenes in all rock types of Saray volcano, could help us to explain the relationship between different rock types. Clinopyroxenes of Saray volcano have diopside, salite and fassaite compositions. The majority of studied clinopyroxenes crystallize under 3-4 kb pressure and 1150 centigrade temperature. Tectono-magmatically speaking, these clinopyroxenes were mostly formed within plate basalts. Although the composition of rock types of Saray volcano is very different, almost constant composition of clinopyroxene in all rock types, show the same origin for all clinopyroxenes. However, it can be concluded that all rock types have the same origin.

The Bozqush, Kaleybar, and Razgah foid-bearing syenites are located in East Azarbaijan province, NW Iran. Mineral chemistry determined for the amphiboles and clinopyroxenes of intrusions to specify elemental exchange, magmatic affinity, and tectonic setting. Chemical composition of the amphiboles varies from magnasio-hastingsite to ferro-pargasite. This study shows that the Kaleybar amphiboles are richer in Ca+IVAl than the Bozqush ones and CaIVAl=SiNa exchange is the main substitution. According to mineral chemistry, the clinopyroxenes are diopside. Considering the atomic proportion of Wo, En and Fs in the studied clinopyroxenes, variation in end-member components mostly involve the interchange of En and Fs. Moreover there is M2CaM1(Fe2+,Mg) = M2NaM1Fe3+  exchange in the clinopyroxenes. The Composition of clinopyroxenes and amphiboles indicate that they were derived from volcanic arc miaskitic magma at relatively low pressures. Based on Al and Ti contents, thermobarometry of the amphiboles show pressures of 6±1 and 7±1 kbar for the Bozqush and Kaleybar intrusions respectively and temperature of 900±100 ˚C.

The studied volcanic alkaline rocks with 32.7+6 Ma years age are croped out along the south – east of Urumiyeh - Dokhtar Volcanic Belt in Kerman province. Based on the TAS classification these rocks are divided in to tephriphonolite and phonolite which belong to high-K alkaline rocks. These rocks are composed of pyroxene, plagioclase, sanidine, nepheline, analcime and titanomagnetite minerals. Diopside is the only pyroxene identified in the study area. In the most of the phenocrysts the amount of MgO in the core is more than the rims while the amount of FeO is high in the rims. This trend shows a normal fractionation during magmatic evolution. The composition of pyroxene phenocrysts is from WO47.8 En38.8 FS13.4 to WO45.6 En35.7 FS18.8. Sanidine is the only K-feldspar present in these rocks and has a composition ranges from Or62.7 to Or93.8. Most of the plagioclase phenocrysts have Ca-rich cores and more Na-rich rims which is attributed to normal magmatic fractionation. The composition range of plagioclase is An50.83 to An59.2. Trapezohedrs of analcime comprise up to 40% of the rocks and the composition of the analcime trapezohedrs are remarkably homogeneous. The analcime is interpreted as having formed by ion-exchange pseudomorphous replacement of primary leucite, either during cooling of the lava or shortly afterwards. Titanomagnetite is a very common equant grain in groundmass of all the studied samples. The Fe-Ti oxide crystals are relatively Ti-rich and are classified as titanomagnetite.