جستجوی مقالات مرتبط با کلیدواژه "پرآلومینوس" در نشریات گروه "زمین شناسی"

Qareh-Dash rhyolites from the Shahindej area are peraluminous rocks with high SiO2 and K2O contents. These rocks are mainly composed of quartz, K- feldspar and rare plagioclase phenocrysts in a fine-grained K-feldspar rich matrix. Geochemically, Qareh-Dash rhyolites show enrichment in LREEs and LILEs and depletion in HREEs.
Field studies, textural and petrographical relations, along with whole rock geochemistry, demonstrate that the parental magma of the Qareh-Dash rhyolites was originated from the crust. The composition of the parental magma was modified due to fractional crystallization of plagioclase and titanomagnetite evidenced by negative Eu, Sr and Ti anomalies in multielement diagrams. The chemical characteristics of Qareh- Dash rhyolites such as Rb/Nb, K/Rb, Rb/Sr, Rb/Ba and Ga/Al ratios are similar to A-Type granites/ rhyolites associated with post- collision tectonic settings. According to Precambrian age for the Qareh-Dash rhyolites, formation of these rocks might be related to extensional phases which were probably taken place after closure of proto- Thetys Ocean.

The studied mylonite granites are exposed as small bodies at the west of Qushchi in the West Azarbaijan Province. These rocks contain orthoclase, microcline, plagioclase, fish muscovite, tourmaline ± garnet as porphyroclast. The matrix is composed of recrystallized quartz, fine grained muscovite and low abundant epidote. According to petrographic and mineral chemistry studies and BSE images, tourmaline and garnet are chemically zoned. The mineral chemistry characteristics of core of tourmaline and garnet crystals indicate magmatic origin for them, while the composition of rim part for these minerals, especially for garnet, is consistent with metamorphic origin. Presence of tourmaline muscovite ± Mn-rich garnet in the West Qushchi mylonite granites and occurrence of these rocks as small bodies within metasedimentary rocks suggested that the west Qushchi mylonite granites are formed by low grade partial melting of the metamorphic rocks. On the basis of the mineral assemblage, it seems that the studied rocks belong to Mg-poor peraluminous leucogranite type rocks.

The investigated granite intrusion is located at the north of Ayghalesi village, east of Takab area. The Ayghalesi granite has been intruded into the Eocene sandstone and conglomerate rocks and low grade metamorphic hornfelses have been metamorphosed host roocks. The main constituent minerals are K-feldspar, plagioclase, quarts and muscovite. Garnrt occurs at minor amounts. The main texture is granular but the pegmatitic texture, myrmecite, graphic and pertite occur as minor ones. Chemically the rocks are granite on the various classification diagrams. The Ayghalesi intrusion body has S-type peraluminous with calc-alkaline affinities. They are calcic-alkali to alkali-calcic on the base of modified alkali lime index (MALI). On the base of discrimination diagrams the investigated rocks has been formed related to the syn-collisional tectonic setting correlated to the Central Iranian and Arabian continents.

The Mishu garnitoid complex, located NW of Mishu Mountains, southwest of Marand and northwest of Iran (East Azarbaidjan), and intruded into the metamorphosed Precambrian rocks (Kahar Formation). Based on petrographic studies, the pluton composed of acid rocks including granodiorite, monzogranite, syenogranite and two-mica granite, all cut by acid and diabasic dykes. The presence of surmicaeous xenoliths are evidences of refractory minerals and restite. Petrographic and geochemical studies indicate that the Mishu plutonic rocks can be classified as S-type granite having calc-alkaline and peraluminous nature. On chondrite and primitive mantle-normalized diagrams, almost all the rocks show enrichment in LILE and LREE, HREE, HFSE depletion as significant negative depletion in Nb, Ta, Eu, Ti, Sr and Ba, which is typical of calc-alkaline magmatism from subduction-zone environment. The geochemical data and position of the studied samples on discriminative tectonic diagrams show that the rocks are compatible with orogenic granitoids.

The Kuh Gabbri granitoide stocks stands out as the most extensively fractioned granite (Rb= 424-749, Sr= 8-37, Ba= 3-110 ppm) located in the Rafsanjan depression and Urumieh- Dokhtar belt. These granites show a strong enrichment in some rare metal contents such as Y, Yb, U, Ta, and Sc. The petrography and geochemistry reveal that these are classified as I- type per aluminous leucogranite, P- poor (P2O5= 0.01 0.03%) and Na2O- rich (3.1-4%).The Gabbri granites show chemical features convergent to A- type granite; these are explained by extensive fractional crystallization of a P-poor, I- type granite magma. These are located in the area of within plate granite and extensional area. The petrography and geochemistry show Gabbri granite are produced of melting continental crust.