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

The Saray volcano is located on the East of the Urmia Lake. This extinct stratovolcano mainly consists of Leucitite lavas and related pyroclasts. Dykes with composition of Leucite phonolite, Lamprophyre, Trachyte and microsyenite intruded into leucitite. Field evidences indicate that minette and trachytic dykes intruded into each other. A microsyenitic stock and dykes outcrops in the central valley of this volcano. The trachytic pyroclasts eruption is the last activity of the Saray volcano and probably caused the destruction of volcanoe’s caldera and formed its current shape. Leucitites maimly consist of leucite and clinopyroxene phonocrysts, minettes consist of biotite and clinopyroxene phenocrysts and trachytes consist of biotite, sanidine and clinopyroxene phenocrysts. The Saray magmatism has potassic to ultrapotassic nature and its geochemical features indicate that this magma should be originated from a micaceous garnet clinopyroxenite mantle. The coexistance of leucitite, lamprophyre and trachyte, could not be explained only by the function of fractional crystallization in leucitite magma. Sanidine is the most abundant feldspar in the Saray volcano. Sanidine megacrysts crystalize in a medium size magma chamber with continuing temperature cycling, so that the magma temperature remains close to the liquidus temperature of the K-feldspar for a long time.

In the Mahabad region accompaniment of trachytes and trachy-andesites with OIB-like alkali-basalts are shown. Trachytes at the Soltan Mountain heights, trachy-andesites as darker enclaves in it and alkali-basalts in the three sites, Khatton Bagh, Bardarashan and Badam are outcropped. Alkali-basalts have shoshonitic, met-aluminous and OIB-like characteristics with LREE/HREE enrichment and generate at deep garnet peridotitic source. Trachytes and its intermediate trachy-andesite enclaves at the Sltan Mountain with shoshonitic, per-aluminous affinity have high LREE/HREE ratios with HFSE and Ti depletion and continental arc relevant signatures. The Soltan Mountain trachytes have adakitic nature which accompany with the High niobium basaltic (HNB) affinity of Badam, Barderashan and Khatoon Bagh basalts of Mahabad and their similarities to Ghorveh HNB could clarify the relationship between adakites and basalts along the Neo-Tethys post collisional activities. Computer modelling clarify the fractional crystallization opportunity for the intermediate to acidic terms production from mantle basaltic liquid. In addition, very high contents of incompatible elements in the most evolved rocks suggest the occurrence of open-system magmatic processes. Continuous fractional crystallization from a primitive basaltic source, similar to post-plateau coeval basalts, towards acidic terms combined with small rates of assimilation (AFC) in a shallow magmatic reservoir, is best explains for the young volcanic association in the Mahabad. These phenomena are occurred after Neo-Tethys closure at the Quaternary.

The rhyolitic and trachytic domes in south of Dastgerd in Qom province, contain garnet phenocrysts. Based on the micro-probe analysis, garnets are almandine rich, and poor in other components. Considering the whole rock chemistry, the magmas of the area have continental origin or at least contaminated with a continental source. Based on chemical composition of biotites, the magmas are peraluminous with continental origin. Several evidences such as lack of any metamorphic xenocrysts or xenoliths, homogeneous composition of garnets, compositional equilibrium between garnet and biotite, lack of metamorphic inclusions in garnet and lack of reaction rims, in addition with the origin of host rocks and whole rock composition, indicate that garnets in the area could be crystallized from a peraluminous magma and they are igneous garnets.