جستجوی مقالات مرتبط با کلیدواژه "قوس قاره ای" در نشریات گروه "زمین شناسی"

The Zagros orogeny occurred with the opening of Neotethys, subduction and closure of ocean between Arabian and central Iranian microplate. The Sanandaj-Sirjan Zone is a metamorphic–magmatic belt, associated with the Zagros Orogeny as parts of the Alpine. The dominant plutonic rocks in the Sanandaj-Sirjan zone are considered to be a response to the subduction of the Neotethys. This paper discusses the mineral chemistry of amphibole and feldspar in the appinitic and granitic rocks which are exposed in SW of Nagadeh area. The appinite rocks consist of a group of coeval plutonic rocks, ranging from ultramafic to felsic in composition in which hornblende and feldspar are the dominant minerals, and typically occurs both as large prismatic phenocrysts and in the finer grained matrix. The composition of minerals in the appinitic and granitic rocks are similar,  and the composition of amphibole is magnesiohornblende and feldspars is orthoclase. Both magmas have calc alkalic characteristics with arc continental tectonic setting. They have derived from the crustal-mantle mixed sources and high magmatic oxygen fugacity. The appinitic rocks and granites have not coeval. Thermobarometric estimates using amphibole data show that the appinitic-granitic magmas crystallized in two storage zones at pressures of 3-5 kbar (shallow crust) and 1-3 kbar (upper crust). The appinitic rocks were derived from partial melting of lithospheric mantle that had been metasomatized by slab-derived fluids, in the shallow crust during Neo-Tethyan slab breakoff. Generally, it is difficult for the hydrous basaltic magmas to ascend through the continental crust, therefore the underplating of the crust by these magmas supplied sufficient heat and water to facilitate the partial melting of the overlying crust to produce the granites associated with the appinite.

The study area is located in the south of Qorveh (Kurdistan Province), strcuctually in the Sanandaj-Sirjan zone. Based on field observations, the study dykes are type of sin-plotonic dykes and based on petrographical studies mafic and dioritic dykes are included gabbro, gabbro-diorite, diorite, monzodiorite and quartz-monzodiorite rocks. Their main minerals are clinopyroxene, orthopyroxene, hornblende, plagioclase, K-feldspar and quartz. Apatite, esphene, zircon and opaque minerals are their accessory minerals. The discrimination diagrams reveal all of the dykes belong to volcanic arc related to an active continental margin setting. It is implied by enrichment of LILE (such as Cs, Rb, U&Pb), depletion of HFSE (Nb, Ba) and high LILE/HFSE in the spider diagrams. The enrichment of LILE and Pb show the crustal contamination. Concentration La/Nb and La/Ta rations as well as the enrichment of LREE and LILE reveal that dykes were derived from enriched lithospheric mantle. I addition, enrichment of LREE elements relative to HREE represent that there are garnet phase or amphibole in source.

Precambrian basement of Central Iran in Lakh Bargheshi area from SW Bardaskan mainly consists of metapelite, metabasite and mylonitic gneiss and has been invaded by Lakh Bargheshi granitic body with the age of Ediacaran-Cambrian. Metapelites mostly are Garnet schist type and encompass mineralogical paragenesis of garnet biotite muscovite quartz feldspar. Metabasites contain of garnet amphibolite and garnet-epidote amphibolite and show mineralogical paragenesis of amphibole feldspar garnet ± quartz ± epidote± whitemica ±rutile ± sphene ±ilmenite. Metamorphic conditions that obtained by Thermocalc software, petrogenetic grids and conventional thermobarometries are compatible for both metapelitic and metabasitic units and include pressure between 7.1 until 12.3 Kb and temperature between 482 until 661°C that nearly are equivalent of high pressure amphibolite and epidote amphibolite facieses that are dominant in the lower continental crust. Epidote and garnet-bearing granitic body of Lakh Bargheshi and host metapelites and metabasites probably representing thickened continental arc induced by Prototethys subduction beneath Iran plate.

The Malayer plutonic complex is located in the northern Sanandaj-Sirjan zone of the western Iran. An intrusive body with granodioritic component known as the Samen granodiorite is in the center of this complex، which is accompanied by other granitic rocks and small mafic bodies. The major part of this intrusive body composed of tonalitic-granodioritic rocks. The monzogranitic rocks، unlike the other plutonic complexes of the Sanandaj-Sirjan zone such as the Alvand pluton constitute a small part of this complex، and probably formed and emplaced after tonalite-granodiorite body. In terms of geochemical characteristics these rocks are calc-alkaline، peraluminous and S-type، while tonalitic-granodioritic rocks are metaluminous and I-type in nature. These granitoids on the spider diagrams show enrichment in LILE (K، Rb and Th) and depletion in HFSE (Nb، P and Ti). Also they are enriched in LREE rather than HREE، the characteristics which are usually observed in the rocks from subduction environments and active continental margins. The biotites in the granodiorites are siderophyllite، amphiboles and plagioclases are hornblende and andesine type. Barometric calculations yield pressures of 1-1. 2 kbar (equal to 3-4 km of depth) for intrusive rocks. Crystallization temperature of the granodioritic rocks in 1Kbar pressure is estimated to be 592. 2 to 756. 9 °C and in 1. 2 Kbar pressure around 591. 2 to 757. 6 °C.