نوع مقاله : مقاله پژوهشی
نویسندگان
1 گروه زمینشناسی، دانشکده علوم، دانشگاه بیرجند، بیرجند، ایران
2 انستیتو علوم زمین، آکادمیا سینیکا، تایپه، تایوان
3 گروه مهندسی معدن، دانشکده مهندسی معدن، عمران، شیمی، دانشگاه صنعتی بیرجند، بیرجند، ایران
چکیده
کلیدواژهها
عنوان مقاله [English]
نویسندگان [English]
Around Bijaem village about 25 Km northwest of Sarbisheh, Tertiary volcanic rocks include of andesite, trachydacite and dacite with pyroclastic deposits such as tuff and breccia are cropped out. The forming minerals of andesite are plagioclase, pyroxene, hornblende and biotite and the dacites are composed of plagioclase, quartz, hornblende and biotite. Based on microprobe analyses, the composition of plagioclases in andesite variable from Ab31 An69 to Ab49An51 and are labradorite type. Clinopyroxenes are augite inclined to diopside and orthopyroxene have enstatite composition. The crystallization temperature of studied clinopyroxene and orthopyroxenes are 1200°C and1150°C respectively and pressure at their crystallization time was 2-5 kb and <2 kb respectively. These rocks have high-K calc alkaline nature and show enrichment of LILE and negative anomaly of Nb, Ti, P, Sr and weak europium anomaly that indicate subduction related calk alkaline lavas. Using discriminant diagrams. based on trace elements, the studied rocks belong to active continental margin. Dy/Yb ratio for Bijaem area andesitic rocks (1.62-1.91) show that their mantle source located at field between spinel and garnet peridotite with 7-10 percent partial melting degree.
کلیدواژهها [English]