سن‌سنجی زیرکن اورانیم - سرب، سنگ‌نگاشتی و زمین‌شیمی توده‌های نفوذی کم عمق در جنوب باختری بیرجند (منطقه‌ی رچ)

Rich area’s sub volcanic bodies in southwest of Birjand have intruded into Upper Cretaceous ophiolite mélange.  These rocks are in diorite porphyry to monzonite porphyry range and their main texture is porphyry with microgranular groudmass. Plagioclase and green hornblende phenocrysts are made about 70% of these rocks. Plagioclases are andesine with albitic and carlsbad twining and distinct zoning   which altered to calcium carbonate in centeral parts.  Hornblende phenocrysts have altered partly to biotite so show a weakly potassic alteration. The average ratio of Ce/Yb in these rocks are 25.40 and shows they belong to enrich magmatic arc. There is a negative anomaly in high field strength elements (HFSE) such as P, Nb and Ti in these rocks which is a geochemical charactestic of continental margin magmatic arc. High ratio of LREE / HREE, Sr/Y (average is 38.14(, and the amount of SiO2 with the absent of Eu negative anomaly show that these rocks are very similar to high SiO2 adakites. High ratio of Sr/Y can be interpreted as high depth melting in plagioclase unstability and garnet stability field. The source of this magma can be an eclogite or garnet amphibolites which is derived from subducted metamorphosed oceanic plate in east of Iran. Dating with zircon uranium – lead show that this magmatic event occurred about 39.1 ± 0.7 Ma (Late Eocene).