پترولوژی و ژیوشیمی سنگ‌های آتشفشانی جنوب تبریز (آتشفشان سهند)

The metabasites of me'raji and chah palang mountains located south of chupanan (central iran) and covered by the paleozoic metamorphic complexes. these metabasites are composed of closely associated metabasalts, metagabbros, and metadiabases. the metabasites of me'raji and chah palang mountains are metamorphosed in greenschist and amphibolite facies, respectively. following the peak metamorphism, these rocks suffered a retrograde metamorphism of greenschist facies. field observations, petrographic and mineralogical features reveal significant differences between both metabasite occurrences. rock forming minerals are plagioclase, clinopyroxene and amphibole. accessory minerals are biotite, illmenite, titanomagnetite and titanite. chlorite, epidote, pumpellyite, leucoxene and calcite are secondary minerals. the chah palang metabasites have higher k2o and tio2 contents in comparison with that of the me'raji metabasites. the na2o content of the me'raji metabasites is 6.86-8.40 (wt%), implying spilitization of pillow lavas by sub-sea floor metamorphism. the hornblende-plagioclase thermometry and al in amphibole barometry reveal different conditions for the metamorphism. the equilibrium temperature for the chah palang area was estimated 562-752 ?c at pressure of 7-8 kbar, while in the me'raji area 426-520 ?c at pressure of 5-6 kbar were obtained.