بررسي سنگ شناسي و ژئوشيميايي بازالت هاي منطقه جنوب املش ( شرق گيلان )

Petrography and Geochemistry of Southern Amlash basaltic rocks (Easthern Guilan)

Basaltic rocks of Southern Amlash are a part of an ophiolitic sequence. Based on field studies these basaltic rocks often are outcropped to pillow lavas form and rarely of lava flow and lava breccias form. Petrographic studies show that these rocks are in the two different groups that are: alkali basalts (containing of titaniumaugite clinopyroxene, plagioclase, olivine, iron and titanium oxides and apatite) and subalkali basalts (including clinopyroxene (diopside to augite), and plagioclase as the main minerals that are rarely have been associated with olivine and sulfide minerals. Most of rocks show oceanic metamorphic and thus initial minerals (plagioclase, clinopyroxene and olivine) have been altered. Geochemical studies indicate that producer magma of these rocks have tholeitic nature from the subalkaline type. Rare earth elements pattern of in these rocks indicates LREE-rich in them. Whereas clear depleted of Zr, Nb, Ti and P elements are visible in these rocks. This is characteristics are specified properties of the suprasubduction environment.In compared distribution pattern of alkaline basalts similarly are rich in LREE and MREE and are clear depleted in HREE elements and shows the OIB nature of them. Accordingly, based on the petrography and geochemical studies, two distinct groups are found in the region.