Causes of different composition of chromitites in Naein and Ashin ophiolites, and its absence in Anark and Jandaq ophiolites (Isfahan province)

There are two types of ophiolites in the west of Central Iran: Mesozoic ophiolites (Naein and Ashin), and Paleozoic or Precambrian ophiolites (Anarak and Jandaq). Field studies show that the Mesozoic ophiolites have considerable masses of chromitite, but there are no chromitite Anarak and Jandaq ophiolites. The study of Mesozoic ophiolites reveals that they have two different types of chromitites. The Naein chromitites are high-Cr whereas the Ashin chromitites are high-Al. The reasons for the chromitite absence in the Anarak and Jandaq ophiolites are lherzolitic system of mantle, low degree of partial melting in mantle rocks and the lack of sequential melt production by mantle. Different composition of orthopyroxenes, difference in degree of partial melting and chemistry of ascending melts are causes of compositional diversity of chromitites in Mesozoic ophiolites.