Abstract:
Chromitites in the Pozantı-Karsantı ophiolite in Turkey mainly occur as podiform chromitites within mantle
harzburgite and stratiform-like chromitites in mantle-crust transition zone. Chromites in chromitites have varing
Cr# from 62.8 to 80.3 and can be divided into two types, namely; intermediate (Cr#: 62.8 – 69.2) and high-Cr
(Cr#: 73.9 – 80.3) types. Major elements of the high-Cr chromitite have an affinity with boninite, whereas the
intermediate chromitite shows transitional features between MORB and boninite. The compositional differences
in clinopyroxene inclusions between intermediate- and high-Cr chromitite, coupled with the relatively high trace
element contents (e.g. V, Ga) in the high-Cr chromitite, indicate distinctive parental magmas. Trace elemental
profile analysis of a nodular chromite grain in one nodular chromitite sample PK14-41 demonstrates significant
but non-systematic variations from the core to the rim, which also confirmed the compositional heterogeneity of
the parental magmas. The presence of primary hydrous mineral inclusions such as amphibole in chromite, together
with Ca-rich minerals (e.g. calcite), reflect the water-rich and Ca-rich characteristics of the parental
magma. The higher fO2 of high-Cr chromitite evidenced by the lower V/Mn values may be due to more oxidized
fluids released from downgoing crustal materials. Thus, we conclude that the parental magmas of the Pozantı-
Karsantı chromitite were derived from a proto-forearc mantle and evolved to higher fO2 with the subduction
initiation at that time, but were water- and Ca-rich in general.
