Initial subduction of Neo-Tethyan ocean: Geochemical records in chromite and mineral inclusions in the Pozanti-Karsanti ophiolite, southern Turkey


LIU X., Su B., Xiao Y., Chen C., UYSAL İ. , JİNG J., ...Daha Fazla

ORE GEOLOGY REVIEWS, cilt.110, 2019 (SCI İndekslerine Giren Dergi) identifier identifier

Özet

Chromitites in the Pozanu-Karsanti 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 bonfnite, 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 fO(2) 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 Pozanti-Karsanti chromitite were derived from a proto-forearc mantle and evolved to higher fO(2) with the subduction initiation at that time, but were water- and Ca-rich in general.