Intermediate chromitite in Kizildag ophiolite (SE Turkey) formed during subduction initiation in Neo-Tethys


Chen C., Su B., Xiao Y., PANG K., ROBINSON P. T. , UYSAL İ. , ...More

ORE GEOLOGY REVIEWS, vol.104, pp.88-100, 2019 (Journal Indexed in SCI) identifier identifier

  • Publication Type: Article / Article
  • Volume: 104
  • Publication Date: 2019
  • Doi Number: 10.1016/j.oregeorev.2018.10.004
  • Title of Journal : ORE GEOLOGY REVIEWS
  • Page Numbers: pp.88-100
  • Keywords: Chromite, Ophiolite, Li isotopes, Parental magma, Subduction initiation, LITHIUM ISOTOPIC SYSTEMATICS, MELT-ROCK INTERACTION, POZANTI-KARSANTI OPHIOLITE, NORTHERN OMAN OPHIOLITE, PODIFORM CHROMITITES, PERIDOTITE XENOLITHS, HIGH-TEMPERATURE, HATAY OPHIOLITE, TECTONIC SIGNIFICANCE, MINERAL CHEMISTRY

Abstract

Chromitites in the Kmildag ophiolite mostly occur in the mantle harzburgites and some of them in crustal cumulate dunites. Olivine in both the dunites and chromitites is highly magnesian (Fo = 90.5-92.8 and 90.2-96.1, respectively), while the coexisting chromite varies widely in composition (Cr# = 52.9-68.6 and 57.1-76.2, respectively), placing it between high-Al and high-Cr varieties. Concentrations of Ni, V and Ga in the chromite (Ni: 741-1310 ppm; V: 521-1227 ppm; Ga: 20-51 ppm) are also highly variable, straddling the range of high-Al and high-Cr chromite. Olivine in the dunites and chromitites has a large range of Li concentrations (0.27-2.47 ppm) and delta Li-7 values (- 7.20-29.90%o). Based on the calculated Al2O3 (12.1-17.2 wt.%) contents, FeO/MgO values (0.92-1.57) and trace element concentrations of the parental magmas of the dunites and chromitites, it is suggested that they are transitional between MORB and boninitic melts, and should have been derived by mixing of geochemically and spatially distinct magmas generated by partial melting of different sources. The Li isotopic compositions of olivine from the dunites and chromitites (except KZ14-38 and K215-38) are neither controlled by diffusion nor fractional crystallization, and thus may be intrinsic features of their parental melts. The range of delta Li-7 values of olivine in the dunites and chromitites is analogous to that of arc lavas and marine sediments, indicating that the chromitites record various degrees of melt penetration. The wide range of Li isotopic variations in olivine and chemistry in chromite from the Kizildag chromitites suggest that the parental melts were originated in a proto-forearc mantle during subduction initiation.