Textural and geochemical studies of detrital Fe–Ti oxides and test of their validity in provenance determination, a case study from Central Iran

Abstract

This paper aims to test the reliability of texture and composition of detrital Fe–Ti oxides in provenance determination, via a case study on the most important siliciclastic unit of Central Iran (Upper Red Formation). Significant exposures of the formation in its basin margins and abundance of detrital Fe–Ti oxides in its component facies nominate it for this study. Samples from representative sections of the formation are studied by SEM, equipped with X-ray analyzer, for textural and compositional properties of the Fe–Ti oxides. In terms of texture, ∼75% of the studied grains are found heterogeneous with ilmenite exsolution/intergrowth in the titanomagnetite host (∼60%), magnetite–hematite exsolution/intergrowth (∼12%) and magnetite–pseudobrookite (∼2%) and magnetite–hematite–rutile (∼1%) intergrowths. Remaining grains (∼25%) are homogenous with titanomagnetite (∼19%), ilmenite (∼5%) and rutile and chromite (∼1%) composition. Four major types of texture (trellis, sandwich, composite and no distinct pattern) are discriminated in the heterogeneous grains, which characteristics and proportion provide significant information on their provenance. In terms of composition, majority of studied grains fall into magnetite–ulvöspinel and ilmenite–hematite solid solution series in the TiO2–FeO–Fe2O3 system. The FeO, MnO, MgO, ZnO, TiO2, Fe2O3, Al2O3 and Cr2O3 contents of the grains are used for their provenance determination.On the basis of results from textural and geochemical properties of the studied grains, intermediate (andesitic to dacitic) to basic volcanic rocks (dissected arc) are determined as parent rocks of the studied grains. These findings are combined with paleocurrent patterns of the hosting facies to locate the transportation pathways of the grains and their source area. Texture and composition of Fe–Ti minerals from nominated parent rocks are studied in similar methods. Comparison of texture and composition of the detrital Fe–Ti oxides with those in their nominated parent rocks clearly confirm the reliability of these parameters in provenance determination. Slight post-depositional alteration of the grains is understood from this comparison.