Petrography and geochemistry of sandstones from the Injana Formation, Hemrin South Mountain, Northern Iraq: Implications for provenance, weathering and tectonic setting

Abstract

The sandstones of Upper Miocene Injana Formation were studied petrographically and geochemically in the Hemrin South Mountain area, northern Iraq. The sandstones vary between arkose and lithic arkose in composition (Q50F24L26) and are compositionally and texturally immature; meanwhile, the Log(Fe2O3/K2O)–Log(SiO2/Al2O3) diagram shows that they are divided between arkose, litharenite and wacke. These sandstones contain a wide spectrum of heavy minerals ranging from the most resistant ultrastable minerals (zircon, rutile and tourmaline), to the least resistant non‐stable minerals (amphiboles and pyroxenes). The provenance indicator diagrams QmFLt and QtFL indicate multi‐sources for these sandstones ranging from transitional craton, arc and recycled sediments. The major element provenance discriminant function plot shows that they are derived mostly from intermediate igneous provenance. All these suggest that the probable source of these sandstones is the igneous‐metamorphic rocks including the ophiolites of the Suture Zone, the imbricate zone, the Shalair‐Sanandaj‐Sirjan Terrane and the complimentary rock units in Turkey and Iran. The presence of glaucophane as the provenance indicator mineral for subduction zones is a further proof of the ophiolites having acted as the source rocks. Geochemically, the sandstones are enriched in Ca, V, Cr, Ni, Cu, Mo, Sn and Sb and depleted in all othe major, trace and rare earth elements (REE) relative to upper continental crust (UCC). The chondrite‐normalized REE pattern shows a distinct negative slope for the LREEs and a slight negative slope for the HREEs with an enrichment of LREE/HREE of 8.11–10.90 and a negative Eu anomaly of 0.70–0.83. The most probable source of REEs is the heavy minerals detected in the sandstones. Tectonically, the studied rocks were derived from collision rifting arc–related settings. The Chemical Index of Alteration (CIA), Plagioclase Index of Alteration (PIA) and Index of Composition Variation (ICV) values of the Injana sandstones suggest that they are compositionally immature and suffered from very weak weathering indicating the proximity of their source rocks and their deposition under dry continental conditions.