Use of feldspar grains in provenance determination and the study of transportation and depositional history, examples from central and NW Iran

Feldspar grains, as a significant provenance indicator, of two terrigenous formations from Central Iran, the Upper Red Formation, and Moghan area, Zivah Formation, are used for provenance determination and the study of transportation and depositional history. The Upper Red Formation (URF) is volumetrically the most important siliciclastic unit of the Central Iran and Zivah Formation (ZF) represents the most important hydrocarbon reservoir in northwest Iran. Two representative sections of the URF in the southern foot hills of Central Alborz and three representative sections of the ZF in the northern foot hills of Talesh Mountains are investigated in this study. The sections represent best outcrops of the formations in their basin margin. Chemical composition, zoning and twining are the main characteristics of the feldspar grains used for this study. Results from facies analysis of the formations show that ~68% of the URF and ~73% of the ZF facies are suitable for this study, for having considerable amount of feldspar grains ( > 5% detrital feldspars). Results from the study of chemical composition, zoning and twining of detrital feldspars of the URF facies indicate dominance of intermediate (andesite to dacite) volcanic rocks in their source region. In the same way, volcanic sources with dominance of basic to intermediate rocks (basalt to andesitic basalt) are determined as provenance of the ZF facies. These results point to the Eocene age volcaniclastic-dominated Karaj Formation (green series) as major source of the URF facies and the Eocene volcanics of the Talesh Mountain (Talesh series) and Middle Eocene Peshtasar Basalt as major sources of the ZF facies. Comparison of the composition, zoning, and twining of the detrital feldspars with those of proposed sources indicate higher alteration/modification of the feldspars of the URF facies. Greater alteration/modification of the feldspars of the URF facies, despite their less humid and warm depositional condition, is related to more rapid deposition and shorter transportation of the ZF facies. These results indicate greater subsidence of the ZF basin and/or uplift of its source region than that of URF. Greater structural deformation of the Moghan area than Central Alborz during development of the studied formations is understood from this study.