Rostami, Alipour, Abedini,
Volume 30, Issue 3 (9-2022)
Abstract
Hormuz and Gachin salt domes are located on the Zagros Belt, about 17 km south and 50 km west of Bandar Abbas, respectively. Extensive outcrops of rhyolite and tuffs are observed in these salt domes. The main constituent minerals of rhyolite include hematite, magnetite, pyrite, chalcopyrite and apatite (Hormuz salt dome). Geochemical evidence indicates that the rhyolite of the Hormuz and Gachin domes belongs to the calc-alkaline to shoshonitic of magmatic series and formed during a tectonic regime of active continental margin volcanic arcs. Absence of negative Nb anomaly and positive anomaly of Pb in Hormuz and Gachin rhyolites indicate magma derived from the mantle source with low contamination from crustal rocks and subduction-dependent. The average of (La/Yb)N and (Ce/Yb)N ratios as index (LREE/HREE) indicate high enrichment of LREE against HREE for Hormuz rhyolite versus Gachin rhyolite,. Strong and positive correlation between ΣREE with Fe, P and Ca oxides as well as positive La and Ce anomalies and negative P anomaly in Hormuz rhyolite samples compared to Gachin samples, are consequence of the presence of apatite mineral in these rocks. The distribution pattern of Light Rare Earth Elements in Hormuz salt dome apatites show a more regular and uniform trend. Thus (LREE) show more adaptation to focus on apatite minerals. The low ratios of Eu/Eu* in apatites of Hormuz (0.01-1.04 ppm) rather than ryholites of Gachin (0.1-3.1 ppm) shows changes in the magma composition during the formation of apatites. In addition, increases in negative Eu anomaly can be due to the crystallization of feldspars that separate Eu from the melt and its concentration; therefore, the Hormuz apatites indicates a high degree of differentiation. In Hormuz salt dome apatites, enrichment of LREE to HREE, negative Eu and positive Ce anomalies and significant ΣREE concentrations up to 8882 ppm as the indicator mineral plays an important role in evaluating the distribution of rare earth elements in the rhyolite of the Hormuz salt dome.
