Genesis Geological Model of Intracontinental Volcanism Contribution in Polymorphic Silica Geodes Formation, Northern Arabian Plate 

The study aims to create a geological model of the role of intracontinental volcanism in the northern Arabian Plate and the formation of various phases of silica in carbonate deposits on the surface of the Ratqa Formation (Early-Late Eocene) in the Western Desert of Iraq, as there are significant amounts of silica have previously mistakenly been attributed to a marine origin. Advanced techniques of transmitted polarized microscope and XRD have provided a perfect identification of the mineralogy of the siliceous geode. Two distinct fluid generations formed the siliceous geode. The first generation consisted of a silica-rich solution, which precipitated silica polymorphs along the cavity’s inner wall, eventually forming the main body of the geode. The second generation involved a Ca-supersaturated solution, which led to the precipitation of calcite in the central space of the geode’s cavity. The porcelainite rocks rich in SiO₂ accompanying the geodes confirm silica amounts’ dominance in the study area, which seawater cannot provide. The findings indicate a novel concept regarding the source of silica geodes, suggesting that intracontinental volcanism in the north of the Arabian Plate, including Saudi Arabia, eastern Jordan, and southeastern Syria, provided the Western Desert of Iraq with volcanic ash by air during the Cenozoic.