Radarsat investigation of a circular feature in east central Jordan

Abstract

A typical ring-like feature, located in east central Jordan about 150km south-east of Amman, is very obvious on Radarsat images. Four concentric circles, but only two perfect ones, were discriminated, ranging in size from about 6km to about 1km in diameter. At first glance, this feature greatly resembles an ideal impact structure. Previous geological studies, geophysical investigations and recent field observation proved the presence of a domal structure that incorporates lower Cretaceous sandstone at the core; middle of the central ring, and successively surrounded by a highly fractured and steeply dipping sequence of Cretaceous and lower Tertiary carbonates and chert. The principal faults and lineaments in the region follow N-W, N-E and E-W trends, the intersection of which is believed to have acted as a preferable place for the emplacement of an igneous body, most probably in the post-Eocene, which causes the domal uplift and the associated ring faults at Jabal Waqf as Suwwan. Interpretation of 1:60 000 aerial photographs and the 1:50 000 topographic maps clearly showed two concentric rings of about 6km and 1km in diameter, coinciding with the presence of steep dissected ridges of Late Cretaceous to Eocene chert and carbonates. Tectonic interpretation of gravity data showed the presence of concentric ring-like faults that greatly coincide with Radarsat imagery interpretation and field evidence. Magnetic data suggested the presence of either a dense non-magnetic igneous intrusion, a carbonate body or an anhydrite dome. Seismic data, on the other hand, confirmed the presence of a highly fractured zone about 6km wide. Merging of Radarsat with Landsat Thematic Mapper (TM) data enables discrimination of surficial deposits, chert and chalk and illustrates certain geological structures and drainage segments. Replacement of Radarsat standard (S7) images for intensity and hue in the IHS transformation and the first principal component of TM bands 7, 4 and 1 enhances lithological and main structural features.