Interpretation of the "Qaret-el-Hanash" structure in the Western Desert (Egypt)
(nearby the Libyan Desert Glass area)

Norbert Brügge, Germany

Upload: 31.01.2018

The Qaret el Hanash is a prominent subvolcanic crater- or dyke-like structure southeast of the Libyan Desert Glass area with a height of 96 m above ground. The slopes of the elevation are covered with broken sandstones.

During an expedition in 1996 traces of an eroded zone of megascopic sandstone breccia, of about 2-m thickness, have been recognized. The breccia occurs within the wall of Qaret el Hanash. Its matrix appears as dull greyish-black material.
Petrographical and mineralogical studies have shown that there are breccias, that consists of local sandstone rock fragments within a matrix of finer quartz grains with glass and several other mineral phases. The results were published in 2004 and declared as evidence of the emergence of Qaret el Hanash by an impact.

However, the most important indication for the emergence of Qaret el Hanash, which I have postulated as subvolcanic structure, are the photos of Ursula Steiner (Switzerland), which come from the southern end of the structure and are available to me. They document clear the subvolcanic origin of Qaret el Hanash impressively. The photos (below) show a strange, partly basaltic (?) melt with many included diverse fragments, among from the Precambrian basement and also yellow jasper. It proves also once again that an iridium entry and PDF's in grains are not an exception criterion to an impact event.

25°04'46"N / 25°56'02"E

A. El-Kammar, I. Arafa, K. A. Soliman & A. Barakat --7th International Conference on the Geology of the Arab World, Cairo University, Feb. 2004, P. 1-7

The rock consists of various fragments of local sandstone, i.e., from the area of the glass distribution itself. Fragments of igneous source have never been recorded (?). The rock fragments range from fraction of mm up to 4-cm in diameter, in the collected specimens. The rock fragments vary in colour from creamy white to brownish-red. They are angular to subrounded and embedded in a dull greyish-black matrix. The microscopic investigation and scanning electron microanalysis confirmed the above-mentioned observation and showed that the matrix consists of shattered and fragmented quartz grains of various sizes. In addition to quartz, the matrix contains many other phases, such as glass, zircon, clay minerals, wollastonite, ilmenite, Mg-ilmenite, rutile and Fe-Cr-Ni specks.

There are several metallic specks of various sizes ranging from 1 micron up to about 10 micron, dispersed in the matrix of Qaret el Hanash breccia. They invade some of the quartz grains. These specks are mainly of irregular outlines and some of them show clear fissures. They are associated with glass and intercalated in some cases with halite. EDAX analyses of such specks indicate that they consist of native Fe, Cr and Ni, in addition to subordinate Si and Ca.   Finer particles of similar appearance have also been noticed by the petrographical microscope through the fractures of some of the quartz grains.

The most interesting achievement of the chemical analyses is the detection of high Ir content (2.0-2.2 ppb) within the breccias. This value represents the highest reported values for the area. The reported value of Ir in other breccias in the area is around 1.6-1.9 ppb. The highest reported concentration of Ir by the previous studies was detected from the black streak portions from the Libyan glass itself is 1.25 ppb. (Barakat 2018)

The flat surface of the Qaret el Hanash breccia Photomicrograph breccia showing shattered and fragmented quartz grains in a matrix of finer quartz admixed with other phases SEM image and EDS analysis of quartz and glass of worm like structure in the matrix Photomicrograph showing finer particles of the Fe-Cr-Ni phase dispersed within the matrix of breccia


Photos by U. Steiner

"Breccia": Former melt with different inclusions