Interpretation of the "Qaret-el-Hanash"
structure in the
the Libyan Desert Glass area)
Norbert Brügge, Germany
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
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
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
25°04'46"N / 25°56'02"E
DISCOVERY OF Fe-Cr-Ni SPECKS WITHIN QARET
EL-HANASH BRECCIA OF THE LIBYAN GLASS AREA SOUTH WESTERN EGYPT
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)
Photos by U. Steiner
"Breccia": Former melt with different inclusions