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Abar al' Uj (AaU) 012 is a clast-rich, vesicular impact-melt (IM) breccia, composed of lithic and mineral clasts set in a very fine-grained and well-crystallized matrix. It is a typical feldspathic lunar meteorite, most likely originating from the lunar farside. Bulk composition (31.0 wt% Al2O3, 3.85wt% FeO) is close to the mean of feldspathic lunar meteorites and Apollo FAN-suite rocks. The low concentration of incompatible trace elements (0.39ppmTh, 0.13ppm U) reflects the absence of a significant KREEP component. Plagioclase is highly anorthitic with a mean of An(96.9)Ab(3.0)Or(0.1). Bulk rock Mg# is 63 and molar FeO/MnO is 76. The terrestrial age of the meteorite is 33.4 +/- 5.2kyr. AaU 012 contains a similar to 1.4x1.5mm(2) exotic clast different from the lithic clast population which is dominated by clasts of anorthosite breccias. Bulk composition and presence of relatively large vesicles indicate that the clast was most probably formed by an impact into a precursor having nonmare igneous origin most likely related to the rare alkali-suite rocks. The IM clast is mainly composed of clinopyroxenes, contains a significant amount of cristobalite (9.0 vol%), and has a microcrystalline mesostasis. Although the clast shows similarities in texture and modal mineral abundances with some Apollo pigeonite basalts, it has lower FeO and higher SiO2 than any mare basalt. It also has higher FeO and lower Al2O3 than rocks from the FAN- or Mg-suite. Its lower Mg# (59) compared to Mg-suite rocks also excludes a relationship with these types of lunar material.

We have investigated the Ash Shutbah circular structure in central Saudi Arabia (21 degrees 37N 45 degrees 39E) using satellite imagery, field mapping, thin-section petrography, and X-ray diffraction of collected samples. The approximately 2.1km sized structure located in flat-lying Jurassic Tuwaiq Mountain Limestone has been nearly peneplained by erosional processes. Satellite and structural data show a central area consisting of Dhruma Formation sandstones with steep bedding and tight folds plunging radially outward. Open folding occurs in displaced, younger Tuwaiq Mountain Limestone Formation blocks surrounding the central area, but is absent outside the circular structure. An approximately 60cm thick, unique folded and disrupted orthoquartzitic sandstone marker bed occurring in the central area of the structure is found 140m deeper in undisturbed escarpment outcrops located a few hundred meters west of the structure. With exception of a possible concave shatter cone found in the orthoquartzite of the central area, other diagnostic shock features are lacking. Some quartz-rich sandstones from the central area show pervasive fracturing of quartz grains with common concussion fractures. This deformation was followed by an event of quartz dissolution and calcite precipitation consistent with local sea- or groundwater heating. The combination of central stratigraphic uplift of 140m, concussion features in discolored sandstone, outward-dipping concentric folds in the central area, deformation restricted to the rocks of the ring structure, a complex circular structure of 2.1km diameter that appears broadly consistent with what one would expect from an impact structure in sedimentary targets, and a possible shatter cone all point to an impact origin of the Ash Shutbah structure. In fact, the Ash Shutbah structure appears to be a textbook example of an eroded, complex impact crater located in flat-lying sedimentary rocks, where the undisturbed stratigraphic section can be studied in escarpment outcrops in the vicinity of the structure. (Less)