The Lonar crater, India, is the only well-preserved simple crater on Earth in continental flood basalts; it is excavated in the Deccan trap basalts of Cretaceous-Tertiary age. A representative set of target basalts, including the basalt flows excavated by the crater, and a variety of impact breccias and impact glasses, were analyzed for their major and trace element compositions. Impact glasses and breccias were found inside and outside the crater rim in a variety of morphological forms and shapes. Comparable geochemical patterns of immobile elements (e.g., REEs) for glass, melt rock and basalt indicates minimal fractionation between the target rocks and the impactites. We found only little indication of post-impact hydrothermal alteration in terms of volatile trace element changes. No clear indication of an extraterrestrial component was found in any of our breccias and impact glasses, indicating either a low level of contamination, or a non-chondritic or otherwise iridium-poor impactor.

We performed high-resolution 40Ar-39Ar dating of mineral separates and whole-rock samples from the desert meteorites Dhofar 300, Dhofar 007, and Northwest Africa (NWA) 011. The chronological information of all samples is dominated by plagioclase of varying grain size. The last total reset age of the eucrites Dhofar 300 and Dhofar 007 is 3.9 +/- 0.1 Ga, coeval with the intense cratering period on the Moon. Some large plagioclase grains of Dhofar 007 possibly inherited Ar from a 4.5 Ga event characteristic for other cumulate eucrites. Due to disturbances of the age spectrum of NWA 011, only an estimate of 3.2-3.9 Ga can be given for its last total reset age. Secondary events causing partial 40Ar loss less than or equal to 3.4 Ga ago are indicated by all age spectra. Furthermore, Ar extractions from distinct low temperature phases define apparent isochrons for all samples. These isochron ages are chronologically irrelevant and most probably caused by desert alterations, in which radiogenic 40Ar and K from the meteorite and occasionally K induced by weathering are mixed, accompanied by incorporation of atmospheric Ar. Additional uptake of atmospheric Ar by the alteration phase(s) was observed during mineral separation (i.e., crushing and cleaning in ultrasonic baths). Consistent cosmic-ray exposure ages were obtained from plagioclase and pyroxene exposure age spectra of Dhofar 300 (25 +/- 1 Ma) and Dhofar 007 (13 +/- 1 Ma) using the minerals specific target element chemistry and corresponding 38Ar production rates.

We have studied the CB carbonaceous chondrites Queen Alexandra Range (QUE) 94411, Hammadah al Hamra (HH) 237, and Bencubbin with an emphasis on the petrographical and mineralogical effects of the shock processing that these meteorite assemblages have undergone. Ironnickel metal and chondrule silicates are the main components in these meteorites. These hightemperature components are held together by shock melts consisting of droplets of dendritically intergrown Fe,Ni-metal/sulfide embedded in silicate glass, which is substantially more FeO-rich (30 40 wt%) than the chondrule silicates (FeO <5 wt%). Fine-grained matrix material, which is a major component in most other chondrite classes, is extremely scarce in QUE 94411 and HH 237, and has not been observed in Bencubbin. This material occurs as rare, hydrated matrix lumps with major and minor element abundances roughly similar to the ferrous silicate shock melts (and CI). We infer that hydrated, fine-grained material, compositionally similar to these matrix lumps, was originally present between the Fe,Ni-metal grains and chondrules, but was preferentially shock melted. Other shockrelated features in QUE 94411, HH 237, and Bencubbin include an alignment and occasionally strong plastic deformation of metal and chondrule fragments. The existence of chemically zoned and metastable Fe,Ni-metal condensates in direct contact with shock melts indicates that the shock did not substantially increase the average temperature of the rock. Because porphyritic olivine-pyroxene chondrules are absent in QUE 94411, HH 237, and Bencubbin, it is difficult to determine the precise shock stage of these meteorites, but the shock was probably relatively light (S2-S3), consistent with a bulk temperature increase of the assemblages of less than ~300 degrees C. The apparently similar shock processing of Bencubbin, Weatherford, Gujba (CBa) and QUE 94411/HH 237 (CBb) supports the idea of a common asteroidal parent body for these meteorites.

The Tagish Lake carbonaceous chondrite consists of heavily aqueously altered chondrules, CAIs, and larger mineral fragments in a fine-grained, phyllosilicate-dominated matrix. The vast majority of the coarse-grained components in this meteorite are surrounded by continuous, 1.5 to 200 m wide, fine-grained, accretionary rims, which are well known from meteorites belonging to petrological types 2 and 3 and whose origin and modification is still a matter of debate. Texturally, the fine-grained rims in Tagish Lake are very similar throughout the entire meteorite and independent of the nature of the enclosed object. They typically display sharp boundaries to the core object and more gradational contacts to the meteorite matrix. Compared to the matrix, the rims are much more finegrained and characterized by a significantly lower porosity. The rims consist of an unequilibrated assemblage of phyllosilicates, Fe,Ni sulfides, magnetites, low-Ca pyroxenes, and forsteritic olivines, and are, except for a much lower abundance of carbonates, very similar to the Tagish Lake matrix. Electron microprobe and synchrotron X-ray microprobe analyses show that matrix and rims are also very similar in composition and that the rims differ significantly from matrix and bulk meteorite only by being depleted in Ca. X-ray elemental mapping and mineralogical observations indicate that Ca was lost during aqueous alteration from the enclosed objects and preferentially crystallized as carbonates in the porous matrix. The analyses also show that Ca is strongly fractionated from Al in the rims, whereas there is no fractionation of the Ti/Al-ratios. Our data suggest that the fine-grained rims in Tagish Lake initially formed by accretion in the solar nebula and were subsequently modified by in situ alteration on the parent body. This pervasive alteration removed any potential evidence for preaccretionary alteration but did not change the overall texture of the Tagish Lake meteorite.

A series of 59 impacts in the laboratory reduced a coherent 460 g piece of the L6 ordinary chondrite ALH 85017 to a coarse-grained regolith. We then subjected the 125-250 micrometer fines from this sample to reverberation shock stresses of 14.567 GPa in order to delineate the melting behavior of porous, unconsolidated, chondritic asteroid surfaces during meteorite impact. The initial pore space (40-50%) was completely closed at 14.5 GPa and a dense aggregate of interlocking grains resulted. Grain-boundary melting commenced at <27 GPa and ~50% of the total charge was molten at 67 GPa; this stress corresponds to typical asteroid impacts at ~5 km/sec. Melting of the entire sample most likely mandates >80 GPa, which is associated with impact velocities >8 km/sec. The Fe-Ni and troilite clasts of the original meteorite melted with particular ease, forming immiscible melts that are finely disseminated throughout the silicate glass. These metal droplets are highly variable in size, extending to <100 nm and most likely to superparamagnetic domains; such opaques are also observed in the natural melt veins of ordinary chondrites. It follows that melting and dissemination of pre-existing, Fe-rich phases may substantially affect the optical properties of asteroidal surfaces. It seems unnecessary to invoke reduction of Fe2+ (or Fe3+) by sputtering or impact-processes--in analogy to the lunar surface--to produce space weathering effects on S-type asteroids. We note that HED meteorites contain ample FeO (comparable to that in lunar basalts) for reduction processes to take place, yet their probable parent object(s), Vesta and its collisional fragments, display substantially unweathered surfaces. Howardites, eucrites, and diogenites (HEDs), however, contain little native metal (typically <0.5%), in contrast to ordinary chondrites (commonly 10-15%) and their S-type parent objects. These considerations suggest that the modal content of native metal and sulfides is more important for space weathering on asteroids than total FeO.

Planar features can develop in quartz during comparatively slow tectonic deformation and during very fast dynamic shock metamorphism. Despite their very different structural nature, tectonically induced deformation lamellae have sometimes been mistaken as shock-induced planar deformation features (PDFs). To understand the formation of deformation lamellae and to address the substantial differences between them and PDFs, we have conducted deformation experiments on single crystals of quartz in a Griggs-type apparatus, at a temperature of 800 degrees C, a confining pressure of 12 kbar, and a strain rate of 0.7- 1.1 x 10^(-6). The deformed samples were analyzed with transmission electron microscopy (TEM) and compared to natural PDFs from the Ries Crater, Germany. TEM revealed that tectonic deformation lamellae are associated with numerous sub-parallel curved subgrain walls, across which the orientation of the crystal changes slightly. The formation of deformation lamellae is due to glide- and climb-controlled deformation in the exponential creep regime. In contrast, the PDFs in shocked quartz from the Ries are perfectly planar, crystallographically controlled features that originally represented amorphous lamellae. Due to postshock annealing and hydrothermal activity they are recrystallized and decorated with fluid inclusions.

Previous Raman investigations on experimentally shocked single-crystal olivine indicated that the olivine Raman bands seemingly shift to a higher wave number with increasing shock pressure. If this effect could be confirmed, Raman analysis of natural shock-metamorphosed minerals could potentially provide an important shock barometric tool. We carried out a Raman spectroscopic study on olivine in a series of natural dunite samples experimentally shocked to pressures between 5 and 59 GPa. In addition, we analyzed olivine grains in a sample of the Cold Bokkeveld C1 meteorite. We studied samples of several dunites with olivine of 90.64-92.00 mole% Fo to determine Raman effects in the region from 200 to 900 cm(-1). Several olivine grains per sample/shock pressure stage were analyzed. Raman analysis, however, showed little or no shift with increasing shock pressure. The shifts to higher or lower frequencies observed were not specific for a given pressure stage, with some grains within a sample showing more shift than others. This finding is unrelated to the crystallographic orientation of analyzed grains and cannot be related systematically to the different degrees of optically determined shock metamorphism of the analyzed grains. We identified an increase in full width at half maximum (FWHM) for the 824 cm^(-1) band with increased shock pressure in the shocked heim samples above 45 GPa and, to a lesser extent, for the 856 cm^(-1) band. Evaluation of band broadening of olivine in the Cold Bokkeveld meteorite showed FWHM values that were much greater (920 cm^(-1)) than those of olivine in the shocked dunite samples (712 cm^(-1)). We concluded that these differences in FWHM are due to differences in chemical composition between the meteoritic and the experimentally shocked olivine. Therefore, using Raman spectroscopy to detect small shifts in wave numbers to higher frequencies with increased shock pressure does not yield consistent effects for polycrystalline dunite. An extra band at 650 cm^(-1) was identified in the Raman spectra of the unshocked Mooihoek dunite and the heim dunite samples shocked to 5, 29.3, and 59 GPa, as well as another at 696 cm^(-1) in all the spectra of the 59 GPa heim sample. The cause of these extra bands is not known. Comparison of these results with Raman spectra of olivine from the Cold Bokkeveld C1 meteorite did not allow us to determine shock pressures for the meteoritic olivine.

The purpose of this paper is to review the results of long-term cooperation between Dieter Stffler and the authors in the field of shock wave deformation of minerals and rocks. First, the principal phenomena of shock wave generation and propagation, predominantly in solid media, are presented, and then analytical and numerical mathematical treatment of shock wave processes on the basis of mass, momentum, and energy conservation laws will be described and discussed. Experimental methods of shock wave investigations by means of impact and explosive techniques are summarized, including hypervelocity acceleration facilities and high-pressure explosive devices. Shock pressure barometry by means of mineralogical evidence of distinct material phase transitions and characteristic shock structures is also discussed.