Luodmila V. Sazonova

Shock metamorphism of plagioclase and amphibole (Experimental data)

The shock metamorphism of plagioclase and amphibole of various chemical compositions from amphibolite and granulite facies schists was studied in experiments with shock wave loading of samples in steel recovery ampoules of plane geometry. A maximum shock pressure was reached after a few circulations of waves in the sample (stepwise shock wave compression) and varied within 26–52 GPa. The recovered samples were examined by the methods of scanning electron microscopy and microprobe and X-ray phase analysis. It is established that an increase in the F, Ti, and K concentrations in amphibole and a decrease in the Ca concentration in plagioclase make these minerals more stable with respect to shock waves. It is shown that the migration of some chemical elements, starting already at the solid phase stage of transformation in plagioclase and amphibole, is intensified at the stage of melting. It is established that isotropization of plagioclase occurs through two different mechanisms. At relatively low pressures, it is caused by the fragmentation of substance at the microlevel and is accompanied by the formation of maskelynite, a typical mineral of meteorites and astrobleme rocks. At higher pressures, isotropization is associated with melting-induced amorphization.

Results of integrated geological-geophysical examination of Makhtesh Ramon area (southern Israel) on diamond-bearing associations

Larson in 1991 put forward a hypothesis on the extremely high development of diamond-bearing kimberlites in the Mid-Cretaceous period. In Israel, the Cretaceous magmatic activity is well known in the central Negev. The first microdiamond in Israel was found in northern Negev and the authors associated its origin with an extraterrestrial event. An integrated analysis of several geological and geophysical factors enables us to select for detailed investigations the area of Makhtesh Ramon canyon situated near the town of Mizpe-Ramon (nothern Negev). Data of aero- and land magnetic surveys as well as self-potential method were analyzed using modern interpreting methods. Application of geochemical/geophysical ion-selective analysis testifies to presence of kimberlite-like bodies located at a small depth. Performed mineralogical analyses of subsurface geological associations allowed to identifying a variety of minerals of diamondiferous association: chrome-diopside, orange garnet, bright-crimson pyrope, picroilmenite, black spinel, olivine, anatase, tourmaline, aggregates of perovskite, yttrium phosphate, moissanite and corundum. The recent geochemical analyses signify to discovering of quasi-kimberlite rock -- meimechite, traces of REE and some platinum group elements also testify presence of diamondiferous associations. Finally, five diamonds (with a size exceeding 1 mm) and more than 400 microdiamonds (< 1 mm) have been discovered in this area. Thus, we can unambiguously concluding that the Makhtesh Ramon area contains typical products of kimberlite pipe destruction.

High‐Pressure Polymorphic Modifications of Minerals in the Products of Impact Metamorphism of Polyminerals Rocks

High‐pressure phases of olivine and pyroxene composition were obtained in laboratory experiments with spherical converging shock waves at Zababakhin All‐Russian Research Institute of Technical Physics. These experiments were conducted with three samples of different composition. The high‐pressure phases developed after biotite and garnet, i.e. minerals that had compositions different from those of the high‐pressure phases. The shock pressure under which these newly formed minerals crystallized were approximately three times higher than the static pressures needed to synthesize these minerals. In nature (in astroblemes these minerals can be preserved only in ejects from the craters, during the super fast quenching of the products of shock metamorphism.

SHOCK METAMORPHISM OF HORNBLENDE AND PLAGIOCLASE IN CONDITIONS OF STEP‐LIKE COMPRESSION OF POLYMINERAL ROCKS

The impact transformations of plagioclase (Pl)—hornblende (Hbl) schist with garnet (Southern Urals) and clinopyroxene–Hbl–Pl schist (Anabar Shield) have been studied with use of recovery assemblies of planar geometry. In the specimens, shock pressures were ranged from 26 to 52 GPa. It was found that an increase of content of F, Ti, and K in a composition of Hbl, as well as a decrease of content of Ca in a composition of Pl, make these minerals more stable to action of shock waves. In experiments with the stepwise shock compression of polymineralic rocks the isotropization of Pl begins at lower pressures than in analogous experiments with monomineralic specimens. Under relatively low pressures, Pl isotropization is caused by its fragmentation on a microscopic scale and is associated with the origin of maskelynite—a typical mineral of meteorites and astroblemes. At higher pressures, Pl isotropization is related to amorphization by means of melting.