...° between specimen pairs, suggests the possibility that the sampling procedures cause significant errors. Laboratory experiments on several kinds of un-consolidated glacial sediments show significant thixotropic remanence resetting toward the ambient magnetic field caused by hammer shocks during sampling...

...P. Blyth Robertson; J. L. Roy Abstract The magnetic characteristics of shocked and unshocked anorthosites of the Charlevoix impact structure have been reexamined to assess the effects of high thermal and alternating field (af) cleaning treatments, and to evaluate any shock-induced features...

...H. R. Wenk Abstract The microstructure of pseudotachylite veins, as analyzed with the transmission electron microscope, displays many features of intense brittle deformation and resembles more closely shock-deformed specimens than a rock first melted and then quenched to a glass and devitrified...

... equivalents. Most of the breccias are composed entirely of clastic material, but at one locality fine-grained felted matrices form a significant component of the breccias, and coronas of clear glass surround quartz grains. The latter breccias also contain microscopic features characteristic of shock...

... between crystal subdomains (mosaicism) within a given sample (η max ), and its usefulness as an index of shock metamorphism at Charlevoix. The complex morphological character of the impact crater can be divided into five concentric zones, which exhibit alternately high and low values of η max...

...H. C. Halls; R. A. F. Grieve Abstract Shock metamorphic effects in samples from the Slate Islands, Lake Superior (48°40' N, 87°00' W) suggest that the islands are part of a meteorite impact structure. The islands form the central uplift of a complex crater and are ringed by a submerged trough...

... percent primitive crust lithologies, 60 percent impact-produced fragmental breccias, and about 30 percent impact-melt rocks with abundant clasts or xenoliths. Both the impact-melt breccias and the fragmental breccias consist of intimate mixtures of superheated shock melt derived from near the point...

... resistivity values and shock metamorphic grade. This is interpreted as due to residual shock effects on the lattice conductivity. These effects are preserved over long periods of time, probably because of rapid cooling that prevented thermal annealing and recrystallization. The highly shock metamorphosed...

... the adjacent Piedmont peneplain; (3) the chaotic orientation of Cretaceous and metamorphic units in the center of the structure, perhaps corresponding to the central rebound area; (4) concentric marginal faults with an estimated displacement of 240 to 300 m; and (5) shock effects in feldspar and quartz...

...RICHARD A. F. GRIEVE Abstract At the Mistastin Lake structure, Labrador, igneous rocks overlying shock-metamorphosed and brecciated Precambrian anorthosite, mangerite, and granodiorite have a preserved thickness of 80 m and have characteristics believed compatible with an origin by impact melting...

...P. B. ROBERTSON Abstract The distribution of particular shock metamorphic effects has been determined in the central uplift of the Charlevoix impact structure. Planar deformation features in quartz occur as much as 10 km from the central peak (Mont des Eboulements), whereas equivalent shock...

...G. H. Faye Abstract Recently, Gibbons, Ahrens, and Rossman (1974) proposed that the irreversible reduction of Mn 3+ to Mn 2+ is responsible for the spectral changes induced by the shock-loading of rhodonite at pressures up to 496 kbar. 19 11 1974 5 6 1975 Copyright © 1975...

...BEVAN M. FRENCH; JAMES R. UNDERWOOD, JR.; EDWARD P. FISK Abstract Shock-metamorphic effects in sandstone samples from two circular structures about 80 km apart in southeastern Libya demonstrate that these structures formed by meteorite impact. The smaller structure is about 2.8 km in diameter...

...Rex V. Gibbons; Thomas J. Ahrens; George R. Rossman Abstract Samples of rhodonite (MnSiO 3 -pyroxenoid from Franklin, New Jersey) have been shock-loaded to pressures up to 496 kilobars. Optical spectral studies of four recovered samples show a decreasing Mn 3+ content upon recovery from...

... surface fracturing commonly occurs. Thus, no spatial correlation between aftershocks and surface fractures is necessarily expected. The lack of correlation between aftershocks and surface fractures is consistent with the fact that most after- shocks occur at depths of 1 to 5 km (R. M. Hamilton, oral...

...Paul D. Fullagar; Michael L. Bottino; Bevan M. French Abstract Sixteen inclusions from the Onaping Formation, a possible meteorite impact breccia at Sudbury, Ontario, were analyzed for Rb, Sr, and Sr isotopic composition. Inclusions ranged from weakly shocked granitic rocks to heterogeneous glassy...

...I. Y. Borg Abstract Polysynthetically twinned sphene occurs in shocked granite surrounding cavities produced by the Hardhat and Piledriver nuclear events at the Nevada Test Site. Commonly two sets of composition planes (twins) at ca 55 deg to each other are developed within individual grains. A few...

...Stephen H. Wolfe; Friedrich Hörz Abstract Shocked scapolite of the composition Me 72-79 Ma 21-28 occurs in the central, maskelynite bearing anorthosite massif of the Manicouagan-Mushalagan structure in Quebec, Canada. Highly shocked scapolite displays multiple sets of “planar features” identical...