Mathematics – Logic
Scientific paper
Jul 1997
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1997m%26ps...32..545v&link_type=abstract
Meteoritics, vol. 32, pages 545-554
Mathematics
Logic
20
Scientific paper
Clasts of deep seated crystalline basement rocks in suevites of the Ries crater, Germany, were catalogued lithologically and classified with regard to their degree of shock metamorphism. The sample suite consisted of eight hundred and six clasts from ten outcrops in fall out suevites and four hundred and forty seven clasts from drill cores in the crater interior encountering crater suevite. These clasts can be grouped into seven types of metamorphic and nine types of igneous rocks. One hundred and forty three clasts, representing these lithologies, were analyzed for major element bulk-composition. The fall out suevite contains on the average 4 vol % of crystalline basement clasts, 0.4 vol % of sedimentary rocks, 16 vol % of glass bodies, some of them aerodynamically shaped, and 79 vol % of grundmass. On the average, 52 % of all crystalline clasts are from metamorphic sources and 42 % of igneous origin. Using the shock classification of Stoffler (1974), 8 % of all crystalline clasts appear unshocked (< 10 GPa), 34, 30 and 27 %, respectively, are shocked to stages I (10-35 Gpa), II (35-45 GPa) and III (45-60 GPa). The bulk composition of suevite glasses is consistent with the modal proportions of crystalline rock types, observed in the clast populations. This indicates that the glasses originate by shock-fusion of a similarly composed basement. The crater suevite contains the same crystalline rock types which occur in the fall out suevites. The bore hole "Nordlingen 1973" yields an average of 62 vol % metamorphic and 38 vol% igneous rocks. The crater suevite differs from fall out suevites by a higher clast/glass ratio, by preponderance (65-95 %) of clasts shocked to stage I only, and by the absence of aerodynamically shaped glass bodies. The source of crystalline clasts and melt particles of suevites is a volume of rocks, located deep in the crystalline basement, to which the projectile transmitted most of its energy, so that only rocks of the basement were shocked by pressures exceeding 10 GPa (deep-burst impact model). Fall out suevite were ejected, propelled by by an expanding plume of vaporized rock, and withdraw from this volume preferentially melt and highly shocked clasts, leaving in the transient cavity the crater suevite with more clasts of modest shock levels and less melt.
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