Suevite of the ries crater, Germany: Source rocks and implications for cratering mechanics

Abstract

ZusammenfassungSuevite sind Impaktbreccien, die in einer montmorillonitischen Matrix geschockte und ungeschockte Mineral-und Gesteinsfragmente aus dem kristallinen Untergrund, Glas-Einschlfisse und eine geringe Menge von sediment~iren Fragmenten enthalten. Es werden Daten fiber die modale Zusammensetzung der Fall-out-Suevite (abgelagert an isolierten Punkten rings um den Krater) und des Krater-Suevits (der eine Schicht unter den nach-Riesischen Seesedimenten im Krater bildet) mitgeteilt. Fall-out-Suevite enthalten aerodynamisch geformte Bomben, die im Krater-Suevit fehlen. Unter Berficksichtigung der feineren Glaskomponenten -nicht nur der groBen Bomben und Fragmente -erh~ilt man ffir den Glasgehalt der Fall-out-Suevite 47 vol%, fiir den des Krater-Suevits 29 vol%. Die kristatlinen Einschtfisse in den Sueviten geh6ren zu den magmatischen und metamorphen Gesteinstypen, die den Untergrund des Riesgebietes aufbauen. Dieser besteht aus einer h6he-ren Lage magmatischer Gesteine (haupts/ichtich Granite) und einer tieferen Serie von Gneisen und Amphiboliten. Auf Grund einer Aufsammlung von 1 200 Kristallineinschliissen aus 13 Suevit-Vorkommen wurde die H~iufigkeit der einzelnen Gesteinstypen in den Sueviteu bestimmt. Die Suevite enthalten im Mittel 46 % magmatische und 54 % metamorphe Gesteinseinschlfisse. Im Gegensatz dazu bestehen die nicht oder nur wenig geschockten kristallinen Ejekta um den Ries-Krater aus 82 % magmatischen und 18 V0 metamorphen Gesteinen.Die mittleren chemischen Zusammensetzungen der kristallinen Gesteinstypen wurden auf Grund yon 138 chemischen Analysen bestimmt. Ein Vergleich mit der Zusammensetzung der Suevit-Glaser ergibt, dab diese durch die Aufschmelzung der Gneise gebildet wurden, welche in einem tieferen Niveau des kristallinen Untergrundes lagen.Die AbstractSuevites are impact breccias with a montmorillonitic matrix that contains shocked and unshocked mineral and rock fragments from the crystalline basement, glass inclusions and a small amount of sedimentary clasts. Data are given of the modal composition of fall-out suevites (deposited at isolated points around the crater) and crater suevite (forming a layer below post-impact lake sediments in the crater cavity). Fall-out suevites contain aerodynamically shaped bombs which are absent in crater suevite. Taking into account not only large glass fragments and bombs, but also the finer fractions, the glass content of fall-out and crater suevites amounts to 47 and 29 vol%, respectively. Crystalline clasts in suevites consist of all igneous and metamorphic rock types that constitute the local basement which consists of an upper layer of igneous rocks (mainly granites) and a lower series of gneisses and amphibolite. Based on a collection of 1 200 clasts from 13 suevite occurrences the average crystalline clast population of suevites was determined. Suevites contain on the average 46 % igneous and 54 % metamorphic clasts. In constrast, weakly shocked and unshocked crystalline ejecta of the Ries structure consist of 82 % igneous and 18 % metamor...

Post‐impact alteration of surficial suevites in Ries crater, Germany: Hydrothermal modification or weathering processes?

“…Zeolites have been recognized in the groundmass and impact glass clasts of surficial suevites by several authors (e.g., Engelhardt and Graup 1984;Osinski et al 2004;Osinski 2005). In this study only harmotome was recognized in one Altenbürg sample (degassing pipe) with amounts of ∼2.7 wt%.…”

“…Newsom et al 1986;Osinski et al 2004;Osinski 2005). It has been generally accepted that these clays formed by postimpact hydrothermal alteration of impact-generated glasses and/or finely comminuted crystalline basement material (Engelhardt 1972;Stähle 1972;Engelhardt and Graup 1984; Newsom et al 1986Newsom et al , 1990. The same was assumed for the origin of calcite in the Ries surficial suevites.…”

Impact lithologies and their emplacement in the Chicxulub impact crater: Initial results from the Chicxulub Scientific Drilling Project, Yaxcopoil, Mexico

“…This pervasive melt-dispersion suggests some form of airborne transport. Rare aerodynamic forms of individual melt objects suggest that some of the material was shaped in free flight, similar to individual melt bombs in the Ries suevites (e.g., Horz 1965;von Engelhardt and Graup 1984). Individual melt volumes followed different trajectories and cooled at different rates, leading to a mixture of molten and solid particles.…”

“…It is also possible that the anhydrite had somewhat patchy distribution and was substantially absent in that portion of the crater cavity that gave rise to the Yax-1 deposits. Very generally, the ejection process during crater growth is substantially centrosymmetric and tends to preserve the specific lithological content of the target along radial traverses (Gault et al 1968;von Engelhardt and Graup 1984).…”

“…6). In the Ries crater, which is the type locality for suevitic meltbearing breccias, crater suevites (deposited within the transient crater) are only 29% melt fragments, and fall-out suevites (deposited outside the transient crater) are 47% melt fragments (von Engelhardt and Graup 1984). Because the Yax-1 (and Yucatán-6) borehole is located outside the transient cavity of Chicxulub, the better comparison is with the relatively melt-rich fall-out suevites, nonetheless, the abundance of melt fragments in the Chicxulub polymict breccias in Yax-1 are nearly twice as abundant as those in the Ries fall-out suevites.…”