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Curved joint sets: Indication of impact-induced fracturing
Abstract
Structural investigations in the Azuara impact structure in north-east Spain have exhibited an unusual joint pattern, which is unfamiliar to structural geologists. 10-15 km distant from the center of the structure Jurassic limestones show curved joint sets in the meter range, which cut the rocks into bars of approximately rhomboidal cross- section. Models of listric faulting as well as sedimentational and diagenetic processes fail to explain the observed features, which rather point to dynamic formation. It is assumed that the curved joint surfaces have resulted from impact-induced dynamic stress modulation of running fractures during the excavation flow. Probably, curved joint sets belong to the regular structural inventory of impact structures.
... no year). This is accompanied by the observation that the Azuara impact structure published since 1985 (Ernstson et al. 1985, 1987, 2002, Müller and Ernstson 1990, Ernstson and Claudin 1990, Ernstson 1994, Ernstson and Fiebag 1992, Claudin and Ernstson (2012, Ernstson and Claudin http://www.impact-structures.com/impact-spain/the-azuara-impactstructure, no year) is not mentioned at all in the discussion of the other basin structures mentioned (Calatayud and Alfambra-Teruel), even in the latest geological literature (e.g. ...
The Iberian System in NE Spain is characterized by a distinctive graben/basin system (Calatayud, Jiloca, Alfambra/Teruel), among others, which has received much attention and discussion in earlier and very recent geological literature. A completely different approach to the formation of this graben/basin system is provided by the impact crater chain of the Rubielos de la Cérida impact basin as part of the important Middle Tertiary Azuara impact event, which has been published for about 20 years. Although the Rubielos de la Cérida impact basin is characterized by all the geological, mineralogical and petrographical impact findings recognized in international impact research, it has completely been hushed up in the Spanish geological literature to this day. The article presented here uses the example of the Jiloca graben to show the absolute incompatibility of the previous geological concepts with the impact structures that can be observed in the Jiloca graben without much effort. Digital terrain modeling and aerial photography together with structural and stratigraphic alien geology define a new lateral Singra-Jiloca complex impact structure with central uplift and an inner ring, which is positioned exactly in the middle of the Jiloca graben. Unusual topographic structures at the rim and in the area of the inner ring are interpreted as strike-slip transpression and transtension. Geological literature that still sticks to the old ideas and develops new models and concepts for the graben/basin structures, but ignores the huge meteorite impact and does not even enter into a discussion, must at best cause incomprehension.
... In agreement with this, these elements are frequently documented in the structural style of the Azuara structure (Fiebag, 1988, Konig, 1988, Katschorek, 1990, Ernstson and Fiebag, 1992 and may be related with impact rather than with tectonics. In a few cases, peculiar structural features occur, which are simply incompatible with tectonic processes (Gwosdek, 1988;Katschorek, 1990;Muller and Ernstson, 1990;Ernstson, 1994). ...
We report on the Azuara impact structure and its Rubielos de la Cérida compa- nion crater, which establish the largest terrestrial doublet impact structure presently known. Both structures have diameters of roughly 35 - 40 km and they have been formed in a purely sedimentary target. From stratigraphic considerations and palaeontologic dating, an Upper Eocene or Oligocene age is very probable Geological mapping has established abundant geologic impact evidence in the form of monomictic and polymictic breccias and breccia dikes, megabreccias, dislocated megablocks, remarkable structural features, extensive impact ejecta and impact sig- natures even in distant autochthonous deposits. The most striking impact evidence for both structures is given by strong shock metamorphism, including melt and dia- plectic glass, planar deformation features (PDFs), different kinds of impact melt rocks (from former silicate melt, carbonate melt, carbonate-phosphate melt) and suevite breccias. Glassy amorphous carbon particles in a solid C-O compound may be related with fullerenes and may originate from a quenched melt of extremely shocked coal or from extremely shocked limestones. It is assumed that the impact had considerable influence on the Mid-Tertiary regional geology of the Iberian System, and we suggest that respective geologic models which have so far not con- sidered this peculiar and far-reaching event, need considerable revision.
Types of gravitational movements in the Flysch Carpathians are related to tectonic and lithologic anisotropy of rock massifs. This article presents the main types of mass movements in the highly anisotropic flysch massifs: lateral spreading and rock flow, topple, translational, rotational and compound sliding and complex type of mass movements, which are illustrated by chosen forms described using structural analysis (joints, faults and other structural planes orientation). Topple is the typical mass movement for double ridges and top trenches (e.g. Gaworzyna in the Beskid Sądecki Mts.). Translational landslides with flat, structural sliding surfaces typical for shallow forms can develop along bedding planes (e.g. Duszatyn, Western Bieszczady Mts.) as well as along joints (Łopuszna, Gorce Mts.) and fault planes (Rzeki, Gorce Mts.). Currently used classification of the “structural landslides” is applied only to translational landslides. Shearing zones of deep-seated landslides are composed of structural sections (of joints, faults, bedding planes) and shearing elements. Consequently, most of the Carpathian landslides have developed as compound type (with non-circular sliding zones) representing complex movements, combined with various types of displacement: rotation, translation and/or topple. Purely rotational movements with circular failure (typical for isotropic material) have developed in the flysch where thick-bedded, hard sandstones are underlain by plastic shales (e.g. Mt. Kostrza in the Beskid Wyspowy Mts.). The influence of anisotropy of these rocks on sliding surface is significantly reduced, and plastic-type rocks stimulate rock flow development, which is usually later transformed into complex landslides with predominant rotational movement (e.g. rotational landslide with topple and flow elements on Mt. Muronka in the Beskid Śląski Mts.). Compound landsliding on Mt. Luboń Wielki (Beskid Wyspowy Mts.) represents an antithetic rotational slide with topple- and rotational-type movements.
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