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Impact breccias and breccia dikes in the Azuara structure

Polymict basal breccia (sawed and polished surface) from the Azuara impact structure (south of Fuendetodos).

Partly melted and/or decarbonized limestone fragments in a dense and extremely hard matrix showing flow texture. Note the 'ghost' component (arrow) where only few well-rounded, interior particles have survived. The basal breccia is considered an equivalent to suevite impactites in other impact structures (also see Ernstson & Fiebag 1992 and The suevite page).

A different aspect of the basal breccia (found near Cucalón). Sawed and polished surface; scale bar = 1 cm.

Azuara impact structure: Polymict basal breccia composed of Paleozoic and Mesozoic components (exposed near Herrera de los Navarros). The whitish zones of the matrix may be composed of decarbonized limestone or/and relics of carbonate melt.

Azuara impact structure: Polymict basal breccia. Note the flow texture and the grading of the components which are preferentially adjusted to the flow. Exposed near Monforte de Moyuela.

Azuara impact structure: shocked polymict breccia with flow texture and plastically deformed components. Near Santa Cruz de Nogueras. Millimeter scale.

Monomict breccia showing intense mortar texture. Note the distinct fitting of most of the components. Muschelkalk limestone, Monforte de Moyuela. Coin diameter 23 mm.

Azuara impact structure: Polymict breccia displaying a component heavily torn to shreds. Note the flow texture, the preserved fitting, and the string of fragments with continuously decreasing size (arrow). Near Santa Cruz de Nogueras.

Azuara impact structure. Shocked polymict breccia with dominating Paleozoic sandstone components (near Santa Cruz de Nogueras). Note the knife-edged fractures and the preserved fitting of the components. This suggests immediate embedding and "freezing" within the matrix after brecciation.

Azuara impact structure. Shocked polymict breccia (near Santa Cruz de Nogueras). Note the whitish crust of the limestone components (arrows), which probably results from decarbonation at elevated temperatures. Comparable decarbonation crusts are observed also in impact breccias of the Ries crater.

Azuara impact structure: Shocked polymict breccia (near Santa Cruz de Nogueras). The components are completely decomposed and sandwiched in the matrix displaying distinct flow texture.

Azuara impact structure: Shocked polymict breccia displaying flow texture and peculiarly decomposed component. Exposed near Santa Cruz de Nogueras.

Azuara structure: polymict impact breccias displaying different matrices in sharp contact. Top: near Santa Cruz de Nogueras; buttom: near Herrera de los Navarros. - At first sight, the breccias might be confused with calcrete. However, the sharp-edged components and shock-metamorphic effects confirm an impact origin.

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