Impact Breccia

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A breccia (Latin word meaning “broken”), in general, is a rock that is a mixture of angular fragments from different types of rocks surrounded by a fine-grained "matrix" that may be similar to or different from the fragmented material. Breccias can be formed in many different geologic processes (tectonic, volcanic, sedimentary) and from a variety of materials. These rocks are extremely common in meteorite impact craters and attest to the destructive power of the impact event. Impact melt breccias and suevites both contain melt derived from the melting of target rocks, however, not all breccias contain melt. The breccia shown in the photo below (right) contains no melt and is simply termed an impact breccia. It contains fragments of gneiss and granite surrounded by a fine-grained matrix of pulverized grains from the same rocks. The gneiss fragments were not subjected to pressures as high as the shocked gneiss from the Haughton impact structure (see our Virtual Tours) so that they remain about as heavy as the original gneiss. In fact, it's hard to tell that these gneiss fragments are shocked— we can only tell this by looking at them under a microscope. Impact breccias can be found in many different settings within impact structures; for example, in the central uplift, in crater-fill deposits, and in the ejecta blanket.

See impact breccias in the Ries impact structure