科研之友
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摘要
The 3.8 km wide Steinheim Basin in SW Germany is a complex impact crater with central uplift hosted by a sequence of Triassic to Jurassic sedimentary rocks. It exhibits a well-preserved crater morphology, intensely brecciated limestone blocks that form the crater rim as well as distinct shatter cones in limestones. In addition, an impact breccia mainly composed of Middle to Upper Jurassic limestones, marls, mudstones and sandstones is known from drilling into the impact crater. No impact melt lithologies, however, have so far been reported from the Steinheim Basin. In samples of the breccia that were taken from drill cores we discovered small silicate particles (up to millimetres in size) that contain Fe-Ni-Co sulphides, as well as target rock clasts (shocked and unshocked quartz, feldspar, limestone) and droplet-shaped particles of calcite. The particles exhibit distinct flow structures and relicts of schlieren and vesicles. From the geochemical composition and the textural properties, we interpret these particles as mixed silicate melt fragments widely recrystallised, altered and/or transformed into hydrous phyllosilicates. Furthermore, we detected schlieren of lechatelierite and recrystallised carbonate melt. On the basis of impactite nomenclature, the glass-bearing impact breccia in the Steinheim Basin can be denominated as %26quot;Steinheim Suevite%26quot;.
- 出版日期2013-9
