China
Africa
Explore chapters and articles related to this topic
Metamorphic Rocks
Published in Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough, Earth Materials, 2019
Dexter Perkins, Kevin R. Henke, Adam C. Simon, Lance D. Yarbrough
Shock metamorphism, sometimes called impact metamorphism, occurs when a meteorite or other extraterrestrial body hits Earth. The impact generates great heat and pressure that can cause mineralogical and textural changes to bedrock. One typical feature is the formation of layers of glassy material, called planar deformation features, within mineral grains. If these features are in quartz grains, we call the grains shocked quartz. Shock metamorphism can also lead to formation of coesite, stishovite, and other high-pressure minerals that normally would never form at Earth’s surface. Additionally, the impact may form shatter cones in country rock—curved fracture surfaces similar to what develops when a flying rock hits a car windshield. Figure 10.36 shows shatter cones associated with a meteorite impact site next to the St. Lawrence River in Quebec.
Impact lithologies – a key for reconstruction of rock-forming processes and a geological model of the Popigai crater, northern Siberia
Published in Australian Journal of Earth Sciences, 2019
V.L. Masaitis, O.V. Petrov, M.V. Naumov
Impact-related lithologies in and around the Popigai crater are exposed over an area of more than one thousand square kilometres and form extended outcrops up to 150 m high and up to 10 km long (Figures 1). The total volume of the preserved products of impact melting (1750 km3; Masaitis et al., 1998) is exceeded only by the volume of melt rocks at the Sudbury impact structure (Grieve, Stoffler, & Deutsch, 1991). The variety of composition and structure of target lithologies opens the possibility of a comprehensive study of the influence of shock compression on different substrata. These underlying rocks underwent various degrees of shock metamorphism, ranging from weak jointing to total melting. The Popigai structure comprises a wide variety of newly formed rocks and minerals produced by the impact. In addition, diamondiferous impact rocks, which arose from shock compression of graphite-bearing gneisses, were discovered there for the first time (Masaitis, Futergendler, & Gnevushev, 1972). Impact rocks containing industrial diamonds form unique mineral deposits with resources measured to be ∼200 billion carats (Masaitis et al., 2013), surpassing the total resources of all diamondiferous kimberlite provinces in the world. These deposits (see also, e.g. Langenhorst, Shafranovsky, Masaitis, & Koivisto, 1999; Masaitis, Shafranovsky, & Grieve, 1999b) have no analogues among other types of commodities. The Popigai structure can thus be regarded as a standard complex impact crater that is most suitable as an empirical base for modelling of both cratering processes and diamond formation and distribution in impact structures.