Riller U., Lieger D., Gibson R.L., Grieve R.A.F., Stöffler D.
School of Geography and Earth Sciences, Origins Institute, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada; Museum für Naturkunde, Humboldt-Universität zu Berlin, Invalidenstrasse 43, 10115 Berlin, Germany; Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P.O. Wits 2050, Johannesburg, South Africa; Earth Sciences Sector, Natural Resources Canada, Ottawa, ON K1A 0E4, Canada
Riller, U., School of Geography and Earth Sciences, Origins Institute, McMaster University, 1280 Main Street West, Hamilton, ON L8S 4K1, Canada; Lieger, D., Museum für Naturkunde, Humboldt-Universität zu Berlin, Invalidenstrasse 43, 10115 Berlin, Germany; Gibson, R.L., Impact Cratering Research Group, School of Geosciences, University of the Witwatersrand, Private Bag 3, P.O. Wits 2050, Johannesburg, South Africa; Grieve, R.A.F., Earth Sciences Sector, Natural Resources Canada, Ottawa, ON K1A 0E4, Canada; Stöffler, D., Museum für Naturkunde, Humboldt-Universität zu Berlin, Invalidenstrasse 43, 10115 Berlin, Germany
Large-volume pseudotachylite bodies in impact structures are dike like and consist of angular and rounded wall-rock fragments enveloped by a microcrystalline and sporadically glassy matrix that crystallized from a melt. Knowledge of the formation of pseudotachylite bodies is important for understanding mechanics of complex crater formation. Most current hypotheses of pseudotachylite formation inherently assume that fragmentation and melt generation occur during a single process. Based on the structure of pseudotachylite bodies at Sudbury (Canada) and Vredefort (South Africa), we show that these processes differ in time and space. We demonstrate that the centimeter-to kilometer-scale bodies are effectively fragment-and melt-filled tension fractures that formed by differential rotation of target rock during cratering. Highly variable pseudotachylite characteristics can be accounted for by a single process, i.e., drainage of initially superheated impact melt into tension fractures of the crater floor. © 2010 Geological Society of America.
Complex craters; Differential rotation; Glassy matrices; Impact melt; Impact structures; Rock fragments; Single process; South Africa; Tension fractures; Time and space; Hydraulic structures; Fracture; basalt; cratering; formation mechanism; fracture; glass; impact structure; structural geology; tension; Canada; Free State; Ontario [Canada]; South Africa; Sudbury; Vredefort Dome