Dear All,
Our Smith Lecture speaker this week is Ben van der Pluijm from the Department of Earth and Environmental Sciences. He is speaking on Smart Clays: States, Dates and Rates. Abstract below.
Smith Lectures are Friday afternoons from 4:00 to 5:00 pm, in Room 1528 C.C. Little Building. A reception is held following the lecture in 2540 C.C. Little. The events are free and open to the public. A full schedule for the term may be found on our website:
http://www.lsa.umich.edu/earth/events/
Best regards, -Anne
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Anne Hudon
Academic Student Services
Department of Earth and Environmental Sciences
University of Michigan
http://www.lsa.umich.edu/earth/
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Abstract:
Clay gouge is common in natural, shallow-crustal fault zones, including strike-slip, normal and reverse fault systems. The remarkable memory of clays provides information on fault mechanics, fault ages, fluid sources and orogenic evolution, as illustrated in active and recent tectonic settings.
Mineralogic and chronologic analysis of fault rocks from drill-cores of the San Andreas Fault Observatory at Depth (SAFOD) at Parkfield (CA) shows that active clay growth occurred at shallow crustal conditions. Brecciated host rock fragments are abundantly coated by polished and/or striated thin-films of hydrated clay minerals, creating an interconnected and pervasive network of displacement surfaces. Ar encapsulation dating of these mixed-layer nanocoatings shows recent crystallization, while laboratory strength experiments of these rocks support the proposal that clay gouge offers an alternative explanation for the fault strength paradox. Today, some SAFOD strands are sites of active creep behavior, reflecting continued (re)activation of clay-weakened zones.
Regional illite ages from fault gouge in the Canadian Rocky Mountain fold-thrust belt show that deformation occurred in distinct orogenic pulses instead of by continuous contraction. These Late Jurassic, mid-Cretaceous, Late Cretaceous, and early Eocene pulses are supported by significant changes in depositional patterns in the adjacent foreland. Orogenic pulses, separated by periods of tectonic quiescence, match plate boundary strain rates and represent deformation partitioning along a long-lived convergent margin.
Stable isotopic work of newly-formed clays in gouge shows a dominance of meteoric fluids in shallow fault zones, as preserved in their H signature. Crustal permeability on geologic time scales is facilitated by episodic, downward flow of surface waters through dynamic opening and closing of spaces in connected, transient fault zone networks that are activated during deformation pulses.
