The detachment era (1977–1982) and its role in revolutionizing continental tectonics

Abstract

After the discovery of thrust-and-nappe structure near the turn of the twentieth century, mountain belts were viewed as a direct expression of horizontal shortening of the continental crust, and continental rifting was viewed as a phenomenon distinct from it. By mid-century, broad consensus had emerged, mainly on the basis of physical reasoning, that thrust-and-nappe structure instead reflected gravity sliding secondary to vertical motions of the crust, as embodied in the influential stockwerk folding hypothesis. In a noteworthy period from 1977 to 1982, informally referred to here as the 'detachment era', not only did the last vestiges of support for the stockwerk hypothesis evaporate, but large-magnitude extension was discovered throughout the Cordillera, manifest primarily by extensional detachments and metamorphic core complexes. Soon afterward extensional detachments were recognized as a global phenomenon, forcing first-order reinterpretation of field relations in most orogens. Although plate tectonics is indisputably the most profound discovery in Earth sciences in the twentieth century, the detachment era arguably had commensurate impact on field-based interpretations of continental tectonics. Three decades later, controversy persists over the origin of metamorphic tectonites in core complexes, and over the existence and mechanics of slip on shallowly dipping extensional detachments.

Rifted continental margins: The case for depth-dependent extension

“…1g) (Jones et al, 1992, Fig. 6;Wernicke, 2009), which we consider as an early stage underdeveloped analogue of rifted margins where lower crust has yet to be removed. To be clear, some Type II African and South American margins are elevated but this is interpreted to result from regional mantle induced dynamical uplift, magmatic underplating, or other mechanisms, for example compression (e.g.…”

“…extension that is uniform with depth but varies laterally. It, like the corresponding derivative models, including depth-dependent extension (Royden and Keen, 1980;Kusznir and Karner, 2007), simple shear (Wernicke, 1981(Wernicke, , 1985, detachment (Lister et al, 1986(Lister et al, , 1991 and other compound models (Wernicke, 2009;Beaumont, 2002, 2003) do not provide insight into the mechanics because they are kinematic descriptions. We don't even know when UE is favored.…”

Evaluating connection of aquifers to springs and streams, Great Basin National Park and vicinity, Nevada

“…Prior to regional extension and block faulting that created much of the present Basin and Range physiography, large-magnitude extension in localized highly deformed and extended areas created metamorphic core complexes (Coney, 1980;Armstrong, 1982;Wernicke, 1992Wernicke, , 2013. Largemagnitude extension in the study area was along a gently to moderately dipping extensional fault (Cooper, 2008;Cooper and others, 2010) that has been called the Snake Range décol-lement by others (1983, 1999), but is here referred to as a detachment fault, as these features are often called (Armstrong, 1982;Wernicke, 1992Wernicke, , 2013.…”

“…Largemagnitude extension in the study area was along a gently to moderately dipping extensional fault (Cooper, 2008;Cooper and others, 2010) that has been called the Snake Range décol-lement by others (1983, 1999), but is here referred to as a detachment fault, as these features are often called (Armstrong, 1982;Wernicke, 1992Wernicke, , 2013. In the northern Snake Range, the gently dipping detachment fault generally separates ductilely deformed and metamorphosed Neoproterozoic and Cambrian rocks that lie beneath the fault from the highly faulted, brittle, deformed, non-metamorphosed Paleozoic rocks above it (Miller and others, 1983;Cooper and others, 2010).…”

The Tooth of Time: Lauge Koch's Last Lecture

“…Orogenic collapse, the thinning of tec-tonically overthickened crust, is a logical inference from East Greenland structure, when viewed as being adjacent to the great thrust nappes of western Norway and in the context of Caledonian collision between Baltica and Laurentia (McClay et al 1986;Hartz and Andresen 1995;Torsvik 1998;Hartz et al 2001;Gilotti and McClelland 2008;Henriksen and Higgins 2008;Cocks and Torsvik 2011). The idea of 'nappe tectonics in an extending orogen' was developed 3 km east of his office at Harvard (Wernicke 1981(Wernicke , 2009), but I know of nothing to suggest that Haller ever viewed East Greenland tectonics in a pre-Atlantic drift framework.…”