Thursday, 20 January 2011

Classic papers in structural geology I

I want to start a series of posts where I will compile abstracts of classic papers in structural geology. These are papers that should be part of the libraries of any structural geologist, and they marked a difference in their time. We are talking about publications from the 80's, 70's, or older, or perhaps younger, that changed the understanding of geology at that time. If possible, I also include a link to a downloadable version of each article*.
Because I am biased by contractional tectonics, please feel free to post in the comments the title of the papers you consider foundational in structural geology.
*Note: I am simply linking a url where you can find each article. I am also pasting here the abstracts, but I am not hosting the articles themselves, so I am not sharing any copyrighted material.

The structural relations of the Cumberland overthrust block are such as would occur if gliding on the thrust plane took place parallel with the bedding along certain shale beds in such a way that the thrust plane followed a lower shale bed for some distance, then sheared diagonally up across the intervening beds to a higher shale, followed that for several miles, and again sheared across the bedding to the surface.
Reasons are given for the belief that subsidiary faults and folds within the block are superficial and do not extend below the thrust plane. This possibility should be borne in mind when exploration of such structures for oil or gas is contemplated.
Study of the Cumberland block throws new light on the broader problems of the nature of folding and faulting in the sedimentary rocks bordering great mountain ranges and on the function of friction in setting limits to the distance through which overthrust blocks can be moved.

Balanced cross sections. Dahlstrom, C.D.A., 1969, Canadian Journal of Earth Sciences, vol. 6, p. 743
Post-depositional concentric deformation produces no significant change in rock volume. Since bed thickness remains constant in concentric thickness remains constant in concentric deformation, the surface area of a bed and its length in a cross-sectional plane must also remain constant. Under these conditions, a simple test of the geometric validity of a cross section is to measure bed lengths at several horizons between reference lines located on the axial planes of major synclines or other areas of no interbed slip. These bed Iengths must be consistent unless a discontinuity, like a decollement, intervene. Consistency or bed length also requires consistency of shortening, whether by folding and (or) faulting, within one cross section and between adjacent cross sections.
The number of possible cross-sectional explanations of a set of data is reduced by the fact that, in a specific geological environment, there is only a limited suite of structures which can exist. This imposes a set of local "ground rules" on interpretation. When these local restrictions are coupled with the geometric restrictions which follow from the law of conservation of volume, it is often possible to produce structural cross sections that have a better-than-normal chance of being right. The concept of consistency of shortening can be extrapolated to a mountain belt as a whole, thereby indicating the necessity for some kind of transfer mechanism wherein waning faults or folds are compensated by waxing en echelon features. These concepts are illustrated diagrammatically and by examples from the Alberta Foothills.


Mountain Belts and the New Global Tectonics. Dewey, J.F. and Bird, J.M., 1970. Journal of Geophysical Research, vol. 75, 14, 2625-2647.
Analysis of the sedimentary, volcanic, structural, and metamorphic chronology in mountain belts, and consideration of the implications of the new global tectonics (plate tectonics), strongly indicate that mountain belts are a consequence of plate evolution. It is proposed that mountain belts develop by the deformation and metamorphism of the sedimentary and volcanic assemblages of Atlantic-type continental margins. These assemblages result from the events associated with the rupture of continents and the expansion of oceans by lithosphere plate generation at oceanic ridges. The earliest assemblages thus developed are volcanic rocks and coarse clastic sediments deposited in fault-bounded troughs on a distending and segmenting continental crust, subsequently split apart and carried away from the ridge on essentially aseismic continental margins. As the continental margins move away from the ridge, nonvolcanic continental shelf and rise assemblages of orthoquartzite-carbonate, and lutite (shelf), and lutite, slump deposits, and turbidites (rise) accumulate. This kind of continental margin is transformed into an orogenic belt in one of two ways. If a trench develops near, or at, the continenal margin to consume lithosphere from the oceanic side, a mountain belt (cordilleran type) grows by dominantly thermal mechanisms related to the rise of calc-alkaline and basaltic magmas. Cordilleran-type mountain belts are characterized by paired metamorphic belts (blueschist on the oceanic side and high temperature on the continental side) and divergent thrusting and synorogenic sediment transport from the high-temperature volcanic axis. If the continental margin collides with an island arc, or with another continent, a collision-type mountain belt develops by dominantly mechanical processes. Where a continent/island arc collision occurs, the resulting mountains will be small (e.g., the Tertiary fold belt of northern New Guinea), and a new trench will develop on the oceanic side of the arc. Where a continent/continent collision occurs, the mountains will be large (e.g., the Himalayas), and the single trench zone of plate consumption is replaced by a wide zone of deformation. Collision-type mountain belts do not have paired metamorphic belts; they are characterized by a single dominant direction of thrusting and synorogenic sediment transport, away from the site of the trench over the underthrust plate. Stratigraphic sequences of mountain belts (geosynclinal sequences) match those asciated with present-day oceans, island arcs, and continental margins.

Thrust systems. Steven E. Boyer, and David Elliott, 1982. AAPG Bulletin; v. 66; no. 9; p. 1196-1230.
Geometric framework; a certain family of lines must exist where thrust surfaces join along branch lines or end at tip lines. The order in which the fault slices form has a marked effect on the geometry of the thrust system. These systems must be identified to understand the provenance of the synorogenic sediments. Part of a thrust belt may be dominated by one particularly large thrust sheet. In front and beneath these dominant sheets, there is a characteristic sequence of thrust systems with a regular pattern to the involvement of basement. New insight into some classic areas Mountain City and Grandfather Mountain windows, in the Southern Appalachians, Jura to the Pennines (in the Western Alps).

End of the first lot :-)

2 comments:

Doug R said...

this is an excellent idea, and hope you expand it. glad to see Boyer and Elliot. seems as if donath and parker GSA Bull on folds, and Hubbert and Rubey's paper on thrust mechanics should be on the list...

rajasthan government jobs said...

great article is shared above