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14/05/2009

 

 

Yakovlev Fedor

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FOLDING formation research

 

Guide:

 

about the study of folded structures of several scale levels into thin-layered flysch-like sediments in a Hinterland

 

I. THE THEORETICAL BASEMENT

 

1. Foreland type of folding vs. Hinterland multi-scale folding: comparison of mechanical properties

 

Foreland (and an intermountain basin also)

Hinterland

Picture to left:

 

The scheme of interrelation of foreland and hinterland parts of fold-thrust belt. The example of island Taiwan structure. The picture after [Biq Chingchang. Taiwan island // Mesozoic-Cenozoic orogenic belts. The Geological Society London 1974. Version after translation in Russian, 1977]

After colored: yellow part foreland (signs 1 Mz basement of foreland, 2 Miocene, 3 Pliocene), 4 - Pleistocene molasses, green part hinterland folding in sing 6 upper Mz lower Miocene slates; red part sign 5 - Pz metamorphic complex.

Foreland

Sediments.

Type: molasses, terrigenous deposits, carbonaceous (limestone) layers.

Thickness of layers: from n0 meters up to n00 meters

Thickness of total cover: 1-5 km, 10 as maximal

Especial properties: The cleavage and metamorphism are rare. Packages of hinterland types of sediments may exist after sliding from upraised hinterland.

Folds.

Sizes: Usual width of folds (from hinge to hinge) are 0,n - n km - near thickness of total sedimentary cover. There are not fractal properties of folds.

Type: Parallel style of large folds. There are combinations of folds and thrusts.

Mechanisms: Mechanisms of separate fold formation (buckling, flattening, flexural flow etc.) are enough for description.

Shortening: Fold related shortening value is not high (1,2 - 1,5).

 

 

 

Basement (Transcaucasian massif and Scythian plate as example).

Type: There is rigid (in-deformable) basement. It is part of a platform. It is main reason for existing of sub-horizontal flat detachment between sedimentary cover units and the basement. Magnitude of displacement of nappies is large (n-n0-n00 km) as usual (not more than n-30 km for Alpine part of Greater Caucasus). The folding of basements rocks took place much earlier only.

Typical tectonic forms

There are thrusts, large folds, nappes etc. The detachment as boundary between sedimentary cover structure and the basement is obligatory.

 

Hinterland

Sediments.

Type: Slates, flysch, flysch-like sediments, terrigenous, carbonaceous layers, alternation competent and incompetent rocks.

Thickness of layers: from 0,01 meters up to 10-50 meters

Thickness of total cover: from 5 15, 20 km as maximal

Especial properties: The cleavage and light metamorphism (green shiest) are usual.

Folds.

Sizes: There are numerous small folds. Usual width of folds of complex of folds (from hinge to hinge) are from 0,1 m up to 0,n - n  km. It is essentially lesser than total thickness of sedimentary cover. There are fractal properties due to fractal properties of layering.

Type: Similar style of small folds. Different size folded structures have hierarchic properties.

Mechanisms: Different size folded structures have hierarchic properties and there are sets of mechanisms for each type of different size structures.

Shortening: Fold related total shortening value is high (1,5-3,0-5,0).

Basement (Grater Caucasus as example).

Type: The metamorphic basement has viscous more than sedimentary cover rocks but 1-2 order more only. A large folds (n km) and sub-vertical faults exist for partition surface basement-sedimentary cover boundary. The rare local detachments exist only. Magnitude of its displacement is local (0,n-n km) only. The folding of basements rocks took place much earlier mainly, but a remobilization of rocks exists also.

Typical tectonic forms

There are numerous folds and complex of different size folded structure. There are thrusts and normal faults. The detachment as boundary between sedimentary cover structure and the basement is absent. Typical forms should be described yet.

 

 

The usage of fold-thrust structure in combination with detachment as analogy to foreland structures is typical error, because the mechanical properties of hinterland sedimentary cover and the basement are quite other then in a foreland.

 

Publications. First in time publication is (Yakovlev F.L. Quantitative methods of analysis of natural formations mechanisms for folds and for systems of linear folding // Problems of tectonophysics. To fortieth anniversary of foundation by M.Gzovsky the Tectonophysics Laboratory in the Institute of physics of the Earth RAS. / Moscow. Publishing of IPE RAS. 2008. pp. 149 188. [in Russian]  PDF-R    New , description on page 155, N 39 in List-En).

 

2009, ,