| 1. |
- Deng, Hongling, 1983-, et al.
(author)
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Mega arrowhead interference pattern in the Central part of the Yanshan Orogenic Belt, North China
- 2015
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In: Journal of Structural Geology. - : Elsevier BV. - 0191-8141 .- 1873-1201. ; 80, s. 25-37
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Journal article (peer-reviewed)abstract
- The Chengde-Pingquan region is located in the central part of the Yanshan Orogenic Belt (YOB). At Daheishan and Pingquan in the central YOB, thrusts and folds of variable trends are displayed in 2 km-scale fold interference patterns. Detailed field mapping was conducted to decipher the geometry of these two superimposed structures. Map-view geometry and stereonet plots for outcrop-scale folds indicate that the superimposed structures form arrowhead interference pattern where NW-SE-trending F1 folds are refolded by later ENE-WSW F2 folding. After remove the effects of later faulting, restored map-views of the superimposed structures show that when the F1 folds have inclined axial surfaces but with no an overturned limb, an arrowhead interference pattern (here called modified type-2 pattern) can form. Our field data and reinterpretation of the findings of previous studies suggest that five major shortening phases have occurred in the Chengde-Pingquan region. The first two phases, which formed the superimposed folds, occurred earlier than the Late Triassic (D1) and during the Late Triassic to Early Jurassic (D2). These two phases were followed by three deformation phases that are mainly characterized by thrusting and strike-slip faulting, which strongly modified the large-scale fold interference patterns.
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| 2. |
- Deng, Hongling, 1983-, et al.
(author)
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Superimposed folding and thrusting by two phases of mutually orthogonal or oblique shortening in analogue models
- 2016
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In: Journal of Structural Geology. - : Elsevier BV. - 0191-8141 .- 1873-1201. ; 83, s. 28-45
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Journal article (peer-reviewed)abstract
- Orogens may suffer more than one phase shortening resulting in superposition of structures of different generations. Superimposition of orthogonal or oblique shortening is studied using sandbox and centrifuge modelling. Results of sand models show that in orthogonal superimposition, the two resulting structural trends are approximately orthogonal to each other. In oblique superimposition, structures trend obliquely to each other in the relatively thin areas of the model (foreland), and mutually orthogonal in areas where the model is thickened during the first phase of shortening (i.e. the hinterland). Thrusts formed during the first shortening phase may be reactivated during the later shortening phase. Spacing of the later phase structures is not as wide as expected, considering they across the pre-existing thickened wedge. Superposition of structures results in formation of type 1 fold interference pattern. Bedding is curved outwards both in the dome and basin structures. Folded layers are dipping and plunging outwards in a dome, while they are dipping and plunging inwards in a basin. In the areas between two adjacent domes or basins (i.e. where an anticline is superimposed by a syncline or a syncline is superimposed by an anticline), bedding is curved inwards, and the anticlines plunge inwards and the synclines outwards. The latter feature could be helpful to determine the age relationship for type 2 fold interference pattern. In tectonic regions where multiple phases of shortening have occurred, the orogenic-scale dome-and-basin and arrowhead-shaped interference patterns are commonly formed, as in the models. However, in some areas, the fold interference pattern might be modified by a later phase of thrusting. Similar to models results, superimposition of two and/or even more deformation phases may not be recorded by structures all over the tectonic area.
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| 3. |
- Deng, Hongling, 1983-
(author)
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Superimposition of Contractional Structures in Models and Nature
- 2015
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Doctoral thesis (other academic/artistic)abstract
- Superimposition of contractional structures is widely observed in different scales in the world. Superimposed structures form due to different processes: change in strain accommodation from one type of structure to another during a single progressive shortening; successive coaxial shortening phases separated by an unconformity; superimposition of different non-coaxial shortening phases. Using results of a series of systematic analogue models and detailed field structural mapping, this thesis focuses on the geometry and kinematics of such superimposed structures that are formed by these three processes. During a single progressive folding, thrusts develop within a fold to accommodate stain variations in different regime of the fold. Limited displacement along these thrusts does not significantly modify the geometry of the fold. However, during multiple shortening phases (coaxial or non-coaxial), early formed structures are modified by the later phase ones. The later thrusts can cut and displace the pre-existing structures. The early folds are tightened or interfered by the later folding phase. Pre-existing thrusts may be reactivated either in dip direction and/or along strike during the later shortening. The pre-existing structures in turn influence development of the later structures, which results in change in structure spacing. An angular unconformity between two shortening phases clearly truncates the early phase structures and separates structures of different levels. Unlike in the post-erosional layers, in the layers below the unconformity, complicated superimposed structures are visible. This thesis shows that geometry and sequence of structures formed during one progressive shortening or multiple shortening phases strongly depend on the mode of the superimposition (coaxial, orthogonal or oblique) and the orientation of pre-existing structures.
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