Journal
TECTONICS
Volume 35, Issue 9, Pages 2082-2116Publisher
AMER GEOPHYSICAL UNION
DOI: 10.1002/2016TC004187
Keywords
out-of-sequence thrusts; polycyclic thrust belts; North China Craton; Yanshan belt
Categories
Funding
- National Natural Science Foundation of China [90814007]
- China Geological Survey, Basic Research Project [1212011121073]
- U.S. National Science Foundation [EAR-1145230]
- Arizona LaserChron Center [NSF-EAR 1338583]
- Directorate For Geosciences
- Division Of Earth Sciences [1338583] Funding Source: National Science Foundation
- Division Of Earth Sciences
- Directorate For Geosciences [GRANTS:13694773] Funding Source: National Science Foundation
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The EW trending Yanshan belt, an intraplate fold-thrust belt located in the northern North China Craton that has experienced several episodes of deformation widely separated in time, is characterized by out-of-sequence thrusts. According to detailed mapping in the central Yanshan belt, five geometric and stratigraphic criteria used to aid in determining whether a thrust has an out-of-sequence geometry or not can be recognized. They are (1) unconformable relationships, (2) inclination of fault surfaces, (3) irregular changes in apparent offset along strike, (4) short fault length relative to apparent offset, and (5) in-sequence geometry. With the help of these criteria, two generations of out-of-sequence thrusts that postdate the original in-sequence thrusting in the central Yanshan belt are recognized. The ancestral southward verging fold-and-thrust belt that formed prior to 180Ma was deformed and cut by two younger generations of faults that are probably more deeply rooted and are constrained to between 172-165Ma and 152-135Ma. A series of thrusts with opposite vergence formed during the last period, resulting in abundant abnormal field relationships such as younger-on-older thrust relations, fold truncation, and cutting down-section. The nature and occurrence of faults in the Yanshan belt implies that superimposed deformation, a common feature in polycyclic orogenic belts, is a mechanism for the generation of out-of-sequence thrusting. This adds to mechanisms already described in the literature, such as maintaining constant critical taper at an orogenic scale, inhibition of the deformation front, and lateral changes in the nature of the decollement horizons.
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