Effects of
Fault
Throw and Mechanical Stratigraphy on
Fault
Architecture in the Lenghu Fold-Thrust Belt, Qaidam Basin, NE Tibet
Abstract
Understanding the detailed fault
architecture at an outcrop scale of reverse faulting is critical for understanding the processes involved in fold-thrust belts as well as predicting the degree of
fault
compartmentalisation, the relationship between folds and faults, the distribution of strain and sub-seismic faulting deformation. Although previous studies have investigated the relationship between faults and folds developed within compressional systems, the detailed
fault
architecture of thrust faults remain poorly constrained, particularly at an outcrop scale. Not only are sub-seismic faults poorly imaged but even seismically resolvable structures are poorly imaged because of either steep dipping nature of reflections or complexity of
fault
architecture at an outcrop scale, which makes it difficult to predict the
fault
zone geometry precisely. The detailed
fault
architecture analysis of an exceptionally well-exposed fold-thrust belt in the Qaidam Basin is reported.
The Lenghu fold-thrust belt, provides an exceptionally well-exposed outcrop example of a reverse fault
-propagation fold, which enables high-resolution fieldwork to collect multiple scale data, including stratigraphy, strikes/dips, shallow subsurface profiles and detailed
fault
outcrop maps. Detailed stratigraphic logging coupled with high-resolution profiles provides a unique insight into the 3D geometry of a thrust
fault
at both regional and an outcrop scale. Integrating the high-resolution
fault
system mapping, we observe that 85-90% of the estimated throw is accommodated on the main
fault
zone, which has sufficient throw to be imaged on a seismic profile, while 15-20% of the throw is accommodated on smaller scale folds and faults that are beyond seismic resolution. The exceptionally exposed outcrops of the Lenghu thrust
fault
was mapped in detail, which allows us to understand the
fault
architecture patterns regarding to the
fault
throw (ranging from tens of centimeters to tens of meters).
Fault
outcrops with comparable
fault
throw but different level of mechanical heterogeneity also allow us to evaluate the control of mechanical stratigraphy on
fault
zone deformation. By coupling the structural observations within a stratigraphic context, we can demonstrate that although the main
fault
controls the overall strain in the system, the local stratigraphy plays a critical role in how the strain is accommodated and whether it is partitioned into single faults, multiple-
fault
splays or folding.
AAPG Datapages/Search and Discovery Article #90323 ©2018 AAPG Annual Convention and Exhibition, Salt Lake City, Utah, May 20-23, 2018