PEI Yangwen, PATON Douglas, KNIPE Rob, LICKORISH Henry, LI Anren, WU Kongyou
Field-based investigation on fault architecture: a case study from the Lenghu fold-and-thrust belt, Qaidam basin, NE Tibetan Plateau
Geological Society of America Bulletin, ISSN: 0094-8276
https://doi.org/10.1130/B35140.1
Abstract: The fault zone architecture of a thrust fault zone is critical for understanding the strain accommodation and structural evolution in contractional systems. The fault architec-ture is also important for understanding fluid flow behaviour both along and/or across thrust fault zones and for evaluating potential fault related compartmentalisation. Be-cause meso-scale (1-100 m) structural features are normally beyond the seismic reso-lution, high-resolution outcrop in-situ mapping (5-10 cm resolution) was employed to study the deformation features of a thrust fault zone located in the Qaidam Basin, northeastern Tibetan Plateau. The excellent exposure of outcrops enables the detailed investigation of the Lenghu thrust fault zone and its architecture. The Lenghu thrust fault, a seismically resolvable fault with up to ~800m of throw, exhibits a large variation of fault architecture and strain distribution along the fault zone. Multiple structural do-mains with different levels of strain were observed and are associated with the fault throw distribution across the fault. Based on previously proposed models and high-resolution outcrop mapping, an updated fault zone model was constructed to charac-terize the structural features and evolution of the Lenghu thrust. The possible parame-ters that impact fault architecture and strain distribution, including fault throw, bed thickness, lithology and mechanical heterogeneity were evaluated. Fault throw distri-butions and linkages control the strain distribution across a thrust fault zone, with local folding processes contributing important elements in Lenghu especially where more incompetent beds dominate the stratigraphy. Mechanical heterogeneity, induced by different layer stacking patterns, controls the details of the fault architecture in the thrust zone. The variations in bed thicknesses and mechanical property contrasts are likely to control the initial fault dips and fault/fracture density. Large fault throws are as-sociated with wide strain accommodation and damage zones, although the relation-ship between the development and width of the fault zone with the throw accumula-tion remains to be assessed. By presenting the high resolution mapping of fault archi-tecture this study provides an insight into the sub-seismic fault zone geometry and strain distributions possible in thrust faults and reviews their application to assessing fault zone behaviour.
