Fault‐related fold styles and progressions in fold‐thrust belts: Insights from sandbox modeling

Abstract

Fault‐related folds of variable structural styles and assemblages commonly coexist in orogenic belts with competent‐incompetent interlayered sequences. Despite their commonality, the kinematic evolution of these structural styles and assemblages are often loosely constrained because multiple solutions exist in their structural progression during tectonic restoration. We use a sandbox modeling instrument with a particle image velocimetry monitor to test four designed sandbox models with multilayer competent‐incompetent materials. Test results reveal that decollement folds initiate along selected incompetent layers with decreasing velocity difference and constant vorticity difference between the hanging wall and footwall of the initial fault tips. The decollement folds are progressively converted to fault‐propagation folds and fault‐bend folds through development of fault ramps breaking across competent layers and are followed by propagation into fault flats within an upper incompetent layer. Thick‐skinned thrust is produced by initiating a decollement fault within the metamorphic basement. Progressive thrusting and uplifting of the thick‐skinned thrust trigger initiation of the uppermost incompetent decollement with formation of a decollement fold and subsequent converting to fault‐propagation and fault‐bend folds, which combine together to form imbricate thrust. Breakouts at the base of the early formed fault ramps along the lowest incompetent layers, which may correspond to basement‐cover contacts, domes the upmost decollement and imbricate thrusts to form passive roof duplexes and constitute the thin‐skinned thrust belt. Structural styles and assemblages in each of tectonic stages are similar to that in the representative orogenic belts in the South China, Southern Appalachians, and Alpine orogenic belts.

The Effects of Fault Geometry and Kinematic Parameters on 3D Fold Morphology: Insights From 3D Geometric Models and Comparison With the Dushanzi Anticline, China

“…Regardless, extension of the fold limb is considered to have occurred during the early stages of folding by the migration of layers through the fold hinge (Mitra, ), which is consistent with the modeling results. Fourth, our focus on the 3D trishear geometry means that all of the models were based on a fault‐propagation folding style, even though previous studies have reported three end‐members (i.e., fault‐bend folding, fault‐propagation folding, and detachment folding) and note that these folding mechanisms may change over time (e.g., Apotria & Wilkerson, ; Bernard et al, ; Dixon & Liu, ; Mitra, ; Storti & Poblet, ; Watkins et al, ; Yan et al, ). Fifth, many studies have identified that the 3D geometry can vary along strike due to the presence of displacement gradients, as well as differences in the geometry of the fault plane and end‐member models (Apotria & Wilkerson, ; Wilkerson et al, , ).…”

New insights into Phanerozoic tectonics of South China: Early Paleozoic sinistral and Triassic dextral transpression in the east Wuyishan and Chencai domains, NE Cathaysia

“…The Jurassic Yanshanian tectonothermal event involved a significant overprint of pre‐Jurassic structures and created a broad NE trending fold‐and‐thrust belt across South China [ Zhou et al ., ; Lin et al ., ; Yan et al ., , , ], associated with northwestward subduction of the paleo‐Pacific Plate [e.g., Zhang et al ., ; Wang et al ., ]. Subsequent Cretaceous tectonism involved crustal extension that led to widespread basin and dome generation and voluminous magmatism [ Gilder et al ., ; Zhou and Li , ; Lin et al ., ; Shu et al ., ; Kusky et al ., ; Li et al ., , , ].…”

Geochronology of early Mesozoic diabase units in southwestern China: metallogenic and tectonic implications

“…1; e.g. Yan et al 2003Yan et al , 2006Yan et al , 2016Wang, Y. J. et al 2013;Qiu et al 2017). The basement in this region consists of metamorphosed Neoproterozoic shallow-marine sandy to argillaceous detrital flysch units that are intercalated with volcanic rocks Qiu et al (2015a).…”