3-D geomechanical restoration and paleomagnetic analysis of fault-related folds: An example from the Yanjinggou anticline, southern Sichuan Basin Yiquan Li a, b, * , Dong Jia a, * , Andreas Plesch c , Judith Hubbard c , John H. Shaw c , Maomao Wang a a Institute of Energy Sciences, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210093, China b State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing 102249, China c Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA 02138, USA article info Article history: Received 24 August 2012 Received in revised form 19 June 2013 Accepted 22 June 2013 Available online 1 July 2013 Keywords: Fault-related fold 3-D restoration Structural curvature Paleomagnetism Sichuan basin abstract We examine the development of the Yanjinggou anticline, a fault-propagation-fold in the southern Longmen Shan, through an integrated study of structural geometry, strain, and paleomagnetism. The 3-D structural and strain restoration models generated in our analysis reveal that the NE-trending Yanjinggou fold has a curved map trace that is convex to the southeast. The fold has three distinct regions charac- terized by different strain patterns: contraction in the core of the fold, extension in the outer arc, and a forelimb with distributed shear. To further understand the kinematics of the Yanjinggou anticline, we performed paleomagnetic analysis on 184 oriented samples collected across the structure. Anisotropy of magnetic susceptibility (AMS) measurements and stepwise thermal demagnetization were conducted. A strike test was applied to the high temperature component (HTC) in order to identify rotation around the arc. The result indicates that the Yanjinggou anticline is a progressive arc, with a minor initial curvature and a dominant secondary curvature related to vertical-axis rotation synchronous with thrusting. The primary curvature and initial development of the structure correlates with the growth of the southern Longmen Shan in Late Miocene. The secondary curvature correlates with displacement extending since Late Pleistocene toward the southeast into the central basin along the detachments that underlie the structure. Lateral gradients in displacement along this underlying detachment provide a mechanism for producing the vertical rotation of the anticline. AMS results and historical earthquake analysis imply that the fault-propagation fold, along with other NE trending structures in the southern Sichuan basin, are tectonically active and accommodate east-west crustal shortening in the basin. By integrating 3-D structural and strain restoration modeling with systematic AMS and paleomagnetic methods using statistical analysis, we closely constrain how the Yanjinggou anticline developed, and provide insights into the formation of fault-related folds with curved shapes in map view, which are common in other fold-and-thrust belts around the world. Ó 2013 Elsevier Ltd. All rights reserved. 1. Introduction Many mountain belts around the world show some degree of curvature in map view, including the Alaskan orocline, the Appa- lachians, the Alps, the Ibero-Armorican arc, the Cantabrian arc, the Rif-Betic, the Aegean arc, and the Himalayas (Ramsay, 1981; Tapponier et al., 1982; Brun and Burg, 1982; Stamatakos and Hirt, 1994; Stewart, 1995; Johnston, 2001; Speranza et al., 2003; Weil and Sussman, 2004). The mountains extend toward the foreland, and the convex structural trends are referred to as salients, first depicted by Miser (1932). The counterpart of a salient is a recess, which is concave toward the foreland. Over the past century, ge- ologists have recognized that the study of oroclines can help in understanding the development of fold-and-thrust belts. Such studies were initiated by Norris and Black (1961), and improved and popularized by studies such as Van der Voo and Channell (1980), Schwartz and Van der Voo (1983, 1984), Bachtadse and Van der Voo (1986), Hirt and Lowrie (1988), Butler et al. (1995), Speranza et al. (1997), Kollmeier et al. (2000), Roperch et al. (2006), Weil (2006), and Weil et al. (2000, 2001 and 2010). * Corresponding author. E-mail addresses: yiquanli@nju.edu.cn (Y. Li), djia@nju.edu.cn (D. Jia). Contents lists available at SciVerse ScienceDirect Journal of Structural Geology journal homepage: www.elsevier.com/locate/jsg 0191-8141/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jsg.2013.06.009 Journal of Structural Geology 54 (2013) 199e214