title: Progressive Indosinian N-S deformation of the Jiaochang structure in the Songpan-Ganzi fold-belt, Western China.
abstract: Integrated field data, microstructural and three-dimensional strain analyses are used to document coaxial N-S shortening and southward increase in deformation intensity and metamorphism at the Jiaochang structure. Two episodes of deformation (D1,D2) with localized post-D2 deformation have been identified in the area. The first deformation (D1) episode is defined by a main axial-plane of parallel folds observable on a micro- to kilometer-scale, while the second episode of deformation (D2) is defined by micro-scale metamorphic folds, associated with E-W oriented stretching lineation. These processes are the result of Indosinian tectonism (Late Triassic to Early Jurassic) characterized by nearly coaxial N-S compression and deformation. This is indicated by E-W trending, sub-parallel to parallel foliation (S1, e.g. axial-plane of folds, and S2, i.e. axial-plane of metamorphic folds, crenulation cleavage) and lineation (L1, e.g. axis of folds, and L2, i.e. stretching lineation, axis of metamorphic folds and B-axis of echelon lens). Most of the porphyroblasts and minerals (e.g. pyrite, biotite) show two growth phases with localized growth in the third phase (muscovite). The progressive D1-D2 structure is widespread in the south of the Jiaochang area, but only D1 structure crops out at the north. The strain intensity (γ), compression ratios (c%) and octahedral strain intensity (εs) are similar across the Jiaochang structure (i.e., γ ≈ 1.8, c ≈ 27%, εs = 0.9), showing a broad range of Flinn values (K = 0.77 to 7.57). The long-axis orientations are roughly symmetric between two limbs of the structure. Therefore, we suggest that the architecture of the Jiaochang structure has been controlled by coaxial N-S shortening and deformation (D1-D2) during the Indosinian tectonic epoch, with insignificant post-D2 deformation.
authors.affiliation: State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation/Chengdu University of Technology, Chengdu, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Deng
authors.forename: Shugen
authors.initials: S
authors.lastname: Liu
authors.forename: Sun
authors.initials: S
authors.lastname: Liu
authors.forename: Luba
authors.initials: L
authors.lastname: Jansa
authors.forename: Zhiwu
authors.initials: Z
authors.lastname: Li
authors.forename: Yong
authors.initials: Y
authors.lastname: Zhong
mesh_terms: D000538:Aluminum Silicates / Q000737:chemistry*; D002681:China; D005296:Ferrous Compounds / Q000737:chemistry*; D005843:Geography; D055593:Geological Phenomena; D005844:Geology / Q000379:methods; D008903:Minerals / Q000737:chemistry*; D013997:Time Factors
chemical_list: D000538:Aluminum Silicates; D005296:Ferrous Compounds; D008903:Minerals; C517971:muscovite; C047410:biotite