The formation of an orocline by multiphase ... - ResearchGate

A.B. Weil et al. / Journal of Structural Geology 22 (2000) 735±756 749superimposed on an original linear anticline, and ismost noticeable in the southern section of the Proza'swestern limb, where an east±west-trending F 3 fold createdan amphitheater structure (Fig. 4). This resultedin a distinct inclination pattern that progressivelychanges from +158 in the north, to ±408 in the south(Fig. 13 between 47 and 57 km).Three fold tests were performed on the southernsites of the Proza domain. A ®rst fold test was performedon a meter-scale (010 m) tight anticline in thesouthern section of the western limb between sitesSL41w and SL41e. The anticline has (sub)parallellimbs and a north±south-trending fold axis with aninterlimb angle of 0348, which conforms to early (F 1 )folding. The in-situ magnetic directions are southeasterlywith shallow inclinations, and upon full tilt correctionbecome more southerly in direction, with steeppositive inclinations in the west and negative inclinationsin the east. A McElhinny (1964) incrementalfold test yielded a maximum kappa at 0% unfoldingwith a +58 inclination (Fig. 14a), which is interpretedas a B magnetization acquired after F 1 and F 2 folding.Fig. 11. (a) Stereographic projection of structurally corrected ViejosB component site means using calculated fold axes as stated in textand shown in Fig. 9. Open symbols represent upper hemisphere projections,closed symbols represent lower hemisphere projections andgray stars represent the reference B direction. (b) Structurally correctedViejos C component site means using calculated fold axes asstated in text and shown in Fig. 9. Open symbols represent upperhemisphere projections, closed symbols represent lower hemisphereprojections and white star represents the reference C direction. (c)Poles to corrected bedding (closed symbols) using individually calculatedrotation parameters for the C component magnetization (forrotation parameters see Table 2). Also shown is the resultant north±south-trending F 1 fold-axis remaining after the removal of F 2 and F 3deformation (black diamond).Table 3Comparison of rotation axes for Viejos Syncline B and C magnetizationsF2 Tectonic Correction Combined Single TectonicCorrectionF3 Tectonic Correction fromB magnetizationSite Number Single Tectonic Correctionfor C MagnetizationRotationFold AxisPlungeRotation Fold AxisTrendFold AxisPlungeRotation Fold AxisTrendFold AxisPlungeRotation Fold AxisTrendFold AxisPlungeFold AxisTrendSL58 60 51 85 60 30 32 19 78 50 67 63 74SL64 264 73 57 249 77 34 19 78 17 284 81 51SL69 264 73 50 249 77 34 19 78 13 276 81 46PL51 55 45 73 60 30 32 19 78 40 66 59 65PL52 55 45 67 60 30 32 19 78 19 63 49 46PL55 264 73 51 249 77 34 19 78 17 284 81 51PL56 264 73 46 249 77 34 19 78 12 274 81 45