Paleomagnetic estimates of total rotation in basement thrust sheets, Axial Zone, Southern Pyrenees.

摘要: Palaeomagnetism is a powerful tool for identifying rotations about any axis. A palaeomagnetic study in basement thrust sheets the southern Axial Zone, Pyrenees, has demonstrated that 3-D can be identified terrain where no other palaeohorizontal markers exist. Three different movement histories are described within stack of six sheets. The lowermost unit experienced doming and tilting horizontal axis at time Lo clockwise rotation vertical 25’. ‘ihe middle four have rotated by 35 60’ been Lilted 40 to 65’ Lhe north. uppermost sheet tilting, indicating Lhrust (or reverse fault) had an original attitude similar its present steep northward dip. This illustrates potential method discriminating between models evolution Pyrenees which invoke structures central region originally attitude, either rooted into zone inhomogeneous shortening lower crust or decolled on shallow fault, those subsequently back-steepened. INTROD1LJCTION geometry internal parts orogenie belts difficult determine since orientation igneous polydeformed basament rocks not known. ‘ihis problem great significance conflicting fundamentally modeis deep structure proposed. surface ex182 E. A. McClelland andA. 311. McCaig pression Tertiary faults shows fanning many authors. Segurel Daignieres (1986), Seguret (1972), Choukroune (1973) favour tectonic interpreiation thrusts steepen downwards crust. Williams ami Fiseher (1984), Parish (1984) prefer thin skinned model ali thmsts assumed originated angles steepened backthrusting piling imbricates antiformal stacks. Deramond et al (1985) propose Lhickskinned root down join basal detachment Moho. (1986) discussed ihe relative merits these modeis. In this papen we will demonstrate estimates made total three-dimensional (3-D) sheets, methods Lherefore may enable us future resolve confliet bet’ween vertical, Lhin thick-skinned Rete preliminary suite late Carboniferous dykes cut Silurian margin Pyrenean zone, south Maladeta granodiorite. area post-Hercynian Triassic redbeds imbricated folded during Alpine southwards directed thrusting. Where preserved overlying Llie palaeomagnetie tilt agree well with amount Lilting bedding. GEOLOGICAL BACKGROUND geology granodiorite Pont de Suert, Mey, (1969). Fig. 1 much simplified sketch map sampling localities. Hercynian deformation affected sediments from Cambro-Ordovician ji age. These intrusives ofthe Bono complex, probably asssociated Stephanian volcanies found Erill Casteli. Unconformably deformed upper Carboniferous, Permian conglomerates aid red sandstones. southward thrusting ocassional stack. Six separate identified. (sheet 1) extends northern edge Nogueras (Figs. 6 7). ends exposure 1. unconformity steeply dipping aL shallowly iorthward indic,ating P aeom anetic estim ates o ta lrtation bsem eni. 83 Z W w t ‘o ~ N ce, <-1 o— 4 D