In:
Tectonics, American Geophysical Union (AGU), Vol. 18, No. 1 ( 1999-02), p. 75-91
Abstract:
In the western Rhenish Massif, the Rhenohercynian fold and thrust belt of the Middle European Varsicides exposes a telescoped complete Devonian to Early Carboniferous passive margin. This permits the analysis of geometry and kinematic processes of passive margin accretion to an erogenic wedge. During Variscan collision (330–300 Ma), the sedimentary cover of the passive margin was shortened by some 50% or 180 km. Crustal scale balancing and restoration reveals a wide, symmetric rift with a central graben. A marginal plateau separated this failed Lower Devonian rift from an Emsian‐Middle Devonian oceanic basin in the south, remnants of which are preserved in the southernmost imbricates and the Giessen‐Harz nappes. The seismically well‐imaged Aachen‐Midi detachment (Faille du Midi) acted as the basal decollement of this thin‐ to thick‐skinned orogenic wedge. It shows a ramp and flat geometry from the blind tip down to middle crustal levels. Owing to its position below the base of the basin fill, the thick synrift sequence and structure controlled structural evolution during contraction by localizing thrust branch lines and by inversion of rift structures, synthetic to the subduction direction, with formation of basement footwall shortcuts. Moreover, the three‐dimensional detachment geometry shows large‐scale oblique ramp‐flat features which control the architecture of the belt and the distribution of metamorphic grade. Rocks and fabrics from the detachment show that the latter was located at the transition into the ductile field at the fossil 300°–400°C isotherm. In the restored section, the detachment trajectory displays a saucershaped geometry rising to the surface at the rear and at the front. This suggests that the basal detachment propagated into the passive margin by ductile failure during lithospheric flexure under the load of an advancing upper plate. The regional pattern of synkinematic metamorphic grade shows varying modes of margin accretion: basal underplating into the orogenic wedge by the shelf slope and marginal plateau with formation of duplex stacks and elongate thrust sheets and frontal accretion of the remaining thicker failed rift in the north into the propagating wedge with formation of several imbricate fans. Cyclical changes in accretion history and/or critical taper are suggested by spaced domains of out‐of‐sequence thickening. These are also related to internal domainal kinematic partitioning of the wedge, controlled by oblique collision.
Type of Medium:
Online Resource
ISSN:
0278-7407
,
1944-9194
Language:
English
Publisher:
American Geophysical Union (AGU)
Publication Date:
1999
detail.hit.zdb_id:
2013221-9
detail.hit.zdb_id:
780264-X
SSG:
16,13
SSG:
13
Permalink