The Grenchenberg Conundrum In The Swiss Jura: A Case For The Centenary Of The Thin-skin Décollement Nappe Model (buxtorf 1907)

摘要

When Buxtorf in 1907 proposed his decollement hypothesis which visualized the Jura fold belt as a "folded decollement nappe" pushed by the Alps, he met with both fervent support of a few and skepticism by the many. As an illustration of recalcitrant problems within the Jura decollement nappe, that remain after 100 years, a model of the Grenchenberg complex is presented within the frame of 3D decollement kinematics, based on a set of rules gleaned from recurrent features in the Jura: (1) that generally progression of decollement was in sequence from south to north, (2) that in any given structure thrusting (with attendant ramp folding) preceded more generalized folding, (3) that progression of decollement was held up at "anchor points" (asperities) where the emerging thrusts and folds developed inflections with dextral transpres-sion in the western and sinistral transpresssion in the eastern flank, (4) that at such asperities more southerly structures, riding piggyback on the moving decollement sheet, often collided with more northerly ones and even merged with them. The asperities occur on fault/flexure lines of Paleogene origin, the Pierre Pertuis anchor point on the Vicques and the Grenchenberg extended anchor domain on the "Schwarzwald" Line (the continuation of the eastern border of the Rhinegraben). These lines produced deformations of the decollement surface in the middle Triassic evaporites which acted as boundary conditions at the bottom boundary of the decollement nappe, which led to stress concentrations and the nucleation of faults.