Oblique crustal detachment in the Variscan Schwarzwald,southwestern Germany |
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| Authors: | Dr A Krohe Prof G H Eisbacher |
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| Institution: | (1) Present address: Institut für Geologie, Universität Bochum, Postfach 102148, 4630 Bochum;(2) Present address: Geologisches Institut, Universität Karlsruhe, Kaiserstraße 12, 7500 Karlsruhe 1, FR Germany |
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| Abstract: | The Schwarzwald is part of the central polymetamorphic crystalline belt of the Variscan Orogen (»Moldanubian Belt«). From north to south it consists of four terranes: the metasedimentary Zone of Baden-Baden, the polymetamorphic Central Schwarzwald Gneiss Complex, the sedimentary — metamorphic Zone of Badenweiler-Lenzkirch, and the Hotzenwald Complex. The largest of these terranes is the Central Schwarzwald Gneiss Complex (CSGC) whose rocks record a history of protracted regional metamorphism and anatectic melt generation. During Variscan convergence between 350 and 325 Ma the CSGC became detached from a high-temperature lower crustal substratum and was emplaced southeastward over Paleozoic clastics, volcanic rocks and crystalline slivers of the Zone of Badenweiler-Lenzkirch and the Hotzenwald Complex. Kinematic indicators suggest that these early convergent movements on retrograde shear zones and the concomitant crustal thickening were superseded by movements on divergent shear zones. The ascent of voluminous granitic plutons from a mid-crustal zone of melt generation into the upper crust was probably triggered by a change in the crustal kinematics from overall convergence to overall divergence at about 325 Ma. In detail this process was probably diachronous. Detachment of upper crust and large scale melt generation in the middle crust of the Schwarzwald was probably facilitated by the tectonic stacking of water-rich pelitic clastics and gneiss slivers, with relatively even proportions of crystalline and pelitic materials. |
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