Thomas Voigt

Late Cretaceous intraplate thrusting in central Europe: Effect of Africa-Iberia-Europe convergence, not Alpine collision

A well-established event of intraplate basin inversion and basement thrusting affected central Europe in Late Cretaceous time. It is widely accepted to have resulted from the collision of the Alpine orogen with Europes margin. At that time an early Alpine orogen, located on the leading edge of the Adria microplate, still lay far southeast of its present-day position and had entered a phase of extension after a first orogenic event characterized by W- to NW-directed thrusting. This configuration is not likely to have induced SSW-NNE–directed thrusting and folding in the future European foreland that was still separated from the Alpine wedge by a strip of oceanic lithosphere. By contrast, the onset of intraplate contraction coincides with an important change in relative motion between the European and African plates. At ca. 90 Ma, Africas SSE-directed sinistral transform motion relative to Europe changed to NE-directed convergence. This agrees well with the timing and kinematics of intraplate thrusting in central Europe. Structures of similar age and kinematics occurring in southern France, Spain, and North Africa suggest that the Late Cretaceous pulse of contraction was caused by pinching west-central Europes thin lithosphere between Baltica and Africa. Only since the onset of N-directed thrusting in the Alps in Paleocene or Eocene time are the kinematics of the Alps and their European foreland compatible, indicating that mechanical coupling between Africa-Europe and the Adria microplate had been achieved.

Thick-skinned thrusting in the northern Tien Shan foreland, Kazakhstan: structural inheritance and polyphase deformation

Abstract The northern front of the Cenozoic Tien Shan mountains in Kazakhstan comprises east- to NE-trending thrust-related basement uplifts. Some of these are open, asymmetric anticlines, whereas others are fault-bounded blocks. Where emergent and exposed, the bounding faults dip steeply at 45–70°. Large-wavelength open folds in the Cenozoic cover also overlie basement structures. The Palaeozoic basement of volcanic, (meta-) sedimentary and granitic rocks contains older structures such as folds, slaty cleavage, faults and dykes. Some Cenozoic faults truncate all earlier structures, just as some Cenozoic folds are independent of the attitudes of underlying stratified basement rocks. The strongest control on the Cenozoic structure is exerted by steep, NW-striking basement faults that induce along-strike segmentation and lateral terminations of some basement ridges. A few of these basement faults had already been reactivated as normal faults during a Cenozoic phase of east–west extension that preceded folding and thrusting. Some normal faults show reactivation as dextral strike-slip faults during the contractional phase, which is still active today. Since the NE to east trend of the main basement ranges has no obvious precursor structures, we interpret the thick-skinned structures to essentially reflect the modern shortening direction, modulated but not dominated by pre-existing basement faults. Variations in local kinematics over time are probably due to strain partitioning in the anisotropic basement, not to changing far-field stresses. The occurrence of steep dip-slip reverse faults apparently unrelated to reactivation presents an unsolved mechanical paradox similar to some low-angle normal faults.

Cenozoic evolution of the Pamir and Tien Shan mountains reflected in syntectonic deposits of the Tajik Basin

Abstract The NE Tajik Basin in Central Asia, compressed between the ranges of the Tien Shan in the north and the Pamir in the south, is a key region for understanding the evolution of these mountain systems. Erosion and deposition history of the NE Tajik Basin and the adjoining orogens since the late Oligocene is reflected in the sedimentary record. The sedimentary rocks of the NE Tajik Basin are composed of thick units of proximal braided river deposits. They reflect large fluvial plains extending from the margins of the Northern Pamir and the Southern Tien Shan mountains, but are not related to the established lithostratigraphic scheme. Almost all Oligocene–Pliocene synorogenic deposits of the NE Tajik Basin were derived from the northern Pamir ranges, except upper Miocene–Recent proximal deposits close to the active margin of the Tien Shan. Initial uplift in some areas of the SW Tien Shan since the Oligocene was followed by a phase of low-energy sedimentation and a predominance of the southern source area. Since the middle Miocene, erosion of the ranges has occurred with the proximal sedimentation of coarse fluvial deposits along the northern margin of the Tajik Basin.

Climatically forced moisture supply, sediment flux and pedogenesis in Miocene mudflat deposits of south-east Kazakhstan, Central Asia

The continental settings of Central Asia witnessed increased desertification during the Cenozoic as a result of mountain uplift and the Paratethys retreat. The interaction of these tectonic‐scale processes with orbitally forced climate change and their influence on Asias atmospheric moisture distribution are poorly constrained. A Miocene succession of continental mudflat deposits, exposed in the Aktau Mountains (Ili Basin, south‐east Kazakhstan), has great potential as a terrestrial palaeoclimate archive. About 90 m of the 1700 m thick succession comprise alluvial mudflat deposits and appear as cyclic alternation of coarse sheet floods, mudflat fines and semi‐arid hydromorphic soils. In this study, bulk‐sediment mineralogy and geochemistry, magnetic susceptibility, sediment colour and palynology are used to reconstruct environmental conditions by determining changes and forcing mechanisms in the intensity of sediment discharge, weathering and pedogenesis. The results presented here indicate four major periods of arid soil formation and one palustrine interval characterized by higher evaporation rates under highly alkaline/saline conditions. A positive correlation between weathering indices and the Mg/Al ratio suggest that these horizons correspond to maximum rates of evapotranspiration and aridity. The formation of mudflat fines is, instead, interpreted as representing higher detrital sediment production by more intense alluvial fan activity during times of higher precipitation. Time series analysis of weathering indices, colour and magnetic susceptibility data yields cycle‐to‐frequency ratios with the potential to represent Milankovitch cyclicity with short and long eccentricity as dominant periodicities. Periods of pronounced aridity, paced by long eccentricity forcing, reflect changes in moisture availability. On longer tectonic timescales, the persistent appearance of gypsum indicates a shift towards more arid conditions. This trend in climate is considered to result from the closure of the eastern gateway of the Mediterranean to the Indian Ocean that restricted circulation and enhanced salinity within the Eastern Paratethys.

Die neogene Entwicklung des zentralen Tien Schan, Kasachstan. Erste Ergebnisse von Apatit-Spaltspurdatierungen und morphotektonischer Analyse von Satellitendaten

Einführung Der Tien Schan ist ein etwa E–W erstrecktes, rund 2500 km langes und bis 250 km breites Gebirge in Zentralasien. Einzelne Gipfel sind über 7000 m hoch. Obwohl durch die Kollision Indiens mit Asien entstanden, ist der Tien Schan ein Intraplatten-Orogen, dessen Hebung lange nach dem Beginn der Kollision vor 50Ma und weit nördlich der Sutur einsetzte (Sobel & Dumitru 1997). Von Tibet ist der Tien Schan durch das kaum deformierte Tarim-Becken getrennt (Abb. 1). Hohe und schroffe Topographie, starke Seismizität (Molnar & Ghose 2000) und GPS-Daten zeigen, dass das Orogen auch heute sehr aktiv ist (Abdrakhmatov et al. 1996, Reigber et al. 2001). Der Tien Schan nimmt gegenwärtig etwa 40% der Gesamtkonvergenz Indiens mit Asien auf. Die Struktur des Tien Schan wird dominiert von E–Wstreichenden, nach N und S gerichteten Überschiebungen (Avouac et al. 1993, Yin et al. 1998), die sich meist deutlich in der Morphologie äußern. Auffallend ist die großräumige Gliederung des Orogens durch NW–SE-streichende dextrale Blattverschiebungen, die auch in das nördliche Vorland reichen (Tapponnier