Tektonik und Magmatismus im NW-Karakorum

Summary

The geological exploration of the NW-Karakoram, carried out by the author during the ‘German-Austrian Himalaya-Karakoram Expedition’ in 1954, allows an insight into the complicated development of the Alpine type mountain building within the ‘syntaxial bend’ of Central Asia.

The ‘zone axiale’ of the NW-Karakoram (“Batura Muztagh”), with its synorogenetic young cretaceous evolution of different granodioritic rocks, seems to mark a boundary-line of influences between the mainly Variscan consolidated ‘Pamir Culmination’, and the Alpine activated ‘Himalaya Syntaxis’. Contrasting to the northern part of the NW-Karakoram (the “Tethys-Karakoram”, see Abb. 2 and 4 / ‘Zones V-Va’), which in all its paleogeography and tectonic features belongs to the southern extremity of the Pamirs, the southern part (‘Zones I–III’) on the other hand shows clear relations to the record of the Himalaya System. Especially the Tertiary (about Oligocene) synorogenetic regeneration (‘granitization’) of the Nanga Parbat Dome at the end of the Jhelum-Wedge, has extended its influences, mainly as dynamometamorphism, up to the ‘zone axiale’ and its crystalline schistose mantle-rocks (‘Zones III–IV’).

The results of a tectonic analysis of the different zones of the actual NW-Karakoram (II–V) show that each zone has its special B-tectonic structure of older deformation (see Abb. 3 and Taf. 15: b₁-b₂, B₃, B₄). Later the entire region was exposed to an unique pressure of a younger act of deformation (B₅), which caused the present actual general striking (WNW-ESE) of the zones. This B-tectonics are succeeded by huge elevations, mainly as different bloc-movement, of the mountain arcs. Contrasting to the synkinematic evolution of the granodioritic axis, distinct dykes of different igneous rocks of acid as well as basic composition, appearing in the zones III-IV-V, are younger than the B-tectonics.

Sections across the NW-Karakoram (Abb. 4) show the change in vergency within the ‘zone axiale’, without a remarkable nappe structure in the whole area.

Zusammenfassung

Im NW-Karakorum, einem ‚Innensegment‘ der großen zentralasiatischen Faltengebirgsscharung, überschneiden sich die Einflüsse der variskisch schon weitgehend konsolidierten „Pamirischen Scharung“ und der jungalpidisch noch hochaktiven „Himalaya-Syntaxis“, wobei die ‚zone axiale‘ des NW-Karakorum die paläogeographische und tektogenetische ‚Schnittlinie‘ darstellt.

Die in den einzelnen Baueinheiten („Zonen“ I bis V) spezifischen Formungspläne, deren relative Altersfolge (b₁-b₂-B₃-B₄) durch eine tektonische Gefügeanalyse ermittelt ist, werden von einem jüngsten B₅-Plan (dem heute vorherrschenden WNW-ESE-Generalstreichen des Gebirges) überprägt. Im Verlaufe dieser letzten radialen Einengung fanden steile, nord- und südvergente Auschiebungen statt. Weiträumige Deckenüberschiebungen sind diesem Baustil fremd!