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Karakoram and Afghanistan |
Dipartimento di Scienze della Terra, Project Ev-K2 CNR, Via Mangiagalli 34, 20133 Milano, Italy
The oldest deformational structures recognized in the Karakoram sedimentary cover north of the Karakoram Axial Batholith (KAB) consist of an E-W deformed belt composed of Permian-early Cretaceous sediments. This belt is overlain with a stratigraphical unconformity by the Cretaceous Tupop conglomerates and subsequent Late Cretaceous marine sediments. In the Chapursan Valley a complex and polyphase antiformal stack consisting of a Permian to Cretaceous succession was recognized. Post-Cretaceous northward and northeastward directions of transport are shown by slip vectors along thrust planes and by fold axes in the Chapursan Valley, whereas NW-SE-trending folds due to northeastward transport were observed in the Shimshal Valley. The north-vergent structure is crossed by successive north-dipping thrusts along the northern side of the Chapursan Valley and along the contact between the sedimentary cover and the northern continuation of the KAB.
The last tectonic phase recognized in the Chapursan Valley caused the activation of an important set of E-W-orientated sinistral strike-slip faults. In the Shimshal Valley, large E-W sinistral and NW-SE dextral faults are present as well, and may be interpreted as a consequence of a NW-SE-directed simple-shear due to deformation along major NW-SE dextral strike-slip faults.
The sedimentary cover of the Karakoram was deformed under anchimetamorphic conditions in the Chapursan Valley, whereas sericite to muscovite low-grade metapelites with occurrence of chloritoid, epidote and biotite are present in the lower Shimshal Valley. Near the Shimshal Pass, andalusite, garnet, muscovite and biotite were found in phyllites at the contact aureole of an important belt of large previously unknown granitic bodies.
