Magnetostratigraphic study of the Kuche Depression, Tarim Basin, and Cenozoic uplift of the Tian Shan Range, Western China

Abstract

Magnetostratigraphic and rock magnetic results from 1006 horizons in Paleogene and Neogene sediments between the upper Kumugeliemu Formation and the base of the Kuche Formation within the Kuche Depression of the Tarim Basin, NW China, are used to evaluate postcollisional uplift and deformation in the Tian Shan Range. Characteristic remanences with both normal and reversed polarity were isolated by thermal demagnetization, generally between 300 and 690 °C, and a composite magnetostratigraphy is constructed from data at 969 accepted levels correlating with polarity chrons C12n to C3r dated between ∼ 31.0 and ∼ 5.5 Ma on the CK95 geomagnetic polarity time scale. Observed height-dependent changes of rock magnetic parameters ( k m and AMS ellipsoid parameters) indicate that these sediments were influenced by weak deformation with the succession accumulated before ∼ 15 Ma recording the effects of compressive deformation. This finding, together with two substantial increases in accumulation rate at ∼ 16–17 and ∼ 7 Ma, define a framework for Cenozoic uplift and deformation of the Tian Shan Range. We argue that thrusting in the south of the range was probably initiated at ∼ 20 Ma and followed by rapid uplift at ∼ 16–17 Ma. On the assumption that sediment accumulation in western China was still predominately tectonically controlled at ∼ 7 Ma, another later pulse of rapid uplift with a much larger regional influence is also recognized in the Tian Shan. The Kuche Depression was subjected to two postcollisional phases of rotational deformation with clockwise rotation prior to ∼ 12 Ma (∼ 1.36°/Ma) succeeded by counterclockwise rotation (at ∼ 1.64°/Ma) after ∼ 12 Ma and possibly continuing to the present day. This rotational deformation is not temporally related to the history of basin formation resolved from the magnetostratigraphy and may be linked to block interactions with adjoining terranes.