Late Cenozoic magnetostratigraphy and anisotropy of magnetic susceptibility of the Baiyanghe section from the Hoxtolgay Basin: Implications for the uplift of the West Junggar Mt Range, NW China

Abstract

To better constrain the tectonic evolution of Central Asia under the influence of the India-Asia collision, we performed combined magnetostratigraphy and anisotropy of magnetic susceptibility (AMS) analysis of the Baiyanghe section on the northern margin of the Hoxtolgay Basin (West Junggar Mt Range, northwestern China). The observed magnetostratigraphy shows a total of 14 pairs of normal and reversed geomagnetic polarity zones in the well-exposed ∼360m thick section. In tandem with two ESR dating results, these zones can be reliably correlated with the geomagnetic polarity time scale (GPTS) from C3An.2r to C1n, and yield an age ranging from ∼7.0Ma to ∼0.2Ma. The long hiatus between the Mesozoic and the late Cenozoic, corresponding to the age of the basal conglomerates, suggests that uplift of the West Junggar Mt Range was initiated at least at ∼7.0Ma ago. Furthermore, the onset of massive conglomerate deposits, as well as marked increases in sedimentation rate, k, T and Pj of AMS, occurred at ∼3.6Ma. These notable changes are coeval with the peak deformation in Central Asia. Considering the depositional diachroneity of the Xiyu conglomerates and the predominantly dry climate in Central Asia since at least the late Cenozoic, we suggest that accelerated uplift of the West Junggar Mt Range at ∼3.6Ma should be the main factor controlling these multiple changes within the Baiyanghe section. Another marked increase in conglomerate content, sedimentation rate and κ occurred at ∼1.1Ma. The cause of this event deserves further investigation in the future.