Rock Magnetism And Magnetostratigraphic Study Of Cenozoic Keleau He Section In Kuche Depression

Cenozoic is an important period of the Tian Shan’s uplift, but details about how and when it were built remain vague. In order to better constrain the uplifting time of the southern Tian Shan and systemically classify the strata of Kuqa depression, we carried out a detail magnetostratigraphic study along Kelasu He section.The Cenozoic strata developed well on the Kelasu He setion, Kuqa depression. About1700oriented samples were collected from section A and section B, between which there was an overlap of60m. Section A covered Kumugeliemu Formation, Suweiyi Formation and the lower part of Jidike Formation, while section B covered the upper part of Suweiyi Formation, Jidike Formation, Kangcun Formation and the lower part of Kuqa Formation.About1600samples,12representative samples were collected for AMS test, rock magnetism test respectively. The results of rock magnetism indicate that hematite and subordinate magnetite are dominant magnetic carriers in the Cenozoic sediments of Kelasu He section. AMS analysis shows a primary sedimentary fabric.Most of the samples we demagnetized have two components:with mean direction of D=2.56°,1=65.76°, k=2.96, a95=2.22, was removed between100℃and350℃, and it must be the VRM of the modern earth magnetic field; The other one was acquired between560℃and580℃.1228samples have stable high-temperature components in total,599of which have normal magnetic field, and the mean direction after tilt correction is D=356.64°,1=47.30°, k=3.96, a95=2.75°. The remaining samples have reversed magnetic field and the mean direction is D=173.05°,1=-46.30°, κ=4.62, α95=2.52°. The results pass through consistency test, reversal test and fold test which indicate that ChRM was obtained when the sediments were depositing.35normal and34reversed polarity chrons were identified from the magnetic polar columns which were based on the inclination of the samples. It shows a good correlation with the GPTS (CK95) between4.1Ma to41.5Ma. It is constrained that the boundary age of the five formations from young to old is6Ma,9.3Ma,23.4Ma,33Ma and41.5Ma respectively. There is a little change at21.3Ma which indicates that the uplift of the southern Tianshan in Cenozoic was initiated at21.3Ma. At～7Ma, the sedimentation rate accumulated to266m/Ma, which may be correlated to the rapid uplift of the southern Tianshan. All the results show that the uplift of Tianshan is a tectonic evolution process, constituted with several impulse uplifts.