Paleomagnetism of the Neoproterozoic diamictites of the Qiaoenbrak formation in the Aksu area, NW China: Constraints on the paleogeographic position of the Tarim Block

The middle to late Neoproterozoic records the transition from the dispersal of supercontinent Rodinia to the subsequent assembly of supercontinent Gondwana. Determining paleogeographic positions of the major cratons during this transition is crucial to understand the displacement histories of these blocks. However, high-quality paleomagnetic results from well-dated rocks during this period remain sparse for the cratons. In this paper, we have carried out a paleomagnetic study of the succession of the Cryogenian Qiaoenbrak formation (Fm) in the Aksu area, NW China, which contains diamictites that are of probable glacial origin. The age of the studied section is constrained at around 730 Ma based on the stratigraphy and recent zircon U–Pb chronologic data. Stepwise alternating field (AF) and thermal demagnetizations generally reveal two-component magnetizations. The low temperature (coercivity) component was removed by ∼300 °C (∼30 mT) and the high temperature (coercivity) component decayed toward the origin, defining the characteristic remanent magnetization (ChRM). Rock magnetic data indicate that magnetite is the major remanence carrier. A negative fold test for an isoclinal soft-sediment fold, the presence of both normal and reversed polarities, and positive conglomerate tests in conjunction with the presence of pristine sedimentary features by microscopic inspections of thin sections suggest that the remanence was acquired shortly after the deposition, i.e. post-depositional remanent magnetization (pDRM), which is very close to the magnetic field at the time of deposition. Fourteen out of 17 sites yield stable ChRMs with a mean direction of Ds = 246.1°, Is = 30.4°, ks = 14.1, α95 = 11.0° in stratigraphic coordinates, corresponding to a paleopole (Q = 6) at λ = 6.3°S, φ = 17.5°E, A95 = 9.1°. Together with geologic constraints, the new paleomagnetic results place the Tarim Block at 16.3 ± 5.6°N adjacent to either the west or east of Australia (WOA or EOA) at around 730 Ma, but the WOA position is preferred based on the overall relatively favorable evidence. In addition, since the studied diamictites of the Qiaoenbrak Fm that are of probable glaciogenic origin yield a low paleolatitude, this study may lend support to the “Snowball Earth” hypothesis during the Neoproterozoic times.

► First detailed paleomagnetic results directly from the Cryogenian diamictites in Tarim are reported.
► Field stability tests suggest that the remanence is likely primary.
► New paleomagnetic results yield a low paleolatitude of 16.3 ± 5.6°.
► The Tarim Block is positioned adjacent to Western Australia at ∼730 Ma.
► The low paleolatitude of diamictites lends support to the snowball earth hypothesis.