Late Neoproterozoic paleomagnetic results from the Sugetbrak Formation of the Aksu area, Tarim basin (NW China) and their implications on the paleogeographic reconstruction and snowball Earth hypothesis

In order to better constrain the Neoproterozoic paleogeographic reconstruction of continents and to improve the understanding of the snowball Earth hypothesis, paleomagnetic collections on Neoproterozoic rocks were carried out in the Aksu area in the northwestern Tarim basin from 2001 to 2005. Six sites of limestone from the Chigebrak formation, 38 sites of sandstone and 4 sites of volcanic rocks from the Sugetbrak formation were sampled. No any stable component can be isolated from the limestone of the Chigebrak formation due to high viscosity. Sixteen sandstone sites present the Permian and/or Present Earth Field (PEF) remagnetization, one red sandstone site shows dispersed directions, one basalt site with an extremely high remanent intensity shows a significantly different magnetic diretcion with others. The remaining 24 sites of sandstone and volcanic rocks reveal stable characteristic remanent component (ChRm) isolated from 500 to 680°. The computed magnetic directions from these components are relatively consistent and significantly distinguished from those of younger ages. Both normal and reverse polarities have been observed though the normal one is dominant, moreover, the positive fold test is revealed after bedding corrections at 95% confidence level. A paleomagnetic pole is, therefore, calculated: Λ=19.1°, Φ=149.7°, k = 11.2, A95 = 9.3° with n = 24, yielding a paleolatitude of ~27°N for the sampling area. In spite of several attempts of geochronogical dating on the volcanic rocks no any direct age has been obtained. The chemostratigraphic correlation of this section with reference ones reveals an average of ~595 Ma for the age for this collection. Comparing paleomagnetic data of the similar ages from Australia and South China as well as other major blocks, the Tarim block seemed being closely located in the north of Australia. A new paleogeographic reconstruction has been attempted which showing a general feature of lower paleolatitude for these blocks. Referring to the paleogeographic reconstruction at about 760Ma proposed by Chen et al. (2004), the continental landmass including the above mentioned blocks seemed having experienced a relatively slow southward kinematic drift and kept their rather low paleolatitude. These observations provide, therefore, evidences to the snowball Earth hypothesis during the Marinoan glaciation episode in the late Neoproterozoic time.