Magnetostratigraphy of the Dali Basin in Yunnan and implications for late Neogene rotation of the southeast margin of the Tibetan Plateau

Abstract

[1] The rotation pattern and fault activity in the southeast margin of the Tibetan Plateau (SEMTP) provide meaningful constraints on the geodynamic evolution of the plateau. However, the lack of Cenozoic paleomagnetic studies and accurate age constraints on Neogene sediments prevents a better understanding of the late Cenozoic tectonic activity in this area. To clarify the tectonic rotation pattern and deformation history of the SEMTP, we report new magnetostratigraphic data from a late Neogene sedimentary sequence in the Dali Basin, northwestern Yunnan Province, China. Rock magnetic analyses indicate that both magnetite and hematite are the main carriers of the characteristic remanent magnetizations (ChRMs). Magnetostratigraphic results show that the sedimentary profile spans from Chron C4n.1r to Chron C2n. The age of the sedimentary sequence in the Dali Basin can thus be paleomagnetically constrained to an interval from late Miocene to early Pleistocene. The basal age of the sediments is~7.6 Ma, which indicates that the unroofing of Diancang Shan and activation of the Dali fault system were initiated at this time. The appearance of conglomerates and syntectonic sediments suggests the reactivation of the Dali fault system at 2.5 Ma. Moreover, the overall mean ChRM direction suggests that the Dali Basin experienced significant (4.4 AE 2.5), but minor post-late Miocene rotation. This indicates that most of the clockwise rotation demonstrated by previous paleomagnetic studies in the SEMTP occurred prior to late Miocene and may be concentrated between Eocene and Miocene, which is contemporaneous with the sinistral slip of the Ailao Shan-Red River fault.

Acquisition of chemical remanent magnetization during experimental ferrihydrite–hematite conversion in Earth-like magnetic field—implications for paleomagnetic studies of red beds

“…Summarizing the results from previous studies (Tauxe et al, 1980;Løvlie et al, 1984;Tauxe and Kent, 1984;Kent et al, 1987;Stokking and Tauxe, 1987;Cogné et al, 1999;Yan et al, 2006;Liu et al, 2011;Li et al, 2013), DRM demagnetization curves appear to have a convex shapes and drop to zero around 670-680 °C (Figure 8a), but those of CRM display a concave shape and decay to zero gradually (Figure 8b). These distinct differences may be used to distinguish CRM from (most of the) DRM in red beds.…”

“…However, most of the DRM continues to unblock to temperatures up to 660-680 °C (Tauxe et al, 1980;Løvlie et al, 1984;Cogné et al, 1999;Yan et al, 2006;Li et al, 2013), distinctly higher than that of our CRM ( Figure 8). Apparently, CRM has a more distributed unblocking temperature spectrum (~200 to 600-650°C) than DRM (mostly 600-680°C).…”

Lake geochemistry reveals marked environmental change in Southwest China during the Mid Miocene Climatic Optimum

“…Third, previous magnetostratigraphic investigations on similar lithological facies in the nearby Dali and Xiaolongtan Basins suggest a sediment accumulation rate of 9-23 cm/ka [45,46]. Considering that the Dali Basin, Xiaolongtan Basin and Wenshan Basin share similar geological settings and lithologies, the sediment accumulation rate in the Wenshan Basin might be similar to that of Dali and Xiaolongtan Basins.…”

Pollen evidence of the palaeoenvironments of Lufengpithecus lufengensis in the Zhaotong Basin, southeastern margin of the Tibetan Plateau

“…The Zhaotong Basin is filled with the late Miocene to Pliocene lacustrine or swampy clays, silts, peaty clays and lignites (Chou and Zhai, 1962;Wang, 2010;Ji et al, 2013). Sediments rich in peaty clays are extensively distributed in the late Neogene basins of the southeastern margin of the Tibetan Plateau (Zhu et al, 2008;Biasatti et al, 2012;Li et al, 2013). Our samples were collected from the STB section (27°19′ 41.8″N, 103°44′13.7″E, with a maximum elevation of~1930 meters above sea level (m a.s.l.…”