Paleogene clockwise tectonic rotation of the Xining‐Lanzhou region, northeastern Tibetan Plateau

Abstract

To help understand the deformational history of the northeastern Tibetan Plateau, paleomagnetic samples were collected from 177 sites and two magnetostratigraphic sections at 16 localities distributed among Upper Jurassic‐Lower Cretaceous to Pliocene sedimentary and subordinate volcanic rocks within the Xining‐Lanzhou region (34–37°N, 101–105°E). A total of 127 sites at 12 localities yielded primary magnetizations confirmed by fold, reversal, and conglomerate tests. Age control on sedimentary rocks is provided by regional synthesis of chronostratigraphic data and our own biostratigraphic and magnetostratigraphic analysis presented in the companion paper by Horton et al. [2004]. Analysis of paleomagnetic declination combined with results from previous studies yield a remarkably consistent trend of vertical axis tectonic rotations across the studied region. Whereas 19.0 ± 7.2° to 37.8 ± 10.6° clockwise rotations are recorded consistently in all paleomagnetic localities in Lower Cretaceous to Eocene rocks, all paleomagnetic localities in Oligocene to Pliocene rocks have recorded minor to insignificant rotations, indicating that the Xining‐Lanzhou region has undergone a wholesale regional clockwise rotation during late Paleogene time. Consistent with regional chronostratigraphic and thermochronologic results, this late Paleogene tectonic rotation confirms that deformation reached regions of the northern Tibetan Plateau shortly after the initial collision of India with Asia. When compared to rotational paleomagnetic results from adjacent regions, several mechanisms can be proposed to explain the clockwise rotation. On the basis of consistency with geologic data we prefer a model involving clockwise rotation of the Xining‐Lanzhou region through right‐lateral shear, and associated shortening, related to northward indentation of the Qaidam basin.

Cenozoic uplift of the Tibetan Plateau: Evidence from the tectonic–sedimentary evolution of the western Qaidam Basin

“…From the Eocene to the Oligocene, the IndianeEurasian plates began their full collision (Patzelt et al, 1996;Wu et al, 2008;Xia et al, 2010). The collision zone itself could not accommodate all of the deformation, thus, forces no doubt propagated to the northern Tibet Plateau, which fits with evidence of deformation and uplift in northern Tibet Dupont-Nivet et al, 2004).…”

Paleomagnetism of the Middle–Late Jurassic to Cretaceous red beds from the Peninsular Thailand: Implications for collision tectonics

“…1, clockwise (CW) rotational pattern has been observed around eastern Himalayan Syntaxis by GPS measurements (Wang et al, 2001;Zhang et al, 2004;Gan et al, 2007;Allmendinger et al, 2007;Simons et al, 2007;Copley, 2008) as well as by paleomagnetic investigations (e.g. Dupont-Nivet et al, 2004;Tanaka et al, 2008). Features of clockwise rotational deformation have also been observed in the Shan-Thai Block, the northern Sundaland Block (Simons et al, 2007;Tanaka et al, 2008) and the Indochina Block (Yang and Besse, 1993;Takemoto et al, 2009).…”

Magnetostratigraphy and depositional history of the Miocene Wushan basin on the NE Tibetan plateau, China: Implications for middle Miocene tectonics of the West Qinling fault zone

“…at least late Oligocene until late Miocene or Pliocene time Dupont-Nivet et al, 2004;Fang et al, 2003;Yue et al, 2000;Shen et al, 2001;Jiang et al, 2007;Hough et al, 2010) and were not internally deformed until the late Miocene ($8 Ma) Fang et al, 2003;Molnar, 2005;Yuan et al, 2003Yuan et al, , 2007Zhang et al, 2006;Lin et al, 2010). The north-trending Jishi Shan did not appear as a barrier between the Xunhua basin and the Linxia basin until the late Miocene ($13 Ma) due to the formation of new thrust faults along the eastern front of the Jishi Shan (Hough et al, 2010;Lease et al, 2011).…”