Paleomagnetism of Middle Triassic Lavas From Northern Qiangtang (Tibet): Constraints on the Closure of the Paleo‐Tethys Ocean

Abstract

We present results from a paleomagnetic study of Middle Triassic lavas (~242–240 Ma) from the northern Qiangtang block to improve our understanding of the timing and kinematics of the closure of the eastern Paleo‐Tethys Ocean. Characteristic remanent magnetization directions carried by magnetite and hematite formed during high‐temperature oxidation during initial cooling of the lavas are successfully isolated by progressive thermal and alternating field demagnetizations. We bin 28 site mean directions into 20 independent direction groups that pass the fold test, average secular variation, and show no rock magnetic or petrographic evidence of weathering. These data establish the first lava‐based paleomagnetic pole of Middle Triassic age for the northern Qiangtang block (62.2°N, 196.4°E, A95 = 5.6°). We compare this pole to coeval poles from the North China Block and Tarim and estimate that the remnant Paleo‐Tethys or Hoh‐Xil‐Songpan‐Ganzi Ocean could have been up to 700 km at ~240 Ma. A comparison of the Triassic latitudinal history between the northern Qiangtang block and the North China Block and Tarim shows that the closure of the Paleo‐Tethys Ocean most likely occurred during the latest Triassic. Our review of published Permian‐Triassic poles from the northern Qiangtang block show that the average south‐north plate velocity of the terrane decelerated from ~8.5 cm/yr during ~300–240 Ma to ~3.6 cm/yr during ~240–210 Ma. We suggest that an arc‐continent collision between the northern Qiangtang block and a Paleo‐Tethys or Yidun arc around or before 240 Ma contributed to this change in plate velocity.

Paleomagnetic and Chronologic Data Bearing on the Permian/Triassic Boundary Position of Qamdo in the Eastern Qiantang Terrane: Implications for the Closure of the Paleo‐Tethys

“…The latter two estimated velocities are similar to that of the Himalayan Terrane (∼15.4 cm/yr) prior to its collision with the Lhasa Terrane (T. S. Yang et al, 2015) Huang et al (2018). The paleomagnetic data of the EQT can be seen in Table S3 (1, P. P. Song et al, 2017;2, Ma et al, 2019; 3, This study; 4, P. P. Song et al, 2020;5, P. P. Song et al, 2015), where Tarim, Eurasia and Gondwana are in Table S4. The solid gray pentagon represents the paleomagnetic data from the EQT was synchronous to the eruption of the Emeishan large igneous province in the SCB during the Late Permian (∼260 Ma, Guo et al, 2004).…”

“…P. Song et al, 2015P. P. Song et al, , 2017P. P. Song et al, , 2020Zhou et al, 2019; this study) (Table S3).…”

“…A total of 29 independent sites, 257 specimens (Figure 2, To better understand the drift history of the EQT during the Permian to Triassic, all 17 available paleomagnetic results from rocks in the region have been compiled (Table S3; Cheng et al, 2012, 2013, K. N. Huang et al, 1992Ma et al, 2019;X. Z. Li et al, 1999;Song et al, 2012;Song et al, 2015Song et al, , 2017Song et al, , 2020X. F. Yang et al, 2017;Zhou et al, 2019).…”

“…N. Huang et al., 1992; 10‐This study; 11‐Zhou et al., 2019; 12‐Cheng et al., 2012; 13‐P. P. Song et al., 2020; 14‐X. Z. Li et al., 1999; 15‐C.…”

Paleomagnetism of the Late Cretaceous Red Beds From the Far Western Lhasa Terrane: Inclination Discrepancy and Tectonic Implications

“…Paleomagnetism is one of the major methods that can be used for quantifying plate paleolatitudes and is thus crucial for constraining the history of plate movement (Achache et al, 1984; Appel et al, 1998; Bian et al, 2019; Cao et al, 2019; Huang et al, 2015; Liebke et al, 2010; Lippert et al, 2014; Ma et al, 2016; Song et al, 2020; Sun et al, 2006; van Hinsbergen et al, 2012; Yang, Ma, Bian, et al, 2015; Yan et al, 2016). Because the Lhasa terrane (LT) was located at the southern margin of Asia prior to India‐Asia collision (Figure 1a), reliable Cretaceous paleomagnetic data from the LT are essential to constrain the locations and geometries of the precollisional margins of Asia.…”