New Late Jurassic to Early Cretaceous Paleomagnetic Results From North China and Southern Mongolia and Their Implications for the Evolution of the Mongol‐Okhotsk Suture

Abstract

To better constrain the evolution of the Mongol‐Okhotsk suture, we carried out new paleomagnetic studies on Sharilyn Formation (~155 Ma) and Tsagantsav Formation (~130 Ma) in southern Mongolia, Amuria Block (AMU), and Tuchengzi Formation (~140 Ma) and Dadianzi/Yixian Formation (~130 Ma) in the Yanshan belt, North China Block (NCB). A total of 719 collected samples (from 100 sites) were subjected to stepwise thermal demagnetization. After a low‐temperature component of viscous magnetic remanence acquired in the recent field was removed, the stable high‐temperature components were isolated from most samples. The high‐temperature components from each rock unit passed a fold test and a reversal test, indicating their primary origins. The corresponding paleomagnetic poles were thus calculated. For AMU, the ~155 Ma pole is at 74.7°N/232.5°E (A95 = 3.7°), the ~130 Ma pole at 74.6°N/194.7°E (A95 = 2.9°); for the NCB, the ~140 Ma pole is at 82.7°N/208.6°E (A95 = 4.3°), the ~130 Ma pole at 80.5°N/197.4°E (A95 = 2.3°). By combining our new results with the published data, we refined the 155–100 Ma segment of the apparent polar wander paths for AMU and NCB, which can demonstrate that these two blocks have been tectonically coherent (AMU‐NCB) during 155–100 Ma. Comparison of the apparent polar wander paths, however, revealed a latitudinal plate convergence of 14.3° ± 6.9° and ~19.0° relative rotation between Siberia and the AMU‐NCB after ~155 Ma. Large‐scale latitudinal convergence likely ceased by ~130 Ma, although some relative rotation between them continued along the Mongol‐Okhotsk suture until ~100 Ma.

A Closure of the Mongol‐Okhotsk Ocean by the Middle Jurassic: Reconciliation of Paleomagnetic and Geological Evidence

“…Fifty‐one sites were combined to yield a 157 ± 4 Ma grand mean paleomagnetic pole for the NCAB at 66.1°N, 208.3°E (A 95 = 5.1°) (Pei et al, 2011; Ren et al, 2016; Yi et al, 2019). This pole is similar to a 155 Ma pole reported from red beds in southern Mongolia (Ren et al, 2018).…”

“…For the Early Cretaceous of Siberia APWP (140–110 Ma), we use the compilation of Ren et al (2018). Two paleopoles that were assumed to have Late Jurassic ages were derived from volcanic rocks that pass both fold and reversal tests (Kravchinsky, Sorokin, et al, 2002; Metelkin et al, 2007) and are therefore of high quality.…”

“…Several Mesozoic APWPs were compiled for Siberia on paleomagnetic data from both sedimentary and volcanic rocks (Didenko, 2015; Metelkin et al, 2012; Ren et al, 2018). There are several key differences between those studies and the APWP compiled in this paper.…”

“…Data are available in Table 1 from Cogné et al (2005), Didenko (2015), Gilder and Courtillot (1997), Kent et al (2015), Kent and Irving (2010), Kravchinsky, Sorokin, et al (2002), Metelkin et al (2007, 2008), Pei et al (2011), Ren et al (2016, 2018), Torsvik et al (2012), Van der Voo et al (2015), Yi et al (2019), Zhao et al (1990), Zhou et al (2017), and Zhu et al (2008).…”

“…Paleomagnetic and geological data, obtained from both sides of the Mongol‐Okhotsk suture in the past several decades, provide important constraints on the evolutionary history of the MOO (Metelkin et al, 2012; Ren et al, 2018; Van der Voo et al, 2015; Zonenshain, 1990; Zorin, 1999). There is a mismatch between the paleomagnetic data and geology‐based models because they suggest vastly different ages for closure of the MOO (Kravchinsky, Sorokin, et al, 2002).…”