Bending of the Western Mongolian Blocks Initiated the Late Triassic Closure of the Mongol‐Okhotsk Ocean and Formation of the Tuva‐Mongol Orocline

• Published in: Tectonics (Washington, D.C.) Vol. 42; no. 5
• Main Authors: Zhao, Pan, Appel, Erwin, Deng, Chenglong, Xu, Bei
• Format: Journal Article
• Language: English
• Published: Washington Blackwell Publishing Ltd 01-05-2023
• Subjects: Cratons; Deformation; Haematite; Late Triassic; Magnetite; Magnetization; Mongolia; Mongol‐Okhotsk Ocean; Oceans; Palaeomagnetism; Paleomagnetic studies; Paleomagnetism; Remanent magnetization; Rocks; Triassic; Tuva‐Mongol Orocline; Tuva; Asia; Siberia; Russia
• ISSN: 0278-7407; 1944-9194
• DOI: 10.1029/2022TC007475

Bending of ribbon continents or arcs is an important tectonic process for reconstructing central Asia. Formation of the striking Tuva‐Mongol Orocline by closure of the Mongol‐Okhotsk Ocean (MOO) has long been proposed, but coupling of the two geological events has not been well illustrated, hindering our understanding of tectonic evolution of central Asia. In order to constrain age of initial closure of the MOO in its western segment and formation of the Tuva‐Mongol Orocline, we performed paleomagnetic studies on the Late Triassic clastic rocks in the Amuria Block (AMB; 17 sites) and the Tarvagatay Block (TVB; 10 sites) of the western Mongolian blocks (WMB) on both sides of the Mongol‐Okhotsk Suture. Rock magnetic investigations show hematite and magnetite as main magnetic carriers of the characteristic remanent magnetization (ChRM). The ChRM directions from both regions pass fold and/or reversal tests and can be considered as primary remanent magnetization. Combining the overlapped new paleomagnetic poles (AMB: λ/φ = 70.4°N/233.8°E, A95 = 4.6°; TVB: λ/φ = 70.5°N/248.2°E, A95 = 9.0°) with geological evidence, we propose that the bending of the WMB following its collision with the Siberia Craton resulted in the Late Triassic closure of the MOO in its western segment, and initiated the formation of the Tuva‐Mongol Orocline.
Plain Language Summary
The Mongol‐Okhotsk Ocean (MOO) was a triangle‐shaped ocean between Mongolia and Siberia about 150 million year ago. A scissor‐like progressive closure of this ocean from the west to the east has been proposed. However, it is still controversial when this ocean began to close in its western segment. In this study, we report coeval Late Triassic paleomagnetic poles from continental blocks on both sides of the suture to constrain when the MOO closed initially. The new data indicate an initial closure of the MOO in the Late Triassic that was caused by bending of the western Mongolian blocks, which also initiated the formation of the Tuva‐Mongol Orocline. This study provides the first paleomagnetic evidence for a Late Triassic initial closure of the MOO.
Key Points
Coeval Late Triassic paleomagnetic poles were obtained from both sides of the Mongol‐Okhotsk Suture
The Tarvagatay and Amuria Blocks on both sides of the Mongol‐Okhotsk Suture show consistent paleolatitudes in the Late Triassic
Bending of western Mongolian blocks led to the Late Triassic closure of the Mongol‐Okhotsk Ocean and formation of the Tuva‐Mongol Orocline