New Paleomagnetic Constraints on the Amalgamation of the Tuva and Mongolia Blocks From Late Carboniferous Andesites in the Mongolia Block

Abstract

The Tuva‐Mongolia collage system comprises the Tuva Block (TVB) and the Mongolia Block (MOB), which are located in the eastern Central Asian Orogenic Belt (CAOB). The timing of amalgamation of the TVB and MOB is unclear. To address this, we conducted a combined geochronological and paleomagnetic study of the andesitic Member 1 of the Baoligaomiao Formation, in the southeastern MOB. The andesites have a U‐Pb zircon age of 314.2 ± 1.7 Ma. A total of 65 paleomagnetic samples from 10 sites were subjected to stepwise thermal demagnetization and had stable magnetic signals. After removal of the low‐temperature viscous components acquired in the recent geomagnetic field, stable high‐temperature components (HTCs) were isolated from most samples. The HTCs passed the fold, conglomerate, and reversal tests, demonstrating their primary origins. Moreover, these andesites have averaged out paleosecular variations. The paleomagnetic pole for the MOB is located at 30.5°N/14.6°E (A95 = 7.4°) at ca. 314 Ma. Combining our new results with published late Paleozoic paleomagnetic poles for the MOB and TVB suggests that the two blocks were distant from each other during the Middle Devonian and merged into a single TVB‐MOB by ca. 315 Ma. The Devonian‐Carboniferous paleomagnetic, paleobiogeographic, and geological data indicate that the multiple microcontinents in the CAOB were separated by numerous ocean basins during the Middle Devonian. At ca. 315 Ma, the TVB‐MOB, Kazakhstan, and Siberia were amalgamated to form a ribbon‐like continent, which was associated with the evolution of the Mongol‐Okhotsk Ocean.