Counter-clockwise rotation of the eastern part of the Mongolia block: Early Cretaceous palaeomagnetic results from Bikin, Far Eastern Russia

Abstract

S U M M A R YWe present palaeomagnetic results from Lower Cretaceous rocks in Bikin area of the Alchan basin (46.5 • N, 134.7 • E), Sikhote Alin orogenic belt, Far Eastern Russia. A high-temperature magnetization component with maximum unblocking temperatures at about 590 • C was isolated from six sites of dacite welded tuffs in the Albian Alchanskaya Formation. The fold tests for these six sites are positive, suggesting that primary magnetization is preserved in the studied rocks. The tilt-corrected mean direction of D = 309.3 • , I = 68.7 • (α 95 = 10.1 • ), with a corresponding palaeopole position at 57.0 • N, 76.8 • E (A 95 = 15.1 • ), indicates a counter-clockwise (CCW) rotation for the studied area. CCW rotation is also indicated from west-directed declinations (D = 249.1 • , I = 64.1 • , α 95 = 11.2 • ) obtained from secondary magnetization of the Berriasian Kultukha Formation. Combining with the previously reported studies, the westdirected Cretaceous palaeomagnetic directions cover widely the eastern part of the Mongolia block. Comparison with 100 Ma palaeomagnetic pole for Eurasia shows that the eastern part of the Mongolia block experienced a CCW rotation of over 36 • with respect to the Eurasian continent later than Late Cretaceous. This rotation is ascribed to post-Late Cretaceous extension that affected the continental basins (the Middle Amur, Sanjiang, Razdolnian, Amur-Zeya and Songliao basins) of the northeast Chinese Plain along the eastern margin of the Mongolia block. Contemporaneous with this CCW rotation, similar extension resulted in clockwise rotation of the eastern part of the North China block.

Tectonic implications of paleomagnetic data from upper Cretaceous sediments in the Oyubari area, central Hokkaido, Japan

“… (a) Regional tectonic framework of the eastern Eurasia. The arrows with closed square are the Cretaceous magnetic declinations for the Eurasian reference; Mongolia and the North China Block (NCB), calculated by Otofuji et al . (2006).…”

“…(2006). Arrows with closed circle represent the paleomagnetic declinations for the eastern Eurasian margin (Bikin, Otofuji et al . 2006; eastern Sikhote Alin, Otofuji et al .…”

Paleomagnetism of Cretaceous rocks in the Jiaodong Peninsula, eastern China: Insight into block rotations and neotectonic deformation in eastern Asia

“…Discussion of the wider geotectonic cause of these large differential block rotations enclosing the extensional province in northeast China and the Russian Far East is beyond the scope of this paper but has been variously ascribed to slab retreat in the NW Pacific [ Northrup et al , 1995], eastward extrusion of eastern Asian terranes due to the India‐Asia collision [ Fournier et al , 2004], mass upwelling of asthenosphere [ Ren et al , 2002; Meng , 2003; Otofuji et al , 2006] and eastward flow of the asthenosphere [ Uyeda and Kanamori , 1979; Flower et al , 2001]. …”

“…An overlap of 95% confidence ovals of certain Cretaceous paleopoles from the Korean Peninsula with results from the vicinity of Benxi in Liaodong led Lin et al [2003] to propose that a single East Liaoning‐Korean Block has existed since the Late Cretaceous and post‐Late Cretaceous CW rotation of this block relative to Eurasia is considered to have accommodated extensional tectonics in northeast Asia [ Ren et al , 2002; Meng , 2003]. However, significant counterclockwise (CCW) rotation is reported from a series of studies in the Russian Far East [ Otofuji et al , 2006, and references therein], and it is clear that more Cretaceous paleomagnetic data are required both to compare block rotations on either side of the TLFZ and to test whether there is paleomagnetic expression of the extensional regime in northeast China.…”

Cretaceous Research: Paleolatitudes and Northward Migration of Crustal Fragments in the NW Pacific Inferred from Paleomagnetic Studies

“…Simultaneous inversion of these areas implies that an amalgamation of migrated terranes occurred by the end of the Paleogene. [34,35] and Otofuji et al [36], respectively. The age range of the Oyubari data (3: [7]) is shorter than the height of the median symbol.…”