No vertical axis rotations during Neogene transpressional orogeny in the NE Gobi Altai: coinciding Mongolian and Eurasian early Cretaceous apparent polar wander paths

Details No vertical axis rotations during Neogene transpressional orogeny in the NE Gobi Altai: coinciding Mongolian and Eurasian early Cretaceous apparent polar wander paths No vertical axis rotations during Neogene transpressional orogeny in the NE Gobi Altai: coinciding Mongolian and Eurasian early Cretaceous apparent polar wander paths

Apr 2008

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008geoji.173..105v&link_type=abstract

Geophysical Journal International, Volume 173, Issue 1, pp. 105-126.

Astronomy and Astrophysics

Astronomy

5

Palaeomagnetism Applied To Tectonics, Continental Tectonics: Strike-Slip And Transform, Asia

Scientific paper

In this paper, we test the role of vertical axis rotations during transpressional mountain building. To this end, we carried out a palaeomagnetic study in the NE Gobi Altai of southern Mongolia, sampling widely exposed lower Cretaceous lavas allowing comparison of rotation histories of the Ih Bogd, Baga Bogd and Artz Bogd restraining bends at the eastern termination of the Bogd strike-slip zone. We provide new 40Ar/39Ar ages to show that the stratigraphy of mafic lavas and fluvio-lacustrine sediments on the southern flanks of Mt Ih Bogd and Mt Baga Bogd have ages between ~125 and ~122 Ma, and a mafic sill that intrudes the sequence has an age of 118.2 +/- 0.8 Ma. The lavas are older than previously dated lavas south of Artz Bogd, with ages of 119-115 Ma. Palaeomagnetic results from the 119-115 Ma lavas south of Artz Bogd show a significant steeper inclination than both results from 125 to 122 Ma lavas of Baga Bogd and Ih Bogd, as well as from newly sampled and previously published younger lavas and necks of the 107-92 Ma Tsost Magmatic Field and Shovon and Khurmen Uul basalts. We explain this result by insufficient averaging of secular variation and small errors induced by overcorrection of bedding tilt. We show that individual lavas in the SE Artz Bogd locality represent individual spot readings of the Earth's magnetic field and integrate all results obtained from lower Cretaceous lavas in the Gobi Altai. We present a pole, or rather, an apparent polar wander path without significant plate motion from the reference positions of Eurasia, from ~125 to 95 Ma, with n = 126, λ = 80.8°, φ = 158.4°, κ = 25.3, A95 = 2.5, palaeolatitude = 48.2 with a scatter Sλ = 16.7 (Sl = 15.3, Su = 17.8) and a regionally consistent direction for the Gobi Altai of D/I = 11.1°/65.9°, ΔD/ΔI = 3.8°/1.9°. This is one of the best-determined palaeopoles/APWP's for Asia. Formation of the Ih Bogd, Baga Bogd and Artz Bogd restraining bends was thus not associated with vertical axis rotations larger than our error margin of ~10°. From this we conclude that the Bogd strike-slip zone is a weak fault zone, in which shear is localized.

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