GPS rotation and strain rates in the Baikal–Mongolia region

Abstract

Current deformation in Pribaikalia, Western and Central Mongolia, and Tuva has been studied from measured horizontal GPS velocities and respective computed strain and rotation rates using 1994–2007 data of the Baikal–Mongolian GPS triangulation network. The GPS velocity field shows two main trends: an NE trend within Jonggaria, the Mongolian Altay, and the Great Lakes Valley and an SE trend in the Hangayn and eastern Gobi Altay mountains, and in the Transbaikalian block of the Amur plate. The velocity magnitudes and vectors are consistent with an SE motion of the Amur plate at a rate of ∼2 mm/year. The derived strain pattern includes domains of crustal contraction and extension recognized from the magnitudes of relative strains. Shortening predominates in the Gobi and Mongolian Altay and in the Khamar-Daban Range, where it is at ɛ 2 = (19.2 ± 6.0)×10 −9 yr −1 being directed northeastward. Extension domains exist in the Baikal rift and in the Busiyngol–West Hangayn area, where the crust is stretching along NW axes at ɛ 1 = (22.2 ± 3.1) × 10 –9 yr –1. The eastern Hangayn dome and the Gobi peneplain on its eastern border show low and unstable strain rates. In central and northern Mongolia (Orhon–Selenge basin), shortening and extension are at similar rates: ɛ 2 = (15.4 ± 5.4)×10 −9 yr −1 and ɛ 1 = (18.1 ± 3.1)×10 −9 yr −1. The strain pattern changes notably in the area of the Mogod earthquake of 1967. Most of rotation throughout Central Asia is clockwise at a low rate of about Ω = 6×10 −9 deg·yr −1. High rates of clockwise rotation are observed in the Hangayn domain (18.1 ± 5.2)×10 −9 deg·yr −1, in the Gobi Altay (10.4 ± 7.5)×10 −9 deg·yr −1, and in the Orhon–Selenge domain (11.9 ± 5.2)×10 −9 deg·yr −1. Counterclockwise rotation is restricted to several domains. One is in western Tuva and northwestern Great Lakes Valley of Mongolia (Ω = 3.7×10 −9 deg·yr −1). Two more counterclockwise rotation regions occur on both flanks of the Baikal rift: along the craton edge and in basins of Transbaikalia on the rift eastern border, where rotation rates are as high as (13.0 ± 3.9)×10 −9 deg·yr −1, while rotation within the Baikal basin does not exceed the measurement error. Another such domain extends from the eastern Hövsgöl area to the Hangayn northern foothills, with the counterclockwise rotation at a highest rate of (16.3 ± 2.8)×10 −9 deg·yr −1.