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|Title:||Internal deformation of the Shan-Thai block inferred from paleomagnetism of Jurassic sedimentary rocks in Northern Thailand|
Yo ichiro Otofuji
|Keywords:||Earth and Planetary Sciences|
|Abstract:||Paleomagnetic samples of red sandstones were collected at 16 sites from the Lower to Upper Jurassic Phu Kradung formation and the Upper Jurassic Phra Wihan formation around Nan City (19.2°N, 101.0°E) in the southern region of the Shan-Thai block. After stepwise thermal demagnetization, a high-temperature component with an unblocking temperature of about 680 °C is isolated from 11 sites. We interpret this to be a prefold characteristic remanent magnetization because of a positive fold test at the 95% confidence level. The tilt-corrected mean paleomagnetic direction from 11 sites is D = 32.3°, I = 33.3°, α95= 12.2°, k = 15.0, which gives a paleomagnetic pole for this area of 60.1°N, 186.5°E with A95= 11.7°. Compared with a Jurassic paleopole for the stable part of the Yangtze block, we observe a clockwise tectonic rotation of 12.8°, which is similar to the observed rotation (18-28°) of the northern region of the Shan-Thai block. This amount contrasts with a large rotation of more than 45° that is estimated from the narrow zone extending from Luxi to Mengla in the central region of this block. This declination aspect suggests that a coherent whole block rotation by about 20° of the Shan-Thai block took place in an earlier phase during indentation of India into Asia and that an internal deformation with additional local rotation between 25° and 77° followed within a limited zone in the central part. The internal deformation of the Shan-Thai block absorbed the stress on the Asian continent induced by indentation of India as well as its coherent whole block motions of clockwise rotation and southward displacement. © 2007 Elsevier Ltd. All rights reserved.|
|Appears in Collections:||CMUL: Journal Articles|
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