Computer Science
Scientific paper
Jun 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002e%26psl.199..473d&link_type=abstract
Earth and Planetary Science Letters, Volume 199, Issue 3-4, p. 473-482.
Computer Science
17
Scientific paper
From exposures at the southeastern end of the Maza Tagh range in the central Tarim Basin (latitude: 38.5°N longitude: 80.5°E), 55 paleomagnetic sites were collected from red mudstones and sandstones of the Miocene Wuqia Formation. Thermal demagnetization revealed a high unblocking temperature characteristic remanent magnetization (ChRM). Five sites collected across a kink fold yield a positive fold test at 99% confidence level. The mean directions computed from normal and reversed polarity sites are antipodal suggesting a primary origin for the ChRM. In stratigraphic coordinates, the final set of 30 site-mean ChRM directions yields a section-mean direction: inclination (I)=29.4° declination (D)=24.7° α95=6.2°. When compared to the Miocene expected direction (at 20 Ma), the observed direction indicates 30.8+/-5.5° flattening of inclination and 15.3+/-6.7° clockwise vertical-axis rotation. Anisotropy of magnetic susceptibility measurements on 155 samples show a strong foliation of 1.092 with a sub-vertical minimum susceptibility axis. These observations indicate a rock-magnetic (depositional or compaction shallowed) origin for the inclination flattening. The clockwise deflection of the observed declination can be interpreted as either: (1) 15.3+/-6.7° clockwise rotation of the entire Tarim Basin since the Miocene; or (2) a local km-scale structural deformation. It is not a simple matter to discard the interpretation of 15.3+/-6.7° clockwise rotation of the Tarim Basin because the fastest rates of rotation determined from global positioning system and slip-rate studies of Quaternary faults could produce such a rotation if extrapolated to 20 Ma. Nevertheless, we argue that local deformation is the preferred interpretation because the map pattern of local structures shows ~20° clockwise deflection toward the southeastern end of the Maza Tagh range where the paleomagnetic samples were collected.
Butler Raymond F.
Dupont-Nivet Guillaume
Guo Zhi
Jia Chenglong
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