Tectonic implications of early-middle Triassic palaeomagnetic results from Hexi Corridor, North China.

A palaeomagnetic study was carried out on low-middle Triassic red beds at Jingtai area of Hexi Corridor. The characteristic higher temperature component (HTC) ( Ds = 304.1°, Is = 38.4°, ks = 33.2, a95= 5.2°, N = 24 sites) isolated by stepwise thermal demagnetization exhibits dual polarity, which passes the McFadden's fold test at the 99 per cent confidence level and reversal test with classification C. Compared with coeval palaeomagnetic results from the North China Block (NCB), this result suggests insignificant palaeolatitude differences ( Pλ) between the observed and that expected at Jingtai area ( Pλ=−0.9°± 4.9° in the early Triassic or Pλ= 4.9°± 4.1° in the middle Triassic). This implies that the Hexi Corridor was the extension of the NCB by the middle Triassic. However, in comparison with early- and middle-Triassic results from the NCB, an anticlockwise rotation of studied area relative to the NCB with Rd= 25.4°± 5.2° or Rd= 26.6°± 4.5° is detected. Our result also suggests that Jingtai area of the western part of NCB was not connected with the Tarim block by the early-middle Triassic. [ABSTRACT FROM AUTHOR]