A new Late Cretaceous paleomagnetic pole for the west of Amuria block (Khurmen Uul, Mongolia)

We present new paleomagnetic results obtained at ten sampling sites from six Upper Cretaceous (92 ± 4 Ma) basaltic lava flows from the westernmost part of Amuria block. The samples were collected in 1999 in the Khurmen Uul region (44.0°N, 103.0°E), Gobi desert (S. Mongolia). Stepwise thermal demagnetization isolated a high temperature component (HTC) carried by magnetite. Five out of ten sites exhibit anomalously high Koenigsberger ratios and low inclinations, which likely resulted from lightning remagnetization. However, three of these sites were only partially remagnetized, allowing us to use remagnetization great-circles to help determine a characteristic magnetization direction for this formation. HTC directions of the eight remaining sites from six distinct flows all possess normal polarity and exhibit better clustering after tilt correction of the flows (ks/kg = 129.3 / 36.6, n = 6). This clustering is ascertained by a positive fold test at the specimen scale within a single flow. We therefore propose that the tilt-corrected HTC represents a primary magnetization. The paleopole computed from the six lava flows HTC mean directions lies at λ = 71.5°N, ϕ = 227.2°E (dp/dm = 5.6° / 8.2°). We discuss the possibility that our pole might not have completely averaged paleosecular variation, because it is based on only 6 independent flows. Finally, this pole is far-sided with respect to the 90 Ma reference pole of Eurasia APWP (Δλ = 10.2° ± 6.1°), but it is consistent, albeit somewhat far-sided too, with other coeval paleopoles from Amuria, and east China.