Paleomagnetism and ⁴⁰Ar/³⁹Ar-dating of late Mesozoic volcanic pipes of Minusinsk depression (Russia)

Volcanic pipes with K-Ar ages 65-49 Ma (Zubkov et.al., 1989) are widespread in the Minusinsk depression. We present the results of the first paleomagnetic investigation on four volcanic pipes (42 samples), accompanied by ⁴⁰Ar/³⁹Ar dating. All four pipes yield a high temperature ChRM component of reversed polarity with mean direction D=178.8, I=62, n=33, k=160.7, a95=7.3. However, some samples from the Bele pipe demonstrate another direction (D=244.3, I=58.2, n=4, k=407.4, a95=4.6). ⁴⁰Ar/³⁹Ar method gave plateau ages of pipes ranging from 74 to 81 Ma. These results cast some doubt on previous K-Ar dating. The paleomagnetic poles corresponding to both directions of magnetization are statistically different from the APWP of Eurasia given by Besse and Courtillot (1991). Paleomagnetic poles from basaltic rocks of the near-Baikal region (Khramov, 1984) are consistent with the first direction identified from Minusinsk depression, but again are different from the APWP of Eurasia. These data, therefore, call into question the validity of the Eurasian APWP to Northern Asia.