Palaeomagnetism and U-Pb dates of the Palaeoproterozoic Akitkan Group (South Siberia) and implication for the pre-Neoproterozoic tectonics
|Location||International Geological Congress,oslo 2008|
|Author||Didenko, Alexei۱; Vodovozov, Vladimir۲; Pisarevsky, Sergei۳; Gladkochub, Dmitry۴; Mazukabzov, Anatoly۴; Donskaya, Tat’yana۴; Stanevich, Arkady۴|
|Holding Date||08 October 2008|
We present new palaeomagnetic and geochronological results from the Late Palaeoproterozoic Akitkan Group in South Siberia. The zircon U-Pb ages of the rhyodacite from the upper part and of the dacite from the lower part of the group are 1863 ± 9 Ma and 1878 ± 4 Ma, respectively. Palaeomagnetic study of sedimentary and some igneous rocks from the upper part of the Akitkan Group isolated a high-temperature characteristic component (D= 193°, I=19°, k=51, á95=7°) supported by two of three applied conglomerate tests. The corresponding palaeomagnetic poles (22.5°S, 97.4°E, dp =1.5°, dm=2.8°) may be considered as representative for the deposition time.
Palaeomagnetic study of the sediments in the lower part of the Akitkan Group isolated a stable primary remanence (D= 189°, I=8°, k=111, á95=5°) supported by positive intra-formational conglomerate and fold tests. The palaeomagnetic pole (30.8°S, 98.7°E, dp=2.5°, dm=5.0°) is nearly coeval with the 1879 Ma Molson B pole from the Superior craton. We used these two poles to compare a relative position of Siberia and the Superior craton in the Late Palaeoproterozoic. It is different from their reconstruction around 1050 Ma. This demonstrates their movements in the Mesoproterozoic.
Until recently Precambrian drift of Siberia was very poorly constrained due to luck of precise geochronology and few reliable palaeomagnetic data. For example, at least six different Siberia-Laurentia reconstructions in the youngest Precambrian supercontinent Rodinia (equally poorly constrained) have been published (see Pisarevsky & Natapov 2003 for an overview.) The Siberian role in pre-Rodinian palaeogeography is still practically unknown. There are only three relatively reliable (i.e., well-dated and properly demagnetized) Siberian palaeopoles of a pre-Rodinian age, namely, 1503 Ma Kuonamka and 1384 Ma Chieress dykes (Ernst et al. 2000), and 1850 Ma Shumikhin granites (Didenko et al. 2003, 2005.) As a result, most of pre-Rodinian global palaeogeographic reconstructions (e.g., Rogers 1996; Zhao et al. 2002) place Siberia in the position next to north Laurentia by analogy with early Rodinian reconstructions (e.g. Hoffman 1991), or based on vague geological suggestions, some of which were made many years ago and are proven to be incorrect. On the other hand, Siberia is very important for the pre-Rodinian palaeogeography, because it was almost surrounded by the Mesoproterozoic passive margins (Pisarevsky & Natapov 2003; Gladkochub et al. 2006b), which means that Siberia could be a core of some Late Palaeoproterozoic - Mesoproterozoic supercontinent in the same way as Laurentia apparently was the core of Rodinia (Dalziel 2007). Consequently, the need of precisely dated and highly reliable Siberian Meso- and Palaeoproterozoic palaeomagnetic poles is obvious.