AGE CONSTRAINS ON THE LIFESPAN OF THE MANYUKUYAKHA BASIN, POLAR URALS

The Manyukuyakha serpentinite mélange is located in the northern part of the Enganepe uplift and is believed to be a relic of Precambrian oceanic crust (Dushin, 1997). It has been interpreted as part of a forearc (Scarrow et al., 2001, Khain et al., 2003) or back-arc (Kuznetsov, 2009) basin. It includes tectonic blocks of Cryogenian immature island arc gabbro, diorite (734±8 Ma, Morgunova and Soboleva, 2007), and tonalite (719±10 Ma, Shishkin et el., 2005) surrounded by a peridotite serpentinite matrix. These blocks are cut by veins of plagiogranite dated at 670±5 Ma (Khain et al., 2003).

The serpentinite mélange zone is located in the map area of Neoproterozoic island arc rocks of the Bedamel Formation and Ediacaran to early Cambrian clastic rocks of the Enganepe Formation. Comparison of the characteristics of detrital zircons from sandstones of the Enganepe Formation sampled directly northeastward from the mélange zone on the upper right tributary of the Manyukuyakha River (Kuznetsov et al., 2010) and from sandstones in the southwest part of Enganepe uplift on the Pravyj Izyavozh and Levyj Izyavozh Rivers reveals important differences. All except one zircons from northeast Enganepe Formation are Neoproterozoic in age (590-760 Ma) and were derived from magmatic rocks (Kuznetsov et al., 2010) whereas zircons from southwest Enganepe Formation, which are variable in color, roundness and age (530-2696 Ma), show provenance from the Neoproterozoic magmatic sources as well as Fennoscandian part of Baltica. These data suggest that these two areas were separated by the Manyukuyakha basin as late as the earliest Cambrian. If a Cryogeneian island arc flanked this same basin, the basin might have existed prior to 734 Ma. This paleobasin, either a back-arc or intra-arc could have closed in the earliest Cambrian Timanian orogeny.

Comparison of the ages of detrital zircons from the southwest part of the Enganepe Formation with the well-known ages of magmatic and metamorphic events in basement rocks of Baltica shows that these sediments were deposited in Ediacaran-Early Cambrian time, in close proximity to the NE passive margin of Baltica, just prior to the Timanian collision.