Tectonics and models for the Neoproterozoic development of accretionary orogens of the western Siberian Craton continental margin
|Category||Tectonic & Seismotectonic|
|Location||International Geological Congress,oslo 2008|
|Author||Vernikovsky, Valery; Vernikovskaya, Antonina; Metelkin, Dmitry|
|Holding Date||27 September 2008|
On the basis on new geological, geochronological and paleomagnetic data it has been established that in the Neoproterozoic a transformation of the Siberian craton western margin from a passive to an active one was taking place. The Neoproterozoic subduction-accretion processes along the Siberian craton western margin were not synchronous; they take in a wide interval of time - from 960 Ma to 630 Ma.
An island arc system started to form at the north-western margin of the Siberian craton approximately 960 Ma. Its fragments were included in the Central Taimyr accretionary belt. Paleomagnetic poles for the 960 Ma acid volcanic rocks in the Three Sisters Lake island arc from this belt have been determined. These poles are very close to the poles of same age for Siberia (Pavlov et al., 2002). These results significantly expand the previously acquired evidences for the forming of island arcs with their subsequent accretion and obduction onto the Taimyr margin of Siberia in the interval of 750-660 Ma.
The succession of the forming of Siberia’s western margin, represented by the Yenisey Ridge accretional orogen, was determined. We assume that the genesis of this structure is a result of three events: a) syn-collisional events (probably outside the Siberian craton), which resulted in the forming of the Teya granites with the age 880-860 Ma in the Central Angara terrane; b) the collision between the Central Angara terrane and the Siberian craton and the forming of the syn- and post-collisional Ayakhta and Glushikha granites with the age 760-720 Ma; c) the forming of island arcs and ophiolites along the margin of the Siberian craton, their accretion and obduction onto the continent in the interval of 700-630 Ma. The last event is of special interest because at the same time in the Tatarka-Ishimba suture zone of the Yenisey Ridge, which is sub parallel to the continental margin, the forming of intrusive and volcanic rocks of various composition and heightened alkalinity was taking place, including alkaline syenites as well as carbonatites and A-type granites. They formed synchronously with the rocks of the island arc complex and their accretion and obduction onto the continental margin of Siberia in the interval of 700-630 Ma. It is quite probable that their forming in the back-arc suprasubduction zone was taking place at the same time that the oceanic plate was subducting below the continent from the western margin of the Siberian craton and reached the asthenospheric layer. The obtained data and the developed models uncover the geodynamic evolution of the forming of accretional orogens in the western margin of the Siberian craton in the Neoproterozoic, prove the nonexistence of Grenvillian events along this margin and allow us to discuss the questions of the mutual location of the Siberian and North-American cratons within the Rodinia supercontinent.