Where does the South Anyui suture go in the New Siberian islands and Laptev Sea?: Implications for the Amerasia basin origin

The South Anyui suture is a major tectonic boundary in NE Asia, believed to represent the remains of an ocean basin which separated Siberia from North America in Jurassic time. Its history also figures prominently in the Mesozoic reconstruction of the Arctic and the origin and evolution of the Amerasia basin. Three types of proposed trends of the South Anyui suture are evaluated. 1) The suture ends near the Kolyma River mouth where it meets the rotational transform. The paper, however, proves that the suture continues further westward up to Big Lyakhov Is. Consequently, a simple geometric rotational model for Amerasia basin origin must be rejected. 2) The suture trends from Big Lyakhov to the Anjou islands. The Anjou islands geology is examined, and it is concluded that the suture could not go through them. Hence, all proposed versions of the rotational hypothesis of the Amerasia basin opening are claimed to be invalid. 3) A proposed Taimyrian connection of the suture is examined, and it is concluded that this model must be rejected as well. The failure of all previously suggested models for the suture extent through the New Siberian islands and Laptev Sea means that in Early Mesozoic there was no oceanic basin that separated the New Siberian-Chukotka terrane from Siberia. Thus Siberia and North America formed a continuous continent in Jurassic time. This paper presents evidence that the South Anyui suture has instead turned back from Big Lyakhov island and followed a sinuous path designated as the Chroma Loop before connecting with the Kolyma Loop suture. On this model the South Anyui suture can be interpreted as a small segment of extensive boundary which separated the Amerasia Jurassic margin and terranes accreted to it from the Pacific. The modern boundary around the North Pacific is also quite sinuous. It was suggested that in Jurassic time it was straighter and the Amerasia ocean was originated as a common back-arc basin. Finally a new two-pole parallelogram hypothesis for the Amerasia basin opening is suggested and the approaches to its verification are outlined. (c) 2008 Elsevier B.V. All rights reserved.