Age of oceanic basalts of Bol’shoi Lyakhov Island (New Siberian Islands): Implication for the western boundary of the South Anyui ocean in the Jurassic

Abstract

Serpentinites and pillow basalts exposed in the southeastern part of Bol’shoi Lyakhov Island are considered the northwestern continuation of the South Anyui suture of Chukotka [1, 2]. However, some researchers doubt that these rocks represent the lithosphere of the Mesozoic South Anyui oceanic basin. According to the rotation hypothesis of the opening of the Amerasian basin, it should be confined to Chukotka structures and not extend to the west [3]. Previous data on the inferred Paleozoic age of the oceanic pillow basalts exposed on the island [4] suggest that the northwestern continuation of the suture is the Paleozoic collisional zone, which lacks a direct relation to the Mesozoic tectonic events in the East Arctic. We present new data on the Middle‐Late Jurassic age of the oceanic basalts of Bol’shoi Lyakhov Island. Consequently, they formed precisely in the South Anyui oceanic basin. These data are of great importance for reconstructing the Mesozoic tectonic evolution of the East Arctic region and for discrediting the validity of the popular rotation hypothesis of the opening of the Amerasian oceanic basin. The southeastern part of Bol’shoi Lyakhov Island comprises diverse complexes of oceanic and island-arc (basic and ultrabasic) rocks [4, 5]. These complexes make up a series of allochthonous slices thrust onto the southeastern margin of the New Siberian continental block. The outcrops of the aforementioned rocks are considered to mark the northwestern continuation of the South Anyui suture—one of the most important tectonic sutures in the East Arctic region (Fig. 1) [1, 6, 7]. The South Anyui suture is a trace of the eponymous oceanic basin, which closed in the Neocomian simultaneously with opening of the Amerasian oceanic basin [1, 6, 8]. A composite collage of island-arc and continental terranes is located south of the suture [6], while the East Arctic continental massif is located north of the suture. Some geologists (for instance, [3]) believe that the eastern part of this massif (Chukotka microcontinent according to [6]) was a fragment of the North American Platform, while its western part was a continuation of the Siberian structures. These two blocks were separated by a hypothetical transform fault, which was formed during opening of the Amerasian basin