Early Paleozoic suprasubduction complexes of the North Balkhash ophiolite zone (Central Kazakhstan): Geochronology, geochemistry and implications for tectonic evolution of the Junggar-Balkhash Ocean

Abstract

The Junggar-Balkhash region in the west of the Central Asian orogenic belt (САОВ) comprises Paleozoic flysch, dismembered ophiolites, cherts, basalts, and olistostromes within its accretionary wedges. The North Balkhash ophiolite zone hosts serpentinite mélange with slivers of early Paleozoic chert, basalt, tuffaceous chert and volcaniclastic rocks. For the first time in the North Balkhash ophiolite zone, we recognized the Cambrian to Early and Middle Ordovician supra-subduction complexes in the plutonic fragments along with the previously known Middle to Late Ordovician OIB, N-MORB, chert and Late Ordovician island arc volcanic slivers.The documented records of North Balkhash supra-subduction complexes therefore span 100 m.y.-long evolution of the early Paleozoic intraoceanic accretionary wedge that went through several reorganizations due to incorporation of oceanic island and oceanic floor units in its front.The Early Cambrian is represented by Tesiktas ultramafic-gabbro-plagiogranite (c. 530 Ma) and Eastern Arkharsu gabbro-dolerite-plagiogranite (520 ± 2 Ma) with boninitic signature, interpreted to have formed in fore-arc setting. The Late Cambrian (498 ± 8 Ma) and Early Ordovician (476 ± 3 Ma) rocks are represented by island arc plagiogranite and diorite blocks in serpentinite melange along with slivers of Middle Ordovician dacite and andesite with lenses of chert rocks, as well as tuff and tuffaceous sandstone.Correlation of the North-Balkhash zone with its possible equivalents in Kazakhstan and NW China revealed the same duration, stages and tectonic settings. Particularly, we propose that the North Balkhash and West Junggar ophiolite melanges can be considered as fragments of the formerly single subduction-accretionary wedge, dextrally displaced for 250 km along the Junggar strike-slip fault during the late Paleozoic to the early Mesozoic.