Tectonostratigraphic evolution of the Carboniferous arc-related basin in the East Junggar Basin, northwest China: Insights into its link with the subduction process

Abstract

The Junggar Basin in northwest China is located in the southern part of Central Asian Orogenic Belt (CAOB). The tectonic mechanisms controlling sedimentary fill through space and geologic time within dynamic subduction environments remains poorly understood in the Junggar Basin. This paper presents an integrated tectonostratigraphic and tectonic evolution of Carboniferous volcanic arcs and associated basin in the East Junggar Basin using multichannel seismic reflection data, well-line data, geochronological and geochemical data. We propose a new tectonic-sedimentary model for the East Junggar Basin during the Carboniferous time based on geochemistry of volcanic rocks and four seismic tectonostratigraphic sequences. The Carboniferous succession of volcanogenic sediments represents progradational sequences mainly supplied from the northeast. The negative Ta, Nb and Ti anomalies, low Rb/Ba ratios (0.01–0.15) and high incompatible trace element (such as Th, U) abundances of the basalts suggest that metasomatism may have occurred during the Late Carboniferous subduction. The northeastward increase of the Ba/La ration, K, Ca and decrease of Na, Ti and Fe indicate the northeast-dipping subduction polarity in the East Junggar Basin. During the Early Carboniferous, tectonism in the East Junggar Basin took place in two stages. Deep marine sediments widely covered the Junggar region, and then the depocenter slightly shifted towards southwest, which probably resulted from the northeast-dipping subduction that led to the southwestward tilting of the Dinan area. During the early stage of the Late Carboniferous, mixed marine and nonmarine deposits initially onlapped the volcanic arc towards the northeast, and then gradually downlapped to the southwest. At the end of the Late Carboniferous, subduction of the Junggar Ocean continued towards northeast and depositional environment became nonmarine. The main axis of the depocenter rapidly migrated towards southwest that resulted from the southwestward tilting of the Luliang region.