Carboniferous tectono-magmatic evolution of the northern Luliang arc: evidence from geochemistry and petrography of Carboniferous volcanic rocks in the northern Luliang Uplift, NW China

The Northern Junggar Basin experienced extensive subduction and a complex tectono-magmatic evolution during the Late Paleozoic, resulting in a heterogeneous distribution of volcanic rocks in the Junggar Basin. In this study, the Carboniferous tectono-magmatic evolution of the northern Luliang arc was described by exploring the petrography and geochemistry of Carboniferous volcanic rocks collected from well Y-2 and outcrop WW′ in the northern Luliang Uplift. The distribution, types, and formation ages of these volcanic rocks were characterized and the volcanic sequence in well Y-1 was divided into upper and lower parts according to vertical variations in selected geochemical data. Then the petrogenesis and tectonic settings of different volcanic rocks were evaluated and this was used to infer the tectono-magmatic evolution of the northern Luliang arc during the Carboniferous. The results indicate that: (1) Carboniferous high-K calc-alkali andesite–dacite associations are distributed in the west of the northern Luliang Uplift, and Lower Carboniferous calc-alkali basalt–dacite–rhyolite assemblages are preserved in its east. (2) The intermediate-acid volcanic rocks in wells Y-1 and Y-2 were derived from calc-alkali basaltic magma through melting of the juvenile lower crust, and geochemical variations indicate increasing addition of slab melting in a subduction-related arc environment. The bimodal volcanic rocks from outcrop WW′ were derived from lithospheric underplating of basaltic magma in an intra-arc extensional setting. (3) The closure of the eastern Keramaili Oceanic basin occurred before the Early Carboniferous, and the tectono-magmatic difference between the east and the west of the northern Luliang Uplift appeared before the Carboniferous period.