Late Paleozoic adakites and Nb-enriched basalts from northern Xinjiang, northwest China: evidence for the southward subduction of the Paleo-Asian Oceanic Plate

Abstract Volcanic rocks consisting of adakite and Nb-enriched basalt are found in the early Devonian Tuoranggekuduke Group in the northern margin of the KazakhstanJunggar Plate, northern Xinjiang, northwest China. The geochemical characteristics of the andesitic and dacitic rocks in this area resemble that of adakites. The relatively high Al 2 O 3 , Na 2 O and MgO content and Mg # values indicate that the adakites were generated in relation to oceanic slab subduction rather than the partial melting of basaltic crust. A slightly higher SrI and a lower e Nd (t = 375 Ma) compared to adakites of mid-oceanic ridge basalt (MORB) imply that slab sediments were incorporated into these adakites during slab melting. The Nb-enriched basalt lavas, which are intercalated in adakite lava suite, are silica saturated and are distinguished from the typical arc basalts by their higher Nb and Ti content (high field strength element enrichment). They are derived from the partial melting of the slab melt-metasomatized mantle wedge peridotite. Apparently, positive Sr anomalies and a slightly higher heavy rare earth element content in these adakites compared to their Cenozoic counterparts indicate that the geothermal gradient in the PaleoAsian Oceanic subduction zone and the depth of the Paleo-Asian Oceanic slab melting are between those of their Archean and Cenozoic counterparts. The distribution of the adakites and Nb-enriched basalts in the northern margin of the Kazakhstan-Junggar Plate, northern Xinjiang, indicates that the Paleo-Asian Oceanic Plate subducted southward beneath the Kazakhstan-Junggar Plate in the early Devonian period

Approximation of Solutions of an Equilibrium Problem in a Banach Space

An equilibrium problem is investigated based on a hybrid projection iterative algorithm. Strong convergence theorems for solutions of the equilibrium problem are established in a strictly convex and uniformly smooth Banach space which also enjoys the Kadec-Klee property

Petrogenesis of the Late Archean (similar to 2.5 Ga) Na-and K-rich granitoids in the Zhongtiao-Wangwu region and its tectonic significance for the crustal evolution of the North China Craton

Petrogenesis of coexisting Late Archean (similar to 2.5 Ga) Na-and K-rich granitoids in the Zhongtiao-Wangwu region is significant for understanding the crustal evolution of the North China Craton (NCC). In this paper, we present new zircon U-Pb age, and whole-rock geochemical and isotope data on a similar to 2.5 Ga Na-and K-rich granitoid suite from the Zhongtiao-Wangwu region, southern NCC. The Na-rich granitoids (TTG) and K-rich granitoids (A-type granites) are zircon U-Pb dated to be 2.45 Ga and 2.49 Ga, respectively. Integrated geochemical data indicate that the TTG were formed by partial melting of the mafic lower crust, while the A-type granites were formed by partial melting of a TTG-like source in the shallower crust. The petrogenesis likely occurred under lithospheric delamination and the subsequent asthenospheric upwelling and mafic magma underplating. We proposed that the coeval occurrence of Na-and K-rich granitoids in the southern NCC is probably ascribed to the partial melting of continental crust at different depths, which could be an important way to induce the Archean crustal reworking and compositional changes at similar to 2.5 Ga