Late Neoarchean plate subduction in Western North China Craton: Evidence from ca. 2.51 Ga to 2.46 Ga basement rocks in Northern Ordos Basin

Abstract

The most poorly exposed and least understood in the North China Craton (NCC) lies largely hidden beneath the Ordos Basin, severely limiting the cognition of the Precambrian tectonic evolution in the western NCC and the tectonic division. Diverse orthogneiss samples collected from four boreholes drilled into the basement of the north side of Hangjinqi Fault Zone (HFZ) in the North Ordos Basin (NOB) are investigated by integrating zircon U-Pb dating, Hf-Nd isotopes, and whole-rock geochemical analyses. The TTG gneiss, quartz-monzonite gneiss, granodiorite gneiss, and amphibolite were emplaced at ca. 2.51–2.46 Ga, of which the amphibolite also recorded the metamorphic age of ca. 1.95 Ga. The TTG gneisses display low MgO, Mg#, Cr, and Ni, high HREE and Rb/Sr, enrichment of LILEs and depletion of Nb, Ta, and Ti, and positive εNd(t) (2.04–4.06) and εHf(t) (3.04–7.59) values, suggesting that they were mainly originated from partial melting of the tectonically thickened mafic island-arc crust. In contrast, the quartz monzonite gneisses and granodiorite gneisses show the geochemical features of Archean sanukitoids with higher MgO, Mg#, Cr, and Ni, and similar εNd(t) (1.34–3.82) and εHf(t) values (3.94–7.32), suggesting that they were derived from the partial melting of the mantle metasomatized by fluids and melts of the subduction. The amphibolites exhibit a mixed characteristic of E-MORB and arc-like geochemical affinities resembling the Mariana back-arc basin, which was derived from the partial melting of spinel lherzolite. The arc and arc-back lithological assemblages suggest that the north margin of the NOB might be in a geodynamic transition period from a compressional regime correlated with plate subduction to an extensional regime correlated with slab rollback during ca. 2.51–2.46 Ga. Combined with previous analytical results, the northern margin of the NOB was most likely in a long-term active continental margin setting during 2.51–1.95 Ga and involved in the collision event between the Yinshan Block and Ordos Block at ca. 1.95 Ga.