New geochronological evidences and diverse arc-related meta-volcanic rock suits from the Northern Liaoning terrane, North China Craton

Abstract

The Northern Liaoning terrane locates at the northeastern margin of the North China Craton (NCC). Two debatable tectonic mechanisms, plate tectonic vs. plume/sagduction, were interpreted to dominate the late Neoarchean Northern Liaoning terrane. Besides, ∼2.57–2.51 Ga supracrustal rocks occur layered or as enclaves within ∼ 2.59–2.50 Ga TTG and potassium-rich granitoid gneisses. This is a logical contradiction that ‘young’ enclaves expose within ‘older’ wall rocks. In this study, new zircon U-Pb dating results exhibit that protoliths for these meta-volcanic rocks in the Huiyuan area, north of the Northern Liaoning terrane, crystallized at ∼ 2.61 Ga and underwent metamorphisms at ∼ 2.54–2.48 Ga. The real crystallization ages for reported metavolcanic rocks in the Northern Liaoning terrane were probably highly underestimated.

In this contribution, garnet–pyroxene amphibolite, amphibolite and (biotite) amphibole gneiss were interbedded and exhibit geochemical affinities to Nb-enriched basalt (NEB), tholeiite and andesite, respectively. NEB exhibits abnormally high Nb, TiO₂ and (Nb/La)_PM values, fractionated REE patterns, and negligible Nb, Ta and Ti anomalies, which was derived from partial melting of slab melts metasomatized mantle wedge with Nb-bearing minerals (i.e., amphibole). Tholeiites yield flat REE patterns, enrichments of LILEs, and depletions of Nb and Zr, which are comparable to primitive arc basalt and interpreted as partial melting of sub-arc mantle wedge previously metasomatized by limited subducted slab-derived fluids. Andesites give fractionated REE patterns and negative HFSE anomalies, among which several andesites are akin to Phanerozoic high-magnesium andesite (HMA), with high MgO, Mg^#, Cr and Ni values, and were generated by interactions between subducted slab-derived melts and sub-arc mantle wedge. Remained normal andesites were hybrids of crustal melts and mantle-derived basaltic melts. Taken together, ∼2.61 Ga NEB, andesite (including HMA samples) and primitive arc basalt associations point to a subduction tectonic mechanism developing in the Northern Liaoning terrane. Plume and subduction mechanisms are not mutually exclusive. More precise spatial and temporal distributions effected by plume and subduction, respectively, and how they interact with each other, need to be further studied.