LA‐ICP‐MS zircon U–Pb age, whole‐rock geochemistry, Sr–Nd–Pb isotope, and zircon Hf isotope constraints on the origin and dynamic setting of Mesozoic mafic dykes, Henan Province, southeastern North China Craton

Abstract

Mafic dykes from the Henan Province within the southeastern North China Craton (NCC) were sampled. Herein, we present new zircon laser ablation-inductively coupled plasma-mass spectrometry U-Pb age, whole-rock geochemical, Sr-Nd-Pb isotopic, and zircon Hf isotopic data for the five areas where these mafic dykes outcrop. The mafic dykes are all dolerite and were emplaced between 121.6 ± 1.1 Ma and 131.7 ± 1.2 Ma. These are characterized by enrichment in some of the large-ion lithophile elements (e.g., Rb, Ba, Th, U, K, and Sr), light rare earth elements, and depletion in high-field-strength elements (Nb, Ta, Hf, and Ti) and Eu (Eu/Eu* is between 0.62 and 0.96) relative to chondrite-and primitive mantle-values. The dykes have high initial Sr isotopic ratios ([ 87 Sr/ 86 Sr] i = 0.7056-0.7058), negative ε Nd (t) ratios (À12.3 to À12.1), relatively constant Pb isotopic ratios ([ 206 Pb/ 204 Pb] i = 16.771-16.778; [ 207 Pb/ 204 Pb] i = 15.461-15.467; [ 208 Pb/ 204 Pb] i = 36.850-36.857), negativeε Hf (t) (À14.9 to À3.5), as well as old Nd (T DM2 ; 2.22-2.54 Ga) and Hf (T DM2 ; 2.99-4.34 Ga) model ages. These geochronological, geochemical, and isotopic data indicate that the investigated Henan Province dykes were likely derived from magmas generated by low to moderate degree partial melting (1.0-10%) of an EM1-like garnet lherzolite mantle source. Moreover, the mafic melts fractionated olivine, clinopyroxene, plagioclase, Ti-bearing oxides (e.g., ilmenite, titanite, apatite, etc.) prior to emplacement, and assimilated only minimal amounts of crustal material. Several possible models have previously been proposed to explain the origin of Mesozoic magma activities in Henan Province. However, here we propose a foundering model for the mafic dykes studied, involving the foundering of eclogite from thickened lower crust due to the collision between the Yangtze Block, Qinling ocean crust, and southeastern NCC.