U–Pb–Hf–O–Nd isotopes and geochemistry of the Neoarchean granitoid gneisses in Eastern Hebei, North China Craton: Implications for crustal growth

Abstract

<p>Neoarchean granitoid gneisses are widely distributed throughout Eastern Hebei, eastern North China Craton, and are dominated by deformed and metamorphosed tonalite–trondhjemite–granodiorite (TTG), diorite, and granite. This study presents the results of systematic zircon U–Pb geochronological, whole-rock geochemical and Sm–Nd isotopic analyses of the Neoarchean granitoid gneisses in Eastern Hebei. These data provide insights into the Archean–Paleoproterozoic multiple tectonothermal events and the petrogenesis of the gneisses in this area. U–Pb ages and cathodoluminescence images of zircons from the granitoid gneisses using laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS) indicate that their magmatic precursors were contemporaneously emplaced between 2546 ± 10 and 2510 ± 10 Ma, reflecting a giant Neoarchean igneous event throughout Eastern Hebei. Subsequently these rocks were subjected to regional amphibolite facies metamorphism at 2.48 – 2.45 Ga. The close spatial and temporal relationships between magmatism and metamorphism at ca. 2.5 Ga suggest a uniform tectonothermal evolution of Eastern Hebei. The granitic gneisses are considered to have mainly originated from the partial melting of juvenile metamorphosed greywackes, with minor involvement of basalts. The large geochemical and isotopic variations within the dioritic and TTG gneisses both provide evidence for the mixing of mafic and felsic magmas, coupled with fractional crystallization. However, the chemical differences between the dioritic and TTG gneisses might be because they originated from different mafic magma sources, viz., basaltic and high-Mg melts. The mafic magma may have also formed the metamorphosed basalt or komatiite within the greenstone belt or evolved via fractional crystallization prior to the magma mixing. Large-scale granitoid activities were possibly related to mafic magma underplating. The combined geochronological, geochemical, and geological data support an Archean proto-mantle plume model for interpreting the geodynamics of the eastern North China Craton during the Neoarchean.</p><p>Acknowledgements Our work was supported financially by Beijing Natural Science Foundation (Grant Number: 8194073), the Science Foundation of China University of Petroleum, Beijing (Grant Number: 2462017YJRC032) and the Science Foundation of State Key Laboratory of Petroleum Resources and Prospecting, China University of Petroleum, Beijing (Grant Number: PRP/indep-4-1702).</p>