The Cretaceous Duimiangou adakite-like intrusion from the Chifeng region, northern North China Craton: Crustal contamination of basaltic magma in an intracontinental extensional environment

Abstract

Zircon U–Pb ages, major and trace element and Sr, Nd and Pb isotope compositions of the Duimiangou (DMG) quartz monzonite from the Chifeng region on the northern North China Craton (NCC) were studied to investigate its derivation, evolution and geodynamic significance. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U–Pb dating yields an emplacement age of 128±1Ma for this intrusion, with numerous Mesozoic inherited zircons clustering at 219±12Ma and 161±3Ma, along with some ancient zircons with ages of 2.5Ga, 1.77Ga and 324Ma. Bulk-rock analyses show that this intrusion is characterized by variable SiO2 (63.4–69.4wt.%), Al2O3 (14.5–16.3wt.%), Na2O+K2O (8.01–8.95wt.%), and Mg# (41.3–48.0). They are enriched in large ion lithophile elements and light rare earth elements without significant Eu anomalies (mostly between 0.89–1.10), and depleted in heavy rare earth elements and high field strength elements, with high Sr/Y (63.7–101.7) and (La/Yb)N (20.5–31.0) ratios. The DMG intrusion formed in an intracontinental extensional setting contemporaneous with the formation of pull-apart basins, metamorphic core complexes and intense magmatism, rather than in a convergent margin. It has homogeneous Sr ((87Sr/86Sr)i=0.7059–0.7066), Nd (εNd(t)=−6.2 to −7.2) and Pb ((206Pb/204Pb)i=17.289–17.375, (207Pb/204Pb)i=15.359–15.463, (208Pb/204Pb)i=37.130–37.472) isotope compositions. Sr–Nd isotope modeling results, plus relatively young Nd model ages (1522–1618Ma) and the presence of relict zircons, suggest that this intrusion could have originated from crustal contamination of newly formed basaltic melts derived from asthenospheric mantle, accompanied by fractional crystallization of K-feldspar, biotite, apatite, Fe–Ti oxides and minor hornblende and plagioclase. Thus, the DMG adakite-like intrusion may record the magmatic event associated with underplating of asthenospheric magma in an intracontinental extensional environment, and both asthenospheric magma underplating and lithospheric delamination may have played important roles in the lithospheric thinning of the northern NCC.