Geochemistry Characteristics of the Late Cretaceous Adakitic Rhyolites of Daxingzhuang Formation and its Genesis in Yixian Area, Western Liaoning Province

The study of the geochemistry of the Late Cretaceous rhyolites of Daxingzhuang Formation in Yixian area, western Liaoning Province, shows that these rocks demonstrate characteristics of adakitic rocks with SiO₂≥68.62%, Al₂O₃≥14.40%, MgO < 1.2% (Mg^# < 0.45), Sr > 360μg/g, Yb < 1.1μg/g, Y < 12μg/g, La/Yb > 40, Sr/Y≥39, Nb/Ta > 17.5 and with δEu weak negative anomaly, LREE enrichment, HREE depletion, HFSEs (Nb, Ta, Ti) strong depletion, lower ¹⁴³Nd/¹⁴⁴Nd ratios (0.511376 to 0.511441, -23.45 to -22.16 in ε_Nd (t)), moderate ⁸⁷Sr/⁸⁶Sr ratios (0.7073 to 0.7074, 32.38 to 32.8 in ε_Sr(t)) which have the features of the enriched mantle EMI. The above geochemical features of the rhyolites indicate the magmas originated from the partial melting of eclogite of the lower thicken basaltic crust of the North China craton and perhaps also represent the thicken crust still existed in partial area of Yanshan orogenic belt. It falicitates the understanding of the processes of the lithosphere thinning of the North China craton during the Mesozoic and Cenozoic period.