Petrogenesis and metallogenesis of the Yanshanian adakite-like rocks in the Eastern Yangtze Block

Many of the Yanshannian intermediate-acid intrusive rocks related to Cu-Au mineralization in the Eastern Yangtze Block are characterized by high Al₂O₃, Sr contents, while low in Y, Yb contents, thus with high Sr/Y, and La/Yb ratios, and variational isotope signatures in particular, e.g. ε_Nd(t) = ?11.92–1.96, (¹⁴³Nd/¹⁴⁴Nd)_i = 0.5120–0.5125, T_DM = 0.70–1.71 Ga, (⁸⁷Sr/⁸⁶Sr)_i = 0.7043 –0.7076. The geochemical characteristics of these rocks suggest that: (1) these rocks are geochemically similar to adakite, which might have been stemmed from the partial melting of thickened basaltic lower crust due to basalt underplating; and (2) the high pressure (1.2–4.0 GPa) and high temperature (850–1150°C) surroundings of the lower crust favor both the fluid and adakite-like magma to generation. Not only can the adakite-like magma carry abundant fluid and Cu-Au ore-froming materials, but also can it bring them to the shallow part with ease and contributes to the Cu-Au mineralization.