Geochronological, geochemical, and Nd-Hf isotopic constraints on the origin of magmatism in the Dabaoshan ore district of South China

SHRIMP and LA-ICP-MS zircon U-Pb dating, Nd and Hf isotope analyses, Ar-40/Ar-39 geochronology, and whole-rock geochemistry indicate three episodes of magmatism in the Dabaoshan ore district, South China: (1) Caledonian dacites (ca. 438Ma); (2) Indosinian dolerites (ca. 210Ma); and (3) Yanshanian granodiorites/porphyries (ca. 165Ma) and basalts (ca. 147Ma). Episode 1 dacites and episode 3 granodiorites/porphyries are enriched in Rb, Th, U, and LREEs and depleted in Nb, Ta, Sr, P, and Ti. The dacites may have been derived from partial melting of Mesoproterozoic-Paleoproterozoic crustal material, whereas the granodiorites/porphyries were derived mainly from partial melting of a late Mesoproterozoic crustal source with minor inputs of mantle material, according to whole-rock epsilon(Nd)(t) and zircon epsilon(Hf)(t) values. The geochemical characteristics of episode 2 dolerites and episode 3 basalts, as well as their positive epsilon(Nd)(t) values (3.3-5.9 and 3.5-4.0, respectively), suggest a depleted mantle source. Taking into account the tectonic evolution of the South China Block, we suggest episode 1 dacites and episode 2 dolerites formed in an extensional setting that resulted from lithospheric delamination during the Caledonian intraplate orogeny and orogenic collapse during the Indosinian intraplate orogeny. Episode 3 granodiorites/porphyries and basalts formed in a back-arc extensional setting in response to the westwards subduction of the Palaeo-Pacific Plate beneath the South China Block. The timing of the three episodes of magmatism coincides roughly with the published ages of mineralization in the Dabaoshan ore district, suggesting a genetic relationship.