No abstract

The vertical and horizontal accretion and recycling of crust play a pivotal role in continental growth. Continent amalgamation and splitting have been widely investigated in the context of supercontinent emergence and destruction (Rogers and Santosh, 2002;Santosh et al., 2009;Roberts and Spencer, 2015), the Paleoproterozoic to Mesoproterozoic Columbia supercontinent being the best candidate with which to investigate supercontinent formation and breakup, recording, as it does, a whole Wilson cycle (e.g., Zhao et al., 2002Zhao et al., , 2004Rogers and Santosh, 2009).Hainan Island recorded complex geological and tectonic evolutionary histories in the Mesoproterozoic and provides comprehensive information on the amalgamation and breakup of the Columbia supercontinent (e.g., Li et al, 2002Li et al, , 2008

No abstract

SHRIMP and LA–ICP–MS zircon U–Pb dating, Nd and Hf isotope analyses, 40Ar/39Ar geochronology, and whole‐rock geochemistry indicate three episodes of magmatism in the Dabaoshan ore district, South China: (1) Caledonian dacites (ca. 438 Ma); (2) Indosinian dolerites (ca. 210 Ma); and (3) Yanshanian granodiorites/porphyries (ca. 165 Ma) and basalts (ca. 147 Ma). 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 εNd(t) and zircon εHf(t) values. The geochemical characteristics of episode 2 dolerites and episode 3 basalts, as well as their positive εNd(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.

The Tuwaishan gold deposit is located at the northeastern end of the Gezhen shear zone in the western part of Hainan Island, South China. It is one of a series of similar gold deposits hosted in the Mesoproterozoic basement rocks and structurally controlled by the Gezhen shear zone. The hydrothermal ore-forming period can be divided into quartz-pyrite-arsenopyrite stage, quartz-pyrite-base metal sulfides stage and quartz-carbonate stage. Eleven gold-bearing quartz vein samples yield δDV-SMOW and δ18OV-SMOW values of −75.9‰ to −54.4‰ and +8.1‰ to +13.7‰, respectively, and the corresponding δ18Owater values range from +3.1‰ to +8.7‰. In addition, the pyrite separates from 14 ore samples yield δ34S values of +4.5‰ to +7.9‰. The H-O-S isotopic data, along with fluid properties of the Tuwaishan and other gold deposits along the Gezhen shear zone, suggest that the ore-forming fluid and materials are of metamorphic rather than magmatic origin. Hence, we propose that the Tuwaishan gold deposit is best classified as orogenic gold deposit that resulted from regional metamorphism. Considering that the Mesoproterozoic basement rocks have experienced amphibolite facies metamorphism prior to the gold mineralization, the metamorphic devolatilization of the Ordovician-Silurian rocks at depth would provide a realistic source of fluid, gold and sulfur for the Tuwaishan and other gold deposits of the Gezhen gold belt.