科研之友
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摘要
The Caledonian and Yanshanian granites are the most widely distributed granites in South China. Previous study show less concern on the genetic link between the two stage granites and their respective contributions to mineralization. Both the Caledonian and the Yanshanian granites are spatially coexisted within the Xiongjiashan molybdenum deposit in Jinxi, Jiangxi Province. This paper presents comprehensive petrological, geochronological, major and trace element, and Sr-Nd-Hf isotopic data for both the Caledonian and the Yanshanian granites developed in this deposit, aiming to systematically unravel the geological and geochemical differences between them, and to probe their genetic link and possible metallogenic relationships. Zircon LA-ICP-MS U-Pb dating results show that the ages of the Caledonian and the Yanshanian granites are similar to 440Ma and similar to 155Ma, respectively. Chemically, the both stage granites show subalkaline, peraluminous and Fe-poor signatures, and are enriched in Cs, Rb, Th, Pb, and LREE, depleted in Ba, Sr, P, Ti, Nb, Ta. However, the Caledonian granites are more enriched in aluminum, while the Yanshanian granites are more enriched in alkaline, and have higher concentrations of Nb, Ta, Th. The Yanshanian granites also show higher Rb/Sr and Rb/Ba, lower K/Rb and LREE/HREE ratios relative to the Caledonian granites, and exhibit more distinct negative europium anomalies, implying they have suffered a higher degree of differentiation. Sr-Nd-Hf isotopic compositions indicate that the Caledonian granites were originated mainly from partial melting of Paleo- to Mesoproterozoic basement crustal rocks, and mantle-derived or juvenile crustal materials were less involved in petrogenesis. The Yanshanian granites have similar Sr-Nd-Hf isotopic compositions to that of the Caledonian granites, and contain more inherited magmatic zircons with Caledonian ages. Integrated geological and geochemical data suggest that the Yanshanian granites were not generated completely from remelting of the Caledonian granites, rather the latter were served only as components of source rocks in the formation of the Yanshanian granites. The molybdenum mineralization in this district was controlled mainly by the Yanshanian magmatic event, and the cryptoexplosion of granitic magma is a critical factor for metallogenesis. The role of the Caledonian granites in the ore-forming process are reflected mainly in two aspects, the first is that they were directly involved in the generation of Yanshanian granites as components of source rocks, thus might supply some ore-forming materials; the second is that they promoted the maturity of crust and enrichments of ore-forming elements, thus indirectly affect the metallogenic process.
- 出版日期2015-3
- 单位南京大学
