南岭构造带基础地质特征与成矿地质背景

Fundamental Geological Features and Metallogenic Geological Backgrounds of Nanling Tectonic Belt

南岭构造带横跨扬子地块、江南造山带以及华夏地块,是中国钨锡铅锌铀等有色金属和铌钽锂铯与稀土等关键金属成矿带.通过综述近十五年来的研究进展,总结了南岭构造带基础地质特征与成矿地质背景.扬子与华夏地块沿永州-桂林-柳州一线于新元古代拼合,但缺乏直接的地质证据,需对龙胜蛇绿混杂岩和鹰扬关混杂岩进行深入研究.新元古代至中生代花岗岩二阶段模式年龄T_(DM2)值揭示2.0~1.2 Ga为南岭构造带的主要地壳增生期.相似的花岗岩特征和构造线方向指示广西期和印支期造山机制均为陆内造山作用,是华南大陆南侧不同板块之间拼贴远程应力场的产物.燕山早期花岗岩ε_(Hf)(t)值沿南岭构造带自西向东显著减小,而T_(DM2)值明显增加,指示湘南-桂北-粤北地区在晚侏罗世经历了古太平洋板块断离和软流圈上涌并发育强烈的壳幔相互作用,为南岭构造带东段华夏地块上钨锡等多金属成矿提供了成矿物质来源和有利的伸展构造背景.南岭构造带西段扬子地块构造相对稳定且显生宙岩浆活动较弱,新元古代大塘坡组和寒武系底部页岩是良好的页岩气勘探目标.综合沉积、岩浆以及构造变形,华南中生代特提斯构造域向古太平洋构造域转换开始于晚三叠世.

The Nanling tectonic belt is located across the Yangtze block, the Jiangnan orogen and the Cathaysia block. It is a metallogenic belt including W-Sn-Pb-Zn-U nonferrous metals, Nb-Ta-Li-Cs and rare earth critical metals. Fundamental geological features and metallogenic geological backgrounds are summarized for the Nanling tectonic belt based on review of the advances during the latest fifteen years. The Yangtze block sutured with the Cathaysia block along the Yongzhou-Guilin-Liuzhou fault at Middle Neoproterozoic era. More attention should be paid to the Longsheng ophiolite mélange and the Yingyangguan mélange due to the lack of direct proofs for above-mentioned suture. Two stage model ages of Neoproterozoic to Mesozoic granitoids imply that 2.0-1.2 Ga is a major crustal growth stage for the Nanling tectonic belt. Similar granitic features and orientations of tectonic lines indicate that both the Kwangsian and Indosinian orogenic mechanisms are intracontinental orogeny, triggered by far-field effect of collage of blocks to the south of the South China Block. From west to east, the values of ε_(Hf)(t) decrease obviously whereas the values of T_(DM2) increase for the Early Yanshannian granitoids along the Nanling tectonic belt. These results indicate that Late Jurassic break-off and foundering of the Paleo-Pacific plate and subsequent asthenosphere upwelling occurred at South Hunan Province, North Guangxi and North Guangdong Province. The crust-mantle interaction supplied metallogenic material and extensional background for the mineralization of W-Sn nonferrous metals in the Cathaysia block. Shale of the Neoproterozoic Datangpo Formation and the Lower Cambrian in the Yangtze block is favorable exploration targets of shale gas due to absence of Phanerozoic magmatic and tectonic activity. On the basis of sedimentation, magmatism and tectonism in the Nanling tectonic belt,Mesozoic tectonic transition from the Tethys to Paleo-Pacific regimes occurred in the South China block during Late Triassic.