粤东北长田地区南雄群沉积岩锆石年代学及其地质意义

粤东北长田盆地是广东省重要的能源盆地之一. 为详细了解该区地质结构、沉积物质特征、示踪砂岩物源等信息，在野外地质调查基础上，利用显微鉴定、电子探针分析（EPMA）和激光剥蚀电感耦合等离子体质谱仪（LA-ICP-MS）等方法，对长田盆地南雄群典型砂岩开展系统研究. 结果表明：研究区白垩系上统南雄群上亚群主要为（含炭质）岩屑石英砂岩，其次为钙质砂岩、（泥质）粉砂岩、细砂岩、砾岩及杂砂岩，普遍发育明显的次生变化和金属矿化现象. 南雄群碎屑锆石研究显示，样品中大部分碎屑锆石具有较好的振荡环带且Th/U值常大于0.4，指示锆石主要为岩浆结晶成因，有少量复杂成因变质锆石. U-Pb谐和年龄可大致分为2506~1666 Ma、1815~941 Ma、510~434 Ma、308~234 Ma、172~99 Ma五组，可与粤东北已知大地构造运动事件相对应，表明研究区的构造-岩浆活动主要受中国东部岩浆构造活动控制，并具有阶段性幕式发展演化的特点. 通过对南雄群碎屑岩岩相学、锆石U-Pb年龄、稀土元素特征的系统分析，并与可能物源区进行对比研究，认为南雄群碎屑物质主要来自长田盆地西缘的中生代岩浆岩侵入体.

ZIRCON GEOCHRONOLOGY FOR SEDIMENTARY ROCKS OF NANXIONG GROUP IN CHANGTIAN AREA,NORTHEAST GUANGDONG: Geological Implication

Changtian Basin is one of significant energy basins in Guangdong Province. To learn the geological structure, sedimentary material characteristics and tracer sandstone provenance in detail, microscopic identification, electron probe microanalysis(EPMA)and laser ablation inductively coupled plasma mass spectrometer(LA-ICP-MS)are used to systematically study the typical sandstones of Nanxiong Group in Changtian Basin on the basis of field geological survey. The results show that the Upper Cretaceous Nanxiong Upper Subgroup is mainly composed of(carbonaceous)lithic quartz sandstone, followed by calcareous sandstone, (argillaceous)siltstone, fine sandstone, conglomerate and greywacke, generally developed with obvious secondary changes and metallization. The analysis of detrital zircons from Nanxiong Group reveals that most of the zircons in the samples have perfect oscillatory bands with Th/U values usually greater than 0.4, indicating the zircons are mainly of magmatic crystallization origin, with a few metamorphic zircons of complex origin. The U-Pb concordant ages can be roughly divided into five groups: 2506-1666 Ma, 1815-941 Ma, 510-434 Ma, 308-234 Ma, and 172-99 Ma, which correspond to the known tectonic events in northeast Guangdong, reflecting that the tectono-magmatic activities in the study area are mainly controlled by the magmatic activities in eastern China, with the characteristics of episodic development and evolution. Based on the systematic analysis of lithography, zircon U-Pb age and REE characteristics of clastic rocks from Nanxiong Group, and comparison with the possible provenance, it is concluded that the detrital materials were mainly derived from Mesozoic magmatic intrusions in the western margin of Changtian Basin.