长江中下游地区晚中生代岩浆岩氧逸度特征及意义

Characteristics of oxygen fugacity of the Late Mesozoic magmatic rocks in the Middle-Lower Yangtze River belt and its significance

长江中下游地区是我国东部重要的多金属成矿区，区内中生代岩浆活动强烈，可分为4个阶段。本文选择代表性岩石，开展了锆石原位微量元素测试，结合全岩数据，应用拟合法、插值法进行锆石氧逸度估算。结果表明：相比插值法，拟合法获得的锆石氧逸度数据结果更加准确集中，分布趋势更加明显，尤其修改的M估计估算方法可有效削弱拟合法估算过程中遇到的轻重稀土元素异常分馏等不利影响。最终确定，基于全岩和锆石微量元素数据的最小二乘法估算结果更加符合实际。长江中下游地区晚中生代4个阶段岩浆岩的氧逸度普遍较高，其中第1和第4阶段岩浆岩氧逸度相似，为高氧逸度岩浆岩，第2与第3阶段岩浆岩的氧逸度较低，表现出晚中生代早期到晚期，岩浆氧逸度从高降低、再升高的变化趋势。各阶段岩浆岩的氧逸度高低与岩浆起源和成矿属性有着良好的对应关系。

The Middle-Lower Yangtze River belt is an important polymetallic mineralized area in the eastern China,where widely cropped out Mesozoic magmatisms which can be divided into four stages. Representative rocks from the four stages magmatisms were selected for the in-situ zircon and whole-rock trace elemental analysis. Using these data, the zircon oxygen fugacity were estimated by methods of interpolation and fitting respectively. The results indicate that fitting method has more advantages over interpolation method on zircons oxygen fugacity estimation, because of more accurate and agminate in oxygen fugacity data and more obvious distribution trend. Besides, the modified M-Estimator method can effectively avoid the abnormally fractionate between the LREE and the HREE during oxygen fugacity estimation by fitting method. Finally,we consider that the least square method based on trace elements of zircon and whole-rock is more consistent with the actual situation. Estimated results show that all the four stages magmatic rocks in the Middle-Lower Yangtze River belt have relatively high oxygen fugacity. Among them, the first and fourth stage magmatic rocks have similar higher oxygen fugacity than the second and third stage rocks. Form the early to late stage magmatisms,the magmatic oxygen fugacity represents a high-low-high trend,which can well correspond to their magma origin and metallogenic attributes.