辽西中生代软流圈底辟体的脉动式上涌

Mesozoic Pulsative Upwelling Diapirs of Asthenosphere in West Liaoning Province

岩石学-地球化学数据揭示了辽西中生代火山岩组分存在的3个特征：（1）Mg^#值和Cr、Ni含量比较高；（2）多数火山岩源自受到地壳物质混染的富集的岩石圈地幔；（3）相当部分火山岩的εNd（t）值偏高．对辽西及其邻区中生代（230～65Ma）火山岩年代学的研究发现：火山活动具有平均间隔20～30Ma的周期性，火山岩活动的峰期为230Ma、190Ma、160Ma、1304120Ma、1104100Ma、80Ma．同时火山岩εNd（t）值在时间上显示了类似的周期性波动．在空间上，中、新生代火山岩有呈环状分布的趋势，从中心向外逐渐变新．根据上述特点，提出辽西晚中生代的火山岩活动可能与软流圈底辟体脉动式上涌有关，研究区被岩石圈断裂围限的特定构造背景为软流圈底辟体的上涌提供了天然通道．

Petrologicos-geochemical data reveals the compositional features of Mesozoic volcanic rocks in West Liaoning： （1） Relatively high values of Mg^# and higher contents of Cr and Ni; （2） Most of volcanic magmas are derived from enriched lithospheric mantle hybridized by crust materials; （3） Considerable volcanic rocks have relatively high εNd （t） values. Chronologic researches on the Mesozoic （230--65 Ma） volcanic rocks in West Liaoning and adjacent areas indicate that the volcanic activities were periodic with an average period of 20--30 Ma, and that the peak ages of the volcanic activities were determined at 230 Ma, 190 Ma, 160 Ma, 130--120 Ma, 110--100 Ma, and 80 Ma, respectively. Temporally, the εNd （t） values of the volcanic rocks also show similar periodic variation responsible for the ages. Specifically, the Mesozoic-Cenozoic volcanic rocks are distributed in a ring-like shape with their ages ranging from old to young in an outward order from the center. These evidences lead to the conclusion that the Late Mesozoic volcanic activities in the study area are related to pulsative upwelling diapirs of asthenosphere, for which a natural passage is provided by the specific tectonic background confined by large-scale lithospheric faults in the study area.