辽东凤凰山正长花岗岩SHRIMP U-Pb年龄、地球化学特征与陆内伸展作用

【研究目的】 辽宁丹东地区发育着一期A型花岗岩，因其特殊的成因演化，特定的构造背景及其重要的地球动力学意义而备受关注。【研究方法】 本文通过对辽宁丹东凤凰山岩体SHRIMP锆石U-Pb年代学、岩石地球化学特征的分析，探讨了该岩体形成时代、岩石成因及地球动力学背景。【研究结果】 辽东凤凰山黑云母正长花岗岩锆石U-Pb年龄分别为（122.3±1.7）Ma、（125.0±1.7）Ma、 （122±2）Ma，代表岩浆结晶年龄，凤凰山正长花岗岩侵位时代属于早白垩世。地球化学分析结果显示，SiO₂含量为65.65%～73.62%，K₂O为3.52%～5.76%，Na₂O为3.64%～4.26%，Al₂O₃为13.4%～15.49%，A/CNK值1.02～1.46，属铝过饱和型。碱度率AR在2.71～5.13，基本在铝质A型花岗岩AR值范围内，FeO_t/MgO比值为4.69～18.05，表现为A型花岗岩的A1和A2过渡类型。Rb/Nb比值为6.02～8.64，明显高于大陆壳的Rb/Nb比值2.2～4.7，说明陆壳物质对岩体成岩影响较大，从而导致Rb的含量增加。相对富集大离子亲石元素Rb、Th， Zr、Hf，亏损Sr、P、Ba、Ti、Nb。稀土总量较高，轻重稀土之间的分馏不明显，Eu具明显的负异常。【结论】 综上，凤凰山正长花岗岩可能产生于陆内剪切相关的伸展环境，应为自中侏罗世开始由板块俯冲引起的东亚大陆边缘构造过程的响应。

SHRIMP U-Pb age, geochemical characteristics and its introcontinental extension of Fenghuangshan syenogranite in the east Liaoning

This paper is the result of the geological survey engineering.Objective] Aperiod of A-type granite is developed in Dandong, Liaoning Province, which has been widely concerned because of its special genetic evolution, specific tectonic setting and important geodynamic significance.Methods] In this paper, the SHRIMP zircon U-Pb chronology and petrogeochemical characteristics of the Fenghuangshan pluton in Dandong, Liaoning Province, were analyzed to explore the formation age, petrogenesis and geodynamic background of the pluton.Results] The zircon U-Pb ages of the biotite syenogranite in Fenghuangshan, Liaodong are (122.3±1.7) Ma, (125.0±1.7) Ma and (122±2) Ma, representing that the magma of the biotite syenogranite in Fenghuangshan crystallized and intruded in the Early Cretaceous. Geochemical analysis shows that the SiO₂ content is 65.65%-73.62%, whereas that of K₂O and Na₂O is 3.52%-5.76% and 3.64%-4.26%, respectively. They also contain 13.4%~15.49% of Al₂O₃, with A/CNK ratio of 1.02-1.46, indicative of their peraluminous nature. The alkalinity rate (AR) ranges from 2.71 to 5.13, and this range is within the AR of aluminous A-type granites. Its FeO_t/MgO ranges from 4.69 to 18.05, which shows the A1 and A2 transition types of A-type granites. The Rb/Nb ranges from 6.02 to 8.64, which display a higher level than that of the continental crust of 2.2-4.7. This implies that continental crust components, which lead to an increase in Rb content, had a significant influence on its formation. The biotite syenogranites are relatively enriched in large ion lithophileelements Rb, Th, Zr, Hf, and depleted in Sr, P, Ba, Ti, Nb. The total content of rare earth elements is high, the fractionation between light and heavy rare earth elements is not obvious, and Eu has obvious negative anomalies. Conclusions] In summary, Fenghuangshan pluton might have been produced in stretching environment related to intracontinental shearing, which ought to be a response to the tectonization of the East Asia continental margins caused by the subduction of plates starting from the Middle Jurassic.