摘要
钾玄质系列火山岩的构造背景一直是地学界讨论的热点。为进一步探明东乡火山盆地火山岩的形成时代及构造演化过程,本文对东乡火山盆地的粗面英安岩进行了岩石学、LA-MC-ICP-MS锆石U-Pb年代学及地球化学研究。锆石U-Pb测年结果显示粗面英安岩的结晶年龄在135.5 ±2.1 Ma和137.3 ±2.3 Ma,属于早白垩世,对应于华南早白垩世的火山岩浆活动。粗面英安岩具有高钾钙碱性过铝质的特征,富集大离子亲石元素,亏损高场强元素,相对富集轻稀土元素(LREE),相对较亏损重稀土元素(HREE),较弱的Eu负异常等特征。据此,本文提出北武夷东乡火山盆地的形成与古太平洋板块向欧亚板块的深俯冲作用有关。地壳缩短加厚,地幔岩浆上升,使地壳受热而引起部分熔融,下部产生的玄武质岩浆经同化混染作用形成英安质岩浆。
The tectonic background of potassium basalt series of volcanic rocks has been a hot topic in geoscience. To further explore the formation period and tectonic evolution process of volcanic rocks in Dongxiang volcanic basin, this paper studies the lithologic, LA-MC-ICP-MS zircon U-Pb chronology and geochemistry of trachydacite in Dongxiang volcanic basin. The zircon U-Pb dating results showed that the crystallization age of the trachydacite was 135.5 ±2.1 Ma and 137.3 ±2.3 Ma, responding to the early Cretaceous volcanic-magmatic events in South China. The trachydacite is characterized by high potassium, calcium and alkaline aluminum, enrichment of large ionophilic elements, loss of high field strength elements, relative enrichment of light rare earth elements (LREE), relative loss of heavy rare earth elements (HREE), weak Eu negative anomaly and other characteristics. Accordingly, we attribute the formation of the Dongxiang volcanic basin to the deep subduction of the ancient Pacific plate to the Eurasian plate. The crust shortens and thickens, and the mantle magma rises, which causes partial melting by heating the crust. The basaltic magma produced in the lower part was assimilated and mixed to form dacite magma.
出处
《地球科学前沿（汉斯）》
2020年第4期312-328,共17页
Advances in Geosciences
基金
《北武夷成矿带东乡浩家岭–上饶梨子坑铜多金属矿成矿规律调查》(项目编号1212011220557).
