台湾利吉混杂岩中蛇纹岩岩石学和U-Pb年代学及其地质意义

Petrology and U-Pb geochronology of the serpentinite in the Lichi mélange of Eastern Taiwan and their tectonic implications

台湾利吉混杂岩位于吕宋岛弧与欧亚大陆发生碰撞(弧陆碰撞)关键地带,是菲律宾海板块和欧亚板块结合带重点研究的区域,其中出露的蛇纹岩可以为研究弧陆碰撞造山过程提供重要细节信息。利吉混杂岩中蛇纹岩岩块原岩为橄榄岩,通过锆石U-Pb年代学分析,得到代表洋壳年龄的橄榄岩形成年龄为17.7±0.5Ma,结合南海洋壳、菲律宾海洋壳年龄和构造背景,判断利吉混杂岩中的蛇纹岩(蛇纹石化橄榄岩)来自马尼拉俯冲系统的弧前盆地,是在利吉混杂岩形成过程中经第二次逆冲混入利吉混杂岩系统的。明确蛇纹岩岩块来源可以为利吉混杂岩形成提供细节信息,为研究弧陆碰撞造山活动和板块运动提供可靠依据。

Lichi Mélange,located along the plate suture between the southeastern Eurasian Plate and the Philippine Sea Plate,is a research focus of the collision of the Luzon Arc with the Eurasian Continent.The serpentinite,as a key component of the Mélange,can provide important information for studying the arc-continent collision.Petrographic study suggests that the protolith of the serpentinite is peridotite and the zircon U-Pb chronology data reveals that the serpentinite was formed 17.7±0.5 Ma.The serpentinite or serpentinised peridotite is supposed to come from a forearc basin in the Manila subduction system,based on their ages and the evolution of the South China Sea and the Philippine Sea as well as their tectonic backgrounds,and became part of the mélange in the second thrust westward.The origin of serpentinite in the Lichi Mélange may provide detailed information and a reliable basis for the study of arc-continent collision orogenic activity and plate tectonic movement.