四川木里杨房沟闪长岩体锆石U-Pb定年、地球化学特征及其构造意义

Geochemical signatures,zircon U-Pb dating and tectonic significance of the Yangfanggou diorite mass in the Muli region,southwestern Sichuan

四川木里地区杨房沟黑云母石英闪长岩体位于甘孜-理塘蛇绿混杂岩带南段以东,其锆石U-Pb年龄值为210±1Ma,表明其成岩年龄为晚三叠世。岩体属于高钾钙碱性系列,其稀土元素配分曲线呈向右缓倾型,轻稀土元素富集明显,Eu负异常明显,表明岩浆演化过程中部分斜长石经历了结晶分离过程。构造环境判别图解显示,木里杨房沟黑云母石英闪长岩形成于与甘孜-理塘蛇绿混杂岩带闭合的火山弧构造环境。

The Yangfanggou biotite quartz diorite mass in the Muli region,southwestern Sichuan lies in the area east of the southern part of the Garze-Litang ophiolitic mélange zone,and belongs to high-K calc-alkaline granitic rock series. The diorite mass gives a SHRIMP zircon U-Pb age of 210 ± 1 Ma,and may be traced back to the Late Triassic in age. Geochemically,the REE distribution curves for the diorite mass display the gently right-leaning patterns. The enrichment of the light rare earth elements and negative Eu anomaly show that part of plagioclase once experienced crystallization-differentiation processes during the magmatic evolution. The discrimination diagrams for tectonic interpretation show that the Yangfanggou biotite quartz diorite mass in the Muli region was formed in the volcanic arc environment associated with the westward subduction of the Garze-Litang ocean. The arc-continent and continent-continent collision of the Garze-Litang ocean gave rise to the asthenospheric upwelling and slab roll-back,and thus led to the formation of the Yangfanggou diorite mass.