闽西南莒林环斑花岗岩特征及地质意义

Characteristics and Geological Significance of the Julin Ringspotted Granite in Southwest Fujian

莒林环斑花岗岩属胡坊复式岩体的重要组成部分,主要岩性为似斑状黑云母正长花岗岩,岩石具更长环斑结构,环斑长石由钾长石内核和斜长石(更长石)外壳环边组成。岩石富Si、NK、K,贫Al、Ca、Mg;LILE元素K、Rb、Th、U、Pb、REE富集,Eu、Ba、Nb、Sr强烈亏损;HFSE元素Zr、Th、Ce富集,P、Ti明显缺失,Nb、Ta、Y、Hf相对亏损;稀土元素总量高、轻稀土富集,具强烈的Eμ负异常(δEμ=0.09~0.34),具A型花岗岩的地球化学特征。2件样品LA-ICPMS锆石U-Pb同位素年龄为(232.9±1.4)Ma、(226±1.4)Ma,属中三叠世,其形成与闽西南地区印支期的阶段性伸展拉张构造背景有关。

Julin ringspotted granite belongs to an important part of Hufang complex rock mass.The main lithology is porphyritic biotite syenite granite with longer ring pattern structure.Ring porphyry consists of a potassium feldspar core and a ring edge of a plagioclase(feldspar)outer shell.Si,NK,K are rich and Al,Ca,Mg are poor in the rocks.K、Rb、Th、U、Pb、REE of LIFE elements are rich and Eu、Ba、Nb、Sr are strongly poor.Zr,Th,Ce HFSE elements of are enrichment and P,Ti are obviously missing and Nb,Ta,Y,Hf are relative deficit.The total amount of rare earth elements is high,the light rare earth is enriched,and the Eμnegative anomaly(δEμ=0.09~0.34)is strong,which has the geochemical characteristics of A-type granite.The U-Pb isotopic ages of the two LA-ICPMS zircons are(232.9±1.4)Ma and(226±1.4)Ma,belonging to the Middle Triassic,which are related to the staged extensional and tensile tectonic setting of the Indosinian period in southwest Fujian.