广东连山地区禾洞高分异花岗岩的锆石U-Pb年代学及岩石成因  

Zircon Geochronology and Petrogenesis of Hedong Highly Fractionated I-Type Granite in Lianshan,Guangdong Province

作　　者：李响[1,2] 王令占[1,2] 涂兵[1,2] 田洋[1,2] 谢国刚[1] 张楗钰[1] 张宗言[1] Li Xiang;Wang Lingzhan;Tu Bing;Tian Yang;Xie Guogang;Zhang Jianyu;Zhang Zongyan(Wuhan Center of China Geological Survey,Wuhan 430205,China;Research Center of Granitic Diagenesis and Mineralization,China Geological Survey,Wuhan 430205,China)

机构地区：[1]中国地质调查局武汉地质调查中心,湖北武汉430205 [2]中国地质调查局花岗岩成岩成矿研究中心,湖北武汉430205

出　　处：《地球科学》2023年第10期3577-3596,共20页Earth Science

基　　金：中国地质调查局项目(Nos.12120113063200,DD20211385).

摘　　要：南岭地区晚中生代花岗岩的岩石成因还存在不同认识.以广东连山地区禾洞高分异花岗岩为研究对象,进行了系统的岩石学、锆石U-Pb年代学、地球化学和Sr-Nd-Hf同位素组成研究.锆石LA-ICP-MS U-Pb定年结果表明,禾洞岩体中细粒黑云母正长花岗岩和中粒黑云母二长花岗岩的成岩年龄分别为159.7±1.4 Ma和160.3±1.7 Ma,指示禾洞岩体为晚侏罗世岩浆活动的产物.地球化学分析显示,禾洞岩体高硅和富碱,SiO_(2)含量为70.02%~75.56%,碱含量(K2O+Na2O)变化于7.74%~8.59%之间,贫铁、镁、钙、钛、磷,铝饱和指数(A/CNK值)为0.96~1.28,具有较高的Rb/Sr比值(2.6~17.8)和显著的铕负异常(0.06~0.52).大多数样品的Ga/Al比值小于2.6,高场强元素Zr+Nb+Ce+Y为118×10^(-6)~313×10^(-6),低于A型花岗岩的下限值,锆石饱和温度也较低(703~801℃),P_(2)O_(5)与SiO_(2)负相关,Y和Th均与Rb呈正相关关系,这些均指示禾洞岩体应为高分异的I型花岗岩.禾洞岩体具较低的ISr值(0.70700~0.71139),较高的ε_(Nd)(t)值(-7.1~-2.6),锆石ε_(Hf)(t)值为-8.4~+2.2.二阶段Nd模式年龄和Hf模式年龄分别为1.30~1.67 Ga和1.04~1.71 Ga.上述同位素数据,结合野外地质特征,表明禾洞岩体在成岩过程中可能发生了壳幔混合作用.在古太平洋板块俯冲形成的伸展构造环境下,禾洞岩体的形成与幔源岩浆沿郴州-临武深大断裂底侵有关.The petrogenesis of Late Mesozoic granites in Nanling Mountains region remains controversial.In this paper,it conducts the comprehensive study of petrology,zircon U-Pb chronology,whole-rock element and Sr-Nd-Hf isotopic geochemistry for the Hedong highly fractionated I-type granite in the Lianshan,Guangdong Province.LA-ICP-MS U-Pb zircon analysis yields 206Pb/238U weighted mean ages of 159.7±1.4 Ma and 160.3±1.7 Ma for the medium-fine-grained biotite syenite granite and medium-grained biotite monzonitic granite respectively,indicating that the pluton was formed in the Late Jurassic.Chemical analyses show that the granite has higher SiO_(2)(70.02%-75.56%)and total alkali(7.74%-8.59%),lower TFeO,MgO,CaO,TiO_(2),P_(2)O_(5),A/CNK values is ranging from 0.96 to 1.28.The granite is also characterized by higher Rb/Sr ratio(2.6-17.8)and pronounced negative Eu anomalies(δEu ranging from 0.06 to 0.52).The Ga/Al ratio of most granite samples are lower than 2.6,and the Zr+Nb+Ce+Y values are ranging from 118×10^(-6) to 313×10^(-6),which are lower than the respective values of A-type granites.The granite is also characterized by low zircon saturation temperatures(703-801°C).The P_(2)O_(5) contents are negatively correlated with SiO_(2) while element Y and Th are positively correlated with Rb.Above geochemical data suggest that the rocks from the Hedong pluton are highly fractional I-type granites.They have relatively low ISr values(0.70700-0.71139),highε_(Nd)(t)values(-7.1 to-2.6)and theε_(Hf)(t)values range from-8.4 to+2.2.Their two stage Nd and Hf model ages are 1.30-1.67 Ga and 1.04-1.71 Ga,respectively.Combining with field observation,it suggests that the Hedong pluton was formed by the mixing of crust-derived magmas and mantle-derived magmas.Under the extension environment triggered by subduction of paleo-Pacific plate,the Hedong pluton might form by the underplate of mantle-derived magmas across the Chenzhou-Linwu trans-crustal fault.

关 键 词：禾洞岩体 高分异I型花岗岩 锆石U-PB年代学 SR-ND-HF同位素 岩石成因 地球化学 岩石学 

分 类 号：P597[天文地球—地球化学]