安徽张八岭隆起南段中生代岩浆作用:岩石成因和构造指示意义  

MESOZOIC MAGMATISM IN THE SOUTH SEGMENT OF THE ZHANGBALING UPLIFT IN ANHUI PROVINCE:PETROGENESIS AND ITS TECTONIC IMPLICATIONS

作　　者：尚德锋 闫峻[1] 宋传中[1] 刘晓强[1] 李全忠[1] SHANG Defeng;YAN Jun;SONG Chuanzhong;LIU Xiaoqiang;LI Quanzhong(School of Resources and Environmental Engineering, Hefei University of Technology,Hefei 230009,Chin)

机构地区：[1]合肥工业大学资源与环境工程学院,安徽合肥230009

出　　处：《矿物岩石》2018年第2期20-30,共11页Mineralogy and Petrology

基　　金：安徽省公益性地质工作项目(编号:2016-g-1-4)

摘　　要：郯庐断裂带南段的张八岭隆起区广泛发育燕山期岩浆岩。其岩石类型以花岗岩、花岗闪长岩、二长岩、闪长岩、花岗闪长岩和石英二长岩为主。包括主要分布在张八岭隆起北段的高镁埃达克岩和南段肥东地区的低镁埃达克岩。本研究选取肥东地区竹园张岩体做研究对象,发现竹园张岩体沿郯庐主断裂带侵位,岩性为闪长岩。通过锆石LA-ICPMS精确定年得到竹园张岩体的年龄为128.2 Ma±2.3 Ma(1个样品),这一年龄与张八岭地区晚中生代燕山期岩浆作用的峰期一致,属于白垩世早期产物。竹园张岩体为中性侵入体,2个样品测定其SiO_2质量分数为57.99%~61.27%,富K(w(K_2O)2.72%~3.35%,属于高钾钙碱性准铝质系列,并具有与埃达克质岩类似的地球化学特征,无明显的Eu异常(Eu/Eu~*=0.95~1.06),富集w(Ba)(1 745×10^(-6)~2 100×10^(-6)),w(U)(1.21×10^(-6)~1.18×10^(-6)),w(K)(3 536×10^(-6)~4 614×10^(-6))等大离子亲石元素,亏损w(Nb)(7.9×10^(-6)~8.9×10^(-6)),w(Ta)(0.4×10^(-6)~0.6×10^(-6)),w(Ti)等高场强元素,A/CNK值小于1,属于准铝质I型花岗岩。竹园张岩体的^(87)Sr/^(86)Sr(t)初始比值为(0.706 1~0.706 2),ε_(Nd)(t)为(-16.66^-19.38)。综合地球化学研究表明,竹园张埃达克质岩石不是由年轻的洋壳部分熔融或同化混染分离结晶(AFC)或岩浆混合形成的,较低的ε_(Nd)(t)、较低的放射性成因Pb(^(206)Pb/^(204)Pb_i=16.495~16.514)进一步岩石成因可能是拆沉下地壳的部分熔融,并可能经历了一定程度的分离结晶作用,岩浆侵位过程中没有明显的中、上地壳混染。Yanshanian magmatie rocks is widely developed in the southern section of the Zhang- baling uplift, southern Tan-Lu fault zone. Granite, granodiorite, monzonite, diorite, granodiorite and quartz monzonite are the main rock types. These rocks including high-Mg adakitie rocks mainly distributed in the northern section of the Zhangbaling uplift,and the low-Mg adakites mainly in the south section of Feidong area. In this paper,the Zhuyuanzhang pluton located in Feidong region is selected as the study object. The Zhuyuanzhang pluton is intruded along the main fault zone of the Tan-Lu fault zone,with lithology of diorite. Zircon LA-ICPMS precision dating yields age of 128.2 Ma±2.3 Ma （1 sample）for the Zhuyuanzhang pluton. This age is consistent with the age peak of the Early Cretaceous magmatism in Zhangbaling areas. Zhuyuanzhang diorite have a intermediate composition with SiO2 content of 57.99% -61.27% （2 sample）, and a higher K20 content of 2.72% ～3.35%, which belongs to high-K calc-alkaline rock series. Moreover, they have adakite-like geochemical signatures with no obvious Eu（Eu/Eu＊=0.95 ～1.06） anomaly. They are enriched in large ion lithospheric elements such as w（Ba） （1 745 × 10-6 ～2 100 × 10-6）, w（U） （1.21X10-6～1.18～10-6）,w（K） （3 536×10-6～4 614×10-6） and depleted in high field strength elements such as w（Nb） （7.9 ×10-6～8.9× 10.6） ,w（Ta） （0.4×10.6 ～0.6 × 10.6 ）Ti, etc. The A/CNK value is less than 1 and belongs to metaluminous I-type granite rocks. Simultaneously, the initial ratio of 87 Sr/88 Sr（t） of Zhuyuanzhang pluton range from 0. 706 1 to 0. 706 2, and εNd（t） from -6. 66 to -19. 38. Integrated geochemical studies indicate that the Zhuyuanzhang adakitic rock was not formed by partial melting of young oceanic crust or assimilation and fractional crystallization （AFC） of mantle-derived magma or magma mixing. The low εnd（t） and low radioactive Pb （206 pb/204 Pbi = 16. 495 ～ 16. 514） isotopic composition indica

关 键 词：埃达克岩 锆石U-PB定年 岩石成因 张八岭隆起 郯庐断裂带 

分 类 号：P597.3[天文地球—地球化学] P581[天文地球—地质学]