海南公爱地区抱板群花岗片麻岩的年代学、地球化学及其构造意义  

Geochemical and Geochronological Characteristics of Granitic Gneisses in the Baoban Group,Gong'ai (Hainan) and its Tectonic Implications

作　　者：张立敏[1] 王岳军[1,2] 李庶波[1] 张玉芝[1] 

机构地区：[1]中山大学地球科学与工程学院,广东广州510275 [2]广东省地质过程与矿产资源探查重点实验室,广东广州510275

出　　处：《大地构造与成矿学》2017年第2期396-411,共16页Geotectonica et Metallogenia

基　　金：国家重点基础研究发展计划(973)项目(2014CB440901);国家自然科学基金项目(41372198;41402165)联合资助

摘　　要：海南岛地处华南陆块南缘,紧邻印支陆块,大地构造位置独特,其地质特征一直备受关注。厘定该地区中元古代岩石的成因对恢复华南中元古代构造演化具有重要意义。海南岛西部公爱地区花岗质岩石与围岩抱板群变沉积岩呈侵入接触关系,绝大部分岩石片麻状构造发育、韧性剪切标志明显。这些岩石高SiO_2、K_2O、Al_2O_3、Rb、U,贫CaO、MgO、FeO^T、TiO_2,铝饱和指数A/CNK>1.1,具S型花岗岩特点,稀土元素配分模式类似于抱板群变沉积岩,全岩ε_(Nd)(t)=-2.02^-2.38,Nd同位素二阶段亏损模式年龄(t_(DM2)^(Nd))为2.2~2.3 Ga,锆石Hf同位素ε_(Hf)(t)=-5.4~4.0,Hf同位素二阶段亏损模式年龄t_(DM2)^(Hf)=1.71~2.53 Ga。对四个代表性花岗片麻岩样品进行LA-ICP-MS锆石U-Pb定年,其^(207)Pb/^(206)Pb加权平均年龄为1444±15 Ma、1439±19 Ma、1433±31 Ma和1450±23 Ma,属中元古代。综合区域研究资料认为,海南岛西部公爱地区中元古代花岗质岩石的熔融源区为类似抱板群变沉积岩组分,推测其产出于大陆边缘构造背景,是哥伦比亚超大陆边缘的增生产物。Hainan Island geotectonically lies in the junction of Eurasian, India-Australia and Philippine plates. It is a key area for better understanding the Mesoproterozoic tectonic evolution of the South China Block, due to the presence of the Mesoproterozoic igneous rocks. The granitic gneisses from the Baoban Group, Gong＇ai area （Hainan Island）, consist mainly of monzogranite that underwent significant shearing deformation. Geochemically, they are characterized by high SiO2, K2O, Al2O3, Rb, U and low CaO, MgO, FeOT, TiO2 contents, with A/NK=1.62-1.84 and A/CNK=1.22-1.51, suggestive of the strongly peraluminous S-type granite. In the chondrite-normalized REE patterns and primitive mantle-normalized trace element spider diagram, they show signatures similar to those of the Mesoproterozoic metasedimentary rocks in the Baoban Group. The granitic gneisses have εNd（t） values ranging from -2.02 to -2.38 with Nd model age of 2.2-2.3 Ga, and εHf（t） values from -5.4 to 4.0 with Hf model age of 1.71-2.53 Ga. The zircon U-Pb dating analyses of four representative samples give the mean weighted ages of 1444± 15 Ma, 1439±19 Ma, 1433±31 Ma and 1450±23 Ma, respectively, which suggest the original granitic rocks were crystallized in Mesoproterozoic. In combination with other available data, it is inferred that the Gong＇ai granitic gneisses, which were previously defined as the crystallize basement were formed at Mesoproterozoic of 1433-1450 Ma, were derived from the continental crustal materials resembling compositionally to the Baoban sedimentary rocks. These rocks might have been generated in the continental marginal setting linked to the marginal accretion of Columbia supercontinent.

关 键 词：花岗片麻岩 中元古代 锆石U-PB年代学 海南 哥伦比亚超大陆 

分 类 号：P595[天文地球—地球化学] P597[天文地球—地质学]