作　　者： ; ; ; ; ;

机构地区： 中国科学院广州地球化学研究所边缘海地质重点实验室

出　　处： 《地球化学》 2007年第1期11-26,共16页

摘　　要： 海南岛奥陶纪火山-碎屑沉积岩矿物、地球化学成分与源区岩性质和沉积构造环境密切相关。岩相学观察和矿物化学分析表明,所研究的岩石主要碎屑矿物由石英、绿泥石(Si:5.8～6.2a.p.f.u.、Mg/(Mg+Fe):～0.45)和白色云母(Si:6.2～6.8a.p.f.u.、Al:4.5～5.7a.p.f.u.)组成,含少量的长石(主要为钾长石)、黑云母(Mg/(Mg+Fe)=0.43、TiO_2=0.01%)和磷灰石等矿物。地球化学特征上,这些岩石普遍具有高SiO_2含量(Al_2O_3/SiO_2=0.07～0.19)、相对高的K_2O/Na_2O比值(1.25～14.71)和高的FeO_(total)+MgO含量(普遍大于5%,最高达11.5%),但微量元素(含REE)含量普遍低于PAAS(NASC),且REE分布模式显示LREE富集((La/Yb)N=6.1～12.5)、Eu负异常或弱负异常(δEu=0.57～0.86)。高的前交代CIA(～84)和PIA(～85)指数、A-CN-K分布模式以及可变的Th/U(2.9～25)比值还说明源区已经历强烈的化学和机械风化作用。低的Ce/Pb比值(2.1～2.8)则反映海南岛早古生代地壳已经历过Pb的富集事件。结合矿物化学成分和区域地质对比,研究区奥陶纪火山-碎屑沉积岩源区主要由变质的岩浆弧花岗闪长岩和弧长英质火山岩组成,少量的铁镁质成分不能排除,因而暗示一个从活动大陆边缘到被动大陆边缘的过渡性沉积构造环境。同时,推测海南岛在早古生代和晚古生代—早中生代可能分别存在一次俯冲增生-碰撞造山事件;海南岛(可能包括华夏地块)应于晚奥陶世后才脱离东冈瓦纳大陆的澳大利亚边缘。 The mineralogical and geochemical compositions of the Ordovician volcanic-elastic sedimentary rocks in Bangxi area, Northwest Hainan Island, South China are intimately related to their provenance and depositional tectonic setting. Petrographical observation assorting with mineral chemical analysis indicates that the studied rocks have a major elastic mineral association of quartz ＋ chlorite （Si = 5.8 - 6. 2 a. p. f. u, Mg/（Mg ＋ Fe） = ～ 0. 45） ＋ white mica （Si =6. 2 -6. 8 a. p. f. u, Al = 4. 5 -5.7 a. p. f. u） with minor feldspar （dominated by K-feldspar）, biotite （Mg/（Mg＋Fe）=0.43, TIO2=0.01% ）, apatite and other transparent minerals （e.g. zircon）. These rocks are also characterized generally by high content of SiO2 （Al2O3/SiO2 = 0. 07 -0. 19）, relatively high ratio of K2O/Na2O （ 1.25 - 14.71 ） and high concentration of FeO2total＋ MgO （generally more than 5% and up to 11.5% ）, as well as by LREE-enriched REE patterns with negative Eu anomaly-weak Eu anomaly （δEu =0. 57-0.86）. However, the concentrations of trace- and rare earth elements in the rocks are generally lower than those of the PAAS and/or NASC. The pre-metasomatized CIA and PIA values of ～ 84 and ～85, respectively, in connection with the A-CN-K modeling and the variable Th/U ratios （2.9-25） commonly suggest that the source area was affected by a strongly chemical and mechanical weathering. The low Ce/Pb ratios of 2. 1 - 2. 8 shown by most of our studied rocks further indicate a variably Pb-enriched Early Paleozoic crust. In concert with the mineral the major source rocks are composed of the metamorphic analysis, granodiorite as a subducted part of accretionary wedge and arc-related felsic volcanics, but minor contribution of mafic rocks to the source area cannot be ruled out. Therefore, it is suggested that the Ordovician volcanic-clastic sedimentary rocks in Bangxi area, Northwest Hainan Island were most likely If it is true, deposited in a transitional tectonic setting from active contin

关 键 词： 奥陶纪 火山 碎屑沉积岩 矿物化学 地球化学 源区岩性质 俯冲造山作用 海南岛

领　　域： [天文地球] [天文地球] [天文地球] [天文地球]