桂北泗里口老堡组硅质岩的常量、稀土元素特征及成因指示  

The Major and REE Geochemistry of the Silikou Chert in Northern Guangxi Province

作　　者：常华进[1,2,3] 储雪蕾[3] 冯连君[3] 黄晶[3] 张启锐[3] 

机构地区：[1]青海师范大学生命与地理科学学院,西宁810008 [2]青藏高原环境与资源教育部重点实验室,西宁810008 [3]中国科学院地质与地球物理研究所,北京100029

出　　处：《沉积学报》2010年第6期1098-1107,共10页Acta Sedimentologica Sinica

基　　金：国家自然科学基金(批准号:40532012;40873007;40603021);中国科学院知识创新工程项目(编号:KZCX3-SW-141)资助

摘　　要：桂北泗里口老堡组为一套埃迪卡拉纪—寒武纪过渡时期(大约550～540Ma)深水盆地沉积的硅质岩。它们的SiO2含量普遍高(平均93.8%);Al2O3含量为0.17%～4.92%,沿剖面自下而上明显增加,上部超过2%;Al/(Al+Fe+Mn)比值多高于0.42;Fe/Ti比值大都小于16.3;Al2O3/(Al2O3+Fe2O3)比值多高于0.4,剖面上部样品的比值为0.8～0.9;Y/Ho比值为26.4～36.9,中、下部样品较高(多高于32),上部样品的比值接近地壳值(27);Eu/Eu*平均值为1.0,正异常不明显。剖面下部样品的∑REE含量低(15.9×10-6～27.1×10-6),具有与现代海水相近的REE配分,没有正的Eu异常,不同于海底的热液流体和与其有关的碧玉的REE配分;中部样品的∑REE含量为26.2×10-6～49.4×10-6,由于所含陆源碎屑的增加,REE配分变得平坦,但仍有海水REE的某些特征;上部样品的∑REE含量为40.5×10-6～59×10-6,显示与平均页岩相似的平坦的REE配分,但∑REE含量仅为平均页岩的大约1/4～1/3。这些常量和稀土元素特征表明,海底热液和陆源碎屑都不可能成为泗里口老堡组硅质岩的重要物源。埃迪卡拉纪—寒武纪过渡时期华南深水盆地厚层硅质岩沉积反映了这一时期大气高CO2浓度,大量陆源化学风化的硅质流入海洋和大量生物的降解可能是造成这些硅质岩形成的基本原因。The Silikou chert in Northern Guangxi Province was deposited in a terminal Ediacaran to early Cambrian（about 550 ～540 Ma） deep ocean basin.It has high SiO2 concentration（average 93.8%） .Al2O3 content ranges from 0.17% to 4.92% and increases from the lower to the upper section which is more than 2% .Al/（Al ＋ Fe ＋ Mn） and Fe/Ti ratios for most of the chert are more than 0.42 and less than 16.3,respectively.Al2O3 /（Al2O3 ＋ Fe2O3） ratios for most of the chert exceeds 0.4 and the ratios are 0.8 ～ 0.9 for chert in the upper section.Y/Ho ratios（26.4 ～ 36.9） are high（more than 32） for chert in the lower and middle section,and are similar to that of the upper crust（27） for chert in the upper section.It has no positive Eu anomalies（average 1.0） for the chert samples.REE concentrations for chert in the lower section（15.9 × 10-6 ～ 27.1 × 10-6） are low relative to PAAS,which are similar to that of the seawater but hydrothermal fluids or jasper related to seafloor-hydrothermal sulfide deposits.Although REE patterns for chert in the middle section become flat since the increase of terrigenous detrital input,they have low REE concentrations（26.2 × 10-6 ～ 49.4 × 10-6） and seawater characteristics.REE concentrations for chert in the upper section range from 40.5 × 10-6 to 59 × 10-6 and they have flat REE patterns that are similar to PAAS,yet REE concentrations are just 1 /4 ～ 1 /3 of the PAAS.The major and rare earth elements characteristics of the Silikou chert suggest hydrothermal fluids and terrigenous detrital input were not main sources of the silica.In fact,huge amounts of dissolved silica derived from chemical weathering due to high CO2concentration in the atmosphere and degradation of organic matter were the basic cause for the basinal chert in South China.

关 键 词：硅质岩 埃迪卡拉纪—寒武纪过渡时期 老堡组 元素 成因 

分 类 号：P534.31[天文地球—古生物学与地层学] P595[天文地球—地质学]