【摘要】 华北陆块南部古元古代熊耳群中的硅质岩主要发育于马家河组沉积岩中,有少量与火山岩共生。通过分析硅质岩的主、微量元素特征,把熊耳群硅质岩分为热水成因和非热水成因两类。热水成因硅质岩表现为低TiO2、MgO、Al2O3和∑REE含量,以及低的A1/(A1+Fe+Mn)比值的特征;其北美页岩标准化的稀土分配模式平坦,但具有Ce负异常与Eu正异常,U/Th>1,反映沉积速率快,受陆源物质的影响小。非热水成因的硅质岩的∑REE含量高,轻稀土富集(LaN/YbN=1.41~9.04),U/Th<1,受陆源物质影响较大。熊耳群硅质岩的Cr/Th比值变化小,表明物源区成分比较单一;其与熊耳群火山岩具有相似的REE配分模式图和蛛网图,也说明物源为熊耳群的英安—流纹质火山岩和玄武—安山质火山岩的混合。硅质岩的Al2O3/(Al2O3+Fe2O3)比值为0.44~0.64、以及Ce/Ce*(0.77~0.94)、LaN/CeN(1.18~1.47)的特征表明,熊耳群硅质岩主要形成于被动大陆边缘环境。熊耳群硅质岩主要形成于海相、海陆交互相等环境。早在古元古代熊耳群时期,熊耳—中条拗拉谷发生强烈的扩张裂解作用,华北陆块南部遭受海水入侵,豫南有些地区已经处于海相环境,晋南垣曲有些地区处于海陆交互相环境,局部地区还处于陆相环境。更多还原

【Abstract】 Palaeoproterozoic cherts from Xiong′er Group in the southern part of the North China block formed in sedimentary rock, but a few in volcanic rocks. The distributions of major and trace elements for cherts demonstrate that cherts were affected by both the hydrothermal process and hydrogenous process. The hydrothermal process might be related with Xiong′er Group volcanism, its geochemical characteristics show the lower concentrations of TiO2, MgO, Al2O3, ∑REE , the lower ratio of A1/(A1+Fe+Mn) and U/Th>1, the NASC-normalized flat REE patterns with weak negative Ce anomalies and positive Eu anomalies. The hydrothermal process was less influenced by the input of terrigenous component due to quick subsidence. However, the hydrogenous genesis cherts were which showed LREE enrichment (LaN/YbN=1.41~9.04) and the high ∑REE, influenced by the input of terrigenous component. The lower ratio of Cr/Th, the chondrite-normalized REE patterns and primitive mantle-normalized trace-element patterns for cherts are consistent with the volcanic rocks of the Xiong’er suggest that the single provenance. The cherts were mainly derived from the mixture of basaltic-andesite and dacite-rhyolite from Xiong′er Group. The characteristics of Al2O3/(Al2O3+Fe2O3), Ce/Ce*(0.77~0.94) and LaN/CeN(1.18~1.47) implied a setting of passive continental margin. The hydrothermal activity is interpreted as having been related to the intensity extensional background in the Xiong′er-Zhongtiao Aulacogen, as early as the Palaeoproterozoic. According to the geological characteristics and the ratio of elements, such as Sr/Ba, Th/U, CaO/(CaO+MgO), the cherts deposited in both marine and marine-terrigenous facies. As a result of transgression toward north, southern part of Henan was in the marine environment, but northern part of Henan was marine-terrigenous, some areas still in continent environment.更多还原