摘要
华北克拉通南部熊耳—中条拗拉谷中广泛发育的古元古界熊耳群火山岩,是华北克拉通结晶基底形成后规模最大、涉及范围最广的火山活动产物,以火山熔岩占绝对优势,沉积岩和火山碎屑岩主要分布在大古石组及马家河组,仅占地层总厚度的4.3%。本文从沉积学角度,探讨熊耳群火山岩的形成环境及其构造背景。底部大古石组碎屑岩主要由一套砂砾岩、砂岩和泥质岩组成。其岩相学特征表明大古石组自下而上的沉积相为河流相—湖泊相—河流相。自下而上对比大古石组剖面中碎屑岩的地球化学数据(Sr、Ga、V)及相应比值(Sr/Ba、Th/U、Zr/Rb),认为大古石组碎屑岩以陆相沉积(河流相和湖泊相)为主,但中后期伴有海侵作用。通过对其泥质岩的主、微量元素地球化学特征的研究,认为大古石组碎屑岩主要来源于花岗质成分,但混有一定量的基性物质;源岩以太古宙地层为主,可能有古元古代地层的加入,经历了中等程度的风化作用,并快速堆积形成的。大古石组碎屑岩形成于被动大陆边缘环境,代表了古元古代末华北克拉通伸展—裂解事件的开始;熊耳群火山岩则是在被动大陆边缘的裂谷环境发育形成的。
The Paleoproterozoic Xiong＇er Group is widely exposed in the Xiong＇er-Zhongtiao aulacogen （failed rift） in the southern margin of the North China craton. It records the most intense magmatism after the formation of the crystalline basement of the North China craton. The Xiong＇er Group is occupied by volcanic lavas as well as minor sedimentary rocks and volcanic clastic rocks （4. 3% in thickness）. The sedimentary rocks occur as interbeds in the Dagushi and Majiahe Formations of the Xiong＇er Group. Writers studied the sedimentary and geochemical characteristics of the siliciclastic rocks from the Dagushi Formation, in an attempt to elucidate the tectonic setting of the North China craton during the Paleoproterozoic. The Dagushi Formation contains conglomerate, sandstone, and mudstone, and could have been formed in fluvial and lacustrine environments. From bottom to top of the Dagushi Formation, the trace element contents （Sr, Ga, V） and ratios （Sr/Ba, Th/U, Zr/Rb） of the mudstone rocks reflected mainly a continental environment. But the later sequences indicate transgression, either due to basin subsidence or glacio-eustasy. The compositions and their ratios of the major and trace elements of the mudstone rocks demonstrate that a derivation from main silicic source rocks and mixing a further higher proportion of mafic component. These siliciclastic rocks were derived mainly from the Archean and minor from Paleoproterozoic in the southern margin of the North China craton. The chemical index of alteration （CIA） indicates an intermediate degree of weathering. The elastic sedimentary rocks were deposited in a passive margin setting. The volcanic rocks of the Xiongfer Group formed in a continental-rift setting in passive continental margin.
出处
《地质论评》
CAS
CSCD
北大核心
2008年第3期316-326,I0001,共12页
Geological Review
基金
国家基础研究发展计划(973项目)“华北大陆边缘造山过程与成矿”(编号2006CB403502)
国家自然科学基金(编号40672058)
中国科学院知识创新工程领域前沿项目(编号GIGCX-04-03)资助课题联合资助的成果
关键词
华北
古元古代
熊耳群
大古石组
地球化学
沉积环境
构造背景
North China
Proterozoic
Xiong＇er Group
Dagushi Formation
geochemistry
sedimentary environment
tectonic setting
