内蒙古固阳绿岩带条带状铁建造地球化学特征与沉积环境讨论
发布时间：2018-11-04 16:34
【摘要】：Algoma型条带状铁建造(BIF)是一种海相化学沉积岩,它发育在太古宙绿岩带的火山-沉积岩序列中,大部分经历了后期变质变形作用。稀土元素具有稳定的地球化学性质,因而被广泛用于指示BIF的原始沉积环境。华北克拉通北缘固阳绿岩带中的BIF(如三合明、公益明、东五分子、公巨成等)赋存于新太古代色尔腾山群的变火山-沉积序列中,普遍经历了绿片岩相—低角闪岩相变质,呈条带状构造,其主要矿物组成为自形—半自形粒状磁铁矿和他形粒状石英,含少量角闪石,局部地区可见石榴石、绿泥石、斜长石等富Al矿物。根据BIF中惰性元素的含量及其相关性,可划分为纯净的BIF和遭受碎屑物质混染的BIF,并通过特征的Co/Th比值判断出这些碎屑物质主要来自于玄武质岩石。纯净及遭受轻微碎屑物质混染的BIF稀土元素特征通过后太古宙页岩(PAAS)标准化后,与现代海水及其他地区典型太古宙BIF相似,均表现为轻稀土相对重稀土亏损,正La、Y异常以及较高的Y/Ho比值(29)。大多数样品发育不明显的负Ce_(PAAS)异常,说明BIF沉淀自缺氧的环境;正Eu_(PAAS)异常明显,说明海水中有高温(250℃)热液的加入,其比例为0~10%。然而,遭受强烈碎屑物质混染的BIF稀土元素特征则具有明显差异。此种类型BIF的出现及分布不均,指示了在BIF沉积之前的局部地区或时间段内,深部海水处于相对动荡的环境。
[Abstract]:The Algoma type banded iron formation (BIF) is a marine chemical sedimentary rock, which developed in the volcanic-sedimentary rock sequence of the Archean greenstone belt, most of which experienced late metamorphism and deformation. Rare earth elements have stable geochemical properties and are widely used to indicate the primitive sedimentary environment of BIF. The BIF in the Guyang greenstone belt on the northern margin of the North China Craton (such as Sanhe Ming, Pe Ming, Dong Wu molecular, Gong Ju Cheng, etc.) occurred in the altered volcano-sedimentary sequence of the NeoArchean Seltenshan Group, and generally experienced greenschist facies and low amphibolite facies metamorphism. The main mineral composition of the structure is as follows: Auto-semiautomorphic granular magnetite and allotropic granular quartz containing a small amount of hornblende and some rich Al minerals such as garnet chlorite plagioclase and so on. According to the content of inert elements in BIF and its correlation, it can be divided into pure BIF and BIF, contaminated by clastic materials. By the characteristic Co/Th ratio, it can be concluded that these clastic materials mainly come from Black Tortoise rocks. The characteristics of BIF rare earth elements of pure and slightly detrital materials mixed with each other, passing through the (PAAS) standardization of post-Archean shale, are similar to the typical Archean BIF in modern seawater and other areas. They all show that the light rare earth elements are relatively heavy rare earth elements, and the positive La, is the same as that of the later Archean Shale. Y abnormality and high Y/Ho ratio (29). Negative Ce_ (PAAS) anomalies are not obvious in most samples, indicating that BIF precipitates from anoxic environment, and positive Eu_ (PAAS) anomalies are obvious, indicating that there is a high temperature (250 鈩，
本文编号：2310463
[Abstract]:The Algoma type banded iron formation (BIF) is a marine chemical sedimentary rock, which developed in the volcanic-sedimentary rock sequence of the Archean greenstone belt, most of which experienced late metamorphism and deformation. Rare earth elements have stable geochemical properties and are widely used to indicate the primitive sedimentary environment of BIF. The BIF in the Guyang greenstone belt on the northern margin of the North China Craton (such as Sanhe Ming, Pe Ming, Dong Wu molecular, Gong Ju Cheng, etc.) occurred in the altered volcano-sedimentary sequence of the NeoArchean Seltenshan Group, and generally experienced greenschist facies and low amphibolite facies metamorphism. The main mineral composition of the structure is as follows: Auto-semiautomorphic granular magnetite and allotropic granular quartz containing a small amount of hornblende and some rich Al minerals such as garnet chlorite plagioclase and so on. According to the content of inert elements in BIF and its correlation, it can be divided into pure BIF and BIF, contaminated by clastic materials. By the characteristic Co/Th ratio, it can be concluded that these clastic materials mainly come from Black Tortoise rocks. The characteristics of BIF rare earth elements of pure and slightly detrital materials mixed with each other, passing through the (PAAS) standardization of post-Archean shale, are similar to the typical Archean BIF in modern seawater and other areas. They all show that the light rare earth elements are relatively heavy rare earth elements, and the positive La, is the same as that of the later Archean Shale. Y abnormality and high Y/Ho ratio (29). Negative Ce_ (PAAS) anomalies are not obvious in most samples, indicating that BIF precipitates from anoxic environment, and positive Eu_ (PAAS) anomalies are obvious, indicating that there is a high temperature (250 鈩，
本文编号：2310463
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