內(nèi)蒙古固陽(yáng)綠巖帶條帶狀鐵建造地球化學(xué)特征與沉積環(huán)境討論
發(fā)布時(shí)間：2018-11-04 16:34
【摘要】：Algoma型條帶狀鐵建造(BIF)是一種海相化學(xué)沉積巖,它發(fā)育在太古宙綠巖帶的火山-沉積巖序列中,大部分經(jīng)歷了后期變質(zhì)變形作用。稀土元素具有穩(wěn)定的地球化學(xué)性質(zhì),因而被廣泛用于指示BIF的原始沉積環(huán)境。華北克拉通北緣固陽(yáng)綠巖帶中的BIF(如三合明、公益明、東五分子、公巨成等)賦存于新太古代色爾騰山群的變火山-沉積序列中,普遍經(jīng)歷了綠片巖相—低角閃巖相變質(zhì),呈條帶狀構(gòu)造,其主要礦物組成為自形—半自形粒狀磁鐵礦和他形粒狀石英,含少量角閃石,局部地區(qū)可見(jiàn)石榴石、綠泥石、斜長(zhǎng)石等富Al礦物。根據(jù)BIF中惰性元素的含量及其相關(guān)性,可劃分為純凈的BIF和遭受碎屑物質(zhì)混染的BIF,并通過(guò)特征的Co/Th比值判斷出這些碎屑物質(zhì)主要來(lái)自于玄武質(zhì)巖石。純凈及遭受輕微碎屑物質(zhì)混染的BIF稀土元素特征通過(guò)后太古宙頁(yè)巖(PAAS)標(biāo)準(zhǔn)化后,與現(xiàn)代海水及其他地區(qū)典型太古宙BIF相似,均表現(xiàn)為輕稀土相對(duì)重稀土虧損,正La、Y異常以及較高的Y/Ho比值(29)。大多數(shù)樣品發(fā)育不明顯的負(fù)Ce_(PAAS)異常,說(shuō)明BIF沉淀自缺氧的環(huán)境;正Eu_(PAAS)異常明顯,說(shuō)明海水中有高溫(250℃)熱液的加入,其比例為0~10%。然而,遭受強(qiáng)烈碎屑物質(zhì)混染的BIF稀土元素特征則具有明顯差異。此種類型BIF的出現(xiàn)及分布不均,指示了在BIF沉積之前的局部地區(qū)或時(shí)間段內(nèi),深部海水處于相對(duì)動(dòng)蕩的環(huán)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，
本文編號(hào)：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，
本文編號(hào)：2310463
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