發(fā)布時(shí)間：2018-05-01 12:07

  本文選題：祁連山木里三露天 + 天然氣水合物��； 參考：《中國(guó)地質(zhì)大學(xué)(北京)》2016年碩士論文

【摘要】：祁連山木里三露天天然氣水合物與碳酸鹽相伴產(chǎn)出是一種常見(jiàn)現(xiàn)象。為了探討碳酸鹽、黃鐵礦的形成與天然氣水合物的關(guān)系,本文對(duì)研究區(qū)31件碳酸鹽樣品、25件黃鐵礦樣品進(jìn)行了礦物學(xué)、微量元素、稀土元素、碳酸鹽碳氧同位素、黃鐵礦硫同位素的分析測(cè)試。根據(jù)對(duì)伴生碳酸鹽和黃鐵礦的野外觀察及鏡下鑒定,碳酸鹽可以分為4種類(lèi)型:(1)薄層狀碳酸鹽,厚2-4cm,主要分布于天然氣水合物層段的泥巖中;(2)薄殼狀碳酸鹽,厚度小于1mm,一般分布于天然氣水合物層段的泥巖微裂隙中;(3)菱形晶簇狀碳酸鹽,晶形較好,主要分布于天然氣水合物附近的泥巖、粉-細(xì)砂巖中;(4)微細(xì)浸染狀碳酸鹽,主要分布于黑色泥巖和炭質(zhì)泥巖中。黃鐵礦分為3種類(lèi)型:(1)薄膜狀,厚度小于1mm,一般分布于天然氣水合物附近的粉-細(xì)砂巖裂隙中;(2)條帶狀,長(zhǎng)度3-5cm,主要分布于灰黑色泥巖中;(3)結(jié)核狀,直徑不超過(guò)1cm,主要分布于黑色泥巖中。分析結(jié)果顯示,不同類(lèi)型碳酸鹽、黃鐵礦的礦物學(xué)、地球化學(xué)特征具有明顯區(qū)別。菱形晶簇狀碳酸鹽具有清楚的晶形,其微量元素含量較低、稀土元素含量較高,Ni/Co7,相比其它三類(lèi)碳酸鹽,認(rèn)為菱形晶簇狀碳酸鹽形成于相對(duì)還原的環(huán)境。并且,不同類(lèi)型碳酸鹽的碳同位素有著明顯區(qū)別。薄層狀和薄殼狀碳酸鹽碳同位素相對(duì)偏正,平均為2.5‰和3.5‰,浸染狀碳酸鹽碳同位素平均-0.13‰,而菱形晶簇狀碳酸鹽相對(duì)偏負(fù),最低達(dá)-6.4‰,平均為-2.41‰。綜合認(rèn)為,菱形晶簇狀碳酸鹽可能與天然氣水合物的分解有關(guān),其碳源部分來(lái)自于天然氣水合物分解釋放的甲烷。薄膜狀黃鐵礦中則觀察到一種新的晶體形態(tài)——八角截面體,具有典型的自生特征。條帶狀黃鐵礦和結(jié)核狀黃鐵礦在鏡下不能觀察到好的晶形,并且顯示被其它礦物所充填,反應(yīng)了較老的形成時(shí)間。與其它兩類(lèi)黃鐵礦相比,薄膜狀黃鐵礦具有相對(duì)較低的硫同位素值,δ34SV-CDT值為-20.9‰~17‰,平均為1.25‰,其形態(tài)與薄片狀天然氣水合物相似,且與天然氣水合物共生或分布在天然氣水合物產(chǎn)出位置附近,其可能是天然氣水合物分解釋放的甲烷與硫酸鹽還原的結(jié)果。通過(guò)研究得出,菱形晶簇狀碳酸鹽和薄膜狀黃鐵礦形成都跟天然氣水合物分解有關(guān),這兩種自生礦物可能記錄了天然氣水合物層曾經(jīng)的頂?shù)捉?可以作為祁連山凍土區(qū)乃至其它凍土區(qū)天然氣水合物勘查的示蹤性性礦物。
[Abstract]:The concomitant production of natural gas hydrate and carbonate in Muli three open air in Qilian Mountain is a common phenomenon. In order to study the relationship between the formation of carbonate, pyrite and natural gas hydrate, the mineralogy, trace elements, rare earth elements, carbonate carbon and oxygen isotopes of 31 carbonate samples and 25 pyrite samples were studied in this paper. Analysis and test of sulfur isotopes in pyrite. According to the field observation and microscopic identification of associated carbonate and pyrite, carbonates can be divided into four types: 1) thin layer carbonate, 2-4 cm thick carbonate, mainly distributed in mudstone of gas hydrate formation and (2) thin shell carbonate. The mudstone with thickness less than 1 mm, which is generally distributed in the microfracture of natural gas hydrate formation, is a rhombic cluster carbonate with good crystal shape. It mainly distributes in mudstone near natural gas hydrate and in silt-fine sandstone. Mainly distributed in black mudstone and carbonaceous mudstone. Pyrite is divided into three types: 1) thin film, less than 1 mm thick, generally distributed in the siltstone / fine sandstone fissure near natural gas hydrate with a length of 3 to 5 cm, and mainly distributed in the gray and black mudstone. Not more than 1 cm in diameter, mainly distributed in black mudstone. The results show that the mineralogical and geochemical characteristics of different types of carbonate and pyrite are obviously different. The rhombohedral cluster carbonate has a clear crystal shape, its trace element content is low, and its rare earth element content is higher than that of other three kinds of carbonate, it is considered that the rhombic cluster carbonate was formed in the environment of relative reduction. Moreover, the carbon isotopes of different types of carbonates are obviously different. The carbon isotopes of thin layer carbonate and thin shell carbonate are relatively positive, with average values of 2.5 鈥，

本文編號(hào)：1829270