本文選題：鉻鐵礦 + 橄欖巖�。� 參考：《蘭州大學(xué)》2015年碩士論文

【摘要】：祁連造山帶位于青藏高原的北緣,是我國(guó)早古生代最重要的板塊縫合帶之一,區(qū)內(nèi)發(fā)育有板塊增生蛇綠巖(套),產(chǎn)出有豆莢狀(蛇綠巖型)鉻鐵礦,玉石溝鉻鐵礦即屬此類型。本文通過(guò)巖石學(xué)及礦物學(xué)、全巖主微量分析、鉻鐵礦流體化學(xué)組分及穆斯堡爾譜分析,探討了祁連山玉石溝純橄巖與方輝橄欖巖成因及鉻鐵礦的成礦機(jī)理,并獲得以下認(rèn)識(shí)：1、玉石溝純橄巖及方輝橄欖巖主量元素中,主要組分為SiO2、MgO和Fe2O3T,純橄巖的Mg#分布范圍為87.19-91.67,平均值為88.81,高于洋中脊地幔橄欖巖的Mg#值；方輝橄欖巖中Mg#值分布范圍為91.58-93.08,平均值為92.18。純橄巖具有LREE富集的稀土配分模式,為巖漿堆晶作用產(chǎn)物。方輝橄欖巖稀土元素具有U型配分模式,是地幔部分熔融殘余的結(jié)果。2、玉石溝鉻鐵礦具有分段釋氣特征,分為200-400℃、400-800℃、800-1100℃三個(gè)釋氣階段,釋氣量(除H20)分別為245.34 mm3/g、2614.47 mm3/g、56.73 mm 3/g。鉻鐵礦流體化學(xué)組分主要為H20和C02,次要組分為CH4、C2H6、H2. SO2、CO等。玉石溝鉻鐵礦的穆斯堡爾譜具有次近鄰效應(yīng),室溫條件下Fe2-的同質(zhì)異能移動(dòng)(IS)值為0.888-0.973mm/s,表明壓力的增高造成鉻鐵礦共價(jià)性增強(qiáng)、二次多普勒效應(yīng)從而導(dǎo)致IS值的變化；室溫條件下Fe2+、Fe3+的四極移動(dòng)(QS)值分別為0.663-1.868 mm/s、0.405-0.485 mm/s,反映了鐵離子的占位及其數(shù)量與鉻鐵礦形成時(shí)的溫度有關(guān),形成溫度與QS值呈反消長(zhǎng)關(guān)系；S(Fe3+)/S(Fe內(nèi)2+)平均值為0.744。3、鉻鐵礦的形成過(guò)程：地幔橄欖巖熔融過(guò)程中,副礦物鉻尖晶石及斜方輝石、單斜輝石的不一致熔融初步富集鉻熔體,進(jìn)一步通過(guò)地幔剪切帶的塑性剪切流作用使鉻熔滴富集,俯沖板片的脫水作用導(dǎo)致洋殼中Si的出溶降低了Cr的溶解度,并在富水和CO2流體的作用下聚集、運(yùn)移。溫壓氧逸度的變化使熔體結(jié)晶分異為橄欖巖及鉻鐵礦,在合適的構(gòu)造位置侵位形成豆莢狀鉻鐵礦
[Abstract]:The Qilian orogenic belt is located on the northern margin of the Qinghai-Tibet Plateau and is one of the most important plate suture zones in early Paleozoic in China. There are plate accretive ophiolite in the area, and there are pod chromite (ophiolite type) in the area, which is the type of chromite in Yushigou. By means of petrology and mineralogy, major microanalysis of whole rock, chemical composition of chromite fluid and Mossbauer spectrum, the genesis of pure peridotite and pyroxenite in Yushigou, Qilian Mountain, and the metallogenic mechanism of chromite are discussed in this paper. The main components of the main elements of the peridotite are Sio _ 2MgO and Fe _ 2O _ 3T. The distribution range of Mg# of the pure olivine is 87.19-91.67, the average value is 88.81, which is higher than that of the mantle peridotite in the mid-ocean ridge. The distribution range of Mg# value in pyroxenite is 91.58-93.08, with an average value of 92.18.8. The pure olivine has LREE enriched REE distribution model, which is the product of magmatic stacking. The peridotite rare earth elements have U-type distribution pattern, which is the result of partial melting of mantle. The Yushigou chromite has the characteristics of gas release, which can be divided into three stages: 200-400 鈩，

本文編號(hào)：1995266