祁连山玉石沟铬铁矿成矿机理研究

发布时间：2018-06-08 08:07

  本文选题：铬铁矿 + 橄榄岩　； 参考：《兰州大学》2015年硕士论文

【摘要】：祁连造山带位于青藏高原的北缘,是我国早古生代最重要的板块缝合带之一,区内发育有板块增生蛇绿岩(套),产出有豆荚状(蛇绿岩型)铬铁矿,玉石沟铬铁矿即属此类型。本文通过岩石学及矿物学、全岩主微量分析、铬铁矿流体化学组分及穆斯堡尔谱分析,探讨了祁连山玉石沟纯橄岩与方辉橄榄岩成因及铬铁矿的成矿机理,并获得以下认识：1、玉石沟纯橄岩及方辉橄榄岩主量元素中,主要组分为SiO2、MgO和Fe2O3T,纯橄岩的Mg#分布范围为87.19-91.67,平均值为88.81,高于洋中脊地幔橄榄岩的Mg#值；方辉橄榄岩中Mg#值分布范围为91.58-93.08,平均值为92.18。纯橄岩具有LREE富集的稀土配分模式,为岩浆堆晶作用产物。方辉橄榄岩稀土元素具有U型配分模式,是地幔部分熔融残余的结果。2、玉石沟铬铁矿具有分段释气特征,分为200-400℃、400-800℃、800-1100℃三个释气阶段,释气量(除H20)分别为245.34 mm3/g、2614.47 mm3/g、56.73 mm 3/g。铬铁矿流体化学组分主要为H20和C02,次要组分为CH4、C2H6、H2. SO2、CO等。玉石沟铬铁矿的穆斯堡尔谱具有次近邻效应,室温条件下Fe2-的同质异能移动(IS)值为0.888-0.973mm/s,表明压力的增高造成铬铁矿共价性增强、二次多普勒效应从而导致IS值的变化；室温条件下Fe2+、Fe3+的四极移动(QS)值分别为0.663-1.868 mm/s、0.405-0.485 mm/s,反映了铁离子的占位及其数量与铬铁矿形成时的温度有关,形成温度与QS值呈反消长关系；S(Fe3+)/S(Fe内2+)平均值为0.744。3、铬铁矿的形成过程：地幔橄榄岩熔融过程中,副矿物铬尖晶石及斜方辉石、单斜辉石的不一致熔融初步富集铬熔体,进一步通过地幔剪切带的塑性剪切流作用使铬熔滴富集,俯冲板片的脱水作用导致洋壳中Si的出溶降低了Cr的溶解度,并在富水和CO2流体的作用下聚集、运移。温压氧逸度的变化使熔体结晶分异为橄榄岩及铬铁矿,在合适的构造位置侵位形成豆荚状铬铁矿
[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，

本文编号：1995266