地球化学-稀土元素标准化计算

1、表中数据为山东济南辉长岩、沂南花岗岩7件样品的REE组成(ppm)1MJNO6D8MJN06071MJND6D91MJN0606MYN0625MYN06251MYN0607La4.996.066.491S.111680.1110Ce12.415.215.140.6226156209Pr1.752.132.0549822.415.619.5Nd8.3510.49.9821.777.453.461.5Sm2.292.652.&44.9011.57.707.19EuOSO0.B41.111.591.400.981.24Gd2.002.322.334.117.395.333.85lb0.330.360

2、.360.641.060.740.42y2.022.212.314.076.174.271.98Ho0.400.440.460.811.180.840.34Er0.981.101.182.003.122.070.91Tm0.130.140.160.280.460.300.14Yb0.951.031.142.093.172.121.05LuI0.130.130.1510.2810.430300.1511,用球粒陨石值对样品的REE组成进行标准化，作其分配模式图，对图件中表达的地球化学特征进行说明；2，计算各样品的Eu/Eu*，并对其地球化学意义进行说明；,3，假设辉长岩中造岩矿物的组成为：CPX

3、45%,PL35%,OL20%。结合课件中提供的REE在矿物和熔体间的分配系数，计算与辉长岩平衡的熔体的REE组成，并作REE配分模式图。解答:1,如下表1-1为常用球粒陨石和原始地幔稀土元素组成，我采用C1球粒陨石数据(Sun&McDonough,1989)对样品的REE进行标准化，得到了下表1-2,再根据对样品REE标准化的数据进行作样品的分配模式图，得到了图1-1常用球粒陨石和原始地幔稀土元素组成(ppm)Cl球粒陨石戡诙原始N-MORBE-MORBOIBLa03703670.550.6872.56337Ce0.6120.9571.441.7757.51580Pr0.0950.13702

4、060.2761.322.059.730.4670.7111.4301.3547.3938.5Sm0.15302310.3470.4442.632.610Eu0.0580.0870.1310.1681.020.913Gd0.205503060.4590.5963.682.977.62Tb0.03740.0580.0870.1080.670.531.05Dy0.254003810.5720.737斗予3.555.6Ho0.05660.08510.1280.1641.010.791.06Er0.165502490.3740.4802.972.312.62Tm0.02550.03560.0540.0

5、740.4560.356035Yb0.17002480.3720.4933.052.372.16Lu0.02540.03810.0570.0740.4550.35+0.3来源12211111：Sun&McDonough,1989：2：Taylor&Mclennan985表1-1MJN0608MJN0607MJN0609MJN0606MYN0625MYN0625MYN0607La21.05525.57027.38476.371489.451337.975464.135Ce20.26124.83724.67366.340369.281254.902341.503Pr18.42122.42121.5

6、7952.421235.789164.211205.263Nd17.88022.27021.37046.467165.739114.347131.692Sm14.96717.32016.60132.02675.16350.32746.993Eu13.79314.48319.13827.41424.13816.89721.379Gd9.73211.29011.33820.00035.96125.93718.735Tb8.8249.6269.62617.11228.34219.78611.230Dy7.9538.7019.09416.02424.29116.8117.795Ho7.0677.774

7、8.12714.31120.84814.8416.007Er5.9216.6477.13012.08318.85212.5085.498Tm5.0985.4906.27510.98018.03911.7655.490Yb5.5886.0596.70612.29418.64712.4716.176Lu5.1185.1185.90611.02416.92911.8115.906表1-2样品配分模式图图1-1通过对样品配分模式图进行分析可知道，沂南花岗岩样品中富集轻稀土元素而亏损重稀土元素，这与花岗岩的成分岩性有一定关系，花岗岩为酸性岩，主要矿物为长石、石英和云母，而这矿物主要富集轻稀土元素，并且从

8、图中可以看出Eu的负异常，说明在岩浆结晶形成花岗岩之前就有长石结晶出来，使岩浆呈Eu的负异常。济南辉长岩的样品配分模式图表现出来的富集轻稀土元素没有沂南花岗岩样品那么显著，富集程度较低，这也与辉长岩的岩性成分有关，辉长岩中主要矿物为辉石和长石，长石富集轻稀土元素较为显著，而辉石相对较富集重稀土元素，但程度不是很显著，所以岩石总体表现较为富集轻稀土元素，但程度不是那么显著。并且从图中可以看出Eu的正异常，只是不是很显著，说明长石结晶出来使岩石呈Eu的正异常。2，Eu/Eu*=2Eu/(Sm+Gd)(其中Eu、Sm、Gd都是为球粒陨石标准化值)，根据这个求出各样品中的Eu/Eu*，如下表1-3：M

9、JN0608MJN0607MJN0609MJN0606MYN0625MYN0625MYN060711171.0121.3701.0540.4340.4430.051表1-3由上表中的Eu/Eu*值可知山东济南的辉长岩为Eu的正异常，说明在岩浆结晶时，长石和辉石先结晶出去形成辉长岩，而长石中富集Eu兀素，所以在辉长岩中Eu为正异常，而后期岩浆因长石的结晶分异而呈Eu的负异常，并且逐渐向酸性过渡，结晶形成酸性岩。可以推测这样品为同源岩浆所形成，主要是形成时间不同导致Eu异常不同和岩性的不同。3,根据课件可查出REE在CPX、PL、OL等矿物和熔体间的分配系数，如下表1-4：Table9-1.Par

10、titionCoefficientsforsomecommonlyusedtraceelementsinbasalticandandesiticrocksdatafromHenderson(1982)*Eu3+/Eu2+Italicsareestimated表1-4在根据总分配系数的公式计算出REE在辉长岩中的总分配系数，如下表1-5：-*1=1儿糸LaCeNdSmEuTbErYbLu总分配系数0.0860.2040.30.4350.9670.4630.4810.1170.400表1-5再根据固体、熔体和总分配系数之间的关系式计算出熔体中REE的组成，得到数据如下表1-6,再C1球粒陨石数据(

11、Sun&McDonough,1989)对熔体的REE进行标准化用计算结果如下表1-7,对其有进行作配分模式图，得到图1-2：MJN0608MJN0607MJN0609MJN0606La58.02370.46575.465210.465Ce60.78474.51074.020199.020Nd27.83334.66733.26772.333Sm5.2646.0915.83911.264Eu0.8270.8691.1481.644Tb0.7130.7780.7781.382Er2.0372.2872.4534.158Yb8.1208.8039.74417.863Lu0.3250.3250.3750.7表1-6MJN0608MJN0607MJN0609MJN0606La244.824297.321318.418888.039Ce99.321121.748120.947325.195Nd59.60074.23171.235154