Research on the trace element contents of granitic rocks

为了弄清韩国和日本东南部花岗岩浆的分异模式，用中子活化分析方法测定了花岗岩的微量元素丰度，特别是稀土元素丰度和Ba、Rb、Sr的关系。韩国侏罗纪花岗岩的稀土配分模式与韩国白垩纪花岗岩的稀土配分模式有很大不同。即侏罗纪的[Eu]/[Eu*]为1.1~0.62，(La/Lu)CN为80~20，稀土总量为100~180ppm；白垩纪为1.1~0.04，38~2.4,100~240。采用瑞利分馏模型作为花岗岩熔体的结晶模型。由于模型计算与白垩纪花岗岩的稀土元素数据很好地吻合，因此建议韩国白垩纪花岗岩为WE…更多的Re主要是通过分离结晶来分异的。侏罗纪花岗岩的稀土配分模式表明，石榴石或锆石是旧变质岩部分熔融的残留物(Tsusue等人，1987A)。根据花岗岩的分布、产状、年龄以及花岗岩的化学和矿物成分，日本西南部已识别出四个花岗岩省。日本西南部中生代和第三纪花岗岩的稀土配分模式与韩国白垩纪花岗岩的稀土配分模式有一定的相似性。即日本西南部花岗岩的[Eu]/[Eu*]值在1.03~0.01之间，(La/Lu)CN值在28~1.2之间，总稀土含量在110~730ppm之间。采用瑞利分馏模型模拟了花岗岩熔体的结晶过程。由于模型计算与观察到的花岗岩稀土配分模式很好地吻合，因此认为日本西南部的花岗岩主要是通过分离结晶来分异的(Tsusue等人，1987b)。McCarthy和Robb(1978)提出，在花岗岩浆原位分离结晶过程中，从斜长-石英-黑云母转变为斜长-石英-K-长石-黑云母，对Ba、Rb、Sr相互关系的丰度有显著影响。在斜长石-石英-黑云母分离过程中，Ba、Rb连续地在固体和熔体中富集，而Sr则亏损。钾长石以固相形式进入，导致Ba逐渐亏损，而Rb则继续富集。总体而言，日本西南部花岗岩的微量元素数据与模型吻合得很好，尽管观测到的数据的分散度比由积云-积云间比例的简单变化所预测的要大一些--可能主要是由于原始熔体中BA、Rb和Sr含量的不同以及同化作用的影响。较少

To clarify the mode of differentiation of granitic magmas of South Korea and Southeast Japan, a neutron activation analysis has been made to measure the trace element abundance, especially rare earth element (REE) abundance and Ba, Rb and Sr relationships of the granitic rocks. The REE patterns of the Jurassic granitic rocks in South Korea are quite different from the patterns of the Cretaceous granitic rocks in South Korea. Namely, the [Eu] /[Eu*] ratio ranges from 1.1 to 0.62, the (La/Lu)cn ratio changes from 80 to 20, and total REE content varies from 100 to 180 ppm for Jurassic patterns, while the same ratios and the total REE content range from 1.1 to 0.04, from 38 to 2.4, and from 100 to 240, respectively, for the Cretaceous patterns. We used the Rayleigh fractionation model as a crystallization model of the granitic melts. Since the model calculation fit the REE data for the Cretaceous granitic rocks very well, it is suggested that the cretaceous granitic rocks in South Korea we … More re mainly differentiated by fractional crystallization. The REE patterns for the Jurassic granitic rocks suggest that participation of garnet or zircon as residues of partial melting of old metamorphic rocks (Tsusue et al., 1987a).Four granite provinces have been recongnized in Southwest Japan on the basis of their distribution, mode of occurrence, age and chemical and mineralogical composition of granitic rocks. The REE patterns of the Mesozoic and Tertiary granitic rocks of Southwest Japan are somewhat similar to the REE patterns of the Cretaceous granitic rocks of South Korea. Namely, [Eu]/[Eu*] ratio ranges from 1.03 to 0.01, the (La/Lu)cn ratio changes from 28 to 1.2, and total REE content varies from 110 to 730 ppm for the granitic rocks of Southwest Japan. We employed the Rayleigh fractionation model to simulate the crystallization of granitic melts. Since the model calculation fit the observed REE patterns for the granitic rocks well, it is suggested that the granitic rocks of Southwest Japan were mainly differentiated by fractional crystallization (Tsusue et al., 1987b).As suggested by McCarthy and Robb (1978), a change in liquidus mineralogy form plagioclase-quartz-biotite to plagioclase-quartz-K-feldspar-biotite during the in situ fractional crystallization of a granitic magma has a marked effect on the abundance of an interrelationships between Ba, Rb and Sr. During plagioclase-quartz-biotite fractionation, Ba and Rb enrich in successive solid and melt, while Sr is depleted. The incoming of K-feldspar as a solid phase causes Ba to be depleted along with Sr insuccessively formed solid, While Rb continues to be enriched. In general, trace element data from the granitic rocks of Southwest Japan fit the model well, although the observed scatter of the data is somewhat greater than predicted by simple variation in cumulus-intercumulus proportions - possibly due, at any rate mainly to a difference in Ba, Rb and Sr contents of original melts and to the effect assimilation. Less