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本文应用EA-MS连线技术(将元素分析仪(EA)与气体质谱仪(MS)连接起来,进行硅酸盐岩石微量碳的含量和同位素比值测定)首次测定了中国东南部花岗岩及其部分磷灰石的全碳含量和同位素组成,结果发现,这些花岗岩的碳含量和同位素组成分布较宽(碳含量为0.04%~0.79%,δ~(13)C值为-7.5‰~-37.0‰)。磷灰石与全岩的δ~(13)C值呈正相关关系,指示自花岗岩浆上升到结晶以来未受到同化混染或热液蚀变扰动,所以全岩碳同位素组成反映了其源区δ~(13)C值的不均一性。对部分全岩进行HCl溶解后分析,结果表明碳在花岗岩中以不同的形式存在(碳酸盐碳和非碳酸盐碳)。碳含量和同位素组成分别成对数正态分布和双峰正态分布,反映了不同含碳储库的地球化学混合。结合已有的Nd、Sr同位素数据,发现碳同位素组成与钕、锶同位素和碳含量之间的相关性呈非简单壳幔两端元混合特征,其中地幔端元的δ~(13)C值约为-7‰,而地壳端元的δ~(13)C值变化较大(-20‰~-35‰),对应的初始Sr同位素比值变化也较大(0.715~0.735),但初始Nd同位素组成相对均一(ε_(Nd)=-18)。部分初始Sr同位素比值<0.710的Ⅰ型花岗岩同样具有低的δ~(13)C值,可能指示其火成岩原岩曾出露过地表,受到了有机碳的混染。
In this paper, the EA-MS connection technology (elemental analyzer (EA) and gas mass spectrometer (MS) was used to determine the content of trace carbon and the isotope ratio of silicate rocks) was used to determine the granite and its parts in southeastern China The results show that the carbon and isotopic compositions of these granites are broad (0.04% ~ 0.79% carbon and δ ~ (13) C) -7.5 ‰ ~ -37.0 ‰ ). The apatite shows a positive correlation with the δ13C value of whole rock, indicating that it has not been perturbed by assimilation or hydrothermal alteration since granitic magma rose to crystallization. Therefore, the whole-rock carbon isotopic composition reflects its δ ~ (13) C value of the heterogeneity. Analysis of part of the whole rock after HCl dissolution shows that the carbon exists in different forms in granite (carbonate and non-carbonate carbon). Carbon content and isotopic composition, respectively, pairs of normal distribution and bimodal normal distribution, reflecting the different carbonaceous reservoir geochemical mixing. Combined with the available Nd and Sr isotope data, it was found that the correlation between carbon isotope composition and neodymium, strontium isotope and carbon content is a non-simple mixture of crust and mantle. The δ 13 C value The δ ~ (13) C value of the crustal end varies greatly (-20 ‰ ~ -35 ‰), and the corresponding initial Sr isotope ratio also varies greatly (0.715 ~ 0.735). However, the initial Nd Isotopic composition is relatively uniform (ε Nd (-) 18). Some type Ⅰ granites with initial Sr isotope ratio <0.710 also have low δ ~ (13) C values, which may indicate that their igneous rocks had exposed to the surface and were contaminated by organic carbon.