华南燕山期佛冈–南昆山花岗岩石成因:来自锆石微量元素、H_(2)O含量及Hf-O同位素的约束  

Petrogenesis of the Yanshanian Fogang-Nankunshan granites in South China:Constraints from zircon trace elements,H_(2)O content,and Hf-O isotopes

作　　者：蔡克鸿 夏小平[1,2] 丁兴 杨晴[1,2] 张乐[1,2] CAI Kehong;XIA Xiaoping;DING Xing;YANG Qing;ZHANG Le(State Key Laboratory of Isotope Geochemistry,Guangzhou Institute of Geochemistry,Chinese Academy of Sciences,Guangzhou 510640,Guangdong,China;CAS Center for Excellence in Deep Earth Science,Guangzhou 510640,Guangdong,China;College of Earth and Planetary Sciences,University of the Chinese Academy of Sciences,Beijing 100049,China)

机构地区：[1]中国科学院广州地球化学研究所,同位素地球化学国家重点实验室,广东广州510640 [2]中国科学院深地科学卓越创新中心,广东广州510640 [3]中国科学院大学地球与行星科学学院,北京100049

出　　处：《地球化学》2024年第3期426-444,共19页Geochimica

基　　金：国家重点研发计划“变革性技术关键科学问题”专项项目(2018YFA0702600)资助。

摘　　要：华南地区发育大规模与稀有金属成矿相关的燕山期花岗岩,其岩石类型与成因存在诸多争议,厘清这些争议有助于理解华南地区的成矿作用。锆石是花岗岩中常见的副矿物,具有非常稳定的物理化学性质,不容易受后期地质作用影响,可以很好地保存其形成时母岩浆的地球化学信息,从而避免全岩地球化学分析的不足。本研究选取华南地区佛冈–南昆山花岗岩中的锆石进行LA-ICP-MS微量元素和Hf同位素研究,结合SIMS氧同位素和H_(2)O含量等数据,探讨佛冈岩体和南昆山岩体的岩石类型和成因。两个岩体的锆石都呈现LREE亏损、HREE富集、Eu负异常、Ce正异常,以及Zr/Hf>55、Eu/Eu~*>0.005、Hf含量低(<1.2%)等特点,明显不同于高分异I型花岗岩,指示母岩浆分异程度较低。同时,锆石的REE+Y与P含量之间的关系表明它们也不是S型花岗岩。佛冈岩体锆石较高的δ18O值(7.97‰~10.29‰)、富集的εHf(t)值(-13.6~-5.7)、较低的H_(2)O含量(核密度峰值317~412μg/g)以及较高的锆饱和温度(799~800℃)表明,佛冈花岗岩可能是源区有高比例沉积物加入的A型花岗岩。南昆山岩体也具有类似的、但变化范围更大的锆石δ18O值(6.34‰~11.11‰)、εHf(t)值(-11.1~1.1)和H_(2)O含量(297~1253μg/g)。锆石Hf-O同位素和H_(2)O含量分析结果显示,二者均具有壳幔混合的特点,其中南昆山花岗岩源区地幔物质加入比例更大。The rock types and petrogenesis of the Yanshanian granites related to the large-scale rare metal mineralization in South China are still controversial,and clarifying these controversies is of great significance for a better understanding of the mineralization in the region.Most of the previous studies were based on whole-rock geochemical compositions which may have been changed by later geological events.As a common accessory mineral in granites,zircon has very stable physical and chemical properties and is not easily affected by later geological processes.It can preserve the geochemical information at the time of its formation and effectively avoid the deficiency of the whole rock powder geochemical analysis.In this study,we selected the Fogang-Nankunshan granites in South China for LA-ICP-MS analysis of zircon trace elements and Hf isotopes.In combination with results of SIMS zircon oxygen isotope and water content,we discussed the rock type and petrogenesis of the Fogang and Nankunshan granites.Zircons from both batholiths are characterized by LREE depletion,HREE enrichment,negative Eu anomaly,positive Ce anomaly,and Zr/Hf ratio>55,Eu/Eu*>0.005,and low Hf content(<1.2%),indicating they are not highly differentiated I-type granites.The relationship between P and REE+Y contents of zircons indicates that they are not S-type granites either.The highδ^(18)O values(7.97‰to 10.29‰),enriched zirconεHf(t)values(-13.6 to-5.7),low water contents(kernel density peak 317μg/g to 412μg/g),and high zirconium saturation temperatures(799 to 800)indicate that the℃℃Fogang granite possibly belongs to A-type granite with a high proportion of sediment incorporated into the source.Similarly,the Nankunshan A-type granites have high but more varied zirconδ^(18)O values(6.34‰to 11.11‰),εHf(t)values(-11.1 to 1.1),and water contents(297μg/g to 1253μg/g).These results show that both the Fogang and Nankunshan granites were generated by melting of mixed crust and mantle materials,and the latter has more mantle material co

关 键 词：花岗岩 锆石 微量元素 HF-O同位素 H_(2)O含量 壳幔混合 

分 类 号：P595[天文地球—地球化学] P581[天文地球—地质学]