Zircon trace‐element compositions in Miocene granitoids in Japan: Discrimination diagrams for zircons in M‐, I‐, S‐, and A‐type granites
Zircon trace‐element compositions in Miocene granitoids in Japan: Discrimination diagrams for zircons in M‐, I‐, S‐, and A‐type granites
复制标题
日本中新世花岗岩中的锆石微量元素组成：M型、I型、S型和A型花岗岩中锆石的判别图
DOI：
10.1111/iar.12466
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发表时间：
2022
期刊：
影响因子：
1.5
通讯作者：
Ohno Takeshi
中科院分区：
文献类型：
--
作者：
Sawaki Yusuke;Asanuma Hisashi;Sakata Shuhei;Abe Mariko;Ohno Takeshi
碎屑锆石对蚀变具有很高的抵抗力，因此可以长期保留有关其形成年龄和母岩浆的信息。地球化学研究人员提出了各种各样适用于碎屑锆石的判别图解。在我们的研究中，我们专注于花岗岩的传统分类方案（地幔，M;火成岩，I;沉积，S;和碱性，A型），并试图表征对这些花岗岩类型之间的差异敏感的锆石微量元素成分。为了实现这一目标，我们研究了从日本西南部的大峰花岗岩和足折深大杂岩体中的花岗岩类中提取的锆石的微量元素组成。锆石在Nb/P、Ta/P、Ce/P、Ce/Nd、Y/P、Th/U、Sc/Yb比值和Eu异常上表现出系统性差异。A型花岗岩中的锆石富含Nb、Ta、Ce和Y，它们的特征清楚地反映了母体中的这些元素。A型花岗岩中锆石的Sc/Yb比值<0.1，与洋岛型锆石相似。尽管它们在全岩水平上的丰度很高，但S型花岗岩中的锆石具有低Nb/P、Ta/P和Th/U比值的特征。这是由于铌，钽，钍在岩浆中的亏损钛铁矿和独居石之前，锆石结晶。一般来说，S型花岗质岩浆表现出还原环境，降低了Ce 4+和Eu 3+的比例。这些效应导致S型锆石中的低Ce/Nd比值和大的负Eu异常。在此基础上，我们建议结合使用Nb/P-Ce/P或Ta/P-Ce/P交会图和Sc/Yb比值来区分M-、I-、S-和A-型花岗岩中的锆石。虽然交会图是使用日本中新世花岗岩类的数据创建的，但判别图是基于每种类型花岗岩的一般特征。
Detrital zircons demonstrate high resistance to alteration and, as such retain information about their formation ages and parental magmas for a long period of time. Geochemical researchers have proposed a wide variety of discrimination diagrams applicable to detrital zircons. In our research, we focused on the conventional classification scheme for granites (Mantle, M; Igneous, I; Sedimentary, S; and Alkaline, A types) and sought to characterize zircon trace‐element compositions that are sensitive to differences among these granite types. To accomplish this, we examined trace‐element compositions of zircons extracted from granitoids in the Ohmine granitic rocks and the Ashizuri plutonic complex in southwestern Japan. The zircons showed systematic differences in Nb/P, Ta/P, Ce/P, Ce/Nd, Y/P, Th/U, and Sc/Yb ratios and the Eu anomaly. Zircons in A‐type granite are rich in Nb, Ta, Ce, and Y, and their signatures clearly reflect those elements in their parental bodies. Sc/Yb ratios of zircons in A‐type granites are <0.1, which is similar to those of ocean‐island‐type zircons. Despite their high abundance at the whole‐rock level, zircons in S‐type granite are characterized by low Nb/P, Ta/P, and Th/U ratios. This is attributable to the depletion of Nb, Ta, and Th in the magma by ilmenite and monazite prior to zircon crystallization. In general, S‐type granitic magmas exhibit reducing environments, which decrease the proportions of Ce4+and Eu3+. These effects lead to a low Ce/Nd ratio and a large negative Eu anomaly in S‐type zircons. On the basis of these findings, we recommend the combined use of Nb/P–Ce/P or Ta/P–Ce/P crossplots and of Sc/Yb ratios to discriminate zircons in M‐, I‐, S‐, and A‐type granites. Although the crossplots are created using data from Miocene granitoids in Japan, the discrimination diagrams are based on the general features of each type of granite.