Trace‐element composition of zircon in <scp>Kofu and Tanzawa</scp> granitoids, <scp>Japan</scp> : Quantitative indicator of sediment incorporated in parent magma
Trace‐element composition of zircon in <scp>Kofu and Tanzawa</scp> granitoids, <scp>Japan</scp> : Quantitative indicator of sediment incorporated in parent magma
复制标题
<scp>甲府和丹泽</scp>花岗岩中锆石的微量元素组成，<scp>日本</scp>：母岩浆中沉积物的定量指标
DOI：
10.1111/iar.12455
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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
锆石是地质年代学研究中最重要的矿物之一。锆石的同位素比值和微量元素反映了它们的母岩浆。许多地球化学工作者提出了各种锆石判别图解，用以指示构造环境和判别烃源岩。由于河口沉积的碎屑锆石主要来源于花岗岩类，因此花岗岩类中锆石的分类具有潜在的意义。在我们的研究中，我们专注于花岗岩形成过程中的沉积物参与，并试图确定锆石中对沉积物掺入变化敏感的微量元素成分。为了实现这一目标，我们研究了日本甲府花岗质杂岩体和丹泽英云闪长岩岩体中花岗岩类和锆石的微量元素组成。在高场强元素（Th、U、Ta、Nb、Hf和稀土元素）中，只有Nb和Ta的含量随着沉积物贡献率的增加而增加。然而，锆石中的Nb和Ta含量没有显示出这种趋势。锆石Y和P含量呈正相关，表明存在一定的磷钇矿替代作用。由于P在火成岩系统中以五价离子的形式存在，它的存在可能会影响锆石中五价体的浓度。当我们将Nb和Ta含量除以P含量时，很明显，锆石Nb/P和Ta/P比值根据沉积物的参与而增加。虽然存在一些例外，我们发现，锆石Yb/Gd比也响应沉积物的参与。我们的数据进一步表明，显着的沉积物掺入花岗岩类中的锆石的特点是低Ce/P含量，这是部分归因于独居石结晶前锆石饱和。这项研究表明，结合这些元素的比例是有用的，用于指示沉积物掺入。
Zircon is one of the most important minerals in geochronologic research. Isotopic ratios and trace elements in zircons are expected to reflect those of their parent magmas. Many geochemical researchers have proposed various discrimination diagrams for zircon to indicate tectonic setting and to identify source rock. Because most detrital zircons accumulated at river mouths are derived primarily from granitoids, the classification of zircon within granitoids is potentially meaningful. In our research, we focused on sediment involvement during granitoid formation and tried to identify trace‐element compositions in zircon that are sensitive to variation in sediment incorporation. To accomplish this, we examined trace‐element compositions of both the granitoids and the included zircons in the Kofu granitic complex and the Tanzawa tonalitic plutons in Japan. Among the high‐field‐strength elements (Th, U, Ta, Nb, Hf, and rare earth elements), only Nb and Ta concentrations in the granitoids increased as the rate of sediment contribution increased. However, the zircon did not show such trends in Nb and Ta content. Zircon Y and P contents exhibited a positive correlation, indicating that xenotime substitution occurs to some extent. Because P exists as pentavalent ions in igneous systems, its presence likely affects the concentrations of pentads in zircon. When we divided the Nb and Ta contents by the P content, it became clear that zircon Nb/P and Ta/P ratios increase depending on sediment involvement. While some exceptions exist, we found that zircon Yb/Gd ratios also respond to sediment involvement. Our data further demonstrated that zircons in granitoids with significant sediment incorporation are characterized by low Ce/P contents, which is partly attributable to monazite crystallization before zircon saturation. This study demonstrates that combining these element ratios is useful for indicating sediment incorporation.