Development of Open Transport of Aqueous Fluid from Pegmatite Revealed by Trace Elements in Garnet
Development of Open Transport of Aqueous Fluid from Pegmatite Revealed by Trace Elements in Garnet
复制标题
石榴石中微量元素揭示伟晶岩中水流体开放传输的进展
DOI：
10.1155/2022/8786250
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发表时间：
2022
期刊：
影响因子：
1.7
通讯作者：
Tsuchiya Noriyoshi
中科院分区：
文献类型：
--
作者：
Nurdiana Astin;Okamoto Atsushi;Uno Masaoki;Tsuchiya Noriyoshi
我们研究了流体流动和元素输运从花岗岩体中地壳，通过确定微量元素的石榴石在伟晶岩有关的石英闪长岩侵入体和变质岩在日本东北部的金加山岛。伟晶岩和黑云母片岩中的石榴子石以富spessartine-（Sps-）almandine-（Alm-）组成为特征，其组成分别为Sps 14 - 69 Alm 22 - 70 Prp 2 - 14 Grs 1 - 13和Sps 16 - 30 Alm 54 - 66 Prp 9 - 16 Grs 3 -6。变质单元中的石榴子石荚具有富含钙铝榴石-（Grs-）的成分（Sps 1 - 4Alm 8 -11Prp0.1-0.4Grs80- 87 Adr 3 -4）。黑云母片岩接触变质作用的峰值温度（T）为600-650°C，峰值压力（P）为0.27- 0.41GPa。石英闪长岩和变质岩中伟晶岩中石英晶体中的原生流体包裹体均一化温度范围较宽（200-380°C）。这些对应于500-700°C的捕集温度，假设盐度为4 wt.%在压力下结晶的石英晶体。石英闪长岩和变质单元中伟晶岩中石榴石的球粒陨石标准化稀土元素（REE）配分模式通常以重稀土富集和负Eu异常为特征，片岩中的REE含量系统地低于伟晶岩。而与伟晶岩相邻的黑云母片岩中石榴石的稀土元素含量与相邻伟晶岩中石榴石的稀土元素含量相近。这些地球化学特征表明，黑云母片岩中的石榴子石生长响应于伟晶岩的流体渗透。此外，石榴子石荚中的富Grs石榴子石及其寄主石英片岩具有平坦的重稀土配分模式，无Eu异常，这可能反映了与斜长石交代有关的交代过程，产生了富Ca-Al流体。我们的研究结果表明，伟晶流体的渗透增强元素的传输和变质反应中地壳。
We investigated the fluid flow and elemental transport from a granitic body to the middle crust by determining the trace element compositions of garnet in pegmatites related to a quartz diorite intrusion and metamorphic rocks on Kinkasan Island, northeast Japan. Garnet in the pegmatites and biotite schists is characterized by spessartine– (Sps–) almandine‐ (Alm‐) rich compositions of Sps14–69Alm22–70Prp2–14Grs1–13and Sps16–30Alm54–66Prp9–16Grs3–6, respectively. A garnetite pod in the metamorphic unit has grossular‐ (Grs‐) rich compositions (Sps1–4Alm8–11Prp0.1–0.4Grs80–87Adr3–4). The peak temperature (T) and pressure (P) conditions of the biotite schist during contact metamorphism were 600–650°C and 0.27–0.41 GPa, respectively. The primary fluid inclusions in quartz crystals within the pegmatites hosted by the quartz diorite and hosted by the metamorphic rocks have a wide range of homogenization temperatures (200–380°C). These correspond to the trapping temperature of 500–700°C, assuming a salinity of 4 wt.% NaClequivalentat pressure of the crystallization of the quartz diorite. Chondrite‐normalized rare earth element (REE) patterns of garnets in the pegmatites in the quartz diorite and metamorphic unit are generally characterized by enrichment of heavy REEs and negative Eu anomalies with the REE contents in the schists which are systematically lower than in the pegmatites. However, garnet in the biotite schists close to the pegmatites has similar REE contents to garnet in the adjacent pegmatites. These geochemical features suggest that garnet in the biotite schists grew in response to fluid infiltration from the pegmatites. Besides, the Grs‐rich garnet in the garnetite pod and its host quartz schist have flat heavy REE patterns and no Eu anomalies, which probably reflect a metasomatic process related to plagioclase replacement that produced Ca‐Al‐rich fluids. Our results suggest that the infiltration of pegmatitic fluids enhances elemental transport and metamorphic reactions in the middle crust.