Two groups of fluid inclusions in the Yunotani eclogite from the Hida–Gaien Belt: Implications for changes of fluid salinity during exhumation
Two groups of fluid inclusions in the Yunotani eclogite from the Hida–Gaien Belt: Implications for changes of fluid salinity during exhumation
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DOI：
10.2465/jmps.190729
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发表时间：
2019
影响因子：
0.7
通讯作者：
Yuzuki Shinji;T. Tsujimori;T. Kawamoto
中科院分区：
文献类型：
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作者：
Yuzuki Shinji;T. Tsujimori;T. Kawamoto
晚古生代羽野谷榴辉岩在经历榴辉岩相峰期变质作用后，经历了蓝片岩相重结晶变形。研究了退变质榴辉岩中不同变质阶段石英畴中的流体包裹体。变斑石榴石的粗粒石英充填压力影中含有高盐度（6.0-8.0 eq mass% NaCl，平均7.2 ± 0.6 eq mass % NaCl（n = 12））的穿晶流体包裹体（Ⅰ组）。而与基质中发育的穿透叶理平行的晚期富石英带（Ⅱ组）中的穿晶流体包裹体则具有较低的盐度[1.1-5.8 eq mass% NaCl，平均值为3.4 ± 1.2 eq mass% NaCl（n = 12）]。流体包裹体痕迹的出现表明，每组分别对应于蓝片岩相重结晶之前捕获的流体和蓝片岩相阶段捕获的流体。在蓝片岩相条件下形成的II组流体包裹体支持俯冲通道中的含水流体具有与海水相似的盐度（~ 3.5当量质量% NaCl）的观点。此外，第I组流体包裹体表明，在俯冲通道榴辉岩相深度的含水流体具有比海水更高的盐度的可能性。
Late Paleozoic Yunotani eclogites in the Itoigawa–Omi area of the Hida–Gaien Belt were subjected to a blueschist–facies recrystallization and deformation after the peak eclogite–facies metamorphism. We studied fluid inclusions in quartz domains of different metamorphic stages in the retrograde eclogite. Coarse–grained quartz filling pressure shadow of porphyroblastic garnets contains transgranular fluid inclusions (Group–I) with high salinity [6.0–8.0 eq mass% NaCl, with a mean value 7.2 ± 0.6 eq mass% NaCl (n = 12)]. In contrast, transgranular fluid inclusions in later stage quartz–rich band (Group–II) in parallel to a penetrative foliation developed in matrix are characterized by lower salinity [1.1–5.8 eq mass% NaCl, with a mean value 3.4 ± 1.2 eq mass% NaCl (n = 12)]. The occurrences of fluid inclusion trails suggest that each group corresponds to the fluids entrapped prior to the blueschist–facies recrystallization and the fluids entrapped during the blueschist– facies stage, respectively. The Group–II fluid inclusions formed at blueschist–facies conditions support the idea that aqueous fluids in the subduction channel have a salinity similar to seawater (~ 3.5 eq mass% NaCl). Moreover, the Group–I fluid inclusions indicate a possibility that aqueous fluids at the eclogite–facies depth in subduction channels possess a salinity higher than seawater.