期刊
JOURNAL OF MINERALOGICAL AND PETROLOGICAL SCIENCES
卷 111, 期 2, 页码 129-143出版社
JAPAN ASSOC MINERALOGICAL SCIENCES
DOI: 10.2465/jmps.150812
关键词
Monazite; Zircon; Partial melting; Brine; Polymetamorphism
类别
资金
- JSPS KAKENHI [23740391, 26400513, 26247094]
- NIPR General Collaboration Project [19-15]
- Grants-in-Aid for Scientific Research [25400518, 23740391, 25302008, 25287132, 26400513, 26247094] Funding Source: KAKEN
Chlorine-rich (>0.3 wt%Cl) biotite inclusions in the core of garnet porphyroblasts in the garnet-sillimanite (Grt-Sil) gneiss from Skallevikshalsen, Lutzow-Holm Complex (LHC), East Antarctica is estimated to be stable under >1.2 GPa, 820-850 degrees C, coexisted with granitic melt as suggested by the nanogranite/felsite inclusions. Rare occurrence of matrix biotite, in spite of the common occurrence of biotite as inclusions in garnet, suggests almost complete consumption of pre-existed matrix biotite during the prograde to peak metamorphism. Brine infiltration during prograde to peak metamorphism in Skallevikshalsen is supported by Cl-rich scapolite described in previous studies. Brine infiltration and progress of continuous biotite-consuming melting reactions were probably responsible for elevating the Cl content of biotite in the studied sample. In situ electron microprobe U-Th-Pb dating of monazite and the in situ laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) U-Pb dating of zircon in the Grt-Sil gneiss revealed that both monazite and zircon has the 'older age population' with similar to 650-580 Ma and the 'younger age population' with similar to 560-500 Ma. The REE and trace element pattern of one of the P-rich patches in the garnet core is different from the P-rich garnet rim. The isotope mapping of the same patch by LA-ICPMS revealed that the patch is also observed as a domain depleted in V-51, Y-89, Ho-165, Er-166, Tm-169, Yb-172, and Lu-175. Clear difference in V-51 concentration between the patch and the garnet rim suggests that this patch is not a continuous part from the garnet rim, but is likely a relic of preexisted garnet. Kyanite included in the patch suggests that the precursor rock was presumably a medium-to high-pressure type metamorphic rock. Presence of the older age population (similar to 650-580 Ma) monazites in Skallevikshalsen and Skallen also suggest that rocks in these areas experienced polymetamorphism, and resetting by the similar to 560-500 Ma metamorphic event was incomplete in these areas. Taking into account the presence of Cl-rich biotite inclusions in garnet, infiltration of brine accompanied by partial melting is one probable event that took place at similar to 560-500 Ma in the Skallevikshalsen area, and part of the monazite possibly recrystallized by this brine infiltration. Detailed microstructural observation using trace element mapping combined with detailed petrography especially focusing on the Cl-bearing minerals as a tracer of brines would become a powerful tool for better interpreting the results of monazite and zircon dating and for investigating the fluid-related crustal processes.
作者
我是这篇论文的作者
点击您的名字以认领此论文并将其添加到您的个人资料中。
推荐
暂无数据