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A review of the genetic mechanisms generating igneous charnockite: CO2 flushing and crystal-melt segregation in mushy reservoirs

文献类型：期刊论文

作者Zhao, Kai4; Xu, Xisheng4; Klemd, Reiner1; He, Zhenyu3; Zhang, Xisong2,4
刊名EARTH-SCIENCE REVIEWS
出版日期2023-02-01
卷号237页码:18
ISSN号0012-8252
关键词Igneous charnockite Orthopyroxene CO 2 flushing Crystal -liquid segregation Crystal mush
DOI10.1016/j.earscirev.2022.104295
英文摘要Igneous charnockites are high-temperature orthopyroxene-bearing granitoids, which constitute an important part of many high-grade terranes. High temperature (typically >750-800 degrees C) is considered to be a key factor regarding the formation of igneous charnockites, because orthopyroxene reacts with hydrous melts to form biotite and/or amphibole at low temperatures as predicted by equilibrium phase relations. Microstructural re-cords of igneous charnockites suggest that the hydrous crystallization reaction occurs at near equilibrium con-ditions. Thus, it remains a puzzling question how orthopyroxene is preserved in granitoids that generally solidify at H2O-saturated solidus temperatures (<700 C). Here, we synthesize mineralogical, petrological, and geochemical data for 32 charnockite plutons worldwide to evaluate the possible preservation mechanisms of orthopyroxene in granitoids. These igneous charnockites are classified as I-A-S types based on their mineral assemblages and whole-rock compositions. The orthopyroxene crystals in the igneous charnockites systemati-cally have lower Al2O3 contents than those in metamorphic rocks, suggesting a magmatic origin of the former. Magmatic orthopyroxene is possibly preserved by two mechanisms, preventing back-reactions with hydrous melts: one mechanism deduced from fluid-inclusion studies highlights the importance of CO2, which can reduce the H2O activity and elevate the solidus temperature to the stability field of orthopyroxene. Physical constraints on fluid transport suggest that this mechanism is feasible when an orthopyroxene-bearing mushy reservoir is flushed by large amounts (>10-20 vol%) of CO2-rich fluids, which could form a permeable flow through bubble channels in the pore medium and significantly elevate the CO2 content (>1000 ppm at pressures of >0.2 GPa) dissolved in the interstitial melts. Available fluid-inclusion studies suggest that such a mechanism may have played an important role in the formation of some I-and A-type charnockites. Nonetheless, deducing the fluid composition solely from fluid-inclusion studies is ambiguous, since the trapping of fluid inclusions may leave a potentially non-representative record due to the different wetting characteristics of CO2 and H2O, as well as post -trapping grain-boundary migration recrystallisation, favoring the entrapment of CO2-rich inclusions. A further alternative mechanism is to extract hydrous melts from an orthopyroxene-bearing mush, thereby restricting the back-reaction of orthopyroxene during progressive crystallization. Igneous charnockites have maximum P2O5 contents of up to 1.0-1.2 wt% at 55-60 wt% SiO2 and Zr contents of up to >400-600 ppm at 60-65 wt% SiO2. The nonsynchronous variations in P2O5 and Zr contents can best be explained by melt extraction from a mush that saturates apatite earlier than zircon during magma evolution. This process produces apatite-and zircon-rich cumulate charnockites that have significantly higher P2O5 and Zr contents than global orthopyroxene-free granitoids. Many I-A-S type charnockites are believed to have formed through this mechanism and represent cumulate granitoids that had lost a significant amount (>20-40%) of hydrous interstitial melt.Our study reveals that the formation of igneous charnockite depends on extreme magmatic processes such as flushing of large amounts of CO2 or high degree of crystal-melt segregation, and not merely on the high tem-perature of crystallization. Further studies on igneous charnockite should shed new light on quantifying the carbon flux and understanding the differentiation of the continental crust.
WOS关键词HIDAKA METAMORPHIC BELT ; A-TYPE GRANITES ; S-TYPE ; ORTHO-PYROXENE ; FLUID INCLUSIONS ; EAST ANTARCTICA ; GARNET-BEARING ; INTERMEDIATE MAGMAS ; SUPERIOR PROVINCE ; MINERAL CHEMISTRY
资助项目Natural Science Foundation of China[41930214] ; Natural Science Foundation of China[41903027] ; Fundamental Research Funds for the Central Universities of China[020614380114] ; Fundamental Research Funds for the Central Universities of China[020614380166]
WOS研究方向Geology
语种英语
出版者ELSEVIER
WOS记录号WOS:000925285300001
资助机构Natural Science Foundation of China ; Natural Science Foundation of China ; Fundamental Research Funds for the Central Universities of China ; Fundamental Research Funds for the Central Universities of China ; Natural Science Foundation of China ; Natural Science Foundation of China ; Fundamental Research Funds for the Central Universities of China ; Fundamental Research Funds for the Central Universities of China ; Natural Science Foundation of China ; Natural Science Foundation of China ; Fundamental Research Funds for the Central Universities of China ; Fundamental Research Funds for the Central Universities of China ; Natural Science Foundation of China ; Natural Science Foundation of China ; Fundamental Research Funds for the Central Universities of China ; Fundamental Research Funds for the Central Universities of China
源URL[http://ir.iggcas.ac.cn/handle/132A11/106788]  
专题地质与地球物理研究所_岩石圈演化国家重点实验室
通讯作者Xu, Xisheng
作者单位1.Friedrich Alexander Univ Erlangen Nurnberg FAU, Geozent Nordbayern, Schlossgarten 5, D-91054 Erlangen, Germany
2.Chinese Acad Sci, Inst Geol & Geophys, State Key Lab Lithospher Evolut, Beijing 100029, Peoples R China
3.Univ Sci & Technol Beijing, Sch Civil & Resource Engn, Beijing 100083, Peoples R China
4.Nanjing Univ, Sch Earth Sci & Engn, State Key Lab Mineral Deposits Res, Nanjing 210023, Peoples R China
推荐引用方式
GB/T 7714		 Zhao, Kai,Xu, Xisheng,Klemd, Reiner,et al. A review of the genetic mechanisms generating igneous charnockite: CO2 flushing and crystal-melt segregation in mushy reservoirs[J]. EARTH-SCIENCE REVIEWS,2023,237:18.
APA Zhao, Kai,Xu, Xisheng,Klemd, Reiner,He, Zhenyu,&Zhang, Xisong.(2023).A review of the genetic mechanisms generating igneous charnockite: CO2 flushing and crystal-melt segregation in mushy reservoirs.EARTH-SCIENCE REVIEWS,237,18.
MLA Zhao, Kai,et al."A review of the genetic mechanisms generating igneous charnockite: CO2 flushing and crystal-melt segregation in mushy reservoirs".EARTH-SCIENCE REVIEWS 237(2023):18.

入库方式： OAI收割

来源：地质与地球物理研究所

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