Experimental Constraints on Formation of Low-Cr# Chromitite: Effect of Variable H2O and Cr2O3 on Boninitic-Magma and Harzburgite Reactions

作     者：Yage Zhao Yanfei Zhang Chao Wang Zhenmin Jin Qijin Xu Yage Zhao;Yanfei Zhang;Chao Wang;Zhenmin Jin;Qijin Xu

作者机构：College of OceanographyHohai UniversityNanjing 210098China State Key Laboratory of Geological Processes and Mineral ResourcesChina University of GeosciencesWuhan 430074China 

出 版 物：《Journal of Earth Science》 (地球科学学刊（英文版）)

年 卷 期：2020年第31卷第4期

页      面：709-722页

核心收录：

学科分类：070904[理学-构造地质学] 0709[理学-地质学] 070901[理学-矿物学、岩石学、矿床学] 07[理学] 

基　　金：supported by the National Programme on Global Change and Air-Sea Interaction (No. GASI-GEOGE-02) the National Nature Science Foundation of China (Nos. 41772040,91858104) the Fundamental Research Funds for the Central Universities,Hohai University (No. 2013/B18020030) 

主　　题：low-Cr#chromitite boninitic magma harzburgite melt-rock reaction 

摘      要：Reactions between a boninitic or basaltic magma and harzburgite at shallow mantle depths are thought to be closely related to the formation of podiform chromitites,but little experimental data is available on these *** this study,a series of experiments were conducted at 1.5GPa and 1 000–1 400 oC to investigate the interactions between boninitic magma and harzburgite in homogenous mixed systems with varied bulk concentrations of water(~0.7 wt.%–10 wt.%)and Cr2O3(~0.2 wt.%–4 wt.%).In the experimental charges,chromite grains can be observed coexisting with orthopyroxene,clinopyroxene±olivine,and quenched melt in the Cr-bearing *** bulk concentration of Cr2O3 in the starting material has a slight effect on compositional changes in the chromites ***,the Cr#(Cr#=100×Cr/(Cr+Al))and Mg#(Mg#=100×Mg/(Mg+Fe))values for the chromites exhibit positive and negative correlations,respectively,with the bulk H2O *** 1 100 oC,chromite Cr#values range from^33–35 to^58–65,and chromite Mg#values range from^70–73 to^55–58when bulk H2O contents in the starting material are increased from^0.7 wt.%to^10 wt.%.The experimentally produced chromites have compositions(as expressed by Cr#,Mg#,and Ni O and Mn O contents)similar to natural chromites from low-Cr#chromitite *** suggest that the interactions between boninitic magmas with varied H2O contents and harzburgite in a shallow mantle wedge could be a possible mechanism that forms the low-Cr#chromitites found in *** emphasize here that H2O may play an important role in the compositional evolutions of natural chromitites.