Journal
JOURNAL OF EARTH SCIENCE
Volume 33, Issue 6, Pages 1535-1548Publisher
CHINA UNIV GEOSCIENCES, WUHAN
DOI: 10.1007/s12583-020-1376-9
Keywords
biotite; mineral chemistry; crystallization; magma mixing; Wangjiazhuang granite; Zanhuang Massif; North China Craton
Categories
Funding
- National Natural Science Foundation of China [42072222]
- Fundamental Research Funds for the Central Universities, China University of Geosciences, Wuhan [CUGL180406, CUGCJ1707]
- Chinese Ministry of Education Fund [BP0719022]
- Open Fund from the State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences, Wuhan [GRMR201901]
- Chinese Academy of Sciences [QYZDY-SSW-DQC017]
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This study conducted a detailed petrographic investigation on the biotite of the Wangjiazhuang granite, revealing distinct differences in chemical compositions between the biotite monzogranite and mafic microgranular enclaves. The analysis of biotite provided insights into the source, physicochemical conditions, and magma mingling/mixing processes of the granite. The differences observed between the two types of rocks suggest continuous interaction between the granitic and mafic magmas.
The Wangjiazhuang granitic pluton is located in the central Zanhuang Domain, the central part of the North China Craton, which is mainly composed of biotite monzogranite with few mafic microgranular enclaves. Biotite is an important ferromagnesian mineral in most of the intermediatefelsic igneous rocks, and its mineral chemistry can record the properties of magma and the petrogenetic physicochemical conditions. In this study, we carried out a detailed petrographic study by electric probe microanalysis on biotite for the biotite monzogranite and mafic microgranular enclaves, to discuss the source, physicochemical conditions, and the magma mingling/mixing processes of the Wangjiazhuang granite. The results show significantly different chemical compositions from the biotite monzogranite and mafic microgranular enclaves. The crystallization of these biotite grains from the biotite monzogranite and mafic microgranular enclaves all occurred in low oxygen fugacity. The biotite grains in biotite monzogranite are rich in Fe, poor in Mg, which belong to siderophyllite. The ratios of [(Fe3+ + Fe2+)/(Fe3+ + Fe2+ + Mg2+)] are between 0.78 and 0.86. The average of FeOT (total FeO)/MgO of biotite grains in biotite monzogranite is 9.02. The MF values [2 x Mg/(Fe2+ + Mg + Mn)] of biotite monzogranite are between 0.31 and 0.47, suggesting biotite monzogranite derived from crustal source rocks (metasedimentary rocks). The formation of granitic rocks including the Wangjiazhuang granite was related to the subduction event at ca. 2.5 Ga which resulted in the melting event, and then induced the early partial melting of TTGs and metasedimentary rocks. The biotite in mafic microgranular enclaves varies from siderophyllite to ferrobiotite, and MF values range from 0.63 to 1.06, suggesting that magma of mafic microgranular enclaves had experienced magma mixing/mingling in various degrees. Biotite monzogranite and parts of mafic microgranular enclaves have a similar crystallized condition, while other mafic microgranular enclaves are different from biotite monzogranite. The differences between biotite monzogranite and mafic microgranular enclaves may be a consequence of continuous interaction between granitic and mafic magmas.
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