科研之友
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摘要
The Shadegai K-feldspar granite in the Wulashan area at the north margin of the North China craton contains abundant mafic microgranular enclaves (MMEs) consisting mainly of monzonite. The MMEs have either a sharp or a gradual contact zone with their host granite, indicating different theological properties of the contrasting magmas. Petrographic observation shows that the MMEs contain various typical textures whose origin can be explained in terms of magma mixing and mingling, including quartz ocelli, rapakivi feldspars, mafic clots, resorption of K-feldspar megacrystals, acicular apatite morphology, inclusion zones in feldspars, and anorthite "spikes" in plagioclase. Microprobe analyses on the rock-forming minerals suggest that magma mixing and mingling played an important role during the formation the Shadegai granite. The host granite magma may be derived from the lower crust, while magma for the MMEs originated from the mantle. LA-ICP-MS U-Pb isotopic dating on zircons from the Shadegai granite and its MMEs obtained similar ages of 233.4 +/- 2.3Ma and 229.7 +/- 1.5Ma, respectively, further indicating the existence of magma mixing and mingling during their genesis. It is thus suggested that the quench of mafic magama upon its incorporation into the relatively cooler felsic host magma resulted in the formation of MMEs with sharp contact zones, chilled margins and more abundant mafic minerals. Subsequent interaction of mafic and felsic magmas caused the decrease in temperature difference of magmas and the formation of MMEs that have gradual contact zone, more abundant felsic minerals and no evident chilled margins.
- 出版日期2015-5
- 单位成都理工大学; 中国地质大学（北京）
