Discovery of deerite from the Aksu Precambrian blueschist terrane and its geological significance  

作　　者：张立飞 姜文波 魏春景 董申保 

出　　处：《Science China Earth Sciences》1999年第3期233-239,共7页中国科学（地球科学英文版）

基　　金：Project supported by the National Natural Science Foundation of China (Grant Nos. 49572157 and 49772103).

摘　　要：Deerite [Fe 12 2+ Fe 6 3+ Si12O40 (OH)10] was first discovered in the metamorphic magnetite-bearing quartzites which are interlayered with blueschists in Aksu Precambrian blueschist terrane. The deerite-bearing mineral association includes (1) deerite + riebeckite + stilpnomelane + ilvaite + magnetite + quartz and (2) deerite + stilpnomelane + magnetite +quartz based on the investigation under microscope. The study of mineral chemistry shows that the deerites from Aksu Precambrian blueschist are Mn-poor deerite similar to that from Alps. But the deerite from Aksu is the nearest to the end member of deerite. According to the equilibrium P-T region of deerite determined by Lattard and Breton (1994), the deerites in metamorphic magnetite-bearing quartzites from Aksu Precambrian blueschists were formed under the conditions of pressure lower than 1.0 Gpa, temperature ranging from 300 to 400°C and about the l0°C/km geothermal gradient.The deerite in metamorphic magnetite-bearing quartzites from Aksu blueschists is the only one Precambrian deerite reported now. This suggests that the earth began to cool, and the modern cooling subduction regime between plates started at Late Proterozoic. The Late Proterozoic may be the important period during the evolution of the earth.Deerite [Fe₁₂²⁺ Fe₆³⁺ Si₁₂O₄₀（OH）₁₀] was first discovered in the metamorphic magnetite-bearing quartzites which are interlayered with blueschists in Aksu Precambrian blueschist terrane. The deerite-bearing mineral association includes ① deerite+riebeckite+stilpnomelane+ilvaite+magnetite+quartz and ② deerite+stilpnomelane+magnetite +quartz based on the investigation under microscope. The study of mineral chemistry shows that the deerites from Aksu Precambrian blueschist are Mn-poor deerite similar to that from Alps. But the deerite from Aksu is the nearest to the end member of deerite. According to the equilibrium P-T region of deerite determined by Lattard and Breton （1994）, the deerites in metamorphic magnetite-bearing quartzites from Aksu Precambrian blueschists were formed under the conditions of pressure lower than 1.0 Gpa, temperature ranging from 300 to 400℃ and about the 10℃/km geothermal gradient. The deerite in metamorphic magnetite-bearing quartzites from Aksu

关 键 词：deerite geothermal gradient (l0°C/km) Precambrian blueschist Aksu of Xinjiang 

分 类 号：P534[天文地球—古生物学与地层学]