Deerite [Fe
12
2+
Fe
6
3+
Si
12O
40 (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.
Keywords deerite - geothermal gradient (l0°C/km) - Precambrian blueschist - Aksu of Xinjiang
Project supported by the National Natural Science Foundation of China (Grant Nos. 49572157 and 49772103)