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湘中北黄土店-仙溪一带发育的中新元古界-下古生界遭受了区域甚低级变质作用.在本地区所采的<2μm的样品中,经 Kisch国际标样校正,冷家溪群伊利石结晶度的Kubler指数为0.18～0.21°△2θ,CuKα,板溪群伊利石结晶度为0.19～0.23°△2θ,震旦系-下古生界伊利石结晶度为0.20～0.29°△2θ.变质温度约为340～240℃.从而可把本区中元古界冷家溪群的区域变质划归浅变质带范围,新元古界板溪群的区域变质划归浅变质-高近变质带的范围,并未普遍达到目前人们认为的绿片岩相或低绿片岩相.震旦系-下古生界的区域变质主要为高近变质带范围,并非前人认为的低绿片岩相或为“未变质沉积盖层”.本区冷家溪群伊利石 b0值变化范围在 0.8989～0.9050nm之间,板溪群-志留系的伊利石b0值变化范围在0.8984～0.9037nm之间,由b0频率累积曲线图,得出本区板溪群-志留系区域变质作用属于中低压变质类型.
The Neoproterozoic-Lower Paleozoic developed in the loess-Xianxi area of Central Hunan Province suffered very low level metamorphism in the region. <2μm samples collected in this area were corrected by Kisch International Standard, The Kubler exponent of illite in Xixi Group is 0.18 ~ 0.21 ° △ 2θ, while that of CuKα and Banxi Group is 0.19 ~ 0.23 ° △ 2θ. The Sinian-Lower Paleozoic illite crystallinity is 0.20 ~ 0.29 ° △ 2θ. The metamorphic temperature is about 340-240 ° C. Therefore, the metamorphic Lengjiaxi Group in this area can be metamorphosed into the metamorphic zone, and the Neoproterozoic Banxi Group has been metamorphosed into shallow metamorphism -Gao near metamorphic belt did not generally reach the present green-schist facies or low-greenschist facies.The regional metamorphism of the Sinian-Lower Paleozoic is mainly the high-near-metamorphic zone, which is not considered as low Greenschist facies or “non-metamorphic sedimentary capstones.” The range of b0 values of illite from Lengjiaxi Group in this area ranged from 0.8989 to 0.9050 nm, and the illite values of Banxi Group-Silurian ranged from 0.8984 ~ 0.9037nm, the accumulation curve of b0 frequency shows that Banxi Group in this area - Silurian metamorphism belongs to the low pressure change Types of.