地学前缘(英文版)
地學前緣(英文版)
지학전연(영문판)
GEOSCIENCE FRONTIERS
2012年
5期
603-611
,共9页
Ultrahigh-temperature metamorphism%Petrology%p-T path%Inner Mongolia Suture Zone%North China Craton
The Khondalite Belt within the Inner Mongolia Suture Zone (IMSZ) in the North China Craton is a classic example for Paleoproterozoic ultrahigh-temperature (UHT) metamorphism.Here we report new spinel-bearing metapelitic granulites from a new locality at Xumayao within the southern domain of the IMSZ.Petrological studies and thermodynamic modeling of the spinel + quartz-bearing assemblage shows that these rocks experienced extreme metamorphism at UHT conditions.Spinel occurs in two textural settings:(1) high Xzn(Zn/(Mg + Fe[[ + Zn) =0.071-0.232) spinel with perthitic K-feldspar,sillimanite and quartz in the rock matrix; and(2)low Xzn (0.045-0.070) spinel as inclusions within garnet porphyroblasts in association with quartz and sillimanite.Our phase equilibria modeling indicates two main stages during the metamorphic evolution of these rocks:(1) near-isobaric cooling from 975 ℃ to 875 ℃ around 8 kbar,represented by the formation of garnet porphyroblasts from spinel and quartz; and(2)cooling and decompression from 850 ℃,8 kbar to below 750 ℃,6.5 kbar,represented by the break-down of garnet.The spinel + quartz assemblage is considered to have been stable at peak metamorphism,formed through the break-down of cordierite,indicating a near isothermal compression process.Our study confirms the regional extent of UHT metamorphism within the IMSZ associated with the Paleoproterozoic subduction-collision process.
