太行山太古宙变质杂岩中富铝片麻岩的变质作用

Metamorphism of Al Rich Gneisses in Taihang Mountain Archean Metamorphic Complex

太行山太古宙变质杂岩中富铝片麻岩主要分布在湾子岩系的底部，常常与大理岩密切伴生或者以似层状体产于花岗质片麻岩中。依据岩石结构和反应关系将变质作用分为早期、中期和晚期三个阶段。早期矿物组合为Ｇｔ（石榴石）＋Ｓｔ（十字石）＋Ｐｌ（斜长石）＋Ｍｓ（白云母）＋Ｂｉ（黑云母）＋Ｒｕ（金红石）＋Ｑｚ（石英）±Ｋ－ｆｓ（钾长石）；中期矿物组合为Ｇｔ＋Ｇｅｄ（铝直闪石）＋Ｂｉ＋Ｐｌ＋Ｉｌｍ（钛铁矿）＋Ｃｏ（刚玉）＋Ｓｉｌ１（毛发状夕线石）＋Ｑｚ＋Ｋ－ｆｓ±Ｍｓ；晚期矿物组合为Ｈｃ＋Ｋ－ｆｓ＋Ｓｉｌ２（针柱状夕线石）。矿物温度压力计和内部一致性热力学计算结果表明早期矿物组合形成于６８０℃和０．８ＧＰａ左右，刚玉、铝直闪石和毛发状夕线石组合形成于７３０℃～７５０℃和０．７ＧＰａ左右的很窄的Ｐ－Ｔ范围内，夕线石和尖晶石矿物组合的形成温度与前一组合相似或略高，压力偏低。在Ｐ－Ｔ空间上上述矿物组合的演化构成了一条近等温减压（ＩＴＤ型）的ＰＴｔ轨迹。

Al rich gneisses in Taihang mountain Archean metamorphic complex are mainly distributed in the lower part of Wanzi stratified rock series and the gneisses usually associate together with various marbles or occurrence by stratified bodies in granitic gneisses. Depending on textural and metamorphic reaction relationships of rocks, we divide the evolution of their metamorphism into three stages.Mineral assemblage in the early stage is garnet + staurolite + plagioclase +muscove+ biotite + quartz + rutile±K feldspar; mineral assemblage in the middle stage is garnet + gedrite + sillimanite 1(hair sill)+biotite +corundum± quartz + plagioclase + ilmenite+K feldspar; mineral assemblage in the later stage is hercynite+sillimanite 2(needle sill)+K feldspar. Through garnet biotite thermometry and internally consistent thermodynamic calculation, we get that garnet, stourolite and rutile assemblage formed at 680℃ and 0 8 GPa, corundum and gedrite present mineral assemblage at a little P T space of 730℃～750℃ and about 0 7 GPa; The temperature of sillimanite and hercynite present mineral assemblage are a little higher than that of second association, yet pressures are less than one of second assemblage. The evolution of above mineral assemblages and P T conditions constructs a clockwise ITD type P T tpath.