五台山晚太古代碰撞造山带的变质作用演化

METAMORPHISM EVOLUTION OF THE LATE ARCHEAN COLLISION OROGENIC BELT IN WUTAISHAN

五台山晚太古代碰撞造山带由三个构造岩片组成，即南部构造岩片——弧前混杂岩带、中部构造岩片——岛弧系和北部构造岩片——弧后混杂岩带，其间以大型逆冲型韧性剪切带相拼合。对三个构造岩片的矿物共生组合及变质反应研究，确定其具有相似的造山型ＰＴｔ轨迹。变质早期至峰期明显的升温升压过程与地壳的拼合作用有关，变质峰期至晚期的近等温降压过程与地壳的纵向伸展作用相联系。三个构造岩片变质程度的差异是由于其所处的大地构造位置不同造成的。

The late Archean collision orogenic belt in Wutaishan is situated in the central part of the North China Plate.It is separated from the high grade gray gneiss terrane at north Hengshan by dutile shear zones (DDZ) distributed over the north side of Hutuo River Cenozoic fault depression,and from the high grade terrane at southwest Fuping by Longquanguan DDZ,to form a wedge shape terrane opening towards southwest.Based on rock association,metamorphic deformation,magmatism and geochronological data,the collision orogenic belt can be subdivided into three tectonic units:the south tectonic section (STS) (fore arc melange zone),the central tectonic section (CTS) (paleo island arc),the north tectonic section (NTS)(back arc melange zone).The boundaries between them are giant DDZ.The rocks in the NTS and STS are metamorphosed to amphibolite facies,whereas those in the CTS to greenschist facies.The differences of metamorphic degrees in the three sections are due to their tectonic environments.Studies on the mineral assemblages and metamorphic reactions indicate similar PTt paths of orogeny for these three tectonic sections.The temperatures and pressures of the metamorphism increased apparently in the three tectonic sections from early to peak stage (STS:500℃,0.4GPa→589￣670℃,0.86GPa;CTS:375￣400℃,<0.5GPa→500￣560℃,0.5GPa;NTS:500℃,0.4GPa→569￣663℃,0.98￣1.36GPa),which mainly related to the crustal subduction of the fore arc and back arc melange zones in the island arc continent,continent continent collisions.The isothermal decompression of the metamorphism from peak to late stage (STS:589￣670℃,0.86GPa→560￣650℃,0.2￣0.3GPa;CTS:500￣560℃,0.5GPa→400￣445,0.1￣0.4GPa;NTS:569￣663℃,0.98￣1.36GPa→560￣650℃,0.2￣0.3GPa) was related to the crustal detachment which was resulted from the extensive longitudinal extension.Tectonism provided the dynamic basis for metamorphism.