山西古元古代吕梁群变质带的重新划分及地质意义

RE DIVISION OF THE METAMORPHIC FACIES ZONATION OF LüLIANG GROUP IN SHANXI PROVINCE AND ITS SIGNIFICANCE

对古元古代吕梁群主变质作用进行了变质带的重新划分，划分出绿泥石带，黑云母带，石榴石带，十字石蓝晶石带和矽线石带五个带。指出变质作用属于中压相系，并认为主变质带是由近南北向的挤压—逆冲作用导致。吕梁群主变质作用是整个华北中部吕梁期（１８００Ｍａ）构造—变质—岩浆活动的一部分。

Luliang Group underwent at least two metamorphic and deformation events in the Precambrian The early geological event is characterized by a weak metamorphism and strong deformation It caused a tight folding of Luliang Group strata with nearly N S direction However, its metamorphic grade is only greenschist facies The late geological event is featured by a stronger metamorphism up to high amphibolite facies It is described as the main metamorphic event and has obvious zoning Metamorphism increases gradually from the North to the South The orientation of main metamorphic zones is almost vertical to the strata strike At least five different zonation patterns were proposed during past twenty years This paper set up a new subdivision of the metamorphic facies zonation of the Paleoproterozoic Luiang Group on the basis of the detailed field mapping and petrographic study All five zones, the chlorite zone, the biotite zone, the almandine zone, the staurolite kyanite zone and the sillimanite zone, are distributed from north to south successively The former four zones are the products of the middle pressure facies series, similar to the typical Barronian metamorphic zones, and the fifth sillimanite zone was formed at lower pressure Sillimanite results from the reaction of St+Ms+Q=Sil+Bi+H 2O The main metamorphism event overprinted and reformed distinctly the early event marks In addition, the late tectonic thermal event led to wide migmatization to the area south of Xichuanhe fault Surveying shows that the main metamorphism is closely related with the Xichuanhe thrust fault activity. The nearly N S compression and thrusting and the heat from depth resulted in the main metamorphism and migmatization The main metamorphism of Luliang Group is a part of the whole structure metamorphism magmatism activity of the central part of North China U Pb dating of zircon indicates that it occurred at 1800±Ma, namely the Luliang orogeny