The Characteristics,Protolith Recovery And Environment Analysis Of The Metamorphic Rocks In The Wulashan Group Halaganlawusu Area,Inner Mongolia

Halaganlawusu is located in the west of Inner Monglia,belonging to the western segment of north margin in the North China Craton.The stratum in the area,subjected to North China Stratigraphic Area,had experienced multiple tectonic evolution stages.Because of the late multi-stage structural compression,transformation and magmatic intrusion,so the stratum developed incompletely.Wulashan Group is the most ancient metamorphic rock series,mainly consist of grey garnet plagiogneiss,biotite plagioclase gneiss,amphibolite and various migmatitic gneiss.The structure of the area is extremely complex,developed deep fault and frequent volcanic-magmatic activities.Based on the study of Wulashan Group spatial distribution and the characteristics of petrology and mineralogy,this paper attempt to recovery the original rocks buildings and their formation environment.The tectonic position is also discussed in this paper,in order to provide available information of rock-forming and ore-forming processes for further study on this area.Different metamorphic rocks exhibit different characteristics in the area.Marbles class have the features of sedimentary rocks,their original rocks are dolomitic marl.Amphibolite exhibit the characteristics of volcanic rocks,the original rocks are intermediate basic volcanic rocks.The original rocks of gneiss are inferred intermediate acidic volcanic rocks,clamping few clastic sedimentary rocks.In the metamorphic rocks,the amount of SiO2 is relatively high,up to 75.37%.Among these,the content of SiO2 in marble is 14.8%～28.87%,averaging 21.35%,which is larger than that of normal carbonate rocks.This suggest the original rocks of marble formed in high Si environment.The content of SiO2 in amphibolite averages from 47.00%to 49.13%,consistent with basalt.Gneiss has a large SiO2 between 71.72%to 75.37%,averaging 73.68%and matching with that of acid rocks.The ∑REE of marbles is low,which vary from 5.18×10-6 to 14.99×10-6,average content is 10.37×10-6.The ∑REE of amphibolite is 30.74x10-6～71.72×10-6,which average value is 52.40×10-6.The REE average content of gneiss is 75.08×10-6.From the chondrite-normalized REE patterns of the metamorphic rocks series,LREE slightly richer than HREE,Eu non-abnormity or slightly negative abnormity.The formation environment of Wulashan Group original rock is mainly vocanic-sedimentary.