Study On Regional Metamorphism Conditions And Chronology Of Foziling Group

The Qinling-Tongbai-Hongan-Dabie-Sulu orogenic belt is formed by the collision of North China and the Yangtze plate.It traverses central China and extends from east to west.Tongbai-Hongan orogenic belt,Dabie-Sulu orogenic belt.Up to now,the study of the Paleozoic evolution of the Qinling-Tongbai-Hongan orogenic belt has been relatively thoroughly studied,But the patterns of eastward to Dabie orogenic belt still unclear due to limitations of research direction,which lead to the uncomprehensive understanding of the giant orogenic belt.At present,as far as the Dabie collision orogenic belt is concerned,the main body records the tectonic events since the Mesozoic,and the Paleozoic geological events are only reflected in the Foziling Group at the northernmost margin of the orogenic belt.Therefore,this group is the key carrier to solve the above problems.The study of the Foziling Group is still relatively "lagging" so far.The main problems are in the following three aspects:(1)Unclear structural attribution;(2)Different understanding of metamorphic attributes,and its metamorphic PT conditions restrict the understanding of the Dabie orogenic belt;(3)Insufficient research on the time limit for deterioration.Since the best way to reveal the orogenic belt is to go deep into systematic metamorphic petrology research,this article intends to focus on metamorphic petrology and chronology,plus a small amount of geochemistry,to further explore the metamorphic level,PT trajectory and Paleozoic evolution and other issues.The main contents and main points of this article are as follows:(1)For the garnet dolomite schist with a complete garnet+plagioclase+biotite+muscovite+quartz complete mineral combination,through detailed analysis of petrography,mineral chemistry,thermodynamics and zircon chronology,the results show that foziling group has undergone four stages metamorphism,the P-T conditions are T=658 ±18? and P=1.08 ± 0.02 Gpa(Stage-I),T=755± 24? and P=1.21±0.04Gpa(Stage-?,T=554 ?+7?,P=1.08 ± 0.02Gpa(Stage-?)and P calibration=0.3?0.6Gpa,T=448?546 ?(Stage-?)respectively.Among four stage,stage-? is composed of chlorite and biotite in the garnet fissures.So that the paper constructed an anti-clockwise PT path with the characteristic of low-pressure granulite-green piece similar isothermal pressure drop.The reason is affected by the heating effect of the Paleozoic diorite magma arc,and the metamorphism time may be 320?340Ma.(2)Main-stage metamorphic conditions:The Foziling Group is mainly composed of quartz schist and mica schist.The temperature and pressure calculation of the characteristic garnet mica/quartz schist and mica schist,the former rock mineral combination is garnet+plagioclase+Biotite+muscovite,choose GB&GBPQ or GM&GMPQ thermostat to jointly solve,average temperature and pressure conditions range:T=573?648??P=0.61?0.85 GPa,reaching the mid-high angle amphibole facies;mica schist minerals are mainly black and white mica,which can only be estimated by pressure calibration combined with black and muscovite Ti thermometers.In this paper,the highest and lowest pressure values in the region are combined and the average value is taken,The pressure calibration is P calibration=0.9Gpa,the temperature range T=543?638?,PT chart shows that it falls into the range of mid-high angle amphibolite facies.Combined with previous studies,this paper will introduce the main temperature and pressure range:P=0.60-1.1Gpa,T=550-665?,reaching the mid-high angle amphibolite facies metamorphism condition,which belongs to mid-high grade metamorphism,reflecting at least two phase metamorphism events of the Foziling Group.(3)In order to determine the formation time,a total of 9 zircon samples were taken,and their age results were obtained using LA-ICP-MS instruments.Among them,8 samples belonged to detrital zircons,with an age range of 3559 ±53?389 ± 14Ma,389± 14Ma,showing that the upper limit of sedimentation is Late Silurian,and the age range of metabolite is 528± 12?304 ±7Ma,Paleozoic oceanic crust;combined with the results of previous studies,a total of 1352 zircon ages are counted,and the histogram shows the peak age:342 Ma,446 Ma,818 Ma,954 Ma,and 2492 Ma,which are almost the same as the peak ages of Liuling Group and Nanwan Flysch in the west.The Foziling Group is the eastward extension of the Qinling Microcontinent.The source is from the Yangtze Plate and North China.Plate and Paleozoic magmatic arc.(4)Through regional geological survey and profile measurement,the lithology of the Fuziling Group is dominated by quartz schist and mica schist,garnet mica/quartz schist,quartzite,a small amount of schistite and marble,etc.,the original rock composition The main body belongs to mixed sandstone,and part of it is clay rock.(5)The Dabie orogenic belt has undergone oceanic subduction-accretion-land-land collision composite orogenic belts.The Foziling Group is similar to the Dabie Mountains as a metamorphic belt.Its late Paleozoic evolution is connected with the Qinling-Tongbai-Hongan orogenic belt.