Metamorphism-deformation Analysises Of The Qinling-Funiushan Tectonic Belt

Qinling orogenic belt is one of the most intense areas of deformation on the earth surface.It’s the result of the collision and the intracontinental orogeny between Yangtze and North China Blocks. The southern margin of the North China Block strongly deformed because of the plate convergence,and everntually be involved in Qinling orogenic belt as an important part. The study area-Funiushan tectonic belt located here, which records the whole process of the orogenic belt’s formation and evolution.So the detail study of its metamorphic and its deformation can help to restore the subduction collsion,to inverse the way the paleoplate converged and moved, which is very important for the establishment of the structure, evolution and dynamics mode in the continental orogenic.This article is based on structural mineralogy and plate tectonics.lt takes Luoluan and Waqiao fault belts,among Qinling-Funiu mountain tectonic belt,and those influenced rocks as markers. The major studies are the macro,micro and ultra-micro metamorphic and deformation characteristics of crystalline rock in this area.Thi-s article focuses on nine cross sections and a longitudinal section-of petrologic combining the analysis of diverse scales to study mineral composition, minerals structure and texture of metamorphic rocks and find out its regularities of distribution to analysi-s the relation between metamorphic facies and tectonic belts. Study diagnostic metamorphic mineral in deformation rocks among fault zone and its two sides,to analysis its type,counts and symbiotic relationship and finally resolving tectonic setting during M-etamorphosis Period.Take advantage of mineral deformation characteristics to study the deformation pattern and mechanism of the tectonic rock, to reveal mineral plastic deformation sequence,especially the diagnostic metamorphic mineral’s crisp-plastic convert deformation mechanism and its influencing factors,such as the temperature,pressure,strain rate and other factors.With the analysis of the deformation and compositional characteristics of the syntectonic metamorphic fluid which formed during the deformation process.we try to get its source and formation age.Through the study for tectonic rock’s metamorphism and deformation characteristics,we divided the metamorphism and deformation facies in the tectonic belt,and we analyzed the relationship between deformation and phase transition of the tectonic rock in the context of syntectonic,and then establish their relationship schema.For the features of the Qinling-Funiushan tectonic belt, reading a lot and summarying the previous research achievements, we understood the regional geological background, the research status and the existing problems.With a large number of wild phenomenon observations and laboratory analysises,we tried a combination of mineralogical and structural geology and a combination of macro,micro and ultra-micro deformation technology to do the researches.And so we achieved the following innovative research results on deformation-metamorphic petrology,tectonic mineralogy,structural geology and geological-hot chronology of events:(1) macro geological characteristics of Funiushan tectonic beltFuniushan tectonic belt is located on the north margin of the North Qinling, bounded by Luo-Luan fault in the north and Wa-Qiao fault belt in the south.As the boundary fault of north Qinling and the northern margin of Qinling tectonic belt, Luoluan fault zone is a tectonic belt composed by a serious of ductile shear zone and the pieces of rock stuck in between with a dozen kilometers wide. It general strike in290°,trend NNE, and inclination to60°and has four phases of deformation. Early subduction from south to north followed by large scale left-lateral slip with many mylonites forming. The third deformation is weak mylonitization and the last deformation is thrusting from north to south. From east to west, the fine-grained mylonite gradually changed into medium-grained and coarse-grained mylonite, which respectively compare to the mylonite in the middle and lower structural layer of the crust, the lower structural layer of the upper crust, and the middle and upper of the upper crust.As the boundary of the Erlangping group and Kuanping group, the Waqiao fault is located in the southern margin of Funiushan tectonic belt with a dozen kilometers wide and it is also composed by many ductile shear zones and brittle-ductile shear zones, which basically have the same occurrence(crosspitch:290°,trend:NNE, inclination:50°). Mylonite, ultramylonite, mylonite mineral σ、δ porphyroclastics,the quartz veins and many other features extensively developed in the fault zone, indicating that the fault zone thrust from the north to the south with sinistral component.(2) microscopic deformation characteristics of Funiushan tectonic belt Rocks in Funiu tectonic belt are mainly mylonite, tectonic schist, mylonitization rock. According to the different components of original rocks, Mylonites are divided into felsic mylonite, carbonate mylonite, mafic mylonite. Through microscopic observation and analysis, we found the entire structure with mineral assemblages and mineral deformation characteristics significantly different from east to west, and with some regularity.①Types of quartz dynamically recrystallization from east to west change from grain boundary migration recrystallization to subgrain rotation recrystallization, then to bulging recrystallization, but transformed into subgrain rotation recrystallization in the west part.②Types of feldspar dynamically recrystallization from east to west change from subgrain rotation recrystallization to bulging recrystallization, but transformed back to s bulging recrystallization in the west part.③Biotite from east to west changes from a light brown-brown hypidiomorphic into tiny flakes green-brownish green augen porphyroclasts, alteration increased. At the same time, muscovite, chlorite and epidote increased. ④The calcite in eastern marble (carbonate) mylonite occurred bulging recrystallization formed the core-mantle structure, but only found fine graining in western marble (carbonate) mylonite, and no significant recrystallization. Aphanitic calcite crystals in Limestone mylonite in Miaozi strong fields has increased due to heat caused shear effect at Miaozi area in Luanchuan County.⑤Hornblende in mafic mylonite occurred a strong plastic deformation, but the dynamic recrystallization only observed in Miaozi profile. Most of the eastern amphibole occurred epidotization and chloritization, Almost all western amphibole occurred actinolition, showing retrograde metamorphism of the original rocks due to ductile shear.⑥Rock texture and structure from east to west change from granoblastic texture and gneiss ic structure gradually into mylonitic texture, schistose structure.⑦Types of mylonite from east to west change from a high-temperature plagioclase K-feldspar superplastic mylonite to the medium temperature quartz-plagioclase plastic mylonite and medium temperature quartz plasticity mylonite, then turn back to the medium temperature quartz-plagioclase plastic mylonite⑧Tectonic schists are particularly developed. Eastern schists have more remaining mylonitic structure inside, indicating tectonic schists are mylonite originally by recrystallization, with the typical plastic deformation. The western schists subjected intense flattening and shearing, brittle crack of mineral particles are very common, are semiplastic tectonic rocks formed under the brittle-ductile conditions. It indicates that eastern schists are suffered tectonism longer and deeper.Mineral deformation characteristics and types of dynamic recrystallization of mylonite and schist in Funiushan tectonic belt shows the temperature and pressure conditions are decreasing from east to west, indicating the eastern uplift is higher than the west in Funiushan tectonic belt.(3) Deformation mechanism, deformation facies and mineral plastic deformation sequence of tectonic rocks.Felsic mylonite is the most common in Funiushan tectonic belt. Dislocation climb creep has become an important deformation mechanism of eastern quartz. It is a high-temperature plastic deformation mechanisms. However the deformation mechanism of western quartz is based brittle microfracture, dislocation glide and recrystallization. The deformation mechanism of eastern feldspar is dislocation creep in main; but microfractures, twinning and recrystallization are common in western feldspar. Therefore, the deformation mechanism of felsic mylonite in east part is formed in the middle crust environment, which mainly contain crystalline plastic deformation and high-temperature diffusion creep; in the western, the plastic deformation mechanism is formed in the lower part of the upper crust and the upper part of the middle crust, controlled by low temperature diffusion creep, grain’s boundary slip and plastic deformation of crystalline. The mineral plastic deformation sequence in Funiushan tectonic belt is:calcite-biotite-quartz- plagioclase-K-feldspar.Deformation phase of felsic mylonite in the Funiushan tectonic belt changes from east to west, followed by two-feldspar deformation phase, quartz-plagioclase deformation phase, quartz deformation phase.(4) The environment of deformation in the Funiushan tectonic belt.1) metamorphic faciesMineral assemblages suggested that the metamorphic phase in the east is lower amphibolite phase and to the west it gradually transformed into high greenschist phase and low greenschist. From east to west, the condition of metamorphic-deformation became lower.2) the temperature of metamorphism and deformationThrough calculations and analyze with the methods including metamorphic phase, recrystallization types of quartz, inclusions’temperature in the quartz veins, the fractal dimension of dynamically recrystallized quartz in mylonite, fabric analysis of quartz, geothermometer of plagioclase and hornblende, and so on, we realize that the formation temperature of Funiushan tectonic belt is in medium-high temperature condition, and it higher in the east than in the west. The formation temperature of Luoluan fault is300-550℃, and the Waqiao fault belt is500-550℃.3) pressure and strain condition①mylonite dynamically recrystallized quartz fractal dimension calculation shows the different stress of Luoluan fault belt is0.32～0.41GPa, strain rate is3.92917E-11～3.17713E-16; the different stress of Waqiao fault belt is32.417～33.524MPa, strain rate is3.45769E-142.14687E-16. Two faults are expressed as differential stress increases gradually from east to west trend, belong to medium strain rate conditions.②syntectonic quartz vein quartz dislocations characterized show the Luoluan fault belt has the characteristics of compression first and later superimposed strong shearing; Waqiao fault belt suffered intense compression first, then supplementary weak shearing. According to the dislocation density calculated differential stress is:0.71～0.87Gpa, strain rate is:2.34445E-11～4.05872E-11.③the pressure calculated by the hornblende aluminum geobarometer shows the pressure of Luoluan fault belt and the Waqiao fault belt are0.75-0.95Gpa and0.60-0.85Gpa respectively.④using Massonne Phengite geobarometer calculated the Funiushan tectonic zone pressure is0.27-0.87GPa.Through the different methods calculated the rock metamorphism and deformation temperature and pressure conditions are basically the same of Funiushan tectonic belt, all those results shown the conditions of temperature and pressure is higher in east than the west. They alse suggest the east part uplifts strong, and the west part uplifts weak.(5) the dynamics characteristic of the Funiushan tectonic beltThe finite strain analysis of Funiushan tectonic belt displayed a strong simple shear in the Luoluan fault belt, but pure shear in the Waqiao fault belt. The Fulin coefficient(K) of Luoluan fault is1.68-15.13, strain ellipsoid is cigar-shaped, reflecting shearing extension feature primarily and west part is stronger than east part. Vorticity analysis(WK>0.75) displayed that the Luoluan fault belt possessed dominating simple shear.The Fulin coefficient(K) of the Waqiao fault belt is between0and, strain ellipsoid is flattened ellipsoid-shaped, reflecting flatten strain. Vorticity analysis (WK<0.75) showed Waqiao fault belt possessed dominating pure shear.(6) chronological characteristics of the Funiushan tectonic beltESR dating of syntectonic quartz veins displayed the shear deformation time of the Luoluan and Waqiao fault belt are372.9±30.0Ma and275.0±20.0Ma respectively. The measured218.0±20.0Ma,120Ma,71.6±7.0Ma age reflect the Yangtze and North China plates converged in late Indosinian and Yanshanian structure thermal event also had some impact on the North Qinling tectonic belt. Chronology shows that the evolution from north to south is successive in each northern part of Qinling tectonic belt. Ages from north to south are gradually new.(7) the correspondence between metamorphic facies deformation phase of the Funiushan tectonic beltThe metamorphism phase and deformation phase have obvious correspondence relationships, for example, from the east to the west,felsic mylonite’s deformation phase gradually changed from two-feldspar deformation phase to quartz-plagioclase deformation phase and then to the quartz deformation phase,which corresponds to the changes from the middle crust to the upper crust.Mineral assemblages suggested that the metamorphic phase in the east is lower amphibolite phase and to the west it gradually transformed into high greenschist phase and low greenschist.From east to west, the condition of metamorphic-deformation became lower.In general, the article take the Luoluan fault belt, Waqiao fault belt and Kuanping group, north margin of Erlangping group, Luanchuan slice, Taowan slice, south margin of Shirenshan, which possess particular tectonism in Funiu mountain tectonic belt, as point cuts. The deformation and tectonic patterns in southern margin of North China plate is ascertained and its lithofacies belt, the direction and the way it functions of principal compressive stress is restored by analyzing details of deformation and the features of strain of Funiu mountain tectonic zone. Through studies of characteristics of metamorphism, formation mode, mechanism and environment, the effect in deformation-metamorphism on surrounding rock by fault belts is analysised and coupling between metamorphic facies and deformation facies is established. Stress, state of strain and evolution of Qinling orogenic belt and large shear zone during orogentic process are further recognized by studies of metamorphism and deformation in tectonic minerals and formation mode.Based on research contents and methods in mineralogy, petrology and micro-tectonics, plate movement and metamorphic-deformation patterns of continental margin is set up and it offers reliable and refined supporting datas and materials for exploring structure, evolution and kinetics problems of continental orogenic belt.