Geochemistry, Age And Petrogenesis Of Granitic Mylonite In Zhalantun Haduohe Area Of The Northern Greater Hinggan Mountains

Haduohe area located in the north greater hinggan mountains,in the Erlian-heihesuture zone which between the Xing’an block and Songnen block.At present, exist thefollowing three questions about the granitic mylonite in Haduohe area.First, thegranitic mylonite in Haduohe area was divided into Xinsheng group(C3-P1)x by thegeological map of1:200000Zhalaiteqi (1972), but after a field geologicalinvestigation and petrographic analysis, the rock combination is mainly a set ofmetamorphic deformation granitic rocks. Second, the present reseach on thechronology and rock geochemistry evidence of granitic mylonite in Haduohe area isin lack. Third, whether the magmatic origin and metamorphic deformation of thegranitic mylonite in Haduohe area was affected by the Erlian-heihe suture zone. Basedon the above three points,this paper study on the granitic mylonite in Haduohe areafrom the aspects of lithology, chronology and rock geochemical, find out the rockcombination and fabric characteristics, protolith formation age, analyzes the rockgeochemical characteristics, and discuss the protolith types and the tectonicbackground, also to explore the petrogenesis and dynamic metamorphism deformationage.1. The rock combination of the granitic mylonite in Haduohe areaThe petrographical facies studies indicate that the granitic mylonite in Haduohearea has mylonitic texture, augen structure or gneissic structure,and containing a fewnew metamorphic minerals,just as biotite, muscovite and Garnet. Confirm the rockcombination is fine grained biotite monzonitic granitic mylonite, fine grained biotitegranitic mylonite, fine grained garnet mica granitic mylonite, fine grained epidotebiotite granitic mylonite, fine grained biotite hornblende monzonitic granitic mylonite,fine grained epidote monzonitic granitic mylonite, fine grained actynolin biotitegranitic mylonite and Fine grained alkali granitic mylonite. 2. The geochemical characteristics of the granitic mylonite in Haduohe areaThe granitic mylonite in Haduohe area has66.4%~77.0%SiO2,and12.12%~16%Al2O3,low Mg[w(MgO)=0.2%~1.89%],δ=1.8~3.12(δ<3.3)，A/CNK=0.93~1.093(<1.1). The total amount of rare earth elements is not high (ΣREE=57.17×10-6~144.37×10-6), rich light rare earth elements and depleted heavy ones, and areenriched in LILE, such as Rb,Ba,U, K, etc., depleted in HFSE, such as Ta,Nb, P, Ti,etc.,and shows a weak negative Eu anomalies (δEu=0.33~1.12). Integrated studyindicates that it’s metaluminous to peraluminuous rocks,and typical high-Kcalc-alkaline I type granite. the nature of original rocks is orthometamorphite.3. The age of the protolith of the granitic mylonite in Haduohe areaZircon U-Pb dating shows that the weighted average age of the granitic mylonitein Haduohe area is303.7±2.5Ma、305.8±1.9Ma、319.1±2.1Ma and320.3±1.9Ma,shows the magma formation age is late carboniferous, and it can be characterized bytwo periods, the first period is around320Ma, the representative rock is fine grainedbiotite granitic mylonite and fine garnet mica granitic mylonite, the second period isaround303Ma, the representative rock is fine grained biotite monzonitic graniticmylonite.4. The causes of the granitic mylonite in Haduohe areaThe granitic mylonite in Haduohe area were formed in the post-collisionenvironment of Xing’an block and Songnen block in Late Carboniferous, and sufferedrelatively strong ductile brittle metamorphism and deformation in Late Early Permianby the post-collision of Xing’an block and Songnen block.