Metamorphic-deformation Process And Regional Structural Significance Of Migmatites In Southern Liaoning

Migmatites are formed by crustal deep melting,which not only has a certain genetic connection with the regional granite,but also has an indicator effect on the evolution of the orogenic belt.Southern Liaoning is located in the southern part of the Eastern Liaoning Peninsula.The Paleozoic crust rock system experienced crustal anatexis in Mesozoic,forming a wide range of migmatites and migmatite gneiss.This paper focuses on the study of regional structure,microstructure,petrography,tectonic chronology,geochemistry and other aspects of the migmatites in southern Liaoning,and discusses the development process of migmatites in southern Liaoning,the corresponding regional geological events,and the meaning in the evolution of the orogenic belt.The migmatites in southern Liaoning are mostly transformed into gneisses,with the NWW-SEE oriented regional gneisses.Several typical outcrop of migmatites with obvious leucosome,melanosome and mesosome developed in the core-edge area.After field observation,according to structural characteristics it is divided into banded migmatite,augen migmatite,dilation structural migmatites and flowage folded migmatites.The leucosome of migmatites enrich feldspar and quartz.Melanosome and mesosome are stroma enriched biotite and amphibole enrichment after melt extraction.Coarse-grained hornblende wrapped round feldspar,quartz and other minerals generally exist in melanosome and mesosome,indicating that the melting reaction of biotite is: Bt + Pl + Qtz + Fluid = Hbl + melt.Some microscopic characteristics show that the biotite has a straight boundary and a stable structure,and some rocks do not contain biotite,it indicates: Pl + Kfs + Qtz + Fluid = melt.The core department(Canchang)mainly develops metatexite migmatites with banded migmatite and augen migmatite.The results of hornblende-plagioclase temperature and pressure gauges are 729.1 ~ 744.6 ? and 4.50 ~ 5.21kbar;The edge department develops diatexite with flowage folded migmatites,dilation structural migmatites and banded migmatites.The results of hornblende-plagioclase temperature and pressure gauges are 814.6 ? and 3.74 kbar.Zircon chronological studies have shown that the migmatites in southern Liaoning were formed in the middle and late Jurassic(163 ± 5Ma),with magmatic zircon in the core area and metamorphic zircon in the edges area.Geochemical results show that leucosome and Jurassic granite have some genetic relationships that leucosome belongs to the low-potassium plaque series,the Jurassic granite belongs to the calc-alkaline series and high-potassium-calcium-alkaline series,and they all belong to Quasi aluminum-weak superaluminum.Migmatites in Longkou area are formed at 25 km.The temperature and pressure conditions are higher at 783~843? and 6.7~7.3kbar.In other areas,the leucosome migrate to 19 km depth to crystallize and form migmatites.The geothermal heating rate in the region is 32.7~37.6?/km,which corresponds to the tectonic setting of the extension and thinning of the lithosphere in the Late Jurassic(163-150Ma)and the upwelling of the asthenosphere.After melting,leucosome rich in Ca and depleted in HFSE are formed.In contrast,granitic magma is rich in K and HFSE elements.