Petrological Characteristics And Geologic Significance Of The Kengbei Complex Rocks In Dongshan County,Fujian Province

The Changle-Nan'ao metamorphism zone,which is located in coastal areas of Fujian,China.And it is different from many inland metamorphic terranes.Previous studies have shown that the Changle-Nan'ao metamorphic belt is a large Mesozoic shear zone.The tectonic zone of southern section of the Dongshan Kengbei complex rocks is located on between the deep deterioration of the eastern tetonic sub-band and the western structure branchs.In the previous work on the basis of the complex rocks in field geology,mineralogy,geochemistry,electron microprobe analysis and geochronology of zircon U-Pb systeman alysis methods,Kengbei complex rocks characteristics mineralogical characteristics and tectonic features.Kengbei complex rocks can be divided into four intrusive stages,the first stage is the Late Jurassic of intrusive rocks(metamorphic age of 151.0±0.5Ma),the lithology is a completely degenerate deformed adamellite and granodiorite;A second stage is the intrusive rocks of the Late Jurassic-Early Cretaceousthe of intrusive rocks(metamorphic age of 142.8±0.5 Ma),the lithology is monzogranitesynogranite and granodiorite;the third stages is the Early Cretaceousthe of intrusive rocks(metamorphic age of 139.7± 1.2 Ma),the lithology is part of the deformed adamellite and granodiorite;the fourth stages is not occur to metamophism and deformation of Early Cretaceous of intrusive rocks(diagenetic age of 106.1±0.9 Ma).The geochemical characteristics show that the rocks is I-type granite with high potassium aluminum and peraluminous calc-alkaline.Chondrite-normalized diagrams show that the curve shape is similar,overall is a right-wing type,REE has a strong fractionation,heavy REE relatively flat.With a strong Eu anomaly,without Ce anomaly,indicating that magma occurs fractional crystallization,and plagioclase and hornblende residue in the source region;Ba?Nb?Ta?Sr and Ti shows a clear negative anomaly,imply that magma originated from crust.Rb content higher than the Ba content,indicates that the source area may have potassium feldspar residual.Nb-Ta negative anomalies related to the subduction zone geochemical characteristics,P negative anomalies indicating that the magma originated from depleted mantle or crust.Spider diagram and REE are basically identical,reflecting the comagmatic evolution characteristics.Temperature and pressure estimates show that the Kengbei complex rocks of partial meltingtemperature of 546?590?,the formation of pressure for 0.40-0.72Gpa,The research of the genetic mineralogy of Turquoise amphiboles shows that,the rock of Kengbei metamorphic grade mainly corresponds to low amphiboles facie-high green schist facie.Mineral composition and geochemical studies have shown that Kengbei complex rocks biotite MgO content between 2.43%to 7.9%,MF = 0.52?0.86,the ?Eu loss,indicating that Kengbei complex rocks is the shell-the crust and mantle-type granite.According to the tectonic discrimination diagrams,the Late Jurassic Cretaceous,which magma belongs to the crust-mantle mixed type(?-type),were formed during changing of tectonic system;The late Jurassic-Early Cretaceous intrusive rocks of magma belongs to the mantle-shell mixedsource(the I-S-type),were formed to plate collision(subduction role)related to the syn-collisionalgranite;as early Cretaceous intrusive rocks,which magma belongs to the shell-mantle mixing source(?-type),the case of tectonic regime from compression to tensionconversion period mantle-crust-derived granite.Kengbei complex rocks granite is a linear distribution,and most of the granite is a product of the same tectonic.Therefore,the granite is the result of the combined effects of mantle-derived fluid,thermal anomalies and stress.