Petrology And Chronology Of Eclogite From The Qianliyan Island In The Yellow Sea And It’s Geological Significance

The Dabie-Sulu UHP metamorphic belt is the result of subduction between the North China plate and the south China plate ,which is the world’s largest ultrahigh pressure metamorphic belt. Geologists in China have obtained lots of achievements of Sulu-Dabie UHP.Qiliyan uplift zone of South Yellow Sea belongs to Dabie-Sulu UHP belt. Qianliyan island is the exposed area of Qianliyan uplift zone,which is an important part of the Sulu-Dabie Orogenic belt .Qianliyan island is the important clues that dabie-sulu orogenic belt extends to the Korean peninsula.because of its special geographical position..The paper made the following main conclusions:(1) Petrological characteristics: mineral generation can be divided into:The first generation of The mineral composition and the Mineral inclusions of Omphacite, rutile and epidote in the garnet; The second generation of The mineral composition: garnet, Omphacite, phengite and rutile. The third generation of The mineral composition:Diopside,sodium feldspar, hornblende, quartz.The forth generation of the mineral composition:Chlorite, quartz, biotite. The first generation of the mineral composition indicates the sub- stage of deep subduction;the second the stage of High-pressure eclogite facies;the third the stage of amphibolite facies; the forth the stage of The green schist facies.(2) Mineralogy characteristics: Garnet generally rich in Alm, poor in Spe components, the components in the five components, respectively:Alm (42.07～52.72%), Spe (0.57～1.21), And (0.61～3.47), Pyr(18.22～29.82), Gro (21.19～28.26) . According to the garnet composition profile, From the core to the edge XMg Increased first and then decreased .while XFe decreased subtly in general, XCa increased gradually. Clinopyroxene mainly consist of Omphacite and diopside.Jadeite components of Omphacite inclusions is 35%;Omphacite predominating in the matrix is 40%-45%; Omphacite in the symplektite is 10-14%.hornblende is mainly Sodium and calcium and calcium.Hornblende that exist in the matrix,in the formal of porphyroblast ,is pargasite.others exists in the symplektite is Magnesium amphibole.Actinolite mainly exist in the fracture. Phengite exist only in the matrix,which has no inclusions In the internal.According to the BSE,from the core to the content edge, content of Si4+ of phengite increased subtly.(3) By using Ravna(2000) Grt-Cpx geothermobarometer,and Waters and Martin(1993 )Grt-Omp-Phe geologic barometer, we have got the peak temperature and pressure of eclogite,namely, 755-759℃; 2.69-2.76GPa, and the temperature-pressure condition of Amphibolite facies,namely, 580-605℃, 1.1-1.3Gpa.(4) Chronology: The weighted average ages of inherited zircon indicates that the original rock of eclogite from the Qianliyan island Formed in the neoproterozoic. While Weighted average age of metamorphic zircon indicates that metamorphic age of eclogite is Triassic.