| The subcontinental lithospheric mantle (SCLM)is an important part of lithsophere, and serves as a bridge that connects the asthenosphere and crust. Recently , understanding of the formation and evolution is largely depended on the recognization of the lithospheric mantle. Researchers believe the North China craton had undergone the lithosphere thinning, based on the studies of the Paleozoic diamond-bearing kimberlite from Fuxian and Mengyin and the mantle xenoliths in Cenozoic basalt. However, whether the lithospheric thinning also happened in the northeastern China, is crucial in constraining the temperal, spatial range, as well as the mechanism of lithospheric thinning.Although exensively studied using mantle xenoliths in volcanic rocks by many Chinese and foreign scientists, treliable method to determine the nature and age of the lithospheric mantle is still lack since the high equilibrium tenperature which excesse the closure temperature of the isotopic systems commonly used. Forthnately, the newly developed Re-Os isotope technique provides a powerful method to determine the nature and age of the lithospheric mantle because of the unique geochemical behavior of the Re-Os system. Therefore this work takes the advantage of the Re-Os isotopic dating technique, studying on the Nuomin and Keluo peridotite xenoliths, combined with the studies of the granite in the area, expecting to provide more new information about the age and nature of the lithospheric mantle. And then investigates the evolution of the lithospheric mantle in Northeastern China, on the basis of the coupling relationship of the SCLM and crust. The Nuomin and Keluo volcano groups locate within the Xing'an-Mongolian Orogenic Belt, and their eruption age is Cenozoic. The peridotite xinoliths collected from Sifangshan of Nuomin, are relatively big and olivary. However, the xinoliths collected from Dayizishan of Keluo are fresh but small. Detailed petrological and mineralogical studies of he xenoliths indicate that the main rock types in Nuomin are harzburgite and spinel lherzolite (clinopyroxene-poor), while that in Keluo are spinel lherzolite and harzburgite. Their mineral association and structural features shows that they are A-type xenoliths, typically samples from lithospheric mantle. According to the results of mineral thermometer, the equilibrium temperature of xenoliths in Nuomin is higher than that in Keluo, which suggests that the former originated deeper than the latter. Different from the Nuomin, the lithospheric mantle of Keluo is stratigraphically layered: the lower part is composed of refractory harzburgite, while the upper part of fertile lherzolite.The major geochemical analyses indicate that both peridotites are depleted in Al2O3 and CaO, and enriched in MgO. At the diagram of major elements, both the xenolishs had the trends of oceanic evolution, like the peridotite xenoliths in Shuangliao and Dashihe. The trace elements and REE suggest that they were metasomtized by various degrees by multi-melts and/or liquids after formation. Sr-Nd-Hf isotopes of the clinopyroxenes from both peridotites are similar and isotopically depleted (ISr<0.7046,εNd(t)>0,εH(ft)>0), and not varying with the lithology.By component comparison, it is concluded that the subcontinental lithospheric mantle of the area is relatively young, but this method can not give out the absolute age, and is not confirm since component is also the function of degree of partial melting. However, it has recently been shown that the Re-Os isotopic technique can be considered as the most reliable method to date the SCLM. The Re-Os dating indicate that the SCLM in Nuomin formed in Paleo-Mesoproterozoic, and that of Keluo formed in Paleoproterozoic. And there was no evidence to suggest the existence of an Anchean cratonic lithospheric mantle.In dorder to constrain the age of the crust in the same area, the granites in Longzhen was also studied. The petrology and geochemistry of the monzonitic granites and granodiorites indicate that they belong to high-K calc-alkaline I-type granite. The zircon U-Pb isotopic age of the plutons indicate that they were formed at 320~310Ma and at about 170Ma, that is, it contains two episodes of magmatism/emplacements, Hercynian and Yanshanian. On the contrary, the granites of different time possess similar Lu-Hf isotope features of highεH(ft)value(6.76~8.80), and the corresponding Hf model ages(TDM2) of 511~958Ma. The isotopic data indicate that the granitic magma mainly originated from the juvenile Neoproterozoic- Phanerozoic accreted crustal materials.In the northeastern China, the crust accreted mainly in the Neoproterozoic, on the concern of the Sr-Nd and Lu-Hf isotopic characteristics of the Phanerozoic granites. While the Os isotope reveales that the SCLM beneathe the juvenile crust was formed during Paleo-Mesoproterozoic, is older than the overlying continental crust. Geochronological data clearly manifest the decoupling between the crust and SCLM, that is, the destruction of the lithospheric mantle.According to the definition of the lithospheric mantle, the SCLM and crust should form at the same time. So the SCLM in the northeastern China should be Neoproterozoic-Phanerozoic. Contrarily, the SCLM beneathe the juvenile crust is Paleo- to Meso-Proterozoic time. Why was that? The analysis indicates that the old SCLM is removed, but we have no idea to discuss the source and the dynamics for the limited datas.We proposed the the studied area had undergone the whole-scale lost of the lithospheric mantle, because there was not the SCLM coupling to the overlying crust. However, it is distinguishing from the North China Craton by the different lost part of the SCLM.Considering the tectonic history in this region, a lithospheric delamination madel is employed to explain the geodynamic processes. During the Neoproterozoic and Paleozoic time, the newly accreted crust formed the isolated Erguna, Xing'an and Songnen terrains; and the crust and the lithospheric mantle were coupling in age. After amalgamated as a composite block, they shifted to the Paleo-Asian tectonic domain and ultimately collided and amalgamated to the Siberia and North China Craton successively. At about 170Ma, the eastern China shifted to the Paleo-Pacific tectonic system and controlled by the subduction of the Pacific plate, and the lithosphere thickened at this period. By the time of Late Jurassic to Early Cretaceous, the thickness of lithosphere arrived at its climax, leading to the gravitational instablility, and ultimate delamination. The delamination caused the asthenospheric upwelling, even directly contacted with the lower crust; and the asthenospheric upwelling subsequently induced the voluminous magmatism in the northeastern China. In the Late Cretaceous and thereafter, the lithosphere began to grow. The Re-Os isotopic evidence indicates that all the SCLM of Neoproterozoic and Phenerozoic time were all lost into the asthenosphere, but the Paloe and Mesoproterozoic lithospheric mantle formed elsewhere accreted beneath the area instead. Then they were carried to the surface by the alkali-basaltic magma which originated from the asthenosphere in Cenozioc.
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