Zircon U-Pb Chronology And Geochemistry Of Mesozoic Intrusive Rocks In Southern Liaoning And Jilin Provinces: Constraints On The Spatial-Temporal Extent Of The North China Craton Destruction

LA-ICP MS zircon U-Pb ages, major- and trace- element, and Sr-Nd isotopic data of the Mesozoic intrusions from southern Liaoning and Jilin provinces have been determined to constrain the natures of magma sources and its spatial variation as well as their tectonic settings. These chronological and geochemical data, together with regional tectonic analysis, provide constraints on the initial time, spatial extent, and dynamic mechanism of the North China Craton destruction. Main achievements are as follows:1. The Mayihe pluton from southern Jilin province consists mainly of gabbro-diorite, granidiorite and monzogranite and have ages of 224- 226 Ma dated by the LA-ICP MS zircon U-Pb method. The Early Cretaceous intrusive rocks from the southern Liaoning and Jilin Provinces are composed mainly of mafic-ultramafic intrusive rocks and granitoids. The dating results for twelve samples range from 137 to 119Ma.2. The gabbro-diorites from the Mayihe pluton have low SiO2 contents and high MgO contents, and are enriched in large ion lithophile elements (LILEs) and light rare earth elements (LREEs), depleted in high field strength elements (HFSEs) and heavy rare earth elements (HREEs). Their initial 87Sr/86Sr ratios andεNd(t) values are 0.7037 and +3.45~ +3.82, respectively. Their TDM1 modal ages vary from 726 to 772Ma. The granitoids from Mayihe pluton have high SiO2 contents and low MgO contents, and belong to metaluminous to weakly peraluminous I-type granitoids. Their initial 87Sr/86Sr ratios andεNd(t) values range from 0.7053 to 0.7058 and from -0.73 to -3.40, respectively.Their TDM1 modal ages are 990 - 1083Ma.3. The Late Triassic intrusive rocks from southern Liaoning and Jilin provinces, together with the Late Triassic intrusive rocks from southern Liaoning (210~213Ma, zircon LA-ICP-MS U-Pb dating method),are composed mainly of mafic rocks and granitoids. The mafic rocks include shoshonitic and tholeiitic rocks, whereas granitoids consist mainly of granodiorite, monzogranite, and minor quartz diorite. The shoshonitic rocks have low SiO2 contents (~ 49.6 wt %) and high Mg# (Mg#>57) and are characterized by enrichment in LILEs, LREEs, and depletion in HFSEs such as Nb, Ta, Zr, Hf and Ti. TheirεNd(t) values (-13.2 to -13.4) andεHf(t) values (-11.0 to -11.5) imply that the primary magma could be derived from partial melting of an enriched lithosphere mantle. The granitoids with high SiO2 and low MgO contents have initial 87Sr/86Sr ratios of 0.7095 ~ 0.7112,εNd(t) values of -10 ~ -15.9, andεHf(t) values of -12.0 ~ -13.9. Their T DM1 modal ages range from 999 to 1558Ma.4. The Early Craterous mafic- ultramafic intrusive rocks from southern Liaoning and Jilin provinces are characterized by low SiO2, high MgO, enrichment in LREEs and LILEs, as well as depletion in HREEs and HFSEs. Their initial 87Sr/86Sr ratios andεNd(t) values range from 0.7056 to 0.7112 and from -6.56 to -20.1, respectively. Their initial 87Sr/86Sr ratios and TDM1 values decrease whereasεNd(t) values increase from southwest to northeast. The Early Craterous granitoids from southern Jilin province have SiO2 = 53.7~ 76.6wt%) and Mg# = 6.09~ 54.37. Chemically, they belong to metaluminous to weakly peraluminous I-type granite and are enriched in LREEs and LILEs and depleted in HREEs and HFSEs. A few highly fractionated granitoids are characterized by depletion in Ba and Sr. Their initial 87Sr/86Sr ratios andεNd(t) values are between 0.7052 and 0.7107, and between -1.93 and -13.9, respectively. Their TDM1 modal ages vary from 994 to 2002Ma. The initial 87Sr/86Sr ratios and TDM1 modal ages for these granitoids decrease whileεNd(t) values increase from southwest to northeast.5. The bimodal rock association for the late Triassic intrusions in the southern Liaoning and Jilin provinces suggests that they could form under an extensional environment. The Sr-Nd compositions of the gabbro-diorite in the Mayihe pluton imply that their primary magma should be derived from partial melting of a depleted lithosphere mantle, which is consistent with the juvenile depleted lithosphere mantle beneath the Xing'an-Mengolia (Xing-Meng) Orogenic belt. However, it is different from an enriched lithosphere mantle beneath southern Liaoning province. The Late Triassic granitoids from southern Jilin province could be originated from partial melting of a juvenile lower crust, which is concord with its tectonic position adjacent to the Xing-Meng orogenic belt. In contrast, the Late Triassic granitoids from southern Liaoning could be mainly derived from partial melting of an ancient lower crust.6. The late Triassic igneous rocks from southern Liaoning and southern Jilin provinces, together with the Late Triassic volcanic rocks in the southern Jilin and Jiazishan syenite in eastern Shandong, make up a late Triassic igneous rocks belt in the eastern NCC oriented in SW-NE direction. This igneous rock belt maily consists of a bimodal rock association, implying that they could form under an extensional setting. Combined with the occurrence of the late Triassic metamorphic zircons and the Neoproterozoic magmatic zircon in the Mesozoic igneous rocks from southern Liaoning and Jilin provinces, we conclude that the late Triassic magmatism could form under an post-collsional extensional setting of the Yangtze Craton and the NCC.7. The geochemical data of the early Cretaceous mafic-ultramafic rocks in the southern Liaoning and Jilin provinces indicate that their primary magmas could be originated from partial melting of the EMII-like lithosphere mantle. Their Sr-Nd isotopic compositions reveal that an enrichment extent gradually decreases from southern Liaoning to southern Jilin provinces. The early Cretaceous lithospheric mantle in southern Liaoning is geochemically similar to that in western Shandong. The EMII-like lithosphere mantle can be related to modification of the delaminated eclogite- or garnet pyroxenite-derived melt. The early Cretaceous granitoids could be mainly derived from partial melting of the lower continental crust, including an ancient and a juvenile crust materials. However, their spatial variations of Sr-Nd isotopic compositions reveal that the proportion of the juvenile crust increase in the magma sources from southwest to northeast. Combined with regional tectonics and Paleo-pacific plate subduction history, it is proposed that the Early Cretaceous magmatism in the eastern NCC could form under an intra-continental extensional environment resulted from the subduction of the Paleo-pacific plate.8. Together with regional tectonic evolution and new research achievements on igneous rocks, the above mentioned lines of evidence imply that the NCC destruction initiate in the late Triassic, and that the destruction mechanism should be delamination resulted from the northwestward subduction and collision of the Yangtze and the North China Cratons. The early Craterous is an important period of the NCC destruction resulted from subduction of the Paleo-Pacific plate beneath the Eurasian continent. The thermal-chemical erosion could be a dominant mechanism to result in the NCC destruction in the early Craterous. The spatial extent of the NCC destruction should include southern Liaoning and minor Jilin provinces.