Late Mesozoic basalts from eastern Zhejiang Sr-Nd-Pb isotope composition of the timing

Title: Late Mesozoic basalts from eastern Zhejiang Sr-Nd-Pb isotope composition of the timing
　　Author: Cui Yurong
　　Degree awarded: China University of Science and Technology
　　Keywords: Late Mesozoic basalt;; under the rocks;; on the rocks;; mantle geochemistry;; eastern Zhejiang
　　Summary:
　　In this paper, eastern Zhejiang Province late Mesozoic basalt in detail zircon geochronology and geochemical studies, attempts to explore the eastern Zhejiang Late Mesozoic lithospheric mantle geochemical evolution of the nature of the relationship Neodymium Magnets over time. SHRIMP U-Pb dating results show that the majority of basaltic rocks under the zircon gives ~ (206) Pb / ~ (238) U age of 120 ± 1 Ma, Th / U ratio range of 0.65 to 2.44, indicating that the zirconium stone for the magmatic, this age represents the study should be the next era of the formation of basalt rocks. Basalt rocks on zircons from the youngest to obtain ~ (206) Pb / ~ (238) U age of 104 ± 2 Ma, Th / U ranges from 0.57 to 3.03, indicating that the zircon is magmatic, this Age may be determined on behalf of the Department of basalt rock formation age. Up and down the rocks basalt, age and previous studies, the results were the stratigraphic range of the corresponding line, they form a significant age difference. Meanwhile, the measurement results also show that, under the basalt rocks in the relative age distribution of zircon is relatively concentrated, the residue of ancient zircon is relatively low, indicating that the formation of basalt, only a small amount of crustal contamination component. On the rocks basalt magmatic content of less, the majority of zircons, and the age of many kinds of distribution larger, covering almost all the South China Block igneous activity times, which indicates that the formation of the basalt may have different source of contamination of continental crust, this crust is likely to contain detrital zircons from different periods of sedimentary rocks / material.
　　In the study, based on the chronology, the paper up and down the eastern Zhejiang Province late Mesozoic basaltic rocks are characterized by elemental geochemistry and Sr-Nd-Pb isotope study. Late Mesozoic basalts in eastern Zhejiang major elements show some range, with alkali-rich, rich in Al and other features. Roof and under rocks Qingtian samples show Ba, Pb, Sr and other large ion lithophile elements (LILE) enrichment of Nb, Ta, Zr and Hf high field strength elements (HFSE) loss characteristics of rare earth elements have shown REE (LREE) enrichment and different degrees of negative Eu anomalies. On the rock Jihua Tan, Xuan Tan, the Xinchang and Yongjia trace elements and rare earth elements such as frames Hill showing the nature and under the rocks are similar, but the Department of Wuyi rock samples showed no Ta, Nb, Hf, Zr, etc. positive / negative anomalies.
　　Element and isotopic discrimination results show that the majority of the sample up and down the rocks by crustal contamination is lower, so the elements and isotopes can be used to trace the nature of the mantle source region. However, on the rocks Xuantan to individual samples in the process of magma rising by a significant crustal material mixed http://www.everbeenmagnet.com/en/products/110-sintered-neodymium-magnets with dye, does not accurately reflect the source of information. Therefore, Xuantan to sample the εNd (T) is the highest value of the subject for discussion. Rocks under the initial isotopic composition of basalt range ISr = 0.70850 ~ 0.70897, εNd (T) = -5.6 ~ -4.1, (~ (206) Pb / ~ (204) Pb) i = 18.21 ~ 18.38, (207Pb / ~ (204) Pb) i = 15.55 ~ 15.58, (~ (208) Pb / ~ (204) Pb) i = 38.26 ~ 38.49. Basalt rocks on the initial isotopic composition ISr = 0.70533 ~ 0.70936, εNd (T) =- 7.1 ~ 3.3, (~ (206) Pb / ~ (204) Pb) i = 17.23 ~ 18.40, (207Pb / ~ ( 204) Pb) i = 15.46 ~ 15.62, (~ (208) Pb / ~ (204) Pb) i = 36.91 ~ 38.62, and a lot more similar to the findings of scholars. One flower Tan, Xuan Tan, the Xinchang and Yongjia sample frame mountain ISr = 0.70734 ~ 0.70936, εNd (T) = -7.1 ~ -2.1, (~ (206) Pb / ~ (204) Pb) i = 18.01 ~ 18.40, (207Pb / ~ (204) Pb) i = 15.54 ~ 15.62, (~ (208) Pb / ~ (204) Pb) i = 37.99 ~ 38.62; Wuyi and Jinhua and Quzhou samples ISr = 0.70533 ~ 0.70589, εNd ( T) = 0.4 ~ 3.3, (~ (206) Pb / ~ (204) Pb) i = 17.23 ~ 18.11, (207Pb / ~ (204) Pb) i = 15.46 ~ 15.53, (~ (208) Pb / ~ ( 204) Pb) i = 36.91 ~ 38.43. Cenozoic basalts ISr is 0.70382, εNd (T) of 7.6, significantly higher than the Mesozoic basalt, showing a loss of features.
　　Late Mesozoic basalts of eastern Zhejiang by major, trace and rare earth element and isotope analysis of the discussion, we can see the material up and down the basalt source rocks have obvious differences, of which there are basalt rocks under lithospheric mantle, crust and altered oceanic crust subducted material contribution, and on the rocks in the lithospheric mantle, or may be similar in nature under rocks basalt lithosphere, asthenosphere mantle, crust and other contributions. Cenozoic basalts clearly have depleted mantle characteristics. Late Mesozoic lithospheric Zhedong the dynamic process of evolution may be related to the Pacific plate subduction or delamination of the lower crust, need more specific discussion of the petrology and / or mantle xenoliths from the supplementary information.
　　Degree Year: 2010