矿床地球化学国家重点实验室知识库

As the special result of lithospheiic extension, nowadays, the invistigation on geology and geochemistry of the mafic dykes (e.g., lamprophyre, dolerite, diabase porphyrite, etc.) has been given special attention. The mafic dykes mainly distribute in America, Canada, Brazil, Australian and China. In addition, the ages of these dykes are between 2.4Ga and 1.0Ga. At present, the Mesozoic and Cenozoic mafic in China were found in North China Craton (NCC), southern China, Tibet and Tarim basin. The studied mafic dykes came from Shanxi Province, northern NCC. Herein, we report U-Pb zircon ages, whole-rock geochemistry, and Sr-Nd isotopic data for representative samples of these dykes. Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) U-Pb analysis of zircons yielded a consistent Late Carboniferous (293. 4 +/- 1. 7Ma) age for one sample of the rocks analyzed during this study. Dolerites within the study area have a narrow range of compositions (SiO2 = 50. 78% similar to 51. 35%, TiO2 = 2. 16% similar to 2. 32%, Al2O3 = 14. 53% similar to 15. 08%, Fe2O3 = 12. 42% similar to 12. 66%, MnO = 0. 13% similar to 0. 16%, MgO = 5. 14% similar to 5. 35%, CaO = 7. 93% 8. 25%, Na2O =3.52% 3. 78%, K2O =1.01% similar to 1. 14%, and P2O5 =0.24% similar to 0. 36%). The dolerites are enriched in light rare earth elements (LREE), large ion lithophile elements (LILE; i.e., Ba, K, and Sr) and high field strength elements (Nb, Ta, and Zr), and depleted in Th, Pb, Nb, P, and Ti. These mafic dykes have relatively uniform (Sr-87/Sr-86)(i) values (0. 70422 similar to 0. 70423), positive epsilon(Nd) (t) values (5. 8 similar to 6. 1), and invariant neodymium model ages (t(DM1) = 0. 67 similar to 0. 72Ga, tp, 2 = 0. 57 similar to 0. 59Ga). These data suggest that these dykes formed from magmas derived from partial melting of a depleted asthenospheric mantle source that fractionated olivine, pyroxene, and Ti-bearing phases without assimilating significant amounts of crustal material. In summary, the generation and emplacement of mafic magmas in Shanxi Province, northern NCC can be attributed to post-subduction and collision (e. g., Paleo-Asian Ocean, Mongolia China Block) lithosphere extension.