Mafic igneous rock, a widely distributed and typical mantle-derived rock, has become a major research source for revealing possible mechanisms for the chemical evolution of the mantle. Combined geological and geochemical studies have been carried out on the Mesozoic and Cenozoic mafic igneous rocks in western Shandong Province, determining the elemental and isotopic compositions of typical samples. Generally, the Mesozoic mafic igneous rocks have enriched lithophile rare earth element (LREE) and large ion lithophile element (LILE) concentrations, low high field strength element (HFSE) abundance, and display highly variable ISr ratios (0.70396-0.71247) and distinctly negative εNd (t) values (-9.20 to -21.21). Compared to the north of western Shandong Province, the Mesozoic mafic rocks in the south have higher total rare earth element (REE) contents (∑REE=325.52 × 10-6-555.75 × 10-6), higher LREE/HREE ratios (17.75-25.97), and higher LILE/HFSE ratios (e.g. La/Nb=6.37-13.85, Th/Nb=0.52-1.53). They also have more radiogenic Sr isotopic compositions, with ISr values of 0.70844-0.71247 and 0.70396-0.70598 respectively. Integrated elemental and isotopic tracing suggest that the Mesozoic mantle of western Shandong Province is generally characterized by the EMI component, which was probably formed by large-scale lithospheric delamination, whereas the mantle source in the south part has been superimposed by the influence of the deep subducted Yangtze continental materials, and thus displays the mixed features of EMI and EMII components. The geochemical characteristics of the Cenozoic basalts are similar to those of the oceanic basalts. It is likely that the rocks were derived from a depleted asthenosphere source but underwent metasomatism shortly before partial melting. From the Mesozoic to the Cenozoic, the nature of the mantle beneath the North China craton evolved from an enriched one to a depleted one. This chemical evolution most likely resulted from an asthenosphere upwelling, which was induced by large-scale lithospheric delamination and thus replaced the original lithospheric mantle with a newly created one.
|Number of pages||13|
|Journal||Diqiu Kexue - Zhongguo Dizhi Daxue Xuebao/Earth Science - Journal of China University of Geosciences|
|Publication status||Published - Nov 2005|
- Mafic igneous rock
- Mantle chemical evolution
- Source tracing
- Western Shandong Province