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Based on the study of LA-ICP-MS zircon U-Pb geochronology and whole-rock geochemistry for the Luojiazhuang diorite porphyries in Menying,western Shandong,the analyzed zircons exhibit oscillatory growth zoning in the cathodoluminescence images and have high Th / U ratios( 0. 15--1. 53),indicating a magmatic origin. In addition,most of the zircons have narrow metamorphic edges,suggesting that late metamorphic events may exist. The youngest group of magmatic zircon207 Pb /206 Pb ages ranging from 2 384 Ma to 2234 Ma,yielding a weighted mean age of 2353 ± 14 Ma,which represents the forming age of the diorite porphyries,as the Early Paleoproterozoic. Geochemically,the samples are characterized by low SiO_2( 54. 54% and 55. 47%),high MgO( 5. 22% and 5. 49%) and Mg~#values( 58 and 59). Moreover,they show enrichment of light rare earth elements and large ion lithophile elements( Rb,Ba and K),depletion of heavy rare earth elements and high field strength elements( Nb,Ta,Zr and Hf),positive anomaly of Pb,and negative anomaly of Ti. The fact implies that the Luojiazhuang diorite porphyries might derive from partial melting of enriched lithospheric mantle and mixed with an amount of continental crust material. In summary,they may form in the compression tectonic setting that stretching along the east-west direction at the North China Craton in the Early Paleoproterozoic.
Based on the study of LA-ICP-MS zircon U-Pb geochronology and whole-rock geochemistry for the Luojiazhuang diorite porphyries in Menying, western Shandong, the analyzed zircons exhibit oscillatory growth zoning in the cathodoluminescence images and have high Th / U ratios ( 0. 15--1. 53), indicating a magmatic origin. In addition, most of the zircons have narrow metamorphic edges, suggesting that late metamorphic events may exist. The youngest group of magmatic zircon 207 Pb / 206 Pb ages ranging from 2 384 Ma to 2234 Ma, yielding a weighted mean age of 2353 ± 14 Ma, which represents the forming age of the diorite porphyries, as the Early Paleoproterozoic. Geochemically, the samples are characterized by low SiO 2 (54.54% and 55.47% ), high MgO (5.22% and 5.49%) and Mg ~ # values (58 and 59). Moreover, they show enrichment of light rare earth elements and large ion lithophile elements (Rb, Ba and K) of heavy rare earth elements and high field strength elements (Nb, Ta, Zr and Hf), positive ano maly of Pb, and negative anomaly of Ti. The fact implies that the Luojiazhuang diorite porphyries might derive from partial melting of enriched lithospheric mantle and mixed with an amount of continental crust material. In summary, they may form in the compression tectonic setting that stretching along the east-west direction at the North China Craton in the Early Paleoproterozoic.