Petrogenesis of Paleoproterozoic diorite porphyries in Luojiazhuang,western Shandong:constraints from LA-ICP-MS zircon U-Pb geochronology and geochemistry |
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| Institution: | 1. College ofEarth Sciences,Jilin University,Changchun 130061,China;2. Research Center ofPalaeontology&Stratigraphy,Jilin University,Changchun 130026,China |
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| Abstract: | 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 (0.1 5-1 .53),indicating a magmatic ori-gin.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 2 234 Ma,yiel-ding a weighted mean age of 2 353 ±1 4 Ma,which represents the forming age of the diorite porphyries,as the Early Paleoproterozoic.Geochemically,the samples are characterized by low SiO2 (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 Paleoprotero-zoic. |
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| Keywords: | Paleoproterozoic diorite porphyry geochronology geochemistry western Shandong |
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