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This paper presents new zircon U Pb ages and Hf isotope data, and whole-rock geochemical and Sr Nd isotopic data, for lamprophyres in the western Shandong area of China. These data provide new insights into the nature of the lithospheric mantle beneath the eastern North China Craton (NCC) during the Early Cretaceous. The lamprophyres are divided into low-Ti (TiO 2 < 1.1 wt%; Ti/Y < 270) and high-Ti (TiO 2 > 2 wt%; Ti/Y > 370) suites, where the Xiaya and Jingziyu minettes are defined as low-Ti lamprophyres and the Jingziyu pyroxene lamprophyres are defined as high-Ti lamprophyres. The igneous zircons yield weighted-mean ages of 126, 132, and 130 Ma for the low- and high-Ti lamprophyres, respectively, indicating these units formed during the Early Cretaceous. The inherited zircons within the Xiaya and Jingziyu minettes define six (2517, 1852, 725, 375, 276, and 236 Ma) and two (2523 and 462 Ma) main age populations, respectively. In comparison, the inherited zircons from the Jingziyu pyroxene lamprophyres yield two main age populations (2523 and 1848 Ma). The low-Ti lamprophyres are enriched in the light rare earth elements (LREE) and large-ion lithophile elements (LILE), depleted in the heavy REE (HREE) and high-field-strength elements (HFSE), and have small negative Eu anomalies. In comparison, the high-Ti lamprophyres are enriched in the LREE but are slightly depleted in the HFSE. The low-Ti lamprophyres also have high 87Sr/86Sr(t) ratios (0.7121–0.7123), low ε Nd (t) values (−18.81 to −18.62), and contain igneous zircons with relatively high ε Hf (t) values (generally between −9.94 and −3.36). In comparison, the high-Ti lamprophyres have 87Sr/86Sr(t) ratios of 0.7066–0.7068, ε Nd (t) values from −5.01 to −4.64, and contain igneous zircons with ε Hf (t) values from −11.77 to −8.50. These data indicate the low-Ti lamprophyres formed from primary magmas generated by the partial melting of an enriched region of the lithospheric mantle that was previously strongly modified jointly by subduction breakoff of the downgoing Yangtze Craton basement material and delamination of the lower continental crust within the NCC. In comparison, the magmas that formed the high-Ti lamprophyres were generated by the partial melting of an enriched region of the lithospheric mantle that was weakly modified by interaction with the lower continental crust of the NCC. Both the low- and high-Ti lamprophyres formed in an extensional tectonic environment during lithospheric thinning, and the presence of these two suites of lamprophyres indicates that lithospheric thinning of the eastern NCC peaked during the Early Cretaceous. • Low- and high-Ti lamprophyres in the western Shandong area formed during the Early Cretaceous. • These lamprophyres indicate that peak lithospheric thinning of the eastern NCC occurred during the Early Cretaceous. • Delamination was an important process during the destruction of the NCC. [ABSTRACT FROM AUTHOR]

This paper reports new whole–rock major– and trace–element and zircon U Pb and Hf O isotopic data for Early Cretaceous granitic rocks on Liaodong Peninsula, NE China, with the aim of constraining continental reworking in the northeastern North China Craton. On the basis of SiO 2 , MgO, and Sr contents and Sr/Y values, the rocks can be divided into three groups. The low–Mg adakitic rocks show zircon U Pb ages of (134–120 Ma), and high SiO 2 (67.11–71.14 wt%) and low MgO (0.53–0.62 wt%) contents, and high Sr (531–1108 ppm) contents, Sr/Y (29.3–132) ratios, with enriched Sr–Nd–Hf–O isotopic compositions, indicating an origin of thickened lower mafic crust. The high–Mg adakitic rocks show ages of (126–114 Ma) and are characterized by low SiO 2 (53.11–63.88 wt%) and high MgO (2.07–8.93 wt%) contents, and high Sr (391–1041 ppm) contents, Sr/Y (23.9–64.1) ratios, with relatively depleted Sr–Nd–Hf–O isotopic compositions, suggesting that they were derived from partial melting of delaminated lower mafic crust. The normal granitic rocks show ages of (127–121 Ma) and high SiO 2 (71.65–77.22 wt%) and low MgO (0.10–0.51 wt%) and Sr (12.1–309 ppm) contents, Sr/Y (0.89–24.5) ratios, with relatively depleted Sr–Nd–Hf–O isotopic compositions, suggesting an origin from lower mafic crust with normal crustal thickness. These constraints, combined with the regional occurrence of A–type granites, bimodal igneous rocks, and metamorphic core complexes, as well as the regional distribution of Mesozoic granitic rocks displaying a younging trend from southeast to northwest for the Jurassic rocks but a reverse trend for the Cretaceous rocks, recorded the roll–back of the Paleo–Pacific plate towards the Eurasian continental margin. [Display omitted] • Discovery of Early Cretaceous low– and high–Mg adakitic and normal granitic rocks on Liaodong Peninsula. • Reworking of lower crust with different properties occurred in Liaodong Peninsula. • The subducted Paleo–Pacific plate rolled back during Early Cretaceous. [ABSTRACT FROM AUTHOR]

Plagioclase has been widely used to reflect the magmatic evolution and the crust-mantle interaction based on its compositional zoning. However, the abilities in recording the adakitic characteristics and the reworking of continental crust are not understood. This paper reports new in-situ plagioclase geochemistry and Pb isotopic compositions of eight Mesozoic granitoid plutons in the northeastern North China Block (NCB). Based on our previous whole-rock and in-situ apatite geochemistry, we divided them into two groups as adakitic rocks and non-adakitic rocks. Comparison and analysis of plagioclase geochemistry in this paper and previous data between these two groups show that plagioclase crystallized from adakitic rocks possesses higher Sr (735–1588 ppm, generally >1000 ppm) concentrations, δEu (δEu = 2Eu N / (Sm N + Gd N ; N represents after primitive mantle normalize) and Sr/Y (1159–81,344, generally >5000) values than those from non-adakitic rocks. Therefore, we believe that the geochemical index of plagioclase Sr–Y–δEu could reserve the adakitic characteristics and then propose two plagioclase geochemical diagrams (Sr/Y versus Y and δEu versus Sr/Y) to identify the adakitic characteristics. Furthermore, the in-situ plagioclase Pb isotopic compositions (206Pb/204Pb ranging from 16.948 to 18.146, 207Pb/204Pb ranging from 15.403 to 15.656 and 208Pb/204Pb ranging from 37.250 to 39.088), together with the rock-assemblages and spatial-temporal distributions of Mesozoic rocks as well as the variations of whole-rock Sr–Nd–Pb and zircon Hf O isotopic compositions reveal the variation of crustal properties during Mesozoic. Late Triassic magmatism originated from reworking of juvenile lower crust in normal thickness. Early Jurassic magmatism were formed by partial melting of ancient thickened lower crust. Late Jurassic magmatism were derived from remelting of ancient lower crust in normal thickness. Early Cretaceous magmatism were derived from reworking of ancient lower crust in different depth. [Display omitted] • The Mesozoic granitoids in northeastern NCB have varied plagioclase trace elements and Pb isotopes. • Plagioclase Sr–Y–δEu provide a new tool in discriminating adakitic characteristics. • In-situ plagioclase Pb isotopic compositions provide new insights in reworking of continental crust. [ABSTRACT FROM AUTHOR]