八达岭基性岩和高探讨:华北和大别-苏鲁造山带中生代岩浆岩的对比Ba-Sr花岗岩地球化学特征及成因

The Mesozoic Badaling complex，emplaced in the northern part of the North China block (NCM)，is composed of gabbrodiorite，quartz diorite，quartz monzonite，monzodiorite，adamellite，moyite and quartz syenite，which are predomi nantly high-K calc-alkaline and subordinately shoshonitic. Their major elements，except that of cumulative gabbrodiorite with substantive magnetite，range widely，e.g.，SiO 2= 46.5 % ~ 75.3 % ，M g O = 5.6 % ~ 0.2%. K 2O/Na2O ratio varies from 0.59 to 1.09 for the intermediate-felsic rocks. The moyite and quartz monzonite have low Ba and Sr abundances and strong nega tive Eu anomaly. However，most intermediate-felsic rocks are consistently characterized with high Ba，Sr and LCEE and low R b ，Y and HCEE abundances，high Sr/Y and La/Yb ratios，distinct N b ，Ta and Ti depletion，as well as absence of negative Eu anomalies，and are comprehensively called high Ba-Sr granitoids. In addition，the mafic rocks and high Ba-Sr granitoids have covariant ma[or elements，and similar incompatible trace element and rare earth element (REE) patterns，with R E E ，Y ，Sr，P and Ti abundances consistently decreasing from basic to felsic rocks. Initial 87Sr/86Sr (0.7051~ 0.7068) and ∈N di —(8.2~-20. 2) of mafic rocks and high Ba-Sr granitoids show EM1-type signature，and are negatively correlated. Geochemical da ta indicate that mafic rocks were derived from partial melting of an enriched subcontinental lithospheric mantle，and high Ba-Sr granitoids were produced from the mafic magmas mainly through fractional crystallization with some crustal contamina tion. fractionation of P- and Ti-bearing accessory minerals，such as apatite and titanite，played an important role in causing the decrease of the REEs with progressive differentiation. The Yanshanian mafic rocks，high Ba-Sr and low Ba-Sr granitic rocks with comparable geochemical characteristics to their correspondents in the Badaling complex are widespread in the east ern part of NCB and the Dabie-Sulu Orogen (DSOB). Hence we propose that the occurrence of Yanshanian igneous rocks in NCB and DSOB had common geodynamic mechanism，and the geochemical characteristics of the Yanshanian igneous rocks from DSOB were not necessarily due to the interaction between the subducted continental crust (Yangtze block) and mantle peridotite. Delamination or lithospheric thinning probably caused the partial melting of the enriched subcontinental lithospher ic mantle beneath NCB and DSOB. Mantle enrichment beneath NCB and DSOB may occur early in Proterozoic，implicated by the similarity of Nd depleted mantle model ages (Tdm).