Ancient Lower Continental Crust Research Articles

Contrasting mineralogical-geochemical compositions of ore-bearing and ore-barren intrusive complexes in the Handan-Xingtai district, North China Craton: Implications for the iron mineralization

The Handan-Xingtai district is located in the western margin of the eastern North China Craton (NCC). It is one of the largest concentrations of iron skarn deposits in China. In the past decades, numerous Mesozoic intermediate-felsic intrusions were reported in this area. However, the genetic relationship between the Mesozoic intrusions and iron mineralization still remain controversial. Here we present mineral compositions, major and trace elements, as well as Sr–Nd isotopic data of both the ore-bearing and ore-barren intrusive complexes. Most of the amphiboles from the ore-bearing complexes are magnesiohastingsites with a small part of them being edenites, whereas those from the ore-barren one are mostly ferropargasites and pargasites. All biotites from the studied complexes are magnesio-biotites. Mineral thermometer and oxybarometry show that the magma of ore-bearing intrusive complexes has lower temperatures but higher oxygen fugacity than those of the ore-barren ones. In addition, all the studied complexes show enrichment in light rare earth elements (LREE) and depletion in heavy rare earth elements (HREE) and high field strength elements (HFSE), with high Sr/Y ratios and insignificant Eu anomalies, similar to adakitic rocks. However, samples from the ore-barren one have obviously higher εNd(t) values (−11.2 to −7.2) than those of ore-bearing ones (εNd(t) = −18.2 to −12.3). Our new results demonstrate that the ore-bearing and ore-barren complexes cannot be genetically related, but evolved via discrete magmatic events. We propose that the ore-bearing complexes were derived from a mixed source, which consists of enriched lithospheric mantle and ancient lower continental crust, whereas the ore-barren one was generated by partial melting of an enriched lithospheric mantle. The major difference between the ore-bearing and ore-barren complexes is involvement of the continental lower crust, which has a greater contribution to the iron mineralization. The magmatism and metallogeny in the Handan-Xingtai district were a result of the extensive craton destruction and lithospheric thinning in the eastern part of the NCC.

U-Pb ages, Hf-O isotopes and trace elements of zircons from the ore-bearing and ore-barren adakitic rocks in the Handan-Xingtai district: Implications for petrogenesis and iron mineralization

The petrogenesis of the Early Cretaceous adakitic intrusions in the Handan-Xingtai district, central North China Craton (NCC), and their genetic association with iron mineralization still remain controversial. Here, we present an integrated study of zircon U-Pb ages and Hf-O isotopes, as well as their trace elements for the ore-bearing and ore-barren complexes in the Handan-Xingtai district. Both of the ore-bearing and ore-barren complexes were emplaced contemporaneously (Early Cretaceous). Zircon εHf(t) and δ18O values of ore-barren complex range from −16.0 to −13.3 and from 6.3‰ to 7.1‰, respectively, whereas those of ore-bearing complexes have variable δ18O (5.7‰ to 8.3‰) and much lower εHf(t) values (−24.3 to −18.3). Furthermore, the ore-bearing complexes also have lower Ti-in-zircon temperatures but higher water contents and oxygen fugacity than those of ore-barren complexes. The zircon Hf-O isotopes, as well as their trace element data, indicate that the parental magma of ore-bearing complexes was a mixture of melts that derived from the enriched lithospheric mantle and ancient lower continental crust, whereas the ore-barren complex was most likely generated by partial melting of the enriched lithospheric mantle. We proposed that the high oxidation states and high water contents of magma, as well as the lower crustal materials may have played key roles in iron mineralization of Handan-Xingtai district.

U-Pb Geochronology, Elemental and Sr-Nd Isotopic Geochemistry of the Houyaoyu Granite Porphyries: Implication for the Genesis of Early Cretaceous Felsic Intrusions in East Qinling

The Early Cretaceous Houyaoyu granite porphyries are located in the south margin of the North China Craton. Field observations, petrography, geochronology, major and trace elemental and Sr-Nd isotopic compositions are reported to elucidate the genesis of the Houyaoyu granite porphyries. SIMS zircon U-Pb analyses for the Houyaoyu granite porphyries yield two concordant ages of 133.2±2.3 (2σ) and 131±1.1 (2σ) Ma, respectively. Major and trace elemental compositions indicate that these porphyries are high-K I-type granites with high contents of SiO2, K2O, Rb, U, Pb, low Nb, Ta, Ti, and P. Initial 87Sr/86Sr ratios range from 0.708 3 to 0.709 7, and eNd(t) values range from -9.13 to -12.3, with corresponding two-stage depleted-mantle Nd model ages (T2DM) varying from 1.57 to 1.91 Ga. This suggests that the Houyaoyu granite porphyries were predominantly derived from ancient lower continental crust, with minor involvement of mantle-derived components. On the basis of the tectonic evolution of the Qinling Orogen and geochemical characteristics of the Houyaoyu granite porphyries, it is proposed that they were formed in an extensional tectonic setting related to lithospheric destruction of the North China Craton, and produced Mo and Pb-Zn mineralization in East Qinling Orogen.