Clastic sedimentary rocks are natural samples of the exposed continental crust over large areas. The Hanjiang （汉江） River drains the northern Yangtze craton, including the South Qinling （秦岭） belt and the northern parts of the Yangtze craton. Detrital zircons from this river thus provide an ideal sample for studying the formation and evolution of the northern Yangtze craton. Here we report laser ablation inductively coupled plasma mass spectrometer U-Pb ages of 122 detrital zircons from one sand sample of the Hanjiang River. The 110 concordant zircons reveal four major age groups of 768, 444, 212, and 124 Ma, which well correlate with known magmatic events in the northern Yangtze craton. A minor group is present at 1 536 Ma, which is less known in the study area. Only seven zircons have ages of 〉1 750 Ma. Our results show that the Early Paleozoic, Late Triassic, and Early Cretaceous are important episodes of zircon growth and crustal growth/reworking in addition to the previously documented Neoproterozoic event. Our results suggest very limited exposures of Paleoproterozoic and Archean rocks in the northern parts of the Yangtze craton.
Zircon U-Pb age, trace elements, and Hf isotopes were determined for granulite and gneiss at Huangtuling （黄土岭）, which is hosted by ultrahigh-pressure metamorphic rocks in the Dabie （大别） orogen, east-central China. Cathodoluminescence （CL） images reveal core-rim structure for most zircons in the granulite. The cores show oscillatory zoning, relatively high Th/U and 176Lu/177Hf ratios, and high rare earth element （HREE）-enriched pattern, consistent with magmatic origin. They gave a weighted mean 20pb/206pb age of （2 766±9） Ma, dating magma emplacement of protolith. The rims are characterized by sector or planar zoning, low Th/U and 176Lu/177Hf ratios, negative Eu anomalies and flat HREE patterns, consistent with their formation under granulite-facies metamorphic conditions. Zircon U-Pb dating yields an age of （2 029±13） Ma, which is interpreted as a record of metamorphic event during the assembly of the supercontinent Columbia. The gneiss has a protolith age of （1 982±14） Ma, which is similar to the zircon U-Pb age for the granulite-facies metamorphism, suggesting complementary processes to granulite-facies metamorphism and partial melting, A few inherited cores with igneous characteristics have 207PB/20PB ages of approximately 3.53, 3.24, and 2.90 Ga, respectively, suggesting the presence of Mesoarchean to Paleoarchean crustal remnants. A few Triassic and Cretaceous metamorphic ages were obtained, suggesting the influences by the Triassic continental collision and postcollisional collapse in response to the Cretaceous extension. Comparing with abundant occurrence of Triassic metamorphic zircons in ultrahigh-pressure eclogite and granitc gneiss from the Dabie-Sulu （苏鲁） orogenic belt, however, very limited availability of aqueous fluid or hydrous melt is evident for zircon growth in the Huangtuling granulite and gneiss during the continental collision. The magmatic protolith zircons from the granulite show a large variation in J76Hf/177Hf ratios from 0.280 809 to 0.28
The Cenozoic basalts from eastern China show commonly high Fe/Mn ratios (average = 68.6 ± 11.5) coupled with OIB-type trace element signature. The Cenozoic basalts form the northern margin and the southern margin of the North China Craton are studied in detail. Model calculations point out that the coupling feature of high Fe/Mn ratio with OIB-type trace element signature of these basalts cannot be produced by neither pyroxene/olivine crystallization nor remelting of previously melted mantle, but require partial melting of a garnet pyroxenite-rich mantle source. Combining these features of the Cenozoic basalts with the Phanerozoic lithospheric evolution of the eastern China, we suggest that the Cenozoic basalts were derived from a garnet pyroxenite-rich mantle source associated with continental crust delamination or oceanic crust subduction.
The addition of 5-10 mL min^-1 nitrogen to the central channel of plasma in Laser ablation Inductively Coupled Plasma Mass Spectrometry （LA-ICP-MS） increases the sensitivities of Cd by a factor of 3 and decreases oxide interferences by one order of magnitude, which allows the direct analysis of trace levels of Cd in glass samples. This simple method shows a great potential for the direct determination of Cd in various kinds of samples.
