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Sediments or clastic rocks can record the evolution history of basins, orogenic processes, crustal uplift and erosion, and even paleo-environments. Detrital minerals such as zircon, garnet, and apatite are useful media for studies of sedimentary sources and basin evolution. Detrital zircon has been widely taken as an indicator for provenances and tectonic evolution of geological terrenes via age distribution patterns. Apatite can remain stable during erosion and transportation and is also considered as an ideal object for source tracing. This mineral normally contains high Sr and negligible Rb. Its Sr isotopic composition can remain almost unchanged after crystallization. Unlike isotopic ages of detrital minerals, Apatite isotopic compositions have been less frequently used for tracing the provenance of sedimentary rocks in the last few decades. In the present study, we report on the Sr isotopic composition of individual apatite grains of Neogene and Jurassic conglomerates from the Hui-Cheng basin in the South Qinling orogenic belt, obtained via thermal ionization mass spectrometry. Detrital apatite grains of Jurassic rocks have narrow ranges of 87Sr/86Sr values from 0.7076 to 0.7100, but those of Neogene rocks gave variant 87Sr/86Sr values from 0.7055 to 0.7534, providing distinct evidence for complex sources of Neogene sedimentary rocks. Analytical results show that the distribution patterns of 87Sr/86Sr values of single-grain detrital apatite fit the distribution patterns of detrital zircon U-Pb from the isotopic ages very well. Detrital apatite Sr isotopic composition can provide essential information for tracing the origins and evolution of sedimentary sources. [ABSTRACT FROM AUTHOR]

Yanshanian magmatisms are intensive in the eastern Jiangnan orogen and can be divided into early (150–136 Ma) and late (136–120 Ma) stages. About these granitic rocks, the petrogenesis and associated tectonic setting are still hotly debated. The Taiping–Huangshan complex, a representative granitic rock in this region, is selected to perform geochemical studies. Three lithologic units have been identified in the Taiping–Huangshan complex: granodiorite, monzogranite, and alkali‐feldspar granite with zircon U–Pb dating results of 149–144 Ma, 148 Ma, and 135–131 Ma, respectively, belonging to the early stage for the granodiorite and monzogranite, and late stage for the alkali‐feldspar granite. The granodiorite and monzogranite have similar major and trace element characteristics with intermediate‐acidic SiO2 contents ranging from 65.9 to 69.7 wt.%, low Mg# values of 35.8–38.4, enriched LREE, Pb, Th, and U contents, and weak Eu anomalies (δEu = 0.71–0.79). The alkali‐feldspar granite is characterized by high SiO2 contents (73.3–76.6 wt.%), low Mg# (2.6–10.0), enriched Th, U, Ta, Pb, and Nd, depleted high‐field‐strength elements, and pronounced negative Eu anomalies (δEu = 0.01–0.19). The granodiorite and monzogranite have consistent εHf(t) (−5.38 to −9.41) and δ18O (7.18‰ to 11.00‰) values, while the alkali‐feldspar granite has elevated εHf(t) values (−0.96 to −6.48) and δ18O values (6.27‰ to 8.34‰). Integrated geochemical characteristics and batch partial melting modelling constrain that the early stage granitic rocks derived from ca. 8% batch melting of the Neoproterozoic juvenile crust, and the late‐stage granites derived from a similar crust source with a little contribution from mantle. From early to late stage, the tectonic setting translated from post‐orogenic to anorogenic and the later corresponded to a back‐arc extensional setting as increasing of the slab subducted angle of the Palaeo‐Pacific Plate. [ABSTRACT FROM AUTHOR]

The major Precambrian crustal growth in the North China Craton (NCC) has been thought to have occurred at ∼2.5 Ga. Here we present secondary ion mass spectroscopy (SIMS) and laser ablation-inductively coupled mass spectrometry (LA-ICP-MS) zircon U-Pb ages and Hf isotope compositions from dioritic and tonalite-trondhjemite-granodiorite (TTG) gneisses of the Neoarchean-Paleoproterozoic metamorphic terrane in the central NCC. Zircons from the trondhjemitic samples yield emplacement ages at 2,702±7 and 2,722±9 Ma. Those from the dioritic gneiss yield an age of 2,704±14 Ma. The TTG gneisses are characterized by a Na-rich and K-poor (Na/K ratiosp2.7, 2.6) nature; strongly fractionated rare earth element patterns ([La/Yb] p35, 20); high Sr (418‰, 318‰) and Sr/Y (78, 49); low Y N (5.4‰, 6.4‰) and YbN (3.0, 3.6); and low MgO (0.89%, 1.10%), Mg# (47, 42), Cr (39‰, 20‰), and Ni (11‰, 8‰), Nb/ Ta (16, 12), which suggests that magmas were derived from the partial melting of a flatly subducted oceanic slab. The dioritic gneiss shows higher MgO (3.17%), Mg# (50), Cr (44‰), and Ni (40‰) and lower Sr/Y (22) and (La/Yb)N (8) ratios, which suggests contamination with mantle peridotite. All zircon grains from these Neoarchean gneisses yield high positive εHf (t) values that range from ε3.5 to ε7.7 and Hf model ages between 2.70 and 2.85 Ga. We propose that the widespread ∼2.5-Ga plutonic event found elsewhere in the NCC may represent a major reworking (melting) event, whereas the ∼2.7-Ga magmatism likely represents the main crustal growth of the NCC, comparable to those of other cratons worldwide [ABSTRACT FROM AUTHOR]

In our previous study on petrogenesis of quartz syenite and granite porphyry, the host rocks of the Late Mesozoic Shapinggou Mo deposit in the Qinling–Dabie orogenic belt, we found that the initial Sr isotopic composition of the host rocks is strongly affected by the degree of K-alteration. Here, we provide further isotopic evidence of the host rocks and their minerals to investigate the geochemical behaviour of trace elements and isotopes during the alteration and to explain the phenomenon of decoupling of Sr–Nd isotopic composition. The quartz syenite and granite porphyry are altered by K-alteration in varying degrees and have high K2O and Rb contents and low Na2O, CaO, Sr, and Ba contents. Rock samples of both quartz syenite and granite porphyry have variable Rb/Sr ratios and initial 87Sr/86Sr values (even < 0.70) but contain quite homogeneous εNd(t) values (−12.8 to −14.8). Minerals from the rocks of moderate to intense K-alteration have very low initial 87Sr/86Sr values (even < −17), while those from the weakly altered rocks have 87Sr/86Sr(t) values of 0.7044 to 0.7084. The same phenomenon of the decoupling in Sr–Nd isotopic composition can be observed from several Mo deposits within the eastern Qinling–Dabie orogenic belt. This fact suggests similar hydrothermal features and a comparable origin for both the magmatic rocks and hydrothermal fluids in this belt. A comparison between porphyry Mo and porphyry Cu deposits shows that elements and the Rb–Sr isotope system have different behaviours during the K-alteration, implying distinct material sources and igneous rocks for porphyry Mo and porphyry Cu deposits, respectively. [ABSTRACT FROM AUTHOR]