Simultaneous determinations of U–Pb dating and Hf isotopes on single zircon grains by excimer laser-ablation quadrupole and multiple-collector ICP-MS and petrologic and ore geochemical studies have been applied to the ore-bearing porphyry of the Jinduicheng porphyritic molybdenum deposit in East Qinling. Lithogeochemical data show that the porphyry is characteristic of high K2O, K-feldspar porphyritic calc-alkaline granitoids with 176Hf/177Hf=0.282020–0.282436 and εHf(t)=?23.7 to ?8.9, which indicates its mixed origin involving a crustal and a mantle component. The weighted average U–Pb age from single zircon grains of the porphyry is 141.5±1.5 Ma. This age coincides with the oldest molybdenite Re-Os model age as dated by others, suggesting that the period of mineralization was almost simultaneous with the porphyry emplacement, or slightly later. The porphyry intrusion and the molybdenum mineralization occurred during the transition from compression to extension in the Jurassic – Cretaceous periods. The corresponding tectonic setting was the intracontinental orogenic and extension stage after collision and orogenesis between the Southern China plate and the Northern China plate. The Jinduicheng porphyry and the deposit's geochemical data indicate that the ore-forming material originated from a mixing of lower crust and upper mantle. When the molybdenum-enriched magma intruded into the upper crust along zones of structural weakness, ore-forming fluid generated by magma crystallization of the porphyry interacted with wall rock or mingled with meteoric water to form the deposit. 相似文献
Three sediment cores were collected from the top to the mouth of Quanzhou Bay, Southeast China, in order to establish sources and historical trends of organochlorine pesticides (OCPs) in the region. The spatial distribution of OCPs in surface sediments implies that Quanzhou Bay received the contamination inputs not only from rivers near the shore, but also from outside the bay. The variation profiles of concentrations clearly showed that OCPs were widely used between 1960s and 1980s in China. A recent increasing trend was found in all cores despite their ban in China in 1983. Different ratios of (DDD+DDE)/DDTs indicated that DDTs at the top of the bay were mainly derived from long-term weather soils, while DDTs near the mouth of the bay were mainly derived from fresh inputs from outside the bay. Higher percentage of gamma-HCH in HCHs deposited after 1990 implies that lindane may have been used recently around Quanzhou Bay. 相似文献
Three undisturbed sediment samples were collected from the intertidal zone of the Jiaojiang Estuary of Zhejiang Province,
China. The sediments were found to contain remarkably low concentrations of organic carbon (<0.6%) and acid volatile sulfide
(AVS) (<30 μmol g−1). The availability of these two substrates likely constrained sulfate reduction and pyritization of several trace metals,
respectively. This was especially true at one station where AVS concentrations in the upper 20 cm averaged less than 0.05 μmol g−1. Although the depth dependence of the degree of trace metal pyritization was generally consistent with expectations based
on redox conditions, depth profiles of reactive-metal and pyrite-metal concentrations in several cases revealed more complex
behavior and a positive correlation between reactive-metal concentrations and pore water metal concentrations. 相似文献
The impact of the Atlantic Multi-decadal Oscillation (AMO) on the ENSO amplitude was investigated through observational analyses. During the past 90 years the interdecadal variability of ENSO intensity is significantly correlated with the AMO. ENSO variability was strengthened (weakened) during a negative (positive) AMO phase. An ocean mixed layer heat budget analysis reveals that the thermocline feedback is the main process regulating AMO negative phase dependent ENSO growth characteristic. A further examination indicates that a strengthened atmospheric response to unit SST anomaly, an enhanced thermocline response to unit wind stress forcing and a strengthened subsurface temperature response to unit thermocline variation all contribute to the enhanced thermocline feedback during the negative phase of AMO. Such changes are attributed to the increase of background moisture, the weakening of mean subtropical cell (STC) and increase of upper ocean vertical temperature gradient respectively.