Late Paleozoic–Early Mesozoic Granite Magmatism on the Arctic Margin of the Siberian Craton during the Kara-Siberia Oblique Collision and Plume Events

We present new structural, petrographic, geochemical and geochronological data for the late Paleozoic–early Mesozoic granites and associated igneous rocks of the Taimyr Peninsula. It is demonstrated that large volumes of granites were formed due to the oblique collision of the Kara microcontinent and the Siberian paleocontinent. Based on U-Th-Pb isotope data for zircons, we identify syncollisional (315–282 Ma) and postcollisional (264–248 Ma) varieties, which differ not only in age but also in petrochemical and geochemical features. It is also shown that as the postcollisional magmatism was coming to an end, Siberian plume magmatism manifested in the Kara orogen and was represented by basalts and dolerites of the trap formation (251–249 Ma), but also by differentiated and individual intrusions of monzonites, quartz monzonites and syenites (Early–Middle Triassic) with a mixed crustal-mantle source. We present a geodynamic model for the formation of the Kara orogen and discuss the relationship between collisional and trap magmatism.

Groundwater quality of the coastal aquifers in the eastern part of Thermaikos Gulf (from Aggelochori to Kallikrateia)

The study area is located in the coastal area of the eastern Thermaikos Gulf, covering an area of 252 km2. The area is characterised by intense agricultural activity, and during the past few years it has undergone considerable residential development. From a geological point of view, the area consists of Quaternary alluvial coastal deposits, river terraces and Neogene deposits (marly limestones and sandstone- marl series). The bedrock formations are Jurassic limestone and Mesozoic granite. The main aquifer system is developed within the sand, gravel, and sandstone layers of the Quaternary deposits as well as within the sandstone-marl series. This paper investigates the relationship between the groundwater quality and groundwater level. Groundwater sampling and water level measurements took place in April and September 2010. The results of chemical analyses indicate degradation of the groundwater quality. The sources of the groundwater pollution are seawater intrusion due to the overexploitation of the coastal aquifers, fertilizers from the agricultural activities and the disposal of untreated wastewater in torrents.

Rb-Sr Isotopic Geochronology and Geological Implications of Dongfeng Gold Deposit in Jiaodong Area

<p>The superlarge Dongfeng gold deposit is located in the Potouqing faults-alteration belt of the eastern part of the ‘Zhao-Lai-gold ore belt’, which belongs to the northwestern part of the Jiaodong area. Tectonically, ore bodies are controlled by faults and gold mainly occurs in the pyrite and polymetallic sulfide-bearing quartz vein. In this paper, Rb–Sr isotopic analysis is carried out with the beresite, which formed by hydrothermal metasomatism, and the Rb–Sr isochron age is 125.5±6.7Ma, indicating this deposit set up in the early Cretaceous of the late Yanshanian. Based on the relationship between the Dongfeng gold deposit and the Mesozoic granite, it is suggested that the formation of the gold deposit is a complex geological process of gradual enrichment and precipitation of the ore-forming elements. The initial ⁸⁷Sr/⁸⁶Sr ratio of the beresite is 0.711502±0.000069, which indicates the ore-forming materials mainly come from the crust. Combined with the complex mineralization process of the Dongfeng gold deposit and the reported H-O isotopic data, it is suggested that the ore-forming materials are mainly derived from the crust with some mantle materials, while the ore-forming fluids are originated primarily from magmatic hydrothermal and mantle with some precipitate water.</p>