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Geological Background (geological + background)
Selected AbstractsStable Isotope Study of the Langshan Polymetallic Mineral District, Inner Mongolia, ChinaRESOURCE GEOLOGY, Issue 1 2000Ping DING The lead isotope study shows that these deposits were probably formed from 2. 0 to 1. 5 Ga, and were deformed and metamorphosed 1. 45 Ga. Ore lead could be a mixture of mantle lead and crustal lead. The C and S isotope results indicate that these deposits were precipitated in closed or semi-closed rift basins, and the source of sulfur might be Proterozoic ocean sulfate. The H and O isotope results indicate that the ,D and ,18O values of rocks were changed by water-rock interaction during metamorphism and hydrothermal alteration. The scale of ,D and ,18O shift of rocks reflects the grade of metamorphism and alteration as well as the water-rock ratios. However, the water-rock ratios in the metamorphic processes of Langshan mineral district were relatively low, and the source of water during metamorphism is suggested to be ancient meteoric water. Based on isotopic results and the geological background, it is concluded that these deposits may belong to Proterozoic sedimentary exhalative (SEDEX) type. [source] Multi-temporal geophysical survey of a Roman bath complex in Montegrotto Terme (Padova, northern Italy)ARCHAEOLOGICAL PROSPECTION, Issue 3 2007E. Finzi Abstract Between 2000 and 2005, several geophysical surveys were carried out by the staff of the Department of Geosciences, University of Padova, on the site of the Terme Neroniane in Montegrotto, near Padova, covering a whole complex of Roman spa buildings. This work represented a good opportunity to compare the effectiveness of various techniques (ground-penetrating radar, magnetic gradiometry and electrical resistivity tomography) and to seek the reasons for differing results. Depth, contrast between composition of the geological background and building materials, good state of structural preservation, and the lack of settlement following the Roman age supported experimental results. Old and more recent excavations, conducted in parallel with the University of Padova surveys, enabled continual comparisons between geophysical models and evidence from the site. Copyright © 2007 John Wiley & Sons, Ltd. [source] Process Analysis of In-situ Strain during the Ms8.0 Wenchuan Earthquake,Data from the Stress Monitoring Station at ShandanACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 4 2009Hua PENG Abstract: There were huge life and property losses during the Ms8.0 Wenchuan earthquake on May 12, 2008. Strain fluctuation curves were completely recorded at stress observatory stations in the Qinghai-Tibet plateau and its surroundings in the process of the earthquake. This paper introduces the geological background of the Wenchuan earthquake and the profile of in-situ stress monitoring stations. In particular, data of 174 earthquakes (Ms4.0,Ms8.5) were processed and analyzed with various methods, which were recorded at the Shandan station from August 2007 to December 2008. The results were compared with other seismic data, and further analyses were done for the recoded strain seismic waves, co-seismic strain stepovers, pre-earthquake strain valleys, Earth's free oscillations before and after the earthquake and their physical implications. During the Wenchuan earthquake, the strainmeter recorded a huge extensional strain of 70 seconds, which shows that the Wenchuan earthquake is a rupture process predominated by thrusting. Significant precursory strain anomalies were detected 48 hours, 30 hours, 8 hours and 37 minutes before the earthquake. The anomalies are very high and their forms are very similar to that of the main shock. Similar anomalies can also be found in strain curves of other shocks greater than Ms7.0, indicating that such anomalies are prevalent before a great earthquake. In this paper, it is shown that medium aftershocks (Ms5.5,6.0) can also cause Earth's free oscillations. Study of free oscillations is of great significance to understand the internal structure of the Earth and focal mechanisms of earthquakes and to recognize slow shocks, thus providing a scientific basis for the prevention and treatment of geological disasters and the prediction of future earthquakes. [source] Contrast in Fluid Metallogeny between the Tianmashan Au-S Deposit and the Datuanshan Cu Deposit in Tongling, Anhui ProvinceACTA GEOLOGICA SINICA (ENGLISH EDITION), Issue 1 2003DU Yangsong Abstract, A comprehensive contrast of ore-forming geological background and ore-forming fluid features, especially fluid ore-forming processes, has been performed between the Tianmashan and the Datuanshan ore deposits in Tongling, Anhui Province. The major reasons for the formation of the stratabound skarn Au-S ore deposit in Tianmashan and the stratabound skarn Cu ore deposit in Datuanshan are analyzed in accordance with this contrast. The magmatic pluton in Tianmashan is rich in Au and poor in Cu, but that in Datuanshan is rich in Cu and Au. The wallrock strata in Tianmashan contain Au-bearing pyrite layers with some organic substance but those in Datuanshan contain no such layers. Moreover, the ore-forming fluids in Tianmashan are dominantly magmatic ones at the oxide and sulfide stages, but those with high content of Cu in Datuanshan are mainly groundwater fluids. In addition, differences in compositional evolution and physicochemical condition variation of the ore-forming fluids result in gradual dispersion of Cu or Au in the late stage of the fluid ore-forming process. This is also an important metallogenic factor for the stratabound skarn Au-S ore deposit in Tianmashan and stratabound skarn Cu ore deposit in Datuanshan. [source] | ||||||||||