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811.
Differentiation Mechanism and Evolution of High-level Magma Chamber at Xiangshan,China 总被引:2,自引:0,他引:2
The calc-alkaline volcanic magmas,which formed the Mesozoic uraniferous volcanic complex of Xiangshan,resulted from partial melting of the mixture of lower crust and enriched mantle with a high mixing proportion in a specific tectonic setting such as active continental margin or ocean-continent collision zone.The preliminary concentrations of Uand Th occur in low-degree par-tial melts.Only small part of these melts was rapidly extracted and erupted and most intruded into the high-level magma chamber(depth:12-13 km) of the compressed upper lithosphere ,in which occurred a strong differentiation which would resulted in strong preconcentrations of the high-hygromagmaphile elements U and Th associated with strong depletion of the 3-d transition ele-ments Ti,Sc,Co,Zr,etc.At the final stage of subduction of the West-Pacific-Kula plate towards the Asian continental plate,the regional tectonic environment was transformed from a compressive in-to a tensional setting.The strongly differentiated,U(and Th) enriched silicic alkalic magmas in high level magma chamber extensively erupted,extruded and intruded.The hydrothermal fluids released as a result of late volcano-degassing and dewatering during crystallization-solidification of magmas,re-sulted in the remobilization,leaching,migration and reconcentration of uranium ,which had been preconcentrated in volcanic rocks.Therefore,specific regional petrogeochemical criteria are expected for the uraniferous volcanic series. 相似文献
812.
813.
Volatile constituents in magmatic inclusions 总被引:1,自引:0,他引:1
Laser Raman microprobe has been applied to the analysis of volatile components in shrinkage gas bubbles of individual magmatic
inclusions in quartz crystal fragments and phenocrystals from the Mesozoic volcanic complexes of Tonglu and Shouchang, Zhejiang
Province. Quantitative analyses are given for CO2, CH4, H2O, CO, H2, N2, H2S, and SO2. In conjunction with the microthermometry and microbarometry data and the chemical composition of magmatic inclusions, the
results permit one to calculate the physico-chemical parametersP
total,fO
2
,fCO
2
,fCH
4
,fH
2O,fCO, andfH
2
at the time individual magmatic inclusions were trapped. Based on the data obtained, some physico-chemical conditions for
the Mesozoic volcanic magma evolution in the Tonglu and Shouchang areas are discussed.
This work shows that this type of studies has become an indispensable new and rising domain in modern magmatic petrology,
especially modern volcanic petrology. It can help us to reconstruct the physico-chemistry of the crystallization-evolution
of a natural magma.
The project was financially supported by the National Science Foundation of China. 相似文献
814.
A marine stratigraphic sequence across the Pliocene / Pleistocene boundary has been found in the north-ern continental shelf of the South China Sea. The marine Quaternary deposits in the Yinggehai Basin may ex-ceed 2,000 m in thickness, probably providing the best section for studying the lower boundary of the marinePleistocene in South China. The vertical succession with planktonic foraminifers and nannofossils revealed inboreholes in the basin has been well correlated with that in the international stratotype section of thePliocene / Pleistocene boundary at Vrica, Italy, resulting in the acquirement of a biostratigraphic boundary at1.64 Ma. This boundary, however, does not coincide with any prominent lithological palaeoenvironmentalchanges in the study area and can hardly be used in geological practice. There are, in contrast, significantchanges at the level of LAD of Globorotalia multicamerata sensu lato located below the above-mentionedboundary. The percentage of planktonic foraminifers in the total population and preservation of foraminiferaltests display great changes at this level corresponding to a clear onlap on the seismic profiles and indicating adepositional hiatus at ca. 2.0-2.5 Ma. Since the level can be widely traced in the Pearl River Mouth Basin andthe Beibu Gulf Basin and well corresponds with the marked depositional environmental changes recorded inthe west Pacific and other regions, it is recommended that the Plio / Pleistocene boundary be drawn at the levelof Gr. multicamerata sensu lato LAD, roughly concurrent with the Gauss / Matuyama turn. 相似文献
815.
816.
This paper describes synthetically the seismic activity, deep and shallow structures and rock dynamic features in and near
Chaoyang—Yixian region. It is supposed that there is a low velocity layer in middle crust and the three-layered crustal velocities
are all lower than that in both sides of the region. There exists uplifts of upper mantle and asthenosphere-low resistance
layer. It is also studied the composition of matter of three-layered crust, low velocity layer, upper mantle and asthenosphere.
In the end the direct relations between the deep and shallow structure, composition and the seismic activity and new activities
of faults in this region are discussed.
The Chinese version of this paper appeared in the Chinese edition ofActa Seismologica Sinica,14, 180–186, 1992. 相似文献
817.
井潮系数,气压系数与地震关系的探讨 总被引:2,自引:0,他引:2
本文就井潮效应及气压效应的变化特征与地震关系,以及地震预报方法可行度进行了分析研究和初步探讨,结果表明气压系数、井潮系数的变化与地震关系复杂。但在判断确认、预报地震强度、地点方面有可取之处,该预报地震新方法值得进一步深入探讨和研究。文中以滇01井为研究对象,以1984年的回归参数为正常动态。分别求出各项参数的均值z_o与标准误差σ_o以z_o-4σ≦z_o+4σ为正常涨落范围。在此以外的单因子N型脉冲,或多因子单脉冲视为异常。其映震率为77.8%,震前异常预报可行率55.6%。地震漏报率为22.2%,地震虚漏报率为44.4%。 相似文献
818.
袁氏剑齿象(新种)(Stegodon yuani sp.nov.)是根据发现于云南省大理白族自治州剑川县东山脚村附近的两颗上第三臼齿建立的。 化石产于早更新世湖泊和滨湖河流相的东山组上部粉砂质粘土层中。它稍原始于东方剑齿象(S.orientalis),而在进化水平上又稍晚于先东方剑齿象(S.praeorintalis)。 相似文献
819.
Water level is an important index for studying hydrologic processes. Water level rise processes were studied in three catchments (catchment I, II, III in Chen Jiagou watershed in the Three Gorge Reservoir Area) with different areas to provide useful information to inform data extension from a gauged-catchment to an ungauged catchment. The results showed that there are seasonal changes in the dominant driving mode of the rise of the water level. The rise of the water level in March is likely mainly driven by the mode of stored-full runoff, and in September or October, it is mainly driven by Horton-flow. The correlation coefficients of all indexes were significant among the three catchments, suggesting that these catchments have similarities and that water level data extension is likely to be completed successfully between the large catchment (III-Catchment) and the small catchment (I-Catchment). It was confirmed that there is good similarity between the 0.6 km2 and 6 km2 catchments, and the data correlation is good between the catchments with the area differences in the Three Gorges Reservoir Area. In addition, the rise processes of the water level in the catchments were not only different under the same rain conditions, but this difference could also change with the rain condition. 相似文献
820.