通过对埋藏古树、泥炭、以及海相贝壳测年资料进行搜集和整理,结果表明:长江下游地区6000 a BP以来古洪水的发生与气候变化有着密切的联系。由于长江下游地区地势低平这一地貌特点,使得海面变化对于研究区洪水发生有着重要的影响,气候变化导致的海面上升对长江下游河段径流的顶托作用导致河流上溯以及地面排水不畅,致使洪水发生频率加大以及洪水危害的程度加强,出现“小水大灾”的现象,长江三角洲地区古洪水发生频率与美洲地区古洪水发生频率的对比研究表明,长江三角地区乃至整个长江流域在大的气候变化趋势上与全球其它地区是相似的,既有全球气候变化特点的同时又具有区域响应的特点,这对于未来研究区洪水发生的预测有着重要意义。 相似文献
Many light rare earth deposits, such as Maoniuping, Dalucao, Panzhihua deposits, are collectively distributed in Panxi rift of Sichuan Province, China, and closely associated with the aegirine quartz syenite-carbonatite complex. Carbon and oxygen isotope studies demonstrate that the carbonatites in the complex are of typical igneous origin related to mantle processes. Electronic microprobe studies show that the fluid-melt inclusions found in the complex are enriched in light rare earth elements (LREE), which suggests that the magma was rich in LREE and could serve as the ore source for the regional LREE mineralization. Both the aegirine quartz syenite-carbonatite complex and the LREE mineralization found therein were derived from the mantle. The rare gas isotope analyses also support that there is a genetic association between the LREE mineralization and mantle processes.
Geological, geophysical, geochemical and remote sensing comprehensive studies show that big ore-prospecting potentiality is contained in the eastern section of the Gangdise Mountains, Tibet.There are various mineralization types with dominant types of porphyry and exhalation. According to their relations with tectonic evolution, they are divided into four kinds of metallogenic series as follows:magnmtic type (Cr, Pt, Cu, Ni) and exhalation type (Cu, Pb, Zn, Ag) ore deposit series related to Neo-Tethys oceanic crust subduction action (125-96 Ma); epithermai type (Au, Ag, Pb, Zn, Sb), altered fractured rock type (Cu, Mo) and skarn rock type (Cu) ore deposit series related to arc-continental collision; porphyry type (Cu, Mo), cryptoexplosion breccia type (Cu, Au, Pb, Zn), shear zone type (Au, Ag, Sb) and skarn rock type (Cu, Fe) ore deposit series with relation to post-orogenic extensional strike-slip. From subductive complex to the north, zoning appears to be crystallization differentiation type (segregation type)-shear zone type (altered rock type)-skarn rock type, epithermai type-porphyry type-porphyry type and exhalation type-exhalation type-hydrothermai filling-replacement type.The ore deposit is characterized by multi-places from the same source, parity and multi-stage, hypabyssal rock from the deep source and poly genetic compound as a whole. 相似文献
根据南海季风试验(SCSMEX)期间南海内区的三个ATLAS(Autonomous Temperature Line Acquisition System)锚碇浮标资料(1998年4月~1999年4月),采用谐波分析方法对南海上层海洋水温年循环、半年循环加以分离,发现无论在年循环还是在半年循环尺度上,18°N附近SCS1站与13°N附近SCS3站的水温变化次表层与表层呈反位相;15°20′N附近SCS2站水温变化基本上次表层与表层同位相.这说明不同区域上层海洋热变化受不同的正压与斜压模态控制.其次,SCS2、SCS3两点水温年循环振幅均在次表层达到极值;而SCS1在表层达到极大值,在100 m深度达到次极大值.3个站位水温半年循环振幅极值均出现在次表层内,这说明该层内的水温半年循环在温度变化趋势中所占的权重比在表层的权重大. 相似文献