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111.
桂北新元古代两类过铝花岗岩的地球化学研究 总被引:24,自引:3,他引:24
广西北部新元古代花岗岩类岩石包括黑云母花岗闪长岩和黑云母花岗岩。地球化学特征表明,黑云母花岗闪长岩与含堇青石的过铝花岗岩(CPG)相当,而黑云母花岗岩则类似于白云母二长花岗岩(MPG)。黑云母花岗岩类是成熟地宙岩石部分熔融作用的产物,而黑云母花岗闪长岩类的形成与地幔柱起源的镁铁质岩浆和地壳起源的过铝质黑云母花岗岩浆之间的混合作用有关。这两类新元古代过铝花岗岩的形成与碰撞造山导致地壳加厚的挤压性构造无关,而与导致Rodinia超大陆裂解的地幔柱上升诱发岩石圈伸展的张性构造相联系。 相似文献
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113.
亚洲500毫巴月平均环流指数(1939—1962年)的谱分析 总被引:1,自引:0,他引:1
本文计算了亚洲500毫巴月平均环流指数的方差谱。结果指出:亚洲经向及纬向环流指数谱的分布是有一定差异的,前者以5个月左右为周期的谐和振动占有显著的地位,而后者则以5个月以上的长周期振动所占的成分较大。 相似文献
114.
A detailed field and laboratory study has been made of a well-exposedglaucophane schist sequence within the Jurassic and CretaceousFranciscan Formation of northern California. Three types ofglaucophane-bearing metamorphic rocks have been distinguishedin and around the area of the detailed study. Each is characterizedby distinctive textures and mineral assemblages that are interpretedto represent different grades of metamorphism within the glaucophaneschist facies. From the combination of small- and large-scale mapping in thearea described it is clear that coarsely schistose blocks, tensof feet in diameter, commonly rest directly upon and withinless intensely metamorphosed terrain. In the Cazadero area theseisolated blocks of coarsely crystalline rocks are concentratedin a band that is roughly concordant with some of the majorfaulting, and their metamorphic fabric shows no consistent relationto local or regional structures. It is tentatively suggestedthat these blocks have been transported upward tectonicallyand that they are not stratigraphically equivalent to the othertypes of glaucophane-bearing metamorphic rocks in the area. Chemical and petrographic evidence indicates that basalt andsediments have been converted to glaucophane-bearing rocks underconditions of metamorphism that were essentially isochemical,except for fugitive components and some minor elements. 相似文献
115.
云和雨的相干散射与雷达气象方程 总被引:1,自引:0,他引:1
研究了云雨质点对雷达波的相干散射,从而推得比较普遍的雷达气象方程。旧的雷达气象方程是新方程在云雨质点互相独立时的特殊表现形式。对新方程作了一些讨论,发现旧方程之所以在某些方面与实验不符,可能是因为忽略了相干散射作用的缘故。 相似文献
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117.
The Taltheilei, Utsingi, McLean and Blanchet formations form a 175–390 m thick carbonate platform-to-basin succession in the lower part of the PaleoProterozoic Pethei Group, preserved in the eastern arm of Great Slave Lake. Carbonates accumulated along the south-east margin of the Slave Craton within a foredeep formed during the collision of the Slave and Churchill Cratons. The rocks include eight, predominantly microbial, carbonate facies that comprise five facies associations representing (1) shallow-water rimmed shelf, (2) shallow-water open shelf, (3) shallow-water ramp, (4) upper slope and deep ramp, and (5) lower slope and basin plain environments. Microbialite facies grew by organically mediated precipitation of spar and micritic cement and trapping and binding of lime mud. These wholly subtidal facies typically reflect progressive shallowing and changing geometry of the lower Pethei sea floor, from ramp, to open shelf, to shallow rimmed shelf, with associated slope and basin plain deposition. Repeated relative sea-level changes influenced platform growth. This resulted in five shallowing upward packages; each separated by an incipient drowning event of varying magnitude. Antecedent topography and the size of the preceding drowning event strongly influenced the initial growth of each interval. This repeated pattern is attributed to interaction between (a) the inherent tendency of microbial carbonates to aggrade vertically, (b) changing sedimentation rates and (c) readjustments of relative base level. The lower Pethei succession is one of few PaleoProterozoic examples of carbonate platform growth within a foreland basin. It has (1) a low gradient profile, (2) extensive slope and basin plain carbonate production and sedimentation, (3) no ooids, (4) minor terrigenous clastic sediments, and (4) a mobile, submergent shelf rim lacking substantial carbonate sand shoals. 相似文献
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119.
T. LEE 《Geophysical Prospecting》1983,31(5):766-781
The presence of a conducting environment about a spherical ore body must be considered when calculating the transient electromagnetic response of the ore body due to a step current flowing in a large circular loop at the earth's surface. Failure to do this can easily lead to errors in excess of 10% in numerical calculations. Moreover, there is only a limited time interval in which the response of the spherical conductor is easily seen. In a poorly conducting ground the resonance response of the sphere is the first to be excited. Later, however, the non-resonance or wave-type response is excited. These waves destructively interfere and finally the response of the sphere decays with time as t?7/2. For a range of times and depths the best loop for detecting the sphere has about the same radius as the sphere. 相似文献
120.