滇西蓝片岩中的角闪石   总被引：5，自引：0，他引：5       下载免费PDF全文

张儒瑗  从柏林 《地质科学》1990,(1):43-53

滇西蓝片岩的原岩为玄武质岩石和泥质岩,其矿物组合分别为Cr(或Win)+Chl±Ab+Ph+Ep±Act+Sph±Qz和Gl+Ph+Alm+Tc+Act+Chl+Qz+Do。哀牢山蓝片岩中的闪石普遍具有成分分带,核心为蓝透闪石,边缘为阳起石。澜沧江带中的蓝片岩,其碱性闪石显示了一定的成分变化,既有青铝闪石、镁钠闪石,也有蓝闪石。另外,在滇西蓝片岩中,共存的碱性闪石和钙质闪石之间存在着较大的成分间断。澜沧江带蓝片岩的变质年龄为193Ma。  相似文献   

某些矿物标型特征的研究现状   总被引：2，自引：0，他引：2  

任耀武 《矿产与地质》1991,5(2):127-131

目前国内外地质科研人员已广泛应用标型矿物或矿物标型特征探讨物质来源、矿床成因.以指导找矿工作,结合工作实践,概述了这方面的研究工作情况.诸如:矿物中微量元素含量标型意义,矿物中元素比值的标型意义,矿物环带标型意义和矿物结晶形态标型意义以及体型矿物组合等  相似文献   

Polyphase metamorphism and the development of the Main Central Thrust   总被引：2，自引：0，他引：2  

A. STÄUBLI 《Journal of Metamorphic Geology》1989,7(1):73-93

ABSTRACT Along a cross-section through the Lesser and Higher Himalayan units at the Kishtwar window area (north-west India), a polyphase, Barrovian-type metamorphism has been delineated in relation to the development of the Main Central Thrust (MCT). In the metapelitic mineral assemblages, three metamorphic phases have been distinguished:

• (a) conditions up to amphibolite grade at moderate to high pressures (alm + rut + ilm + kya + qtz) characterize the M₁ phase;
• (b) pressure release and/or temperature increase as a result of movement along the MCT and the formation of gneiss domes in the Higher Himalaya, as expressed by oriented (N70°-100° E) fibrolite, defines the M₂ phase; and,
• (c) finally during uplift of the Kishtwar window area, a retrogressive M₃ phase is characterized by the assemblage quartz-muscovite-chlorite.

Both optically zoned and single-stage garnets have been examined with the electron microprobe to determine their element partitioning. Normal zoning has been found in samples below the MCT in the Lesser Himalaya, indicating prograde growth during the M₂ phase, whereas tectonically above, in the Higher Himalaya unit, the garnets reveal double-stage growth with a complex zoning pattern due to reaction-partitioning during M₁ and M₂ and reverse-zoning at their rims during the retrogressive M₃ phase. Geothermometry on metapelites along a cross-section through the MCT zone and the Higher Himalaya imply distinct readjustments of garnet-biotite exchange equilibria and indicate isothermal conditions (500-600° C) throughout the section during the M₃ retrogression. Pressure calculations (gro-an-kya-qtz and alm-rut-ilm-kya-qtz) suggest a decrease in pressure towards the top of the section (6-7.5 to 4.5-5 kbar), as corroborated by fibrolite replacing kyanite. The spatially inverse metamorphism exposed within the Lesser Himalaya of the Kishtwar window is regarded as a product of polyphase metamorphism combined with ongoing thrusting and shearing and is reflected by condensed M₂ isograds around the Kishtwar window.  相似文献   

湘南界牌岭含锡花岗斑岩的岩石学特征   总被引：3，自引：0，他引：3  

喻爱南 《湖南地质》1992,(1)

界牌岭含锡花岗斑岩是岩浆作用晚期强烈分异之产物。该岩体具有富硅(S1O_271.95～76.71％)和碱(K_2O4.25～6.92％),贫铁(Fe_2O_3+FeO为1.17～2.94％)和镁(MgO0.17～0.58％),富挥发分氟(F 0.013～3.38％)和成矿元素,分异指数(DI>85)高的特征,为陆壳重熔型花岗斑岩,且为成矿母岩。岩体围岩蚀变—矿化分带较明显,锡矿化主要集中在黄玉—萤石—云英岩化带内。界牌岭斑岩为陆壳重熔型含锡花岗斑岩。  相似文献   

Identification of potential areas for the occurrence of strong earthquakes in Himalayan arc region   总被引：4，自引：0，他引：4  

S C Bhatia  T R K Chetty  M B Filimonov  A I Gorshkov  E Ya Rantsman  M N Rao 《Journal of Earth System Science》1992,101(4):369-385

Morphostructural zoning (MSZ) scheme of the Himalayan arc region as obtained from a joint study of topographic, geological and tectonic maps as well as satellite imagery is analysed. Three types of morphostructures have been determined: territorial units (blocks of different ranks), linear zones limiting these blocks (lineaments) and intersections of the lineaments (knots). Comparison of MSZ scheme with the know seismicity indicates epicenters of strong earthquakes (M≥6·5) clustered around some of these knots. Pattern recognition method is used to determine seismically potential areas for the occurrence of recognition method is used to determine seismically potential, for the occurrence of strong earthquakes of magnitude ≥M ₀. We have carried out two such studies for the Himalayan arc region, one forM ₀=6·5 and the other forM ₀=7·0. Out of a total number of 97 knots, 48 knots are found to be seismically potential for the occurrence of earthquake ofM≥6·5. The results of the study forM ₀=6·5 were presented in the symposium on “Earthquake Prediction” held in Strasbourg, France, March 1991 (Gorshkovet al 1991). The epicenter of Uttarkashi earthquake of magnitude,M _b=6·6 that occurred in the late hours of 19th October 1991 (UTC) lies in the vicinity of one such knot. The second study carried out subsequently shows that only 36, knots are potential for the occurrence of earthquakes ofM≥7·0, which include the knot, associated with theUttarkashi earthquake.  相似文献   

Spatial optimization for regionalization problems with spatial interaction: a heuristic approach   总被引：2，自引：0，他引：2  

Kamyoung Kim  Denis J. Dean  Hyun Kim 《International journal of geographical information science》2016,30(3):451-473

Spatial optimization techniques are commonly used for regionalization problems, often represented as p-regions problems. Although various spatial optimization approaches have been proposed for finding exact solutions to p-regions problems, these approaches are not practical when applied to large-size problems. Alternatively, various heuristics provide effective ways to find near-optimal solutions for p-regions problem. However, most heuristic approaches are specifically designed for particular geographic settings. This paper proposes a new heuristic approach named Automated Zoning Procedure-Center Interchange (AZP-CI) to solve the p-functional regions problem (PFRP), which constructs regions by combining small areas that share common characteristics with predefined functional centers and have tight connections among themselves through spatial interaction. The AZP-CI consists of two subprocesses. First, the dissolving/splitting process enhances diversification and thereby produces an extensive exploration of the solution space. Second, the standard AZP locally improves the objective value. The AZP-CI was tested using randomly simulated datasets and two empirical datasets with different sizes. These evaluations indicate that AZP-CI outperforms two established heuristic algorithms: the AZP and simulated annealing, in terms of both solution quality and consistency of producing reliable solutions regardless of initial conditions. It is also noted that AZP-CI, as a general heuristic method, can be easily extended to other regionalization problems. Furthermore, the AZP-CI could be a more scalable algorithm to solve computational intensive spatial optimization problems when it is combined with cyberinfrastructure.  相似文献   

基于信息扩散理论的四川盆地农业旱灾风险评估          下载免费PDF全文

陈建杰  余锦华 《大气科学学报》2016,39(5):712-720

采用四川盆地农业旱灾灾情资料数据,基于信息扩散理论,研究了不同风险水平下的农业旱灾发生的概率及其分布,并对四川盆地的农业旱灾风险进行区划。结果表明:正态信息扩散方法可以较好地拟合农业旱灾受灾率的风险分布。与20世纪末相比,21世纪初四川盆地的眉山、重庆等地区发生受灾率xi≥10%和xi≥40%的农业旱灾风险增加。以受灾率xi≥5%和xi≥40%的超越概率作为农业旱灾风险区划阈值,四川盆地农业旱灾风险表现出区域性差异,农业干旱灾害高风险区位于巴中、中江、泸县等地区;西部地区发生农业干旱灾害的风险较小,与该地区丰富的降水量以及平原地形有关。该风险区划结果较为合理,可为当地政府防范农业旱灾提供决策依据。  相似文献   

云南澜沧地区南角河银多金属矿床的地质特征及成因     

杨贵来  杨伟光  莫宣学  曾普胜  和中华  解通 《地质通报》2006,(Z2)

南角河银多金属矿是在地质调查过程中发现并评价的一个具有大型找矿远景的矿床。矿床产于临沧-勐海复式花岗岩基南段西侧与新元古界澜沧群变质岩的接触断裂破碎带(白章断裂)中,矿体呈脉状,形态单一。同位素及成矿流体分析结果表明,成矿物质主要来源于花岗岩和澜沧群地层,成矿流体以大气降水下渗加热上升回返并混合少量岩浆热液为特征,以花岗岩和澜沧群变质岩为矿源层,以断裂破碎带为赋存空间,为具有明显垂向分带特征的低温热液矿床。  相似文献   

Variable parent magmas and recharge regimes of the Parinacota magma system (N. Chile) revealed by Fe, Mg and Sr zoning in plagioclase   总被引：4，自引：0，他引：4  

Catherine Ginibre  Gerhard Wrner 《Lithos》2007,98(1-4):118-140

Zoning patterns of An content and Fe, Mg and Sr concentrations in plagioclase phenocrysts in andesites from Parinacota Volcano (N. Chile) reflect alternating recharge events with two chemically distinct mafic magmas. These magmas are characterized by low and high Sr contents, similar to two recent mafic flank eruptions. One end-member basaltic andesite shows large Sr enrichment and Heavy Rare Earth depletions and thus equilibrated with lower-crustal rocks at depth where plagioclase (high Sr) is unstable, and garnet (high HREE, Y) is stable. A second end-member magma is lower in Sr, Ba contents and has REE patterns typical for parent magmas elsewhere in the Central Andes.

The number of recorded recharge events increases after a catastrophic sector collapse and during the subsequent rebuilding of the stratocone. Variations of An, Fe and Mg contents and morphology of zones suggest also changes in water pressure, including decompression under water under-saturated and water-saturated conditions. Evidence for decompression is more present in post-collapse samples, suggesting that the change in the volcano dynamics involves changes in magma chamber location. This shows the importance of the cone collapse event in the volcano's magmatic evolution. We propose that both end-members are only seen at the surface of Parinacota Volcano because of the particular dynamics of this volcanic system and that similar processes might occur in other volcanic centres of the Central Volcanic Zone.  相似文献   

Monazite begets monazite: evidence for dissolution of detrital monazite and reprecipitation of syntectonic monazite during low-grade regional metamorphism   总被引：2，自引：0，他引：2  

Birger Rasmussen  Janet R. Muhling 《Contributions to Mineralogy and Petrology》2007,154(6):675-689

Back-scattered electron (BSE) imaging and X-ray element mapping of monazite in low-grade metasedimentary rocks from the Paleoproterozoic Stirling Range Formation, southwestern Australia, reveal the presence of distinct, high-Th cores surrounded by low-Th, inclusion-rich rims. Previous geochronology has shown that the monazite cores are older than 1.9 Ga and overlap with the ages of detrital zircon grains (∼3.5–2.0 Ga), consistent with a detrital origin. Many cores have scalloped and embayed surfaces indicating partial dissolution of former detrital grains. Textural evidence links the growth of the monazite rims (∼1.2 Ga) to deformation and regional metamorphism during the Mesoproterozoic Albany-Fraser orogeny. These results indicate that high-Th detrital monazite is unstable under low-grade metamorphic conditions (<400°C) and was partially or completely dissolved. Dissolution was followed by near-instantaneous reprecipitation and the formation of low-Th monazite and ThSiO₄. This reaction is likely to operate in other low-grade metasedimentary rocks, resulting in the progressive replacement of detrital monazite by metamorphic monazite during regional prograde metamorphism.  相似文献