Sm–Nd and U–Pb dating of high-pressure granulites from the Złote and Rychleby Mts (Bohemian Massif, Poland and Czech Republic)     

U. LANGE  M. BRÖCKER  R. ARMSTRONG  E. TRAPP  K. MEZGER 《Journal of Metamorphic Geology》2005,23(3):133-145

In the Orlica‐?nie?nik complex at the NE margin of the Bohemian Massif, high‐pressure granulites occur as isolated lenses within partially migmatized orthogneisses. Sm–Nd (different grain‐size fractions of garnet, clinopyroxene and/or whole rock) and U–Pb [isotope dilution‐thermal ionization mass spectrometry (ID‐TIMS) single grain and sensitive high‐resolution ion microprobe (SHRIMP)] ages for granulites, collected in the surroundings of ?ervený D?l (Czech Republic) and at Stary Giera?tów (Poland), constrain the temporal evolution of these rocks during the Variscan orogeny. Most of the new ages cluster at c. 350–340 Ma and are consistent with results previously reported for similar occurrences throughout the Bohemian Massif. This interval is generally interpreted to constrain the time of high‐pressure metamorphism. A more complex evolution is recorded for a mafic granulite from Stary Giera?tów and concerns the unknown duration of metamorphism (single, short‐lived metamorphic cycle or different episodes that are significantly separated in time?). The central grain parts of zircon from this sample yielded a large spread in apparent ²⁰⁶Pb/²³⁸U SHRIMP ages (c. 462–322 Ma) with a distinct cluster at c. 365 Ma. This spread is interpreted to be indicative for variable Pb‐loss that affected magmatic protolith zircon during high‐grade metamorphism. The initiating mechanism and the time of Pb‐loss has yet to be resolved. A connection to high‐pressure metamorphism at c. 350–340 Ma is a reasonable explanation, but this relationship is far from straightforward. An alternative interpretation suggests that resetting is related to a high‐temperature event (not necessarily in the granulite facies and/or at high pressures) around 370–360 Ma, that has previously gone unnoticed. This study indicates that caution is warranted in interpreting U–Pb zircon data of HT rocks, because isotopic rejuvenation may lead to erroneous conclusions.  相似文献   

A palaeomagnetic study of a Caledonian ophiolite     

G. K. Taylor 《Geophysical Journal International》1988,94(1):157-166

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东秦岭造山带核部杂岩水热系统演化机制     

赵东林  胡能高  徐柏青  宋国强 《地球科学与环境学报》1996,(1)

东秦岭造山带核部杂岩，在高温高压环境下曾出现大量流体，由溶解作用产生的流体在变形分解带内运移，形成古水热循环系统，该水热系统使岩石中如铀等大离子富集成矿，水岩相互作用造成秦岭杂岩中稀土元素四重分布效应．  相似文献   

江苏省淤泥质海岸潮沟系统   总被引：17，自引：1，他引：16  

张忍顺  王雪瑜 《地理学报》1991,46(2):195-206

江苏省淤泥质潮滩是最适于潮沟系统发育的潮滩之一。本文分析了影响潮沟系统发育的诸因素,进行了潮沟系统形态与潮差的相关分析,并把江苏的潮沟系统与沪、浙、闽等省市的潮沟系统进行了对比。主要结论如下:1.影响潮沟发育的主要因素是在落潮后期才存在的沟渠效应;2.潮沟和潮盆是潮滩上规模较大的韵律地形;3.粉沙级沉积物最宜于发育潮沟;4.潮沟的某些形态特征与潮差有非常好的线性相关;5.陆地迳流干扰了潮沟发育过程。  相似文献   

3D MODEL STUDY ON FOG OVER COMPLEX TERRAIN—PART Ⅰ:NUMERICAL STUDY     

石春娥  孙学金  杨军  李子华 《Acta Meteorologica Sinica》1996,(4)

A three-dimensional fog model,suitable for precipitous and complex terrain,is designed contain-ing four prognostic variables—wind speed,potential temperature,specific humidity and mixing ratioof liquid water.The model considers turbulent exchange,the long-wave radiation on the ground sur-face and in the air.the short-wave solar radiation,the evaporation and condensation of moisture andthe surface heat budget and so on.In order to make the model run steadily on precipitous and complexterrain,we have improved the method of calculating horizontal pressure gradient force in the terraincoordinate system.The results coincide on the whole with the actual situation.  相似文献   

Radar Observations of Taurid Complex Meteor Showers in 2003: Activity and Mass Distribution     

P. Pecina  V. Porub–an  D. Pecinová  J. Toth 《Earth, Moon, and Planets》2004,95(1-4):681-688

Results of Ondřejov radar observation of Taurid complex meteor showers, i.e. ζ Perseids, β Taurids, S and N Taurids, performed in 2003, are presented. We have found some mass segregation within ζ Perseid, β Taurid and S Taurid showers. We have also established conspicuous lack of long duration echoes (with T ⩾ 3 s resp. T ⩾ 5 s) in S and N Taurid showers. The lack within remaining showers is not so pronounced but still persists.  相似文献   

Oxide Mineralogy and Magnetic Properties of the Koidu Kimberlite Complex, Sierra Leone, West Africa     

S. E. Haggerty  R. B. Hargraves  L. A. Tompkins 《Geophysical Journal International》1990,100(2):275-283

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A theory of spectral analysis based on the characteristic property of a linear dynamic system   总被引：3，自引：1，他引：2  

M. Kumazawa  Y. Imanishi  Y. Fukao  M. Furumoto  A. Yamamoto 《Geophysical Journal International》1990,101(3):613-630

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鲁西铜石中生代复式岩体岩石谱系单位划分及成因   总被引：1，自引：0，他引：1       下载免费PDF全文

孔令广  甘延景 《山东国土资源》2001,17(2):23-27

铜石岩体就位于燕山早期,有五次脉动侵入活动,相应地可建立五个单元,归并为铜石超单元;岩浆末期形成细晶岩、霏细岩,热膨胀形成隐爆角砾岩、侵入角砾岩及沉陷角砾岩等.铜石岩体具有花岗岩类高位深成复式岩体特征.  相似文献   

Geochemical constraints of the eclogite and granulite facies metamorphism as recognized in the Raobazhai complex from North Dabie Shan,China     

Y. L. Xiao  J. Hoefs  A. M. Van Den Kerkhof  S. G Li 《Journal of Metamorphic Geology》2001,19(1):3-19

A combined study of major and trace elements, fluid inclusions and oxygen isotopes has been carried out on garnet pyroxenite from the Raobazhai complex in the North Dabie Terrane (NDT). Well‐preserved compositional zoning with Na decreasing and Ca and Mg increasing from the core to rim of pyroxene in the garnet pyroxenite indicates eclogite facies metamorphism at the peak metamorphic stage and subsequent granulite facies metamorphism during uplift. A P–T path with substantial heating (from c. 750 to 900 °C) after the maximum pressure reveals a different uplift history compared with most other eclogites in the South Dabie Terrane (SDT). Fluid inclusion data can be correlated with the metamorphic grade: the fluid regime during the peak metamorphism (eclogite facies) was dominated by N₂‐bearing NaCl‐rich solutions, whereas it changed into CO₂‐dominated fluids during the granulite facies retrograde metamorphism. At a late retrograde metamorphic stage, probably after amphibolite facies metamorphism, some external low‐salinity fluids were involved. In situ UV‐laser oxygen isotope analysis was undertaken on a 7 mm garnet, and impure pyroxene, amphibole and plagioclase. The nearly homogeneous oxygen isotopic composition (δ¹⁸O_VSMOW = c. 6.7‰) in the garnet porphyroblast indicates closed fluid system conditions during garnet growth. However, isotopic fractionations between retrograde phases (amphibole and plagioclase) and garnet show an oxygen isotopic disequilibrium, indicating retrograde fluid–rock interactions. Unusual MORB‐like rare earth element (REE) patterns for whole rock of the garnet pyroxenite contrast with most ultra‐high‐pressure (UHP) eclogites in the Dabie‐Sulu area. However, the age‐corrected initial ε_Nd(t) is ? 2.9, which indicates that the protolith of the garnet pyroxenite was derived from an enriched mantle rather than from a MORB source. Combined with the present data of oxygen isotopic compositions and the characteristic N₂ content in the fluid inclusions, we suggest that the protolith of the garnet pyroxenite from Raobazhai formed in an enriched mantle fragment, which has been exposed to the surface prior to the Triassic metamorphism.  相似文献