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The quiet-day geomagnetic field variation data from the recently commissioned Nagpur geomagnetic observatory, which has augmented the currently active latitudinal chain of Indian magnetic observatories, are analysed for the year 1993- The variations for diurnal frequencies (Sq) recorded at Nagpur do not follow the expected trend with latitude. This is most conspicuous in the northward horizontal ( X ) component. The anomalous behaviour at Nagpur is also seen in the diurnal harmonic amplitudes when compared with those of the neighbouring stations Alibag (south of Nagpur) and Ujjain (north of Nagpur). This behaviour is attributed to the presence of electrically conducting anomalous sources in the vicinity of Nagpur. The anomalous internal source is inferred to be located at relatively shallower depths and is highly localized. 相似文献
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计算了对应于各个UT小时的24个经度带的Sq地下感应场对外部施感场的响应函数,应用Schmucker'sApproximateEuristic反演方法,计算了这些经度带的地下等效层及其电导率分布,得到了地壳-上地幔电导率经向分布的大致图案。对该结果的分析研究得出,全球电导率经向分布存在着极大的不均匀性,在0-400km深度范围内,太平洋和大西洋为低导区;欧亚大陆与美洲大陆为高导区。电导率分布特征与岩石层结构有明显的相关性:在俯冲带,低导区由海洋向大陆下插入;在大洋中脊表现为高导电性。反演结果与地震层析成像结果的比较表明,地下高电导区和低电导区的位置分别对应于地震波低速区和高速区。 相似文献
24.
Françoise Roger Jean-Patrick Respaut Maurice Brunel Philippe Matte Jean-Louis Paquette 《Comptes Rendus Geoscience》2004,336(1):19-28
We present new U–Pb results on felsic Augen orthogneisses from the Axial Zone of the Montagne Noire (French Massif Central). The data indicate Ordovician ages, 456±3 and 450±6 Ma for two samples collected at ‘Pont-de-Larn’ and ‘Gorges d'Héric’, respectively. These ages are interpreted as the igneous emplacement age of the granitic protolith. To cite this article: F. Roger et al., C. R. Geoscience 336 (2004). 相似文献
25.
Philippe Matte 《Comptes Rendus Geoscience》2002,334(10):773-779
The Palaeozoic of the western Pyrenees shows two superposed tectonics easily defined by their different geometry and the major unconformity of the Permian sediments and volcanics on the Devono-Carboniferous series: an Hercynian tectonic found only in the pre-Permian series, characterised by kilometric westward recumbent folds with a weak cleavage; a Pyrenean tectonic, characterised by tight east–west folds, upright to overturned to the south with slaty cleavage, which is the only deformation found in the Permian and Mesozoic series and the second deformation in the pre-Permian Palaeozoic. The Hercynian folding, roughly perpendicular to the trend of the Pyrenees characterises the northern branch of the Ibero-Armorican virgation. To cite this article: P. Matte, C. R. Geoscience 334 (2002) 773–779. 相似文献
26.
地磁Z分量日变"低点位移"异常成因分析 总被引:2,自引:0,他引:2
本文基于对地磁Z分量日变"低点位移"异常和太阳静日变化内外源场等效涡旋电流体系时空演化特征的分析,提出了"电磁炉效应"假说,以解释地磁Z分量日变"低点位移"异常的成因.本文认为,起源于地球内部和外部涡旋电流体系所产生的太阳静日变化Sq,作为一个持续的交变磁场,切割地壳深部的高导低速层,形成涡旋电流并产生热能,致使高导低... 相似文献
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《International Geology Review》2012,54(16):2060-2082
The Kazda?? Massif was previously considered as the metamorphic basement of the Sakarya Zone, a microcontinental fragment in NW Anatolia. Our new field mapping, geochemical investigations, and radiometric dating lead to a re-evaluation of previous suggested models of the massif. The Kazda?? metamorphic succession is subdivided into two major units separated by a pronounced unconformity. The lower unit (the Tozlu metaophiolite) is a typical oceanic crust assemblage consisting of ultramafic rocks and cumulate gabbros. It is unconformably overlain by a thick platform sequence of the upper group (the Sar?k?z unit). The basement ophiolites and overlying platform strata were subjected to a single stage of high-temperature metamorphism under progressive compression during the Alpine orogeny, accompanied by migmatitic metagranite emplacement. Radiometric age data obtained from the Kazda?? metamorphic succession reveal a wide range of ages. Metagranites of the Kazda?? metamorphic succession define a U–Pb discordia upper intercept age of ca. 230 Ma and a lower intercept age of 24.8 ± 4.6 Ma. This younger age agrees with 207Pb/206Pb single-zircon evaporation ages of 28.2 ± 4.1 to 26 ± 5.6 Ma. Moreover, a lower intercept age of 28 ± 10 Ma from a leucocratic metagranite supports the Alpine ages of the massif within error limits. Reconnaissance detrital zircon ages constrain a wide range of possible transport and deposition ages of the metasediments in the Sar?k?z unit from ca. 120 to 420 Ma. Following high-temperature metamorphism and metagranite emplacement, the Kazda?? sequence was internally imbricated by Alpine compression, and the lowermost Tozlu ophiolite thrust southward onto the Sar?k?z unit. Field mapping, internal stratigraphy, and new radiometric age data show that the Sar?k?z unit is the metamorphic equivalent of the Mesozoic platform succession of the Sakarya Zone. The underlying metaophiolites are remnants of the Palaeo tethys Ocean, which closed during the early Alpine orogeny. After strong deformation attending nappe emplacement, the unmetamorphosed Miocene Evciler and Kavlaklar granites intruded the tectonic packages of the Kazda?? Massif. During Pleistocene time, the Kazda?? Massif was elevated by EW trending high-angle normal faults dipping to Edremit Gulf, and attained its present structural and topographic position. Tectonic imbrication, erosion and younger E–W-trending faulting were the main cause of the exhumation of the massif. 相似文献
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???????????????????????????????????????б??????????t??????????????????????????????????????????????????????????????????????????????????????DEM?? 相似文献
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利用积累的磁照图——S_q曲线,通过计算机进行S-q图象编整处理后作对比分析,对局部磁异常(S_q时段)变化进行探讨,总结地震孕育过程震磁效应的相关性,更好地为地震预报提供依据。 相似文献