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931.
C. PONCE J. F. SIMANCAS A. AZOR D. J. MARTÍNEZ POYATOS G. BOOTH‐REA I. EXPÓSITO 《Journal of Metamorphic Geology》2012,30(7):625-638
The early (Devonian) collisional stage in SW Iberia has been investigated through the analysis of deformation in the Cubito‐Moura schists, the main lithology of an Allochthonous Complex putatively rooted in the suture between the Ossa‐Morena and South Portuguese zones. The first deformation in these schists (D1) is recorded as a S1‐L1 mylonitic fabric well preserved in early quartz veins. Subsequent D2 deformation caused the main folds and the main (S2) foliation. After restoration, the stretching lineation (L1) trends at a small angle with the Ossa‐Morena/South Portuguese suture. This trend, together with the top‐to‐the‐east kinematics determined from quartz microfabric is indicative of an oblique left‐lateral collisional scenario in SW Iberia. Chlorite–white K‐mica–quartz ± chloritoid multi‐equilibrium calculations yield P–T conditions in the range 0.9–1.2 GPa and 300–400 °C, during the first collisional stage. P–T conditions during D2 were 0.3–0.8 GPa and 400–450 °C, thus indicating an important stage of exhumation of the Allochthonous Complex during these two collisional events, after subduction of the Ossa‐Morena Zone margin under the South Portuguese Zone continental crust. In the general context of the Variscan orogen, dominated by dextral collision, the left‐lateral convergence in SW Iberia can be explained in terms of the Avalonian salient represented by the South Portuguese Zone, which would impinge between Iberia and Morocco. 相似文献
932.
Dehydration and anatexis of ultrahigh‐pressure (UHP) metamorphic rocks during continental collision are two key processes that have great bearing on the physicochemical properties of deeply subducted continental crust at mantle depths. Determining the time and P–T conditions at which such events take place is needed to understand subduction‐zone tectonism. A combined petrological and zirconological study of UHP metagranite from the Sulu orogen reveals differential behaviours of dehydration and anatexis between two samples from the same UHP slice. The zircon mantle domains in one sample record eclogite facies dehydration metamorphism at 236 ± 5 Ma during subduction, exhibiting low REE contents, steep MREE–HREE patterns without negative Eu anomalies, low Th, Nb and Ta contents, low temperatures of 651–750 °C and inclusions of quartz, apatite and jadeite. A second mantle domain records high‐T anatexis at 223 ± 3 Ma during exhumation, showing high REE contents, steeper MREE–HREE patterns with marked negative Eu anomalies, high Hf, Nb, Ta, Th and U contents, high temperatures of 698–879 °C and multiphase solid inclusions of albite + muscovite + quartz. In contrast, in a second sample, one zircon mantle domain records limited hydration anatexis at 237 ± 3 Ma during subduction, exhibiting high REE contents, steep MREE–HREE patterns with marked negative Eu anomalies, high Hf, Nb, Ta, Th and U contents, medium temperatures of 601–717 °C and multiphase solid inclusions of albite + muscovite + hydrohalite. A second mantle domain in this sample records a low‐T dehydration metamorphism throughout the whole continental collision in the Triassic, showing low REE contents, steep MREE–HREE patterns with weakly negative Eu anomalies, low Th, Nb and Ta contents, low temperatures of 524–669 °C and anhydrite + gas inclusions. Garnet, phengite and allanite/epidote in these two samples also exhibit different variations in texture and major‐trace element compositions, in accordance with the zircon records. The distinct P–T–t paths for these two samples suggest separate processes of dehydration and anatexis, which are ascribed to the different geothermal gradients at different positions inside the same crustal slice during continental subduction‐zone metamorphism. Therefore, the subducting continental crust underwent variable extents of dehydration and anatexis in response to the change in subduction‐zone P–T conditions. 相似文献
933.
Geochemistry and Genesis of the Late Jurassic Granitoids at Northern Great Hinggan Range: Implications for Exploration 总被引:2,自引:1,他引:1
<正>The Longgouhe and Ershiyizhan intrusions of the Late Jurassic,located in the Upper Heilongjiang Basin of the northern Great Hinggan Range,are closely related to porphyry Cu-Au mineralizations.In lithology the intrusions are quartz diorite,quartz monzodiorite and granodiorite of high-K calc-alkaline series,with minor aspects of shoshonite series.Their SiO_2 and Al_2O_3 contents range from 61.37%to 66.59%and 15.35%to 17.06%,respectively.The MgO content ranges from 2.02%to 3.47%,with Mg~# indices of 44-59.The(La/Yb)_N and Eu/Eu~* values range from 16.85 to 81.73 and 0.68 to 0.93,respectively,showing strong differentiation rare earth element(REE) patterns similar to those of adakites.The rocks are enriched in Ba,Sr and light REE(LREE),obviously depleted in Nb and Ta,slightly depleted in Rb and Ti,and poor in Yb and Y,with Yb and Y contents of 0.31-1.32 ppm and 4.32-12.07 ppm,respectively.As indicated by Sr/Y ratios of 67.74-220.60,the rocks are characterized by low-Y and high-Sr contents,which characterize the adakites in the world.Holistically, geochemical tracers suggest that the interested intrusions are adakitic rocks.Given that the Paleo-Asian Ocean and Mongol-Okhotsk Ocean were closed in the Late Paleozoic and Permian-Middle Jurassic,respectively,the interested intrusions should be formed by partial melting of delaminated crust,which had been thickened during collisional orogeny between the Siberian and Mongolian-Sinokorean continents. 相似文献
934.
基于ESSG的空间轨道目标管理与碰撞检测方法 总被引:1,自引:1,他引:0
随着航天科技的快速发展,大量的空间目标(航天器与空间碎片)占用了有限的轨道资源,极大地改变了空间环境,影响了正常的航天发射、空间科学活动及其安全。该文针对空间目标的特点与安全性,提出了利用地球系统空间格网(ESSG)对空间轨道目标进行格网化管理的思路,介绍了格网管理的原理,设计了轨道目标碰撞检测方法。重点探讨了空间轨道目标对格网的映射、静态和动态空间目标的数据导入、空间目标碰撞风险检测等基本问题;设计了一个原理性实验,验证了该文方法的可行性。 相似文献
935.
Vessel-based observations of water column structure and flow near a shallow-crested seamount are used to quantify the physical disturbance induced by that seamount. The implications of this disturbance on the ‘feeding hole’ hypothesis are then examined based on data from moored thermistors and acoustic current profilers, as well as vessel-based acoustic sounding-derived biomass estimates, currents, and conductivity-temperature-depth profiles from a 55 km square grid of stations around the crest. Mean currents in the region of 0.2 m s?1 are comparable to observations from surface drifters whereas the semidiurnal tidal flow amplitude was one third of this. Thorpe Scale-based estimates of energy dissipation rate were in the range 10?9 to 2.10?8 W kg?1 and vertical diffusivities Kz were in the range 10?4 to 10?3 m2 s?1. Turbulence levels were higher upstream of the seamount–likely due to the influence of nearby seamounts Rumble IV and V. There was no evidence of a Taylor Cap in the Rumble III velocity field. The sounder data provide some evidence of a feeding hole and analysis based on diffusivities suggests that this might persist downstream of the seamount for as much as 7 days. 相似文献
936.
V. N. Kodagali 《Marine Geodesy》2013,36(2):83-90
Abstract The morphology of a seamount at 12°35'S and 76°16'E is studied. This conical seamount has a maximum height of 1275 m (water depth 4135 m) and covers an area of about 189 sq km. The maximum basal extension is about 24 km. The mount is gentler and lengthier on the western flank and steeper and shorter on the eastern flank. A conspicuous flat steplike feature is present on the western flank. Slope angles are high (up to 35°). The trend of the seamount is approximately NNE‐SSW. Dredging yielded basalts containing ferromanganese encrustations indicating its volcanic origin. 相似文献
937.
汪新 《中国海洋湖沼学报》1994,12(1):42-45
Taiwan Channel and environs developed typical collision structural zones in the Zhejiang-Fujian coast and Taiwan central mountain, analysis of which revealed their Late Mesozoic collision orogenesis. 相似文献
938.
U—Pb Dating of Marble Assoicated With Eclogite from the Dabie Mountains,East China 总被引:13,自引:0,他引:13
Marble is associated with ultrahigh pressure eclogite in the Dabie Mountains, East China. U-Pb isotope data for the marble
define a238U-206Pb isochron age of 435 ± 45 Ma with an initial206Pb/204Pb value of 18.075 ± 0.006. The age of ∼435 Ma is interpreted to represent the time of limestone diagenesis rather than the
time of metamorphic resetting accompanied by the formation of the ultrahigh pressure eclogites at Triassic. The paleontologic
and stratigraphic studies also favor a local excursion in the carbon isotopic composition of the latest Ordovician water within
a sedimentary basin between the Sino-Korean and Yangtze cratons. Because the latest Ordovician limestone was involved in the
eclogite formation, the continental collision between the Yangtze and Sino-Korean plates would postdate Ordovician.
This project was financially supported by the National Natural Science Foundation of China and the Chinese Academy of Sciences. 相似文献
939.
S. Bhattacharya 《Journal of Earth System Science》1997,106(3):65-75
Three major episodes of folding are evident in the Eastern Ghats terrain. The first and second generation folds are the reclined type; coaxial refolding has produced hook-shaped folds, except in massif-type charnockites in which non-coaxial refolding has produced arrow head folds. The third generation folds are upright with a stretching lineation parallel to subhorizontal fold axes. The sequence of fold stylesreclinedF 1and coaxialF 2, clearly points to an early compressional regime and attendant progressive simple shear. Significant subhorizontal extension duringF 3folding is indicated by stretching lineation parallel to subhorizontal fold axes. In the massif-type charnockites low plunges ofF 2folds indicate a flattening type of deformation partitioning in the weakly foliated rocks (magmatic ?). The juxtaposition of EGMB against the Iron Ore Craton of Singhbhum by oblique collision is indicative of a transpressional regime. 相似文献
940.
INTRODUCTIONE丑dhquMes re the result ofsuddenfauting In the ea耐h crust;It Is an expression dstructurafrllust劝ilityinthe ealth.China Is a re9on with active Intraplatefauting and Intn叩late ellhqu吐es.Many resea。hers have studied the genesis and mechanism ofealthop业es In China and neighboringegions fom the vlemplnt Of continental geology(Ma et al,1986;Ding et al,1991;Luo,1979;Zhang,1979;Zhang,1979;Wang et al,1979;Zhang et al,1994).The。search results showthatsome certain relat… 相似文献