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1.
Christopher I. Chalokwu Alexei A. Ariskin Evgeny V. Koptev-Dvornikov 《Geochimica et cosmochimica acta》1996,60(24):4997-5011
A characteristic feature of the Partridge River intrusion of the Keweenawan Duluth Complex is the approximately fivefold to ninefold increase in the concentrations of incompatible elements in the lower zone compared with cumulates stratigraphically higher. The concentrations of incompatible elements decrease from the lower zone upward to steady state values, which is ascribed to variations in the proportions of trapped liquid rather than variable degrees of fractional crystallization of a single parental magma. The calculated average composition of trapped liquid using our algorithm is similar to typical Keweenawan low-alumina, high Ti---P basalts associated with the Duluth Complex but is different from the leading edge ferrodioritic liquid quenched in the chilled margin of the intrusion. This difference suggests that the chilled margin does not represent the original (parental) magma composition from which the whole intrusion solidified, and that the enrichment of incompatible elements may be related to the local flotation of magmatic suspensions. To test the latter hypothesis numerically, we have used heat-mass transfer models, assuming a sheet-like magma chamber, to calculate the parameters of the model that best reproduce the observed distribution of incompatible elements in a mush zone at the base of the Partridge River intrusion. The results indicate that a mush zone enriched in the incompatible elements is produced if the velocity of movement of the lower solidification front into the magma body was less than the floating velocity of the bulk crystal mush. The dynamic parameters that best reproduce the observed distribution of incompatible elements include a magma emplacement pressure of 2 kbar, critical crystallinities of 50–68% in the mush zone from which the liquid is being expelled, and an emplacement temperature of 1160°C for the initial magma. 相似文献
2.
Evgeny Kh. TURUTANOV Evgeny V. SKLYAROV Valentina V. MORDVINOVA Anatoly M. MAZUKABZOV Viktor S. KANAYKIN 《地学前缘》2021,28(5):260-282
地学断面是指地壳的垂直剖面,主要通过对地质和地球物理资料的综合分析来揭示构造带的性质及其空间关系。横断面的研究所采用的数据基本包括100 km宽区域地质图、上地壳的地质剖面图、重磁图(沿横断面的重磁剖面图)以及地壳的地震波速度、密度和其他地球物理属性的剖面图。这些数据被用于构建综合的数据剖面图(结果图),以展示各种地球动力学条件下(裂谷、海洋、碰撞带、造山盆地、大陆地台和岩浆弧,包括安第斯岛弧、活动大陆边缘、海沟、弧前和弧后盆地)的特定的岩石组构。本项目的研究目标是根据研究区现存的地质和地球物理数据的综合解释,统一图例,建立研究区深部剖面,以确定地体的空间关系及其在板块构造方面的地球动力学性质。 前人已分别对东西伯利亚南部和蒙古境内的多个地体进行了构造划分,并对它们的地球动力学性质和时空关系进行了分析。研究结果显示该系列地体为早古生代、中晚古生代和晚古生代—早中生代的岛弧和微大陆。此外,研究还识别出了中—晚古生代和晚古生代—早中生代安第斯型活动大陆边缘、晚古生代—早中生代被动大陆边缘和早白垩世裂谷。与岛弧和安第斯型活动大陆边缘相关的岩体被推覆至相邻大陆和微陆块上,部分推覆宽度可达150 km。目前已开展泥盆纪到晚侏罗世时期蒙古-鄂霍次克海地区的古地球动力学重建。 “非地槽”型花岗岩类岩浆作用在板块构造方面找到了直接且合理的解释,其中泥盆纪—石炭纪和二叠纪—三叠纪岩浆作用区域对应于安第斯型活动大陆边缘,中—晚侏罗世岩浆作用则与西伯利亚/蒙古-中国大陆板块碰撞有关。碰撞岩浆作用中亚碱性(地幔)元素的存在及其所在的构造区域在很大程度可以说明蒙古-鄂霍次克海闭合后,巨厚大陆岩石圈下曾经发生过持续的大洋裂谷活动(地幔热点)。在早白垩世时期,大陆裂谷活动影响到了同一时期正在发生的大陆汇聚作用。 西伯利亚南部边界大部分具有安第斯型活动大陆边缘性质,这也是蒙古—鄂霍次克缝合线沿线蛇绿岩数量较少的原因。因为当汇聚大陆一个具有安第斯类型的活动边缘,而另一个具有被动边缘时,前者的大陆地壳会最终逆冲到后者之上,并因此破坏掉先前出露的蛇绿杂岩体。部分被破坏的蛇绿岩块是俯冲带保留下来的海山残余,其可能成为增生-俯冲楔体的混沌复合体的一部分。然而,由于快速俯冲作用,这种楔形体在晚二叠世—早侏罗世的积累并不是西伯利亚活动边缘的典型特征。 沿地学断面综合的地质和地球物理资料分析表明,亚洲大陆是在显生宙时期由部分前寒武纪微陆块构造拼贴而成的。前寒武纪地块间存在不同宽度的已变形且剥蚀强烈的显生宙火山弧,它们也被归类为特定地体。 相似文献
3.
Henning Lorenz David G. Gee Evgeny Korago Galina Kovaleva William C. McClelland Jane A. Gilotti Dirk Frei 《地学学报》2013,25(6):496-503
The Novaya Zemlya fold‐and‐thrust‐belt is the northern continuation of the late Palaeozoic Uralide Orogen. Little is known about its deeper structure and the basement history of the adjacent Barents and Kara shelves. Based on geological evidence and detrital zircon analysis of 28 samples from the northeastern and stratigraphically deepest part of the archipelago, we demonstrate that Cambro‐Ordovician turbidite‐dominated deposition was almost exclusively sourced from rocks consolidated during the Timanian orogeny (Timanian basement). A profound change in provenance occurred near the end of the Ordovician. Over 90% of the zircons from Silurian and about 80% from Devonian strata have ages characteristic of the Sveconorwegian Orogen, implying uplift of these rocks in the vicinity of Novaya Zemlya. The presence of Sveconorwegian and Grenvillian rocks in the high Arctic suggests revision of recent reconstructions of the Rodinia supercontinent, its break‐up and subsequent Caledonian orogeny. 相似文献
4.
Due to their potential retention capacity, clay minerals have been proposed for use in the engineered barriers for the storage of high-level radioactive actinides in deep geological waste repositories. However, there is still a lack of data on the sorption of actinides in clays in conditions simulating those of the repositories. The present article examines the sorption of two lanthanides (actinide analogues) in a set of smectitic clays (FEBEX bentonite, MX80 bentonite, hectorite, saponite, Otay montmorillonite, and Texas montmorillonite). Distribution coefficients (Kd) were determined in two media: water and 0.02 mol L−1 Ca, the latter representing the cement leachates that may modify the chemical composition of the water in contact with the clay. The Kd values of the lanthanides used in the experiments (La and Lu) varied greatly (25-50 000 L kg−1) depending on the ionic medium (higher values in water than in the Ca medium), the initial lanthanide concentration (up to three orders of magnitude decrease inversely with lanthanide concentration), and the examined clay (up to one order of magnitude for the same lanthanide and sorption medium). Freundlich and Langmuir isotherms were used to fit sorption data to allow comparison of the sorption parameters among smectites. The model based on the two-site Langmuir isotherms provided the best fit of the sorption data, confirming the existence of sorption sites with different binding energies. The sites with higher sorption affinity were about 6% of the total sorption capacity in the water medium, and up to 17% in the Ca medium, although in this latter site sorption selectivity was lower. The wide range of Kd values obtained regarding the factors examined indicated that the retention properties of the clays should also be considered when selecting a suitable clay for engineered barriers. 相似文献
5.
The dynamical behavior of low and moderately high optical depth regions of Saturn's ring system of discrete, mutually gravitating, and inelastically colliding particles is studied by simplified local N-body simulations in Hill's linearized equations context. The focus is on a statistical analysis of time-evolution of fine-scale structures seen in the simulations and the comparison between theoretical predictions and computer experiments. Prospects for the Cassini spacecraft mission are briefly summarized. 相似文献
6.
The linear theory and N-body simulations are used to present a new, alternative model of the galaxy A0035-324 (the “Cartwheel”), which is the most
striking example of the relatively small class of ring galaxies. The model is based on the gravitational Jeans-type instability
of both axisymmetric (radial) and nonaxisymmetric (spiral) small-amplitude gravity perturbations (e.g., those produced by
spontaneous disturbances) of a dynamically cold subsystem (identified as the gaseous component) of an isolated disk galaxy.
The simplified model of a galaxy is used in which stars (and a dark matter, if it exists at all) do not participate in the
disk collective oscillations and just form a background charge. In the theory presented here, a case for both purely radial
solutions and purely spiral solutions to the equations of motion of an infinitesimally thin gaseous disk is made, which is
associated with both a radial density wave and a dominant spiral density wave which propagate outwards creating a rough ring
and a number of spiral arms. Through three-dimensional numerical simulation of a collisionless set of many particles, I associate
these gravitationally unstable axisymmetric waves and nonaxisymmetric waves with growing clumps of matter which take on the
appearance of a ring and spokes of mass blobs. 相似文献
7.
Victor G. Kornilov Vladimir M. Lipunov Evgeny S. Gorbovskoy Aleksander A. Belinski Dmitry A. Kuvshinov Natalia V. Tyurina Nikolai I. Shatsky Anatoly V. Sankovich Aleksander V. Krylov Pavel V. Balanutsa Vadim V. Chazov Artem S. Kuznetsov Dmitry S. Zimnuhov Victor A. Senik Andrey G. Tlatov Aleksander V. Parkhomenko Denis V. Dormidontov Vadim V. Krushinsky Ivan S. Zalozhnyh Aleksander A. Popov Sergey A. Yazev Nikolai M. Budnev Kirill I. Ivanov Evgeny N. Konstantinov Oleg A. Gress Oleg V. Chvalaev Vladimir V. Yurkov Yury P. Sergienko Irina P. Kudelina 《Experimental Astronomy》2012,33(1):173-196
Presented paper describes the basic principles and features of the implementation of a robotic network of optical telescopes MASTER, designed to study the prompt (simultaneous with gamma radiation) optical emission of gamma-ray bursts and to perform the sky survey to detect unknown objects and transient phenomena. With joint efforts of Sternberg astronomical institute, High altitude astronomical station of the Pulkovo observatory, Ural state university, Irkutsk state university, Blagoveshchensk pedagogical university, the robotic telescopes MASTER?II near Kislovodsk, Yekaterinburg, Irkutsk and Blagoveshchensk were installed and tested. The network spread over the longitudes is greater than 6?h. A further expansion of the network is considered. 相似文献
8.
Evgeny Griv 《Monthly notices of the Royal Astronomical Society》2006,365(3):1007-1011
The possibility that protoplanetary gaseous discs are dynamically unstable to axisymmetric and non-axisymmetric gravity perturbations (e.g. those produced by spontaneous disturbances) with characteristic scales larger than the vertical scale height is discussed analytically, using a local Wentzel–Kramers–Brillouin (WKB) approach. It is shown that such discs might be clumpy, and these gravitationally bound clumps may later collapse to become giant planets ('hot Jupiters'). The chief aim in this paper is to underscore a fact of vital importance for application in the planetary formation process: gravitationally unstable non-axisymmetric (spiral) perturbations can effectively transport both the angular momentum and the mass in a spatially inhomogeneous disc. 相似文献
9.
One of the problems encountered in a variety of near-surface investigations is detecting and mapping localized heterogeneities. The heterogeneities may be classified under two kinds of objects: (1) a point diffractor that can be considered as an approximation of a small quasi-isometric, such as small karstic cavities and caves; (2) a linear diffractor roughly approximating an elongated object, such as a tube or fault plane. The point and linear diffractors generate two types of seismic diffraction: tip and edge waves, respectively. During the last few decades, different methods were proposed by many researchers for detecting these heterogeneities utilizing seismic waves diffracted by them. An alternative method for detecting point diffractors using a time-reversal principle combined with focusing analysis is proposed in this study: we present an extension of the time-reversal method for linear diffractors. It consists of a coherent summation of seismic energy along edge-diffraction traveltimes. Real data examples show the feasibility and efficiency of the proposed method. 相似文献
10.
Railroad operating experience in permafrost conditions has shown that deformations of embankments on thawing foun-dations last for a long time. After an initial period of heat settlement due to permafr... 相似文献