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11.
G. Diego Gatta Nicola Rotiroti Martin Fisch Milen Kadiyski Thomas Armbruster 《Physics and Chemistry of Minerals》2008,35(9):521-533
The elastic and structural behaviour of the synthetic zeolite CsAlSi5O12 (a = 16.753(4), b = 13.797(3) and c = 5.0235(17) Å, space group Ama2, Z = 2) were investigated up to 8.5 GPa by in situ single-crystal X-ray diffraction with a diamond anvil cell under hydrostatic conditions. No phase-transition occurs within the P-range investigated. Fitting the volume data with a third-order Birch–Murnaghan equation-of-state gives: V 0 = 1,155(4) Å3, K T0 = 20(1) GPa and K′ = 6.5(7). The “axial moduli” were calculated with a third-order “linearized” BM-EoS, substituting the cube of the individual lattice parameter (a 3, b 3, c 3) for the volume. The refined axial-EoS parameters are: a 0 = 16.701(44) Å, K T0a = 14(2) GPa (βa = 0.024(3) GPa?1), K′ a = 6.2(8) for the a-axis; b 0 = 13.778(20) Å, K T0b = 21(3) GPa (βb = 0.016(2) GPa?1), K′ b = 10(2) for the b-axis; c 0 = 5.018(7) Å, K T0c = 33(3) GPa (βc = 0.010(1) GPa?1), K′ c = 3.2(8) for the c-axis (K T0a:K T0b:K T0c = 1:1.50:2.36). The HP-crystal structure evolution was studied on the basis of several structural refinements at different pressures: 0.0001 GPa (with crystal in DAC without any pressure medium), 1.58(3), 1.75(4), 1.94(6), 3.25(4), 4.69(5), 7.36(6), 8.45(5) and 0.0001 GPa (after decompression). The main deformation mechanisms at high-pressure are basically driven by tetrahedral tilting, the tetrahedra behaving as rigid-units. A change in the compressional mechanisms was observed at P ≤ 2 GPa. The P-induced structural rearrangement up to 8.5 GPa is completely reversible. The high thermo-elastic stability of CsAlSi5O12, the immobility of Cs at HT/HP-conditions, the preservation of crystallinity at least up to 8.5 GPa and 1,000°C in elastic regime and the extremely low leaching rate of Cs from CsAlSi5O12 allow to consider this open-framework silicate as functional material potentially usable for fixation and deposition of Cs radioisotopes. 相似文献
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利用矿物地质温压计估算变质高峰期温压条件、退变质作用温压条件。研究表明,本区为鲁苏构造带的北延部分,代表本区晚元古代华南陆块与华北陆块的碰撞及三叠纪华北陆块向华南陆块推覆事件的发生和演化。 相似文献
14.
U. Altenberger R. Schmid R. Oberhänsli 《International Journal of Earth Sciences》2008,97(6):1301-1314
As part of the Yangtze plate, segments of the Dabie Shan terrane of Central China underwent ultra-high pressure metamorphism
during Triassic subduction. We studied the geochemistry of the abundant eclogites to evaluate the nature of the protoliths
and their geodynamic setting. Although some previous geochemical work exists, the analyses and interpretation herein are based
on a new subdivision of the ultra-high pressure sequence into basement and cover units (Changpu and Ganghe Unit), revealing
new and important results. In addition, eclogites of the so-called HP Unit south of the UHP units were studied. Whereas the
large ion lithophile elements indicate postmagmatic, metasomatic changes of some samples, the high-field strength elements
and the rare earth elements display original magmatic trends. The geochemical characteristics of the eclogites of the ultra-high
pressure areas display a strong dependence on their “structural” and geographic position. The eclogites of the basement and
the Changpu Unit indicate melt intrusion and extrusion in a continental rift system, i.e. during extensional tectonics. In
contrast, the Ganghe Unit is characterized by a pronounced chemical homogeneity. The composition of the eclogites indicates
generation from a mantle source highly influenced by slab-derived fluids. Those of the HP Unit show similar characteristics.
Magmatism of the Ganghe and HP Unit probably occurred in a continental arc setting. A similar age for both units, geographically
and/or tectonically separated, is possible. The geodynamic interpretation based on the geochemistry of the four units points
to a Neoproterozoic scenario in which the protoliths of the HP and the cover units could have been of similar age and deposited
in one evolving geological system. A rift-related larger-scale basin might have formed, e.g. a continental back-arc basin
behind a magmatic arc after or simultaneous to sedimentation and magmatism in the magmatic arc. Alternatively, magmatism occurred
in independent geodynamic settings, distinct in time and space. The units were juxtaposed during exhumation, after subduction
to varying depths. 相似文献
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大别山榴辉岩一片麻岩杂岩的成因 总被引:2,自引:1,他引:1
大别山榴辉岩由辉长岩、大陆拉斑玄武岩和少量泥灰质经高压变质作用形成。大别地块可划分出四个形成条件不同的榴辉岩区,它们代表一种构造-岩石组合体。片麻岩杂岩中各种高压变质岩类的发现证明它们与榴辉岩一起经历了原地高压变质过程。二者变质作用P-T参数的差异归因于抬升过程中退变质反应速度的不同。不同地区榴辉岩退变质组合及P-T条件与围岩的一致性表明,大别杂岩现今所展示的“递增”变质带是由榴辉岩相退变质作用形成的。高压榴辉岩-片麻岩杂岩的产生是印支期扬子与华北两个大陆板块碰撞的结果。 相似文献
17.
Tectonometamorphic evolution of the Bohemian Massif: evidence from high pressure metamorphic rocks 总被引:4,自引:0,他引:4
The Variscan orogenic belt, of which the Bohemian Massif is a part, is typically recognized for its characteristic low pressure, high temperature metamorphism and a large volume of granites. However, there are also bodies of high pressure rocks (eclogites, garnet peridotites and high pressure granulites) which are small in size but widely distributed throughtout the Massif. Initially the high pressure rocks were considered to be relicts of a much older orogenic event, but the increasing data derived from isotopic and geochronological investigations show that many of these rocks have Palaeozoic protoliths. Metamorphic ages from the high pressure rocks define no single event. Instead, a number of discrete clusters of ages are found between about 430 Ma and the time of the dominant low pressure event at around 320–330 Ma.Most of the eclogite and granulite facies rocks are assigned to allochthonous nappes that arrived close to the end of the low pressure event, but before final granite intrusion. The nappes contain a mixture of different units and the relationship between rocks with high pressure relicts and host gneisses with no apparent signs of deep burial is still problematic. Some of the high pressure rocks retain evidence of multiple stages of partial re-equilibration during uplift. Moreover, it can be shown in certain instances that host gneisses also endured a multistage metamorphic development but with a peak event convergent with one of the breakdown stages in the enclosed rocks with high pressure relicts. It thus appears that the nappe units are composite bodies probably formed during episodic intracrustal thrusting. Fluids derived from prograde dehydration reactions in the newly under thrusting slab are taken to be the catalysts that drove the partial re-equilibrations.On the scale of the whole Massif it can be seen within the units with high pressure relicts that the temperature at the peak recorded pressure and that during the breakdown are variable in different locations. It is interpreted that regional metamorphic gradients are preserved for given stages in the history and thus the present day dismembered nappe relicts are not too far removed from their original spatial distribution in an original coherent unit. From the temperature information alone it is highly probable that the refrigerating underthrusting slab was situated in the north-west. However, this north-west to south-east underthrusting probably represents the major 380–370 Ma event and is no guide to the final thrusting that emplaced the much thinned nappe pile with high pressure relicts.Granite genesis is attributed to the late stage stacking, during the final Himalayan-type collision stage, of thinned crust covered by young, water-rich, sediments — erosion products of the earlier orogenic stages. Regional metamorphism at shallow depths above the voluminous granites was followed by final nappe emplacement which rejuvenated the granite ascent in places.
Correspondence to: P. J. O'Brien 相似文献
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W. U. Reimold 《Earth, Moon, and Planets》1995,70(1-3):21-45
Only since several decades has impact cratering been recognized as an important surface process on all planetary bodies in the Solar System. However, as the process has not yet been effectively introduced into geological curricula, it is necessary to inform a wider public about its importance for (i) planetary formation and (ii) evolution, (iii) the understanding of this process as a geological process, (iv) the terrestrial impact crater record and its limitations, and (v) the recognition criteria for terrestrial impact structures, as well as (vi) the need of improvement of the impact cratering record in the light of the potential danger of an impact catastrophe on this planet. It is, particularly for developing countries, of interest to examine the economic and educational-environmental potential of impact structures. That it is possible to carry out an effective, low-budget geological investigation of impact structures within a Second World environment is demonstrated by the discussion of the progress that has been made in recent years with regard to the Southern African impact crater record. Several recommendations on how to improve, on the one hand, the terrestrial impact crater record and, on the other, their general working situation by activation of workers in Developing Countries are discussed. 相似文献
20.