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1.
A garnet-omphacite-kyanite-coesite geothermobarometer is constructed to estimate the peak metamorphic pressure of ultrahigh-pressure
(UHP) eclogites. For this we use a quaternary regular solution model for garnet, and propose a new model for sodic pyroxene
that assumes double site solid-solution (Na,Ca)M2(Al,Fe3+,Fe2+,Mg)M1Si2O6, where cations in the M2- and the M1-sites mix randomly but with inter-site interactions, not only between nearest neighboring
cations but also between next nearest neighboring cations. In the new model, overall excess interaction parameters are quantitatively
deduced from the previous experimental data and critical temperature, and the activity of the jadeite component agrees reasonably
with that based on the Landau theory. Furthermore, the relations of the calculated order parameter to temperature and composition
are consistent with other experimental works. These facts support the usefulness of the new model. Application of our geothermobarometer
to kyanite eclogite gave metamorphic conditions around 3.4 GPa and 800 ∘C for both samples from the Dora Maira Massif, Western Alps, and from Rongcheng County, in the Su-Lu region of eastern China.
Received: 30 December 1996 / Accepted: 25 August 1997 相似文献
2.
Two types of biotite isograd are defined in the low-grade metamorphism of the Wazuka area, a Ryoke metamorphic terrain in the Kii Peninsula, Japan. The first, BI1, is defined by the reaction of chlorite+K-feldspar= biotite+muscovite+quartz+H2O that took place in psammitic rocks, and the second, BI2, by the continuous reaction between muscovite, chlorite, biotite and quartz in pelitic rocks. The Fe/Mg ratios of the host rocks do not significantly affect the reactions. From the paragenesis of pelitic and psammitic metamorphic rocks, the following mineral zones were established for this low-pressure regional metamorphic terrain: chlorite, transitional, chlorite-biotite, biotite, and sillimanite. The celadonite content of muscovite solid solution in pelitic rocks decreases systematically with the grade of metamorphism from 38% in the chlorite zone to 11% in the biotite zone. Low pressure does not prohibit muscovite from showing the progressive change of composition, if only rocks with appropriate paragenesis are chosen. A qualitative phase diagram of the AKF system relevant to biotite formation suggests that the higher the pressure of metamorphism, the higher the celadonite content of muscovite at BI1, which is confirmed by comparing the muscovites from the Barrovian and Ryoke metamorphism. 相似文献
3.
The structure of the cosmic ray electron halo of a starburst galaxy depends strongly on the nature of galactic wind and the
configuration of the magnetic field. We have investigated these dependencies by solving numerically the propagation of electrons
originating in starburst galaxies, most likely in supernova remnants. The calculations are made for several models for the
galactic winds and for the configuration of the magnetic fields for comparison with observations. Our simulation of a quasi-radio
halo reproduces both the extended structure of ∼9 kpc and the subtle hollow structure near the polar region of the radio halo
that are observed in the starburst galaxy NGC 253. These findings suggest the existence of strong galactic wind in NGC 253.
相似文献
4.
山东海阳所麻粒岩向过渡榴辉岩转化的变质动力学过程及其构造意义 总被引：8，自引：3，他引：5
在山东半岛东南端的乳山海阳所,角闪岩和长英质片麻岩呈互层产出.在某些角闪岩层的中心残留有弱变形的麻粒岩和强变形的过渡榴辉岩(斜长石榴辉岩)团块.在弱变形的麻粒岩团块中发育有窄的(<1cm)剪切条带.沿着这些剪切条带和在强变形过渡榴辉岩团块中,原麻粒岩被转化为含斜长石的过渡榴辉岩.变形和流体在这一转化过程中加速了元素扩散和迁移的速度,在变形强和有流体加入的部位麻粒岩向榴辉岩转化的程度明显增强.麻粒岩相矿物组合(Cpx-Ⅰ+Opx+Pl-Ⅰ+ Hbl-Ⅰ + Grt-Ⅰ+ Ilm)及其花岗变晶结构被完好地保存于弱变形的麻粒岩中,其矿物成分显示出0.8～0.9 GPa和780℃～830℃的麻粒岩相变质条件.榴辉岩相叠加在麻粒岩中形成了一系列的环边状矿物和结构:环边状石榴石(Grt-Ⅱ)形成于麻粒岩相斜长石(Pl-Ⅰ)和暗色矿物(如Cpx-Ⅰ、Opx和Hbl-Ⅰ)的交界处,细粒石榴石(Grt-Ⅱ)、富钠单斜辉石(Cpx-Ⅱ)和石英形成于麻粒岩相角闪石(Hbl-Ⅰ)的外缘.同时榴辉岩相叠加造成麻粒岩相单斜辉石边缘钙契尔马克组份的降低和硬玉组份的升高.但在弱变形的麻粒岩中,麻粒岩相单斜辉石(Cpx-Ⅰ)的外缘并无榴辉岩相单斜辉石形成.沿着弱变形麻粒岩中的剪切条带和在过渡榴辉岩中,榴辉岩相矿物[Grt-Ⅱ+ Omp/Di(Cpx-Ⅱ)+ Ab(Pl-Ⅱ)+ Qtz + Hbl-Ⅱ+ Ky + Zo + Rut]广泛发育,它们的定向排列形成了明显的面理.其形成的温压条件为1.0～1.4 GPa和560℃～680℃,为过渡榴辉岩相变质.虽然其中仍然残留有被拉长的麻粒岩相单斜辉石,但它们含有很高的硬玉组份,且其外缘环绕有细粒的钠质透辉石或绿辉石(Cpx-Ⅱ).海阳所榴辉岩相变质的温压条件远远低于位于海阳所东南和东北的苏鲁超高压变质带中柯石英榴辉岩变质的温压条件.因此海阳所地区代表一条不同于超高压变质带的冷榴辉岩带,它可能与大别山南部的冷榴辉岩带相当.苏鲁超高压变质带的南部边界位于海阳所以北. 相似文献
5.
6.
Although much is known about overall sediment delivery ratios for catchments as components of sediment production and sediment yield, little is known about the component of temporary sediment storage. Sediment delivery ratios focused on the influence of storm-related sediment storage are measured at Matakonekone and Oil Springs tributaries of the Waipaoa River basin, east coast of New Zealand. The terrace deposits of both tributaries show abundant evidence of storm-related sedimentation, especially sediment delivered from Cyclone Bola, a 50 year return rainfall event which occurred in 1988. The sediment delivery ratio is calculated by dividing the volume of sediment transported from a tributary to the main stream by the volume of sediment generated at erosion sites in the tributary catchment. Because the sediment delivery volume is unknown, it can be calculated as the difference between sediment generation volume and sediment storage volume in the channel reach of the tributary. The volume of sediment generated from erosion sites in each tributary catchment was calculated from measurements made on aerial photographs dating from 1960 (1:44 000) and 1988 (1:27 000). The volume of sediment stored in the tributary can be calculated from measurements of cross-sections located along the tributary channel, which are accompanied by terrace deposits dated by counting annual growth rings of trees on terrace surfaces. Sediment delivery ratios are 0·93 for both Matakonekone catchment and Oil Springs catchment. Results indicate that Oil Springs catchment has contributed more than twice the volume of sediment to the Waipaoa River than the Matakonekone catchment (2·75 × 106 m3 vs 1·22 × 106 m3). Although large volumes of sediment are initially deposited during floods, subsequent smaller flows scour away much of these deposits. The sediment scouring rate from storage is 1·25 × 104 m3 a−1 for Matakonekone stream and 0·83 × 104 m3 a−1 for Oil Springs stream. Matakonekone and Oil Springs channels respond to extreme storms by instantaneously aggrading, then gradually excavating the temporarily stored sediment. Results from Matakonekone and Oil Springs streams suggest a mechanism by which event recurrence interval can strongly influence the magnitude of a geomorphic change. Matakonekone stream with its higher stream power is expected to excavate sediment deposits more rapidly and allow more rapid re-establishment of storage capacity. Copyright © 1999 John Wiley & Sons, Ltd. 相似文献
7.
Garnet-orthopyroxene and orthopyroxene-clinopyroxene relationships in simple and complex systems 总被引：10，自引：2，他引：10
Use of simple mixing models of orthopyroxene and garnet solid solutions enables extrapolation of experimentally determined equilibria in the MgSiO3-Al2O3 system to uninvestigated parts of pressure-temperature-composition space. Apparent discrepancies in the experimental data for simple and multicomponent systems may be explained by considering the effect of CaO and FeO on reducing pyrope activity in the garnet solid solutions. Equilibration pressures of natural garnet-orthopyroxene assemblages may be calculated, provided temperatures are known, from a combination of the experimental data on the MgSiO3-Al2O3 system and analyses of coexisting natural phases.Despite the presence of a compositional gap in the system, the solubility of enstatite in diopside coexisting with orthopyroxene can also be approximately treated by an ideal solution model. An empirical approach has been developed to take account of Fe2+ on the orthopyroxene-clinopyroxene miscibility gap in natural systems in order to calculate equilibration temperatures of 2-pyroxene assemblages. The model presented reproduces almost all of the available experimental data for multicomponent systems to within 60° C. 相似文献
8.
In pelitic schists of the Sanbagawa metamorphic belt, sphene, rutile, and ilmenite occur as discrete grains, in composite aggregates, and as inclusions in garnets. Textural relationships, disposition of inclusions in garnet, and the compositions of ilmenites suggest that the titanium-bearing accessories stable at the peak metamorphic conditions were as follows: sphene in the chlorite zone, sphene plus rutile in the garnet zone, and ilmenite in the highest grade of the belt, the biotite zone. Rutile appears in the garnet zone as a consequence of Ca incorporation into garnet and a progressive increase in
.Retrograde reactions were responsible for the composite aggregates of rutile, sphene and ilmenite and these must be carefully evaluated before prograde relationships between titanium-bearing accessories can be properly understood. 相似文献
9.
Tsuyoshi Morohashi Shohei Banno Masao Yamasaki 《Contributions to Mineralogy and Petrology》1974,47(3):187-196
Single whole crystals of calcic augite from M. Etna, Sicily, which display both sector and oscillatory zoning, have been serially sectioned and the form of the sectors mapped out. The principal intersectorial chemical variation is shown to be that of Ti and Al by as much as 39% (cation %) change in each, and the least variation, that of Ca (showing a 0.77 to 3.20% change). For each of three isochronous surfaces the ratio of Ti∶Al is shown to be individually constant no matter what the sector and this is thought to indicate near equilibrium conditions at the crystal/liquid interface. In addition to sector zoning these crystals display two types of concentric banding, having dimensions of about 0.25 mm, 20 μm. The 20 μm banding is shown to be both optically and chemically oscillated. Relative diffusion rates of cationic species in the melt, and growth rates of crystal faces are thought to play an important role in the formation of the oscillations, and the sector zoning. 相似文献
10.
Shohei Kozu Apsorn Sardsud Doungrutai Saesaengseerung Cherdchan Pothichaiya Sachiko Agematsu Katsuo Sashida 《地学前缘(英文版)》2017,8(6):1479-1493
The Khok Kruat Formation is the upper part of the Khorat Group, which consists of upper Lower Cretaceous non-marine sedimentary rocks in northeastern Thailand. Many dinosaur footprints have been known from the upper Lower Cretaceous (Aptian–Albian) Khok Kruat Formation at the Huai Dam Chum (Tha Uthen) site, northeastern Thailand. Approximately 600 tracks occur in thin mudstone layer of the northern part of the outcrop at the Huai Dam Chum track site. Two types of footprints, small-sized theropod and crocodylomorph are imprinted with mud cracks and ripple marks on the thin mud layer. Most of footprints are referred to cf. Asianopodus, and are imprinted by small-sized theropoda, probably ornithomimosauria. Theropod tracks are mainly separated into two groups, Group A and Group B. From ichnological viewpoints, the small-sized theropod track assemblage indicates the herd behaviour and its idiosyncratic group composition. In particular, the histogram of size-frequency measurements of Group A shows the anomalous bimodal distribution. We consider that there are two hypotheses; the first one is due to the male-female difference, and the second is a result of the different growing stage. 相似文献