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1.
Mihoko Hoshino Mitsuyoshi Kimata Norimasa Nishida Masahiro Shimizu 《Physics and Chemistry of Minerals》2010,37(5):255-263
Euhedral dissakisites from Trimouns dolomite mine, France, is compositionally zoned. Back-scattered electron (BSE) images
reveal that each of the described dissakisite crystals has three distinct compositional zones: normal zoned core (Mg-rich),
oscillatory zoned middle (Ca–Al-rich) and homogeneous rim (Fe–ΣREE-rich). The latter zone with Fe2+ > Mg corresponds to allanite-(Ce). Dissakisite-(Ce) also displays pronounced zoning in Fe/Mg which may suggest that the temperature
of crystallization continuously decreased from core to rim. Despite a systematic increase in Fe/Mg of the dissakisite with
an allanite rim, there is no monotonic decrease in the REE zoning: the normal zoned core and homogeneous rim are rich in La,
Ce and Pr, but the relatively REE-poor oscillatory zoned middle is relatively abundant in Y, Sm and Gd. Discontinuous variation
in REE content of the dissakisite, with the allanite rim may indicate a localized change in either the relative concentration
of various ligands or pH of the crystallizing fluid. Observations under the polarizing microscope confirm that the different
zones have simultaneous extinction. These chemical and optical observations suggest that epitaxial crystallization of dissakisite,
from Trimouns, passes through three formation stages. The ternary Fe2+–Mg2+–(Al + Fe)3+ diagram illustrates that in general dissakisite can be classified into two groups, (Al + Fe)3+-rich and an Mg-rich; dissakisite from Trimouns belongs to the former group. Chondrite-normalized REE patterns of dissakisites
from Trimouns are similar to those of allanites formed by hydrothermal fluids. In conclusion, it is clear from the above two
geochemical characteristics that dissakisites from Trimouns are of (Al + Fe)3+-type, and were derived from hydrothermal fluids. 相似文献
2.
Two kinds of mylonite series rocks, felsic and mafic, have been recognized in the NW-striking shear zone of the Jiapigou gold
belt. During ductile deformation, a large amount of fluid interacted intensively with the mylonite series rocks: plagioclases
were sericitized and theAn values declined rapidly, finally all of them were transformed to albites; dark minerals were gradually replaced by chlorites
(mostly ripidolite). Meanwhile, large-scale and extensive carbonation also took place, and the carbonatization minerals varied
from calcite to dolomite and ankerite with the development of deformation. The δ13C values of the carbonates are −3.0‰ – −5.6‰ suggesting a deep source of carbon. The ductile deformation is nearly an iso-volume
one (f
v≈1). With the enhancement of shear deformation, SiO2 in the two mylonite series rocks was depleted, while volatile components suchs as CO2 and H2O, and some ore-forming elements such as Au and S were obviously enriched. But it is noted that the enrichment of Au in both
the mylonite series rocks did not reach the paygrade of gold. The released SiO2 from water-rock interactions occurred in the form of colloids and absorbed gold in the fluid. When brittle structures were
formed locally in the ductile shear zone, the ore-forming fluids migrated to the structures along microfractures, and preciptated
auriferous quartz because of reduction of pressure and temperature. Fluid inclusion study shows that the temperature and pressure
of the ore-forming fluids are 245–292°C and 95.4–131.7 MPa respectively; the salinity is 12.88–16.33wt% NaCl; the fluid-phase
is rich in Ca2+, K+, Na+, Mg2+, F− and Cl−, while the gaseous phases are rich in CO2 and CH4. The δD and δ18O, values of the ore-forming fluid are −84.48‰ – −91.73‰ and −0.247‰ – +2.715‰ respectively, suggesting that the fluid is
composed predominantly of meteoric water.
This project is financially supported by the National Natural Science Foundation of China (No. 9488010). 相似文献
3.
First phase folds F1 developed in polydeformed Ajabgarh Group rocks of Proterozoic age are studied using various geometrical methods of analysis
for compatibility of homogeneous strain in both class 1–3 pairs by correlatingt′
ga/α plots with existing curves for competent layers and matchingt
ga/α plots with the flattening curves for the incompetent layers.
F1 folds were initiated by the process of buckling but underwent [(λ2/λ1) = 0.2 to 0.7] for competent layers andR- values of 1.1 to 5 for incompetent layers. The varying flattening is also revealed by the geometry of folds. The apparent
buckle shortening of folds which ranges between 49 and 67 per cent with a majority of the folds having shortening values between
50% and 55% (exclusive of layer parallel strain) and inverse thickness method strain up to 50%. Besides flattening, the fold
geometry was also modified by the pressure solution. This is borne by the presence of dark seams rich in phyllosilicates and
disseminated carbonaceous material offsetting limbs of buckled quartz veins in slates 相似文献
4.
R. B. S. Yadav J. N. Tripathi D. Shanker B. K. Rastogi M. C. Das Vikas Kumar 《Natural Hazards》2011,56(1):145-167
The return periods and occurrence probabilities related to medium and large earthquakes (M
w
4.0–7.0) in four seismic zones in northeast India and adjoining region (20°–32°N and 87°–100°E) have been estimated with
the help of well-known extreme value theory using three methods given by Gumbel (1958), Knopoff and Kagan (1977) and Bury (1999). In the present analysis, the return periods, the most probable maximum magnitude in a specified time period and probabilities
of occurrences of earthquakes of magnitude M ≥ 4.0 have been computed using a homogeneous and complete earthquake catalogue prepared for the period between 1897 and 2007.
The analysis indicates that the most probable largest annual earthquakes are close to 4.6, 5.1, 5.2, 5.5 and 5.8 in the four
seismic zones, namely, the Shillong Plateau Zone, the Eastern Syntaxis Zone, the Himalayan Thrusts Zone, the Arakan-Yoma subduction
zone and the whole region, respectively. The most probable largest earthquakes that may occur within different time periods
have been also estimated and reported. The study reveals that the estimated mean return periods for the earthquake of magnitude
M
w
6.5 are about 6–7 years, 9–10 years, 59–78 years, 72–115 years and 88–127 years in the whole region, the Arakan-Yoma subduction
zone, the Himalayan Thrusts Zone, the Shillong Plateau Zone and the Eastern Syntaxis Zone, respectively. The study indicates
that Arakan-Yoma subduction zone has the lowest mean return periods and high occurrence probability for the same earthquake
magnitude in comparison to the other zones. The differences in the hazard parameters from zone to zone reveal the high crustal
heterogeneity and seismotectonics complexity in northeast India and adjoining regions. 相似文献
5.
Edward Castañeda-Moya Victor H. Rivera-Monroy Robert R. Twilley 《Estuaries and Coasts》2006,29(5):751-764
The structural attributes and zonation patterns of mangrove forests in a dry environmental setting were evaluated in relation
to gradients of soil resources, soil regulators, and hydroperiod between October 2000 and August 2001 in the Gulf of Fonseca,
Honduras. Transects perpendicular to the edge of tidal channels were established at four mangrove sites, each sectioned into
three mangrove zones (fringe, transition, and scrub) based upon distinct tree-height gradients. Porewater sulfide concentrations
among zones were normally below levels of detection (<0.03 mM) and mean redox values ranged from 163.4±9.9 to −42.4±15.8 mv,
indicating slightly reducing conditions in all zones. Mean porewater NOx
− and PO4
3− concentrations were not significantly different among zones and ranged from 3.3±0.5 to 4.5±0.4 μM and from 0.05 ±0.02 to
0.18±0.04 μM, respectively. Soil nitrogen concentrations were 1–3 mg g−1 in all zones, and mean nitrogen:phosphorus atomic ratios were <20 (range: 12.9–14.9), indicative of fertile wetland soils.
Mean basal areas were significantly different among mangrove zones (fringe > transition) and were coupled with differences
in height within species and zones.Avicennia germinans occupied areas with higher elevations associated with higher salinities ranging from 80 to 140 g kg−1 in the dry season.Rhizophora mangle dominated lower elevations where salinities ranged from 38 to 57 g kg−1 in both the dry and wet seasons. Spatial analysis on mangrove seedlings along transects confirmed that seedling distribution
along the intertidal profile was statistically correlated with conspecific adults, indicating that survival and growth of
seedlings in different intertidal locations are closely matched to canopy membership. The sharp transition (<100 m) in forest
structure and distribution of mangrove species along the intertidal zone of subhumid coastal environments demonstrate common
zonation patterns where species distribution and species-specific habitat suitability are mediated closely with tolerance
to soil regulators (high soil salinity) rather than resource availability. 相似文献
6.
The crystal structure of Bi2Al4−x
Fe
x
O9 compounds (x = 0–4) has striking similarities with the crystal structure of mullite. A complete substitution of Al by Fe3+ in both octahedral and tetrahedral sites is a particular structural feature. The infrared (IR) spectra of the Bi2M4O9 compounds (M = Al, Fe3+) are characterised by three band groups with band maxima in the 900–800, 800–600 and 600–400 cm−1 region. Based on the spectroscopic results obtained from mullite-type phases, the present study focuses on the composition-dependent analysis of the 900–800 cm−1 band group, which is assigned to Al(Fe3+)–O stretching vibrations of the corner-sharing MO4 tetrahedra. The Bi2Al4O9 and Bi2Fe4O9 endmembers display single bands with maxima centred at 922 and 812 cm−1, respectively. Intermediate Bi2Al4−x
Fe
x
O9 compounds exhibit a distinct splitting into three relatively sharp bands, which is interpreted in terms of ordering effects within the tetrahedral pairs. Thereby the high-energy component band of the band triplet relates to Al–O–Al conjunctions and the low-energy component band to Fe–O–Fe conjunctions. The intermediate band is assigned to stretching vibrations of Al–O–Fe or Fe–O–Al configurations of the corner-sharing tetrahedral pairs. Bands in the 800–600 cm−1 range are assigned to low-energy stretching vibrations of the MO4 tetrahedra and to M–O–M bending vibrations of the tetrahedral pairs. Absorptions in the 600–400 cm−1 range are essentially determined by M–O stretching modes of the M cations in octahedral coordination. 相似文献
7.
Mineral equilibria modeling involving solid solution calculations has been combined with mineral assemblage information from
the alteration zones associated with gold mineralization to determine the T and X
CO2 conditions for the formation of the Magdala gold deposit at Stawell, Victoria, Australia. Economic gold mineralization is
primarily hosted within the stilpnomelane alteration zone of the Stawell Facies that is adjacent to the Magdala Basalt. Evolution
of the Magdala gold deposit involved at least three fluid infiltration events: (1) a CO2-bearing fluid during the D2 deformation event produced carbonate spots throughout the chlorite zone; (2) a CO2–S–K-bearing fluid, accompanied the D3–4ab deformation and produced a muscovite zone and siderite rims on ankerite; and (3) a CO2–K–S–Au-bearing fluid during the D4c deformation event produced the stilpnomelane zone of the Stawell Facies, the proximal and distal alteration zones within
the Magdala Basalt, and the main economic gold mineralization. Mineral equilibria modeling constrains the temperature of formation
of the Magdala deposit to T = 345–390°C at 3kbar, substantially lower than indicated by other previous classical thermobarometry methods. Furthermore,
this method has allowed the characterization of the mineralizing fluid and constrained its composition to X
CO2 < 0.08 at 3kbar. The timing and composition of the mineralizing fluids are similar to that of metamorphic fluid generated
from devolatilization of a greenstone pile with peak of metamorphism occurring earlier and at deeper levels in the crust. 相似文献
8.
M. V. Eselevich 《Astronomy Reports》2010,54(2):173-183
The perturbed zones and shocks preceding coronal mass ejections (CMEs) are studied using the data of the Mark 4, LASCO C2,
and LASCO C3 coronagraphs. Detection of the perturbed zone indicating the presence or absence of the shock is most reliable
in a frame moving with the frontal structure of the CME. The ability to correctly measure the width δ
F
of the shock front using the Mark 4 and LASCO C2 data is established. The front width δ
F
observed along the streamer belt at distances R < 5 R
⊙ from the center of the Sun is of the order of the mean free path of protons. This means that the energy dissipation in the
shock front is collisional at such distances. At distances R ≥ (10 − 15) R
⊙, a new discontinuity with a front δ*
F
≪ δ
F
is formed in the leading portion of the front. Within the errors, δ*
F
≈ (0.1–0.2) R
⊙ is independent of the distance R and is determined by the LASCO C3 spatial resolution. Initially, the discontinuity on the scale δ*
F
is weak and coexists with the front with width δ
F
. The relative amplitude of this discontinuity increases and the brightness profile behind it flattens as long as the distance
R increases. This transformation of the brightness profile from a front of width δ
F to a discontinuity of width δ*
F
≪ δ
F
is explained as a transition from a collisional to a collisionless shock. 相似文献
9.
Gertrude Friedl Rob A. Cooke Friedrich Finger Neal J. McNaughton Ian R. Fletcher 《Mineralogy and Petrology》2011,102(1-4):63-75
In an attempt to better constrain the timing of Variscan HP-HT metamorphism in the SE Bohemian Massif we have dated zoned zircons from a garnet-kyanite granulite of granitic composition from the Dunkelsteiner Wald Massif, Lower Austria, by means of sensitive high-resolution ion microprobe (SHRIMP) technique. In order to combine isotopic information with crystal growth textures, CL and BSE images were systematically taken from the dated zircons. A characteristic threefold concentric zoning was found in many zircons. This involves pre-Variscan protolithic cores followed by two distinct metamorphic/anatectic overgrowth shells of Variscan age. The inner overgrowth shell is characterized by a weak CL but bright BSE signal, and yields high contents of uranium (0.1 to 0.2 wt.%). A pooled U-Pb Concordia age for this zone is 342.0?±?3.0?Ma (n?=?11, MSWD?=?0.12). The second, outer, overgrowth shell is always bright in the CL image, dark in the BSE image, and has generally low uranium contents (mostly <500?ppm). A pooled U-Pb Concordia age for this zone is 337.1?±?2.7?Ma (n?=?11, MSWD?=?0.22). These results imply that the Variscan HT crystallisation history of the Moldanubian granulites took place over a period of a few million years and was not an extremely rapid subduction-exhumation process. SHRIMP measurements in the protolithic cores yield a cluster of (sub)concordant ages between ??390 and 460?Ma and a few outliers at higher ages mostly represented by cores in cores. Core domains, which are large, homogeneous and with undisturbed igneous oscillatory zoning, yielded preferentially ages between 430 and 460?Ma. We therefore consider that granitic protolith formation took place at that time. The still older inner cores are interpreted as inherited into the granitic melt. 相似文献
10.
Mario Tribaudino Fabrizio Nestola Marco Bruno Tiziana Boffa Ballaran Christian Liebske 《Physics and Chemistry of Minerals》2008,35(5):241-248
The high temperature volume and axial parameters for six C2/c clinopyroxenes along the NaAlSi2O6–NaFe3+Si2O6 and NaAlSi2O6–CaFe2+Si2O6 joins were determined from room T up to 800°C, using integrated diffraction profiles from in situ high temperature single crystal data collections. The thermal
expansion coefficient was determined by fitting the experimental data according to the relation: ln(V/V
0) = α(T − T
0). The thermal expansion coefficient increases by about 15% along the jadeite–hedenbergite join, whereas it is almost constant
between jadeite and aegirine. The increase is related to the Ca for Na substitution into the M2 site; the same behaviour was
observed along the jadeite–diopside solid solution, which presents the same substitution at the M2 site. Strain tensor analysis
shows that the major deformation with temperature occurs in all samples along the b axis; on the (010) plane the higher deformation occurs in jadeite and aegirine at a direction almost normal to the tetrahedral–octahedral
planes, and in hedenbergite along the projection of the longer M2–O bonds. The orientation of the strain ellipsoid with temperature
in hedenbergite is close to that observed with pressure in pyroxenes. Along the jadeite–aegirine join instead the high-temperature
and high-pressure strain are differently oriented. 相似文献
11.
N. V. Chukanov A. A. Mukhanova R. K. Rastsvetaeva D. I. Belakovsky S. M?ckel O. V. Karimova S. N. Britvin S. V. Krivovichev 《Geology of Ore Deposits》2011,53(7):583-590
Oxyphlogopite is a new mica-group mineral with the idealized formula K(Mg,Ti,Fe)3[(Si,Al)4O10](O,F)2. The holotype material came from a basalt quarry at Mount Rothenberg near Mendig at the Eifel volcanic complex in Rhineland-Palatinate,
Germany. The mineral occurs as crystals up to 4 × 4 × 0.2 mm in size encrusting cavity walls in alkali basalt. The associated
minerals are nepheline, plagioclase, sanidine, augite, diopside, and magnetite. Its color is dark brown, its streak is brown,
and its luster is vitreous. D
meas = 3.06(1) g/cm3 (flotation in heavy liquids), and D
calc = 3.086 g/cm3. The IR spectrun does not contain bands of OH groups. Oxyphlogopite is biaxial (negative); α = 1.625(3), β = 1.668(1), and
γ = 1.669(1); and 2V
meas = 16(2)° and 2V
calc = 17°. The dispersion is strong; r < ν. The pleochroism is medium; X > Y > Z (brown to dark brown). The chemical composition is as follows (electron microprobe, mean of 5 point analyses, wt %; the ranges
are given in parentheses; the H2O was determined using the Alimarin method; the Fe2+/Fe3+ was determined with X-ray emission spectroscopy): Na2O 0.99 (0.89–1.12), K2O 7.52 (7.44–7.58), MgO 14.65 (14.48–14.80), CaO 0.27 ((0.17–0.51), FeO 4.73, Fe2O3 7.25 (the range of the total iron in the form of FeO is 11.09–11.38), Al2O3 14.32 (14.06–14.64), Cr2O3 0.60 (0.45–0.69), SiO2 34.41 (34.03–34.66), TiO2 12.93 (12.69–13.13), F 3.06 (2.59–3.44), H2O 0.14; O=F2 −1.29; 99/58 in total. The empirical formula is (K0.72Na0.14Ca0.02)(Mg1.64Ti0.73Fe0.302+ Fe0.273+Cr0.04)Σ2.98(Si2.59Al1.27Fe0.143+ O10) O1.20F0.73(OH)0.07. The crystal structure was refined on a single crystal. Oxyphlogopite is monoclinic with space group C2/m; the unit-cell parameters are as follows: a = 5.3165(1), b = 9.2000(2), c = 10.0602(2) ?, β = 100.354(2)°. The presence of Ti results in the strong distortion of octahedron M(2). The strongest lines of the X-ray powder diffraction pattern [d, ? (I, %) [hkl]] are as follows: 9.91(32) [001], 4.53(11) 110], 3.300(100) [003], 3.090(12) [112], 1.895(21) [005], 1.659(12) [−135], 1.527(16)
[−206, 060]. The type specimens of oxyphlogopite are deposited at the Fersman Mineralogical Museum in Moscow, Russia; the
registration numbers are 3884/2 (holotype) and 3884/1 (cotype). 相似文献
12.
Ilya V. Veksler Yana M. Fedorchuk Troels F. D. Nielsen 《Contributions to Mineralogy and Petrology》1998,131(4):347-363
The evolution of nephelinitic melts in equilibrium with mica-bearing liquidus assemblages and melting relations have been
studied on two silica-undersaturated joins of the KAlSiO4– Mg2SiO4– Ca2SiO4– SiO2– F system at atmospheric pressure by quench runs in sealed platinum capsules. Fluorine has been added to the batch compositions
by the direct exchange of fluorine for oxygen (2F− = O2−). The first join is the pseudo-ternary Forsterite – Diopside – KAlSiO3F2 system. Forsterite, diopside, F-phlogopite and leucite crystallisation fields and a fluoride-silicate liquid immiscibility
solvus are present on the liquidus surface of the join. Sub-liquidus and sub-solidus phases include akermanite, cuspidine,
spinel, fluorite and some other minor fluorine phases. The second system is the pseudo-binary Akermanite – F-phlogopite join
that intersects the Forsterite – Diopside – KAlSiO3F2 join. Akermanite, forsterite, diopside, F-phlogopite, leucite and cuspidine are found to crystallise on the join. Forsterite
(fo) and leucite (lc) are related to F-phlogopite (phl) by a reaction with the fluorine-bearing liquid: fo + lc + l = phl,
and the reaction proceeds until forsterite or leucite are completely consumed. The reaction temperature and resulting phase
association depend on batch composition. Thus, leucite is not stable in the sub-solidus of the Akermanite – F-phlogopite join,
but is preserved in a part of the Forsterite – Diopside – KAlSiO3F2 system where forsterite reacts out, or does not crystallise at all. The phlogopite-in reaction has an important effect on
the composition of the coexisting liquid. The liquids initially saturated in forsterite evolve to extremely Ca rich, larnite-normative
residuals. The experimental data show that larnite-normative melilitolites can crystallise from evolved melilititic melts
generated from “normal” melanephelinitic parental magmas with no normative larnite. The evolution towards melilitites requires fractionation of phlogopite-bearing assemblages under volatile pressure.
Received: 3 June 1997 / Accepted: 5 January 1998 相似文献
13.
Bin Chen K. Suzuki W. Tian B. M. Jahn T. Ireland 《Contributions to Mineralogy and Petrology》2009,158(5):683-702
We report petrological, chemical and Os–Nd–Sr isotopic data for the Gaositai ultramafic complex from northern North China
craton (NCC) to reveal its petrogenesis. The complex shows features of Alaskan-type intrusions, including (1) the concentric
zoning from dunite core, to clinopyroxenite and hornblendite in the rim, and the common cumulative textures; (2) the abundance
of olivine, clinopyroxene and hornblende, and the scarcity of orthopyroxene and plagioclase, and (3) the systematic decrease
in Mg# of ferromagnesian phases from core to rim, accompanied by the Fe-enrichment trend of accessory spinel. The different
rock types show highly varied, radiogenic Os isotopic ratios (0.129–5.2), and unradiogenic Nd isotopic composition (εNd(t) = −8 to −15), but are homogeneous in ISr ratios (0.7054–0.7066). The (187Os/188Os)i ratios are found to be anti-correlated with εNd(t) values and whole-rock Mg# as well. These data suggest significant crustal contamination during magma evolution. The crustal
contaminants are dominantly Archean mafic rocks in the lower crust, and subordinate TTG gneisses at shallower crustal levels.
The parental magma was hydrous picritic in composition, derived from an enriched lithospheric mantle source above a subduction
zone. The zoned pattern of the complex formed probably through “flow differentiation” of a rapidly rising crystal mush along
a fracture zone that was developed as a result of lithospheric extension in a back-arc setting in the northern margin of the
NCC at ca. 280 Ma. 相似文献
14.
The Andaman-Sumatra subduction zone is seismically one of the most active and complex subduction zones that produced the 26
December 2004 mega thrust earthquake (Mw 9.3) and large number of aftershocks. About 8,000 earthquakes, including more than
3,000 aftershocks (M ≥ 4.5) of the 2004 earthquake, recorded during the period 1964–2007, are relocated by the EHB method. We have analysed this
large data set to map fractal correlation dimension (Dc) and frequency-magnitude relation (b-value) characteristics of the seismogenic structures of this ~3,000-km-long mega thrust subduction zone in south-east Asia.
The maps revealed the seismic characteristics of the Andaman-Sumatra-Java trenches, West Andaman fault (WAF), Andaman Sea
Ridge (ASR), Sumatra and Java fault systems. Prominent N–S to NW–SE to E–W trending fractal dimension contours all along the
subduction zone with Dc between 0.6 and 1.4 indicate that the epicentres mostly follow linear features of the major seismogenic
structures. Within these major contours, several pockets of close contours with Dc ~ 0.2 to 0.6 are identified as zones of
epicentre clusters and are inferred to the fault intersections as well as asperity zones along the fault systems in the fore
arc. A spatial variation in the b-value (1.2–1.5) is also observed along the subduction zone with several pockets of lower b-values (1.2–1.3). The smaller b-value zones are corroborated with lower Dc (0.5–0.9), implying a positive correlation. These zones are identified to be the
zones of more stress or asperity where rupture nucleation of intermediate to strong magnitude earthquakes occurred. 相似文献
15.
We determined the forward rate constant (K+) for the Fe2+–Mg order–disorder between the M2 and M1 sites of orthopyroxene (OPx), which is described by the homogeneous reaction Fe2+ (M2) + Mg(M1) ↔ Mg(M2) + Fe2+ (M1), by both ordering and disordering experiments at isothermal condition and also by continuous cooling experiments. The
rate constant was determined as a function of temperature in the range of 550–750°C, oxygen fugacity between quartz–fayalite–iron
and Ni–NiO buffers, and at compositions of 16 and 50 mol% ferrosilite component. The K+ value derived from disordering experiment was found to be larger than that derived from ordering experiment at 550°C, while
at T>580°C, these two values are essentially the same. The fO2 dependence of the rate constant can be described by the relation K+ α (fO2)
n
with n=5.5–6.5, which is compatible with the theoretically expected relation. The Arrhenius relation at the WI buffer condition
is given by
where C
o represents the total number of M2 + M1 sites occupied by Fe2+ and Mg per unit volume of the crystal. The above relation can be used to calculate the cooling rates of natural OPx crystals
around the closure temperature (T
c) of Fe–Mg ordering, which are usually below 300°C for slowly cooled rocks. We determined the Fe–Mg ordering states of several
OPx crystals (∼ Fs50) from the Central Gneissic Complex (Khtada Lake), British Columbia, which yields T
c ∼290°C. Numerical simulation of the change of Fe2+-Mg ordering in OPx as a function of temperature using the above expression of rate constant and a non-linear cooling model
yields quenched values of ordering states that are in agreement with the observed values for cooling rates of 11–17°C/Myr
below 300°C. The inferred cooling rate is in agreement with the available geochronological constraints. 相似文献
16.
Summary Batiferrite, ideally Ba[Ti2Fe10]O19, was found in the Quaternary volcanic rocks near üdersdorf, Graulai, and Altburg, western Eifel area, Germany. The new mineral
typically occurs as euhedral platy grains in cavities of melilite- and leucite-nephelinite basalts. Associated minerals are
hematite, magnetite, titanite, g?tzenite, clinopyroxene, nepheline, and biotite. It exhibits a hexagonal tabular habit flattened
on {0001}, diameter 0.5–1 mm, thickness 20–125 μm, and {10&1macr;3}, {10&1macr;0} as observable forms. The mineral is opaque, of black
color with submetallic lustre, and shows a ferrimagnetic behavior. VHN50 is 793 with a range of 710–841 from ten indentations. The quantitative reflectance measurements of Ro/Re on oriented grains in air and oil immersion, respectively, are [%]: for 470 nm 22.1/20.1 and 8.4/7.1, for 546 nm 21.0/19.4
and 7.8/6.6, for 589 nm 20.2/18.8 and 7.4/6.3, and for 650 nm 19.3/18.3 and 6.8/5.9. The bireflectance is distinct (air) to
weak (oil), and parallel (0001) a moderate anisotropy with straight extinction can be observed. Typical microprobe analyses
give [wt%] K2O 0.28–0.33, Na2O 0.17–0.20, SrO 0.46–0.55, BaO 11.80–12.17, MgO 1.27–1.47, Al2O3 0.31–0.33, TiO2 13.11–13.63, MnO 2.38–2.57, Fe2O3 61.36–63.12, FeO 5.49–5.86 (Fe3+/Fe2+ calculated for charge compensation), which is equivalent to (Ba0.84Na0.06K0.06Sr0.05)1.01(Fe8.48
3+Fe0.86
2+Ti1.82Mg0.37Mn0.37Al0.06)11.96O19 as the average composition based on 19 oxygen atoms. Batiferrite is a magnetoplumbite-type mineral with hexagonal symmetry,
space group P6
3
/mmc (no. 194), a = 5.909(1) ?, c = 23.369(4) ?, V = 706.6(2) ?3, Z = 2, and a calculated density of 5.016 gcm−3. The structure was refined to R1 = 0.031 for 278 unique reflections with Fo
2 > 4σ (Fo
2) and R1 = 0.079 for all 452 unique observations using single crystal X-ray data. The strongest reflections of the X-ray powder diffraction
pattern are [d
obs, I/Io, (hkl)]: 2.631, 100, (114); 2.799, 80, (107); 1.478, 70, (220); 2.429, 60, (203); 1.672, 50, (217). The new mineral is comparable to the other Ba containing magnetoplumbite-type minerals haggertyite and
hawthorneite, the iron content, however, is much higher and in the range of magnetoplumbite. The large cation site (A) is
dominated by Ba, and four of the five remaining crystallographic cation sites in the structure are dominated by Fe (M1, 2,
3, 5), the octahedrally coordinated M4-site is dominated by Ti. No oxygen vacancy on the O3-site like in plumboferrite can
be observed. Batiferrite is named for its main chemical composition and the relationship to the M-type hexaferrites (polytype
5H).
Received December 14, 1999; accepted March 2, 2000 相似文献
Zusammenfassung Batiferrit, ein neues ferrimagnetisches Mineral des Magnetoplumbit-Typs aus den quart?ren Vulkaniten der West-Eifel, Deutschland Das neue Mineral Batiferrite, mit der Idealformel Ba[Ti2Fe10]O19, wurde an drei Fundpunkten in den Quart?ren Vulkangesteinen der westlichen Eifel, Deutschland, in der N?he von üdersdorf, Graulai und Altburg gefunden. Das neue Mineral tritt typischerweise bl?ttchenf?rmig in kleinen Hohlr?umen von Melilith- und Leucit-Nephelininit Basalten auf. Vergesellschaftete Minerale sind H?matit, Magnetit, Titanit, G?tzenit, Klinopyroxen, Nephelin und Biotit. Der Habitus ist hexagonal tafelig nach {0001}, mit einem Durchmesser von 0.5–1 mm und einer Dicke von 20–125 μm, zus?tzlich k?nnen die Formen {10&1macr;3} und {10&1macr;0} beobachtet werden. Das Mineral ist opak, hat eine schwarze Farbe mit einem leicht metallischen Glanz, und ist ferromagnetisch. Die H?rte VHN50 ist 793 mit einem Bereich von 710–841 aus 10 Eindruckbestimmungen. Die quantitativen Reflexionsmessungen von Ro/Re an orientierten K?rnern in Luft beziehungsweise ?limmersion, ergaben [%]: für 470 nm 22.1/20.1 und 8.4/7.1, für 546 nm 21.0/19.4 und 7.8/6.6, für 589 nm 20.2/18.8 und 7.4/6.3, und für 650 nm 19.3/18.3 und 6.8/5.9. Die Bireflexion ist deutlich (Luft) bis schwach (?l) und parallel (0001) kann eine mittlere Anisotropie mit gerader Ausl?schung beobachtet werden. Eine typische Mikrosondenanalyse ergibt [wt%] K2O 0.28–0.33, Na2O 0.17–0.20, SrO 0.46–0.55, BaO 11.80–12.17, MgO 1.27–1.47, Al2O3 0.31–0.33, TiO2 13.11–13.63, MnO 2.38–2.57, Fe2O3 61.36–63.12, FeO 5.49–5.86 (Fe3+/Fe2+ berechnet zum Ladungsausgleich), die mittlere chemische Formel auf der Basis von 19 Sauerstoffatomen lautet (Ba0.84Na0.06K0.06Sr0.05)1.01 (Fe8.48 3+Fe0.86 2+Ti1.82Mg0.37Mn0.37Al0.06)11.96O 19. Batiferrit ist ein Mineral der Magnetoplumbitgruppe, hat hexagonale Symmetrie mit der Raumgruppe P63/mmc (Nr. 194), a = 5.909(1) ?, c = 23.369(4) ?, V = 706.6(2) ?3, Z = 2, und einer berechneten Dichte von 5.016 gcm−3. Die Struktur wurde aus Einkristall-R?ntgendaten bis zu einem R1-Wert von 0.031 für 278 Fo 2 > 4σ(Fo 2), und einem R1-Wert von 0.079 für alle 452 Fo 2 verfeinert. Die st?rksten Beugungsreflexe der Pulver-R?ntgendaten sind [dobs, I/Io, (hkl)]: 2.631, 100, (114); 2.799, 80, (107); 1.478, 70, (220); 2.429, 60, (203); 1.672, 50, (217). Das neue Mineral weist deutliche ?hnlichkeiten zu den anderen beiden Ba-reichen Mineralen Haggertyit und Hawthorneit der Magnetoplumbit-Gruppe auf, jedoch ist der Eisengehalt wesentlich h?her und im Bereich des Minerals Magnetoplumbit. Der gro?e Kationenplatz (A) ist von Barium dominiert, vier (M1, 2, 3, 5) der restlichen fünf kristallographischen Kationenpl?tze in der Struktur sind fast ausschlie?lich mit Fe, die oktaedrisch koordinierte M4-Position ist überwiegend mit Ti besetzt. An der O3-Position konnte kein Sauerstoffdefizit wie in Plumboferrit festgestellt werden. Batiferrit ist nach seiner chemischen Beschaffenheit und nach seiner Zugeh?hrigkeit zu den M-Typ Hexaferriten (Polytyp 5H) benannt.
Received December 14, 1999; accepted March 2, 2000 相似文献
17.
Faruk Aydin Richard M. Thompson Orhan Karsli Hinako Uchida Jason B. Burt Robert T. Downs 《Contributions to Mineralogy and Petrology》2009,158(1):131-147
Chemical and structural data are reported for C2/c pyroxene phenocrysts collected from three potassic series (Group A: basanite-tephrite, Group B: tephrite-phonolitic tephrite,
Group C: alkaline basalt-trachybasalt) of the Neogene alkaline volcanics (NAVs) in northeastern Turkey, in order to investigate
the evolution of the magmatic plumbing system and the location of magma chamber(s) with crystallization conditions. The rock
series hosting the clinopyroxene phenocrysts show generally porphyritic texture and have a variable phenocryst-rich nature
(20–58%), with phenocryst assemblages characterized by cpx ± ol ± plag ± foid ± amp ± bio. The clinopyroxene phenocrysts can
be chemically classified as Ti- and Fe3+-rich Al-diopsides for Groups A and B (AB-cpxs) and Ti- and Fe3+-poor Al-diopsides for Group C (C-cpxs). They have poorly variable composition, clustering in the diopside field. Structurally,
the diopside groups have nearly similar a (ranging from 9.73 to 9.75 ?), V
cell (437.2–440.9 ?3), and 〈beta〉 angle values (106.01°–106.23°), but some differences in polyhedral parameters and geometries of the AB-cpxs and C-cpxs have
been observed. For example, the AB-cpxs are characterized by larger c (5.27–5.30 vs. 5.25–5.28 ?), V
T (2.27–2.30 vs. 2.23–2.28 ?3), and V
M2 (25.53–25.72 vs. 25.41–25.59 ?3) values and smaller b (8.87–8.88 vs. 8.88–8.91 ?) and V
M1 (11.49–11.63 vs. 11.64–11.83 ?3) values with respect to the C-cpxs. In addition, the AB-cpxs show higher values of V
M2/V
M1 (2.20–2.23) due to large V
M2 and small V
M1 compared to the V
M2/V
M1 ratios of the C-cpxs (<2.19). Such differences in the crystal structure of the AB-cpxs and C-cpxs from the NAVs are partly
related to different crystallization pressures, but mostly related to variation in melt composition and, possibly, the influence
of other crystallizing mineral phases. In particular, R(M2-O1) and R(M1-O2) (i.e. bond lengths) differences in the clinopyroxenes
of different groups support the presence of evolved host rocks with different alkaline character (i.e. silica-undersaturated
Groups A–B and silica-saturated Group C). Based on the cpx-geothermobarometry, the crystallization pressures for the C-cpxs
are lower than 4.5 kbars, but the AB-cpxs have relatively high-pressure values (5.6–10.6 kbars), suggesting that the AB-cpxs
crystallized in higher pressure environments. The relatively higher crystallization temperatures of the AB-cpxs also indicate
higher cooling rates. The P–T estimates suggest that the source regions of the clinopyroxene phenocrysts from the NAVs were crustal magma chambers in a
closed plumbing system at a moderate- to low-pressure regime. 相似文献
18.
Basem A. Zoheir 《Mineralium Deposita》2008,43(1):79-95
The Betam gold deposit, located in the southern Eastern Desert of Egypt, is related to a series of milky quartz veins along
a NNW-trending shear zone, cutting through pelitic metasedimentary rocks and small masses of pink granite. This shear zone,
along with a system of discrete shear and fault zones, was developed late in the deformation history of the area. Although
slightly sheared and boudinaged within the shear zone, the auriferous quartz veins are characterised by irregular walls with
a steeply plunging ridge-in-groove lineation. Shear geometry of rootless intra-folial folds and asymmetrical strain shadows
around the quartz lenses suggests that vein emplacement took place under a brittle–ductile shear regime, clearly post-dating
the amphibolite-facies regional metamorphism. Hydrothermal alteration is pervasive in the wallrock metapelites and granite
including sericitisation, silicification, sulphidisation and minor carbonatisation. Ore mineralogy includes pyrite, arsenopyrite
and subordinate galena, chalcopyrite, pyrrhotite and gold. Gold occurs in the quartz veins and adjacent wallrocks as inclusions
in pyrite and arsenopyrite, blebs and globules associated with galena, fracture fillings in deformed arsenopyrite or as thin,
wire-like rims within or around rhythmic goethite. Presence of refractory gold in arsenopyrite and pyrite is inferred from
microprobe analyses. Clustered and intra-granular trail-bound aqueous–carbonic (LCO2 + Laq ± VCO2) inclusions are common in cores of the less deformed quartz crystals, whereas carbonic (LCO2 ± VCO2) and aqueous H2O–NaCl (L + V) inclusions occur along inter-granular and trans-granular trails. Clathrate melting temperatures indicate low
salinities of the fluid (3–8 wt.% NaCl eq.). Homogenisation temperatures of the aqueous–carbonic inclusions range between
297 and 323°C, slightly higher than those of the intra-granular and inter-granular aqueous inclusions (263–304°C), which are
likely formed during grain boundary migration. Homogenisation temperatures of the trans-granular H2O–NaCl inclusions are much lower (130–221°C), implying different fluids late in the shear zone formation. Fluid densities
calculated from aqueous–carbonic inclusions along a single trail are between 0.88 and 0.98 g/cm3, and the resulting isochores suggest trapping pressures of 2–2.6 kbar. Based on the arsenopyrite–pyrite–pyrrhotite cotectic,
arsenopyrite (30.4–30.7 wt.% As) associated with gold inclusions indicates a temperature range of 325–344°C. This ore paragenesis
constrains f
S2 to the range of 10−10 to 10−8.5 bar. Under such conditions, gold was likely transported mainly as bisulphide complexes by low salinity aqueous–carbonic fluids
and precipitated because of variations in pH and f
O2 through pressure fluctuation and CO2 effervescence as the ore fluids infiltrated the shear zone, along with precipitation of carbonate and sericite. Wallrock
sulphidation also likely contributed to destabilising the gold–bisulphide complexes and precipitating gold in the hydrothermal
alteration zone adjacent to the mineralised quartz veins. 相似文献
19.
D. V. Lazurkin 《Doklady Earth Sciences》2011,437(1):323-325
This method pertains to oil and gas geology and to geology of sedimentary basins prospective for oil and gas. It includes
identifying catagenesis zones in drilled areas within the sedimentary cover of the basin based on assay results for drill
cores and cuttings using the standard methods. Analysis is primarily made in order to determine rock catagenesis based on
the optical characteristics of vitrinite. A correlation between catagenesis zones and layer seismic velocities obtained from
regional and exploration seismic data is made for a drilled area. Both the layer seismic velocities and the degree of rock
catagenesis increase with depth under the influence of increasing rock density. Correlations between layer velocities and
the degree of rock catagenesis have been established. The following ratios have been determined for the Scotian shelf, Canada,
and the Barents shelf, Russia: a protocatagenesis zone (the cap) corresponds to layer seismic velocities (V
lay) of 1.5–3.3 km/s, a mesocatagenesis zone (the principal hydrocarbon generation area) corresponds to V
lay of 3.3–5.0 km/s, and an apocatagenesis zone (an area with a very low hydrocarbon potential) corresponds to V
lay of over 5.0 km/s. An advantage of the new method of identification of catagenesis zones is that it can be used prior to drilling.
Its conceptual originality and cost efficiency lie precisely in this. 相似文献
20.
The Rotoiti (~120 km3) and Earthquake Flat (~10 km3) eruptions occurred in close succession from the Okataina Volcanic Centre at ~50 ka. While accessory mineral geochronology
points to long periods of crystallization prior to eruption (104–105 years) and separate thermal histories for the magmas, little was known about the rates and processes of the final melt production
and eruption. Crystal zoning patterns in plagioclase and quartz reveal the thermal and compositional history of the magmatic
system leading up to the eruption. The dominant modal phase, plagioclase, displays considerable within-crystal zonation: An37–74, ~40–227 ppm MgO, 45–227 ppm TiO2, 416–910 ppm Sr and 168–1164 ppm Ba. Resorption horizons in the crystals are marked by sharp increases (10–30%) in Sr, MgO
and XAn that reflect changes in melt composition and are consistent with open system processes. Melt inclusions display further evidence
for open system behaviour, some are depleted in Sr and Ba relative to accompanying matrix glass not consistent with crystallization
of modal assemblage. MI also display a wide range in XH2O that is consistent with volatile fluxing. Quartz CL images reveal zoning that is truncated by resorption, and accompanied
by abrupt increases in Ti concentration (30–80 ppm) that reflect temperature increases ~50–110°C. Diffusion across these resorption
horizons is restricted to zones of <20 μm, suggesting most crystallization within the magma occurred in <2000 years. These
episodes are brief compared to the longevity (104–105 year) of the crystal mush zones. All textural and compositional features observed within the quartz and plagioclase crystals
are best explained by periodic mafic intrusions repeatedly melting parts of a crystal-rich zone and recharging the system
with silicic melt. These periodic influxes of silicic melt would have accumulated to form the large volume of magma that fed
the caldera-forming Rotoiti eruption. 相似文献