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1.
H. W. Nesbitt A. G. Schaufuss G. M. Bancroft R. Szargan 《Physics and Chemistry of Minerals》2002,29(1):72-77
Synchrotron excited X-ray photoelectron spectra (SXPS) of hexagonal pyrrhotite reveal three distinct Fe 3d-derived photopeaks within its outer valence band. The t
2gα band (majority spin) is centered at about 2.5 eV, the e
g
α band at about 1.0 eV and the t
2gβ (minority spin) contribution at about 0.25 eV. From these data the ligand field splitting energy is 1.5 (±0.2) eV and the
majority spin pairing energy is 2.25 (±0.2) eV. These are the first such XPS measurements for this mineral. S 3p-derived bonding and non-bonding bands are identified, with the former centred at about 6.5 eV and the latter near 4.5 eV.
The XPS results are remarkably consistent with SCF-Xα scattered wave molecular orbital calculations. Although the calculations
and the collected spectra are consistent, they differ from a recent interpretation of the pyrrhotite valence band. An explanation
for the discrepant results is provided. Auger resonant enhancement of Fe 3d photopeaks at 60 eV photon energy results in the
t
2gα emission (at 2.5 eV) being strongly enhanced and broader than the t
2gβ emission (0.25 eV). The explanation of these observations requires the presence of weak Fe–Fe π and π* crystal (molecular) orbitals located near 2.5 eV, and separated by no more than about 0.5 eV. The π-bonded crystal orbitals
are derived from weak mixing of adjacent Fe t
2g atomic orbitals along the c crystallographic axis.
Received: 15 June 2000 / Accepted: 11 June 2001 相似文献
2.
On the Ratios between Elastic Modulus and Uniaxial Compressive Strength of Heterogeneous Carbonate Rocks 总被引:3,自引:3,他引:0
V. Palchik 《Rock Mechanics and Rock Engineering》2011,44(1):121-128
The ratios M
R = E/σ
c for 11 heterogeneous carbonate (dolomites, limestones and chalks) rock formations collected from different regions of Israel
were examined. Sixty-eight uniaxial compressive tests were conducted on weak-to-strong (5 MPa < σ
c < 100 MPa) and very strong (σ
c > 100 MPa) rock samples exhibiting wide ranges of elastic modulus (E = 6100–82300 MPa), uniaxial compressive strength (σ
c = 14–273.9 MPa), Poisson's ratio (ν = 0.13–0.49), and dry bulk density (ρ = 1.7–2.7 g/cm3). The observed range of M
R = 60.9–1011.4 and mean value of M
R = 380.5 are compared with the results obtained by Deere (Rock mechanics in engineering practice, Wiley, London, pp 1–20,
1968) for limestones and dolomites, and the statistical analysis of M
R distribution is performed. Mutual relations between E, σ
c, ρ, M
R for all studied rocks, and separately for concrete rock formations are revealed. Linear multiple correlations between E on the one hand and σ
c and ρ on the other for Nekorot and Bina limestone and Aminadav dolomite are obtained. It is established that the elastic modulus
and M
R in very strong carbonate samples are more correlated with ρ−σ
c combination and ε
a max, respectively, than in weak to strong samples. The relation between M
R and maximum axial strain (ε
a max) for all studied rock samples (weak-to-strong and very strong) is discussed. 相似文献
3.
The electrical conduction in the mineral ilvaite was studied between ≈170 and 450 K. A natural ilvaite from Elba (Italy) was
found to be semiconducting with a DC conductivity 1.8×10–3 (Ωcm)–1 at 300 K, measured parallel (∥) to the [001] direction; perpendicular (⊥) to [001] it was 1.4×10–5 (Ωcm)–1, i.e. the conductivity is highly anisotropic. The conduction is effected by a hopping charge transport between localized
levels in the energy gap associated with activation energies E
A
=0.3–0.5 eV. It is concluded that impurities (Mg,Al,Mn) may play a decisive role in the charge hopping transport ∥ [001] that
is basically governed by Fe2+-Fe3+ pairs on A-sites of the lattice as the source of electrons. Although the EA-values were similar for both measured directions, the sign of thermopower is different which points to different charge transfer
mechanisms. The bulk DC conductivity σDC
AC for measurements ∥ [001], obtained by extrapolation of AC data using impedance spectroscopy, could only be determined at
T<300 K owing to sample–electrode interfacial effects. In contrast, the bulk σDC
AC⊥ [001] showed a slight break at ≈380 K that may reflect the structural phase transition monoclinic→orthorhombic at ≈345 K.
From AC conductivity measurements in the frequency range 20 Hz–1 MHz at T<300 K, a dispersive character of electronic relaxation was found, resembling that of amorphous semiconductors and of impurity
conduction in crystalline semiconductors where it was ascribed to charge hopping processes of electrons between localized
levels of cation pairs or clusters of limited lengths.
Received: 4 August 1997 / Revised, accepted: 12 January 1998 相似文献
4.
Aierken Sidike I. Kusachi S. Kobayashi K. Atobe N. Yamashita 《Physics and Chemistry of Minerals》2008,35(3):137-145
The emission and excitation spectra of yellow luminescence due to S2
− in scapolites (#1 from Canada and #2 from an unknown locality) were observed at 300, 80 and 10 K. Emission and excitation
bands at 10 K showed vibronic structures with a series of maxima spaced 15–30 and 5–9 nm, respectively. The relative efficiency
of yellow luminescence from scapolite #2 was increased up to 117 times by heat treatment at 1,000°C for 2 h in air. The enhancement
of yellow luminescence by heat treatment was ascribed to the alteration of SO3
2− and SO4
2− to S2
− in scapolite. 相似文献
5.
Zircon reaction and stability of the U-Pb isotope system during interaction with carbonate fluid: experimental hydrothermal study 总被引:4,自引:0,他引:4
N. G. Rizvanova O. A. Levchenkov A. E. Belous N. I. Bezmen A. V. Maslenikov A. N. Komarov A. F. Makeev L. K. Levskiy 《Contributions to Mineralogy and Petrology》2000,139(1):101-114
The interpretation of metamorphically induced U-Pb isotopic discordance requires a thorough understanding of zircon-fluid
interactions. With this aim we have studied the behaviour of metamict and crystalline zircon phases and their U-Pb systems
by cathodoluminescence after treatment by 2M Na2CO3 solution at T = 200–800 °C and P = 1–5 kbar for 3–14 days, X-ray diffraction, microprobe and isotope dilution analysis. The data indicate that zircon transformation
under hydrothermal conditions depends on the experimental conditions and the degree of structural damage. Reconstitution of
defective and impurity-enriched zones of metamict zircon (homogenization of impure element concentrations and increase of
crystallinity) was observed at 400 °C and P = 1 kbar. Considerable lead and uranium loss occurred under these conditions. As a result of zircon dissolution, newly formed
baddeleyite accommodating U from 2M Na2CO3 solution and Zr-Na-silicate were recognized. This process intensified with increasing pressure. Study of crystalline zircon
indicates that migration of U and Pb took place only during dissolution of zircon at T above 650 °C. In the presence of carbonate-ions essential U and Pb amounts are lost from metamict zircon at a lower P-T than is typical for greenschist facies metamorphism.
Received: 4 October 1997 / Accepted: 6 December 1999 相似文献
6.
Single-crystal electron paramagnetic resonance (EPR) spectra of a gem-quality jeremejevite, Al6B5O15(F, OH)3, from Cape Cross, Namibia, reveal an S = 1/2 hole center characterized by an 27Al hyperfine structure arising from interaction with two equivalent Al nuclei. Spin-Hamiltonian parameters obtained from single-crystal
EPR spectra at 295 K are as follows: g
1 = 2.02899(1), g
2 = 2.02011(2), g
3 = 2.00595(1); A
1/g
e
β
e
= −0.881(1) mT, A
2/g
e
β
e
= −0.951(1) mT, and A
3/g
e
β
e
= −0.972(2) mT, with the orientations of the g
3- and A
3-axes almost coaxial and perpendicular to the Al–O–Al plane; and those of the g
1- and A
1-axes approximately along the Al–Al and Al–OH directions, respectively. These results suggest that this aluminum-associated
hole center represents hole trapping on a hydroxyl oxygen atom linked to two equivalent octahedral Al3+ ions, after the removal of the proton (i.e., a VIAl–O−–VIAl center). Periodic ab initio UHF and DFT calculations confirmed the experimental 27Al hyperfine coupling constants and directions, supporting the proposed structural model. The VIAl–O−–VIAl center in jeremejevite undergoes the onset of thermal decay at 300 °C and is completely bleached at 525 °C. These data
obtained from the VIAl–O−–VIAl center in jeremejevite provide new insights into analogous centers that have been documented in several other minerals. 相似文献
7.
Jiang-Feng Qin Shao-Cong Lai Chun-Rong Diwu Yin-Juan Ju Yong-Fei Li 《Contributions to Mineralogy and Petrology》2010,159(3):389-409
Petrogenesis of high Mg# adakitic rocks in intracontinental settings is still a matter of debate. This paper reports major
and trace element, whole-rock Sr–Nd isotope, zircon U–Pb and Hf isotope data for a suite of adakitic monzogranite and its
mafic microgranular enclaves (MMEs) at Yangba in the northwestern margin of the South China Block. These geochemical data
suggest that magma mixing between felsic adakitic magma derived from thickened lower continental crust and mafic magma derived
from subcontinental lithospheric mantle (SCLM) may account for the origin of high Mg# adakitic rocks in the intracontinental
setting. The host monzogranite and MMEs from the Yangba pluton have zircon U–Pb ages of 207 ± 2 and 208 ± 2 Ma, respectively.
The MMEs show igneous textures and contain abundant acicular apatite that suggests quenching process. Their trace element
and evolved Sr–Nd isotopic compositions [(87Sr/86Sr)i = 0.707069–0.707138, and εNd(t) = −6.5] indicate an origin from SCLM. Some zircon grains from the MMEs have positive εHf(t) values of 2.3–8.2 with single-stage Hf model ages of 531–764 Ma. Thus, the MMEs would be derived from partial melts of the
Neoproterozoic SCLM that formed during rift magmatism in response to breakup of supercontinent Rodinia, and experience subsequent
fractional crystallization and magma mixing process. The host monzogranite exhibits typical geochemical characteristics of
adakite, i.e., high La/Yb and Sr/Y ratios, low contents of Y (9.5–14.5 ppm) and Yb, no significant Eu anomalies (Eu/Eu* = 0.81–0.90),
suggesting that garnet was stable in their source during partial melting. Its evolved Sr–Nd isotopic compositions [(87Sr/86Sr)i = 0.7041–0.7061, and εNd(t) = −3.1 to −4.3] and high contents of K2O (3.22–3.84%) and Th (13.7–19.0 ppm) clearly indicate an origin from the continental crust. In addition, its high Mg# (51–55),
Cr and Ni contents may result from mixing with the SCLM-derived mafic magma. Most of the zircon grains from the adakitic monzogranite
show negative εHf(t) values of −9.4 to −0.1 with two-stage Hf model ages of 1,043–1,517 Ma; some zircon grains display positive εHf(t) of 0.1–3.9 with single-stage Hf ages of 704–856 Ma. These indicate that the source region of adakitic monzogranite contains
the Neoproterozoic juvenile crust that has the positive εHf(t) values in the Triassic. Thus, the high-Mg adakitic granites in the intracontinental setting would form by mixing between
the crustal-derived adakitic magma and the SCLM-derived mafic magma. The mafic and adakitic magmas were generated coevally
at Late Triassic, temporally consistent with the exhumation of deeply subducted continental crust in the northern margin of
the South China Block. This bimodal magmatism postdates slab breakoff at mantle depths and therefore is suggested as a geodynamic
response to lithospheric extension subsequent to the continental collision between the South China and North China Blocks. 相似文献
8.
The Sakharjok Y-Zr deposit in Kola Peninsula is related to the fissure alkaline intrusion of the same name. The intrusion
∼7 km in extent and 4–5 km2 in area of its exposed part is composed of Neoarchean (2.68–2.61 Ma) alkali and nepheline syenites, which cut through the
Archean alkali granite and gneissic granodiorite. Mineralization is localized in the nepheline syenite body as linear zones
200–1350 m in extent and 3–30 m in thickness, which strike conformably to primary magmatic banding and trachytoid texture
of nepheline syenite. The ore is similar to the host rocks in petrography and chemistry and only differs from them in enrichment
in zircon, britholite-(Y), and pyrochlore. Judging from geochemical attributes (high HSFE and some incompatible element contents
(1000–5000 ppm Zr, 200–600 ppm Nb, 100–500 ppm Y, 0.1–0.3 wt % REE, 400–900 ppm Rb), REE pattern, Th/U, Y/Nb, and Yb/Ta ratios),
nepheline syenite was derived from an enriched mantle source similar to that of contemporary OIB and was formed as an evolved
product of long-term fractional crystallization of primary alkali basaltic melt. The ore concentrations are caused by unique
composition of nepheline syenite magma (high Zr, Y, REE, Nb contents), which underwent subsequent intrachamber fractionation.
Mineralogical features of zircon-the main ore mineral—demonstrate its long multistage crystallization. The inner zones of
prismatic crystals with high ZrO2/HfO2 ratio (90, on average) grew during early magmatic stage at a temperature of 900–850°C. The inner zones of dipyramidal crystals
with average ZrO2/HfO2 = 63 formed during late magmatic stage at a temperature of ∼500°C. The zircon pertaining to the postmagmatic hydrothermal
stage is distinguished by the lowest ZrO2/HfO2 ratio (29, on average), porous fabric, abundant inclusions, and crystallization temperature below 500°C. The progressive
decrease in ZrO2/HfO2 ratio was caused by evolution of melt and postmagmatic solution. The metamorphic zircon rims relics of earlier crystals and
occurs as individual rhythmically zoned grains with an averaged ZrO2/HfO2 ratio (45, on average) similar to that of the bulk ore composition. The metamorphic zircon is depleted in uranium in comparison
with magmatic zircon, owing to selective removal of U by aqueous metamorphic solutions. Zircon from the Sakharjok deposit
is characterized by low concentrations of detrimental impurities, in particular, contains only 10–90 ppm U and 10–80 ppm Th,
and thus can be used in various fields of application. 相似文献
9.
The spin Hamiltonian (SH) parameters (g factors g
x
, g
y
and g
z
and the hyperfine structure constants A
x
, A
y
and A
z
) and local structure for the rhombic Rh4+ and Ir4+ centers in TiO2 (rutile) are theoretically studied from the perturbation formulas of these parameters for a low spin (S = 1/2) d
5 ion under rhombically distorted octahedra. In the calculations, the ligand orbital and spin–orbit coupling contributions
as well as the influence of the local lattice distortions are taken into account using the cluster approach. The local axial
elongation ratios are found to be about 1.7 and 3 times, respectively, larger for the Rh4+ and Ir4+ centers than that (≈0.0075) for the host Ti4+ site in rutile, while the perpendicular distortion angles (≈−0.28° and −0.42°, respectively) are more than one order in magnitude
smaller than the host value (≈−9.12°). This means that the impurity centers exhibit further elongations of the oxygen octahedra
and much smaller perpendicular rhombic distortions as compared with those of the host Ti4+ site in TiO2. The above local lattice distortions can be mainly ascribed to the substitution of the host Ti4+ by the nd
5 impurities, which may induce different physical and chemical properties for the metal–ligand clusters. In addition, the influence
of the Jahn–Teller effect on the local structure may not be completely excluded. The calculated SH parameters show reasonable
agreement with the observed values. 相似文献
10.
M. R. Krbetschek J. Götze G. Irmer U. Rieser T. Trautmann 《Mineralogy and Petrology》2002,76(3-4):167-177
Summary ?Feldspar specimens covering the whole Or–Ab–An ternary have been investigated by cathodoluminescence (CL), photoluminescence
(PL), radioluminescence (RL) and radiophosphorescence (RP) spectrometry. A red luminescence emission, which is commonly explained
by Fe3+ lattice defects, is a characteristic feature of all the spectra. Different shifts of the peak-wavelength between ∼680–750 nm
(1.82–1.65 eV) were observed with varying feldspar composition. Despite the dependence of the peak position on the Ca/Na ratio,
initially described for CL in the 1970s, there is also a shift induced by changing NaK composition. The observed effects can
be explained by known relations that the peak position of the red luminescence emission in feldspars can be affected both
by the structural state of the feldspar and the site occupancy of the trivalent iron. In the case of alkali feldspars another
factor may influence the peak-shift. The incorporation of the larger potassium ion causes non-linear variations of the cell
dimensions and therefore Fe–O bond distance. The behaviour of the red peak-shift dependent on the feldspar composition is
not equal for all types of luminescence investigated. This is most likely caused by the different luminescence excitation
mechanism.
Received December 3, 2001; revised version accepted March 25, 2002 相似文献
11.
Qiugen Li Shuwen Liu Zongqi Wang Zhuyin Chu Biao Song Yanbin Wang Tao Wang 《International Journal of Earth Sciences》2008,97(3):443-458
Detrital zircon U–Pb ages, whole-rock Nd isotopic, and geochemical data of metasedimentary rocks from the Wutai Complex in
the Central Zone, North China Craton, have been determined. Compositionally, these rocks are characterized by a narrow variation
in SiO2/Al2O3 (2.78–3.96, except sample 2007-1), variable Eu anomalies, spanning a range from significantly negative Eu anomalies to slightly
positive anomalies (Eu/Eu* = 0.58–1.12), and positive ε
Nd (t) values (0.1–1.97). The 18 detrital zircons of one sample yielded age populations of 2.53 Ga, 2.60 Ga, and 2.70–2.85 Ga.
Geochemical data reveal intermediate source weathering, varying degrees of K-metasomatism in the majority of these metasedimentary
rocks, whereas other secondary disturbances seem to be negligible. Detailed analysis in detrital zircon U–Pb geochronology,
whole-rock Nd isotope, and geochemistry shows that these metasedimentary rocks are derived from a mixed provenance. The predominant
derivation is from the late Archean granitoids and metamorphic volcanics in the Wutai Complex, and there is also input of
older continental remnants, except TTG gneisses, from the Hengshan and Fuping Complexes. The sediments were probably deposited
in fore-arc or/and intra-arc basins within an arc system. 相似文献
12.
Single-crystal electron paramagnetic resonance (EPR) spectra of fast-electron-irradiated quartz, after annealing at 120 and
200°C, reveal five new E′ type centers, herein labeled
E 5¢ , E 6¢ , E 7¢ , E 8¢ , \textand E 9¢ E_{ 5}^{\prime } ,\,E_{ 6}^{\prime } ,\,E_{ 7}^{\prime } ,\,E_{ 8}^{\prime } ,\,{\text{and}}\,E_{ 9}^{\prime } . Centers
E 5¢ , E 7¢ , \textand E 9¢ E_{ 5}^{\prime } ,\,E_{ 7}^{\prime } ,\,{\text{and}}\,E_{ 9}^{\prime } are characterized by the orientations of the unique principal g and A(29Si) axes close to a short Si–O bond direction, hence representing new variants of the well-established E 1¢ E_{ 1}^{\prime } center. Centers E 6¢ E_{ 6}^{\prime } and E 8¢ E_{ 8}^{\prime } have the orientations of the unique principal g and A(29Si) axes approximately along a long Si–O bond direction, similar to the E 2¢ E_{ 2}^{\prime } centers. Therefore, these new E′ type centers apparently arise from the removal of different oxygen atoms and represent variable local distortions around
the oxygen vacancies. 相似文献
13.
Single-crystal and powder electron paramagnetic resonance (EPR) spectroscopic studies of natural amethyst quartz, before and
after isochronal annealing between 573 and 1,173 K, have been made from 90 to 294 K. Single-crystal EPR spectra confirm the
presence of two substitutional Fe3+ centers. Powder EPR spectra are characterized by two broad resonance signals at g = ~10.8 and 4.0 and a sharp signal at g = 2.002. The sharp signal is readily attributed to the well-established oxygen vacancy electron center E
1′. However, the two broad signals do not correspond to any known Fe3+ centers in the quartz lattice, but are most likely attributable to Fe3+ clusters on surfaces. The absolute numbers of spins of the Fe3+ species at g = ~10.8 have been calculated from powder EPR spectra measured at temperatures from 90 to 294 K. These results have been used
to extract thermodynamic potentials, including Gibbs energy of activation ΔG, activation energy E
a, entropy of activation ΔS and enthalpy of activation ΔH for the Fe3+ species in amethyst. In addition, magnetic susceptibilities (χ) have been calculated from EPR data at different temperatures. A linear relationship between magnetic susceptibility and
temperature is consistent with the Curie–Weiss law. Knowledge about the stability and properties of Fe3+ species on the surfaces of quartz is important to better understanding of the reactivity, bioavailability and heath effects
of iron in silica particles. 相似文献
14.
Jin-Hui Yang Fu-Yuan Wu Simon A. Wilde Lie-Wen Xie Yue-Heng Yang Xiao-Ming Liu 《Contributions to Mineralogy and Petrology》2007,153(2):177-190
In situ zircon U–Pb and Hf-isotopic data have been determined for mafic microgranular enclaves and host granitoids from the
Early Cretaceous Gudaoling batholith in the Liaodong Peninsula, NE China, in order to constrain the sources and petrogenesis
of granites. The zircon U–Pb age of the enclaves (120 ± 1 Ma) is identical to that of the host monzogranite (120 ± 1 Ma),
establishing that the mafic and felsic magmas were coeval. The Hf isotopic composition of the enclaves [ε
Hf(t) = +4.5 to −6.2] is distinct from the host monzogranite [ε
Hf(t) = −15.1 to −25.4], indicating that both depleted mantle and crustal sources contributed to their origin. The depleted mantle
component was not previously revealed by geochemical and Nd and Sr isotopic studies, showing that zircon Hf isotopic data
can be a powerful geochemical tracer with the potential to provide unique petrogenetic information. Some wall-rock contamination
is indicated by inherited zircons with considerably older U–Pb ages and low initial Hf isotopic compositions. Hafnium isotopic
variations in Early Cretaceous zircons rule-out simple crystal–liquid fractionation or restite unmixing as the major genetic
link between enclaves and host rocks. Instead, mixing of mantle-derived mafic magmas with crustal-derived felsic magmas, coupled
with assimilation of wall rocks, is compatible with the data.
Electronic supplementary material Supplementary material is available in the online version of this article at and is accessible for authorized users. 相似文献
15.
A total of 87 direct shear tests in a large direct shear-box apparatus have been used to investigate the strength and dilatancy
of sand–gravel mixtures. This paper focuses on the differences in behaviour between a silica sand (yellow Leighton Buzzard
sand) and sand–gravel mixtures obtained by adding fractions of two kinds of gravel to the sand. The purpose is to find a relation
between the grain-size characteristics of the materials and the shearing resistance. Experimental results are analysed in
terms of the frictional and dilatant contributions to the strength of mixtures as a function of their relative density, and
are compared with dilatancy theories and empirical equations. The addition of gravel to the mixtures, even at low fractions
(less than 0.1 by volume), causes an increase in peak friction angle (Φ ′peak) which results both from higher dilatancy at failure (ψmax) and higher constant volume friction angle (Φ ′cv). Use of the minimum voids ratio (emin) of the materials allows the data for the two families of mixtures to be normalized and interpreted in terms of Φ ′cv and the ratio (Φ ′peak − Φ ′cv)/ψmax. The relationships between relative density (Dr), ψmax and Φ ′peak − Φ ′cv are only partly explained on a physical basis, so we develop empirical equations to predict the peak shear resistance of
sand–gravel mixtures (up to gravel contents of 0.5) on the basis of easily measurable quantities. Such equations constitute
a practical tool to overcome the problems arising from the impracticality of testing coarse material in the standard shear-box
apparatus. 相似文献
16.
Time-resolved luminescence spectra of natural and synthetic hydrous volcanic glasses with different colors and different
Fe, Mn, and H2O content were measured, and the implications for the glass structure are discussed. Three luminescence ranges are observed
at about 380–460, 500–560, and 700–760 nm. The very short-living (lifetimes less than 40 ns) blue band (380–460 nm) is most
probably due to the 4T2(4D) →6A1(6S) and 4A1(4G) →6A1(6S) ligand field transitions of Fe3+. The green luminescence (500–560 nm) arises from the Mn2+ transition 4T1(4G) →6A1(6S). It shows weak vibronic structure, short lifetimes less than 250 μs, and indicates that Mn2+ is tetrahedrally coordinated, occupying sites with similar distortions and ion–oxygen interactions in all samples studied.
The red luminescence (700–760 nm) arising from the 4T1(4G) →6A1(6S) transition of Fe3+ has much longer lifetimes of the order of several ms, and indicates that ferric iron is also mainly tetrahedrally coordinated.
Increasing the total water content of the glasses leads to quenching of the red luminescence and decrease of the distortions
of the Fe3+ polyhedra.
Received: 30 July 2001 / Accepted: 15 November 2001 相似文献
17.
T. Geisler 《Physics and Chemistry of Minerals》2002,29(6):420-429
Raman spectroscopy and the powder diffraction technique have been used to monitor the recovery process of two partially metamict
zircons (2.6 and 4.8 × 1018
α-decays g−1) from Sri Lanka during a series of isothermal annealing experiments in the temperature range from 870 to 1622 K. These experiments
show for the first time that structural recovery in partially metamict zircon proceeds via three distinct recovery stages,
each of which occurs within a distinct time-temperature regime. Whereas the first two stages have previously been recognized
(recovery of damaged crystalline remnants and epitaxial recrystallization), the third stage has not yet been identified as
a single activated process. It is suggested that anisotropic defect annealing during the first stage at low temperatures,
where the structure recovers preferentially along the a(b) plane, produces a geometrical situation where large structural rearrangements are necessary to remove the remaining defects
inside the crystalline material. This situation is approximately reached when the amorphous domains start to recrystallize.
The reason for anisotropic annealing can be found in a different connectivity between polyhedral linkages in both directions
of the zircon lattice. High apparent activation energies, in the range of 6.4 to 7.9 eV, were determined for the third recovery
stage from the Raman data, which are interpreted to reflect large structural rearrangements (i.e. polyhedral tilting) associated
with the final recovery of the c axis. This explains the occurrence of a distinct recrystallization stage without defect annealing. Finally, it should be
mentioned that the first recovery stage is not necessarily expected to occur in less damaged zircon crystals (<∼2 × 1018
α-decays g−1), since less stable defects along the basal plane might have already been self-annealed during radiation damage accumulation
under ambient temperatures.
Received: 6 September 2001 / Accepted: 25 February 2002 相似文献
18.
Shuan-Hong Zhang Yue Zhao Alfred Kröner Xiao-Ming Liu Lie-Wen Xie Fu-Kun Chen 《International Journal of Earth Sciences》2009,98(6):1441-1467
Recent zircon dating identified several late Carboniferous to early Permian hornblende gabbro–diorite–quartz diorite–granodiorite–tonalite–granite
plutons in lithological assemblages at the northern margin of the North China Block (NCB) that were previously regarded as
Archaean to Palaeoproterozoic. Our geochronological results indicate that emplacement of these plutons was a continuous process
during the late Carboniferous to early Permian, from 324 ± 6 to 274 ± 6 Ma, and lasted for at least 50 Ma. In this paper,
the early Permian components with compositions from gabbro to granite within the intrusive complex were studied. The early
Permian plutons exhibit calc-alkaline or high-K calc-alkaline, metaluminous geochemical features and highly variable SiO2 contents. They have no significant Eu anomaly in their REE patterns, and in primitive-mantle-normalized spidergrams they
display depletion in Th, U, Nb, Ta, P and Ti, and enrichment in Ba, K, Pb and Sr. The granitoid bodies within these plutons
display I-type and adakitic geochemical signatures. The early Permian rocks exhibit low whole-rock initial 87Sr/86Sr ratios from 0.70520 to 0.70615 and have negative whole-rock ε
Nd(t) values ranging from −17.4 to −9.3 and zircon ε
Hf(t) values of −23.2 to −10.5. The gabbros exhibit higher ε
Nd(t) values from −11.1 to −9.3 and ε
Hf(t) values from −16.5 to −10.5, and one granodiorite exhibits an even lower ε
Nd(t) value of −17.4 and zircon ε
Hf(t) values of −23.2 to −15.1. Geochemical, Sr–Nd and in situ zircon Hf isotopic compositions suggest that the hornblende gabbros
were derived from a metasomatized lithospheric mantle, and the diorite and quartz diorite were generated from a gabbroic magma
by fractional crystallization, coupled with differential assimilation of ancient lower crustal material. The granodiorite
was likely derived from partial melting of ancient lower crust with involvement of some mantle components. Involvement of
both lithospheric mantle and ancient lower crust in the generation of the early Permian plutons indicates strong crust–mantle
interaction in the northern NCB. Petrological associations as well as geochemical and Sr–Nd–Hf isotopic results show that
the early Permian plutons were emplaced along an Andean-type active continental margin during southward subduction of the
Palaeo-Asian oceanic plate beneath the NCB. Integration of our results with previously published data for late Carboniferous
and late Permian to middle Triassic intrusions suggests that the continental arc on the northern margin of the NCB existed
for at least 50 Ma during the late Palaeozoic, and final amalgamation of the Mongolian arc terranes with the northern NCB
likely occurred during a period from ~270 to ~250 Ma, i.e, in the late Permian to earliest Triassic. 相似文献
19.
Fluid-assisted zircon and monazite growth within a shear zone: a case study from Finnmark,Arctic Norway 总被引:1,自引:0,他引:1
Christopher L. Kirkland Martin J. Whitehouse Trond Slagstad 《Contributions to Mineralogy and Petrology》2009,158(5):637-657
The U–Pb ages, REE content, and oxygen isotopic composition of zircon rims developed within a major shear zone in the Kalak
Nappe Complex (KNC), Arctic Norway have been determined along with the age of monazite crystals. Different generations of
granitic veins have been distinguished based on both field criteria and monazite ages of 446 ± 3 and 424 ± 3 Ma. Within each
of these veins, inherited zircon cores are mantled by homogeneous low CL-response zircon rims which yield a range of concordant
U–Pb dates of ca. 470–360 Ma. Significant numbers of zircon rims coincide with the timing of monazite crystallization. The
zircon rims have moderate light REE enrichment compared to cores, distinctive (Sm/La)
n
values of less than 12, and La between 0.3 and 10 ppm. This indicates free elemental exchange between newly formed zircon
rims and the surrounding matrix. The rims have calculated accumulated alpha-radiation dosages corresponding with a crystalline
structure and δ18O values of 1‰. This implies rim crystallization directly from a zirconium-saturated hydrothermal fluid which was modified
by some silicate melt. Growth of the zircon rims was prolonged and locally variable due to preferential fluid flow. A third
type of zircon can be recognized, forming both rims and cores, with high alpha-radiation doses, and significant enrichment
in La, Pr, and Eu. These are interpreted as low-temperature hydrothermally altered metamict zircons. The high volatile input
and partial melting in the shear zone favoured prolonged zircon rim growth due to its ability to easily nucleate on inherited
seeds. On the other hand, monazite, susceptible to dissolution and re-growth, crystallized in brief episodes, as has been
predicted from theoretical phase diagrams. From a regional perspective, these results elucidate cryptic Ar–Ar cooling ages,
providing the first record of a Late Ordovician heating and cooling phase within the KNC prior to the climactic Scandian collision. 相似文献
20.
A worldwide dataset of organic material from 553 samples belonging to coal and carbonaceous materials was used to analyze
the evolution of hydrogen index (HI) and bitumen index (BI) with increasing thermal maturity. Basic statistical analyses were
applied to detect the boundary lines of HImax and BImax in delineating the upper and lower limits of the HI and BI bands for the majority of samples. In addition, cross-plots of
HI or BI versus maturity (Ro% and T
max) also provide criteria for defining the HImax and BImax boundary lines. The constructed HI and BI bands are broad at low maturities and become narrower with increasing thermal maturities.
The petroleum generation potential is completely exhausted at the vitrinite reflectance of 2.0–2.2% or T
max of 510–520°C. An increase in HI implies extra petroleum generation which was related to changes in structure of organic materials.
A declining BI means that the oil expulsion window starts to occur at the vitrinite reflectance range of 0.75–1.05%. The petroleum
potential can be divided into four different areas based on the cross-plot of HI versus Ro%. The highest petroleum potential
area is located in section II with Ro = 0.6–1.0% and HI > 100. The oil generation potential is rapidly exhausted at section
III with Ro > 1.0%. This result is also in accordance with the result of curve regression of HI versus Ro% based on 80 samples
with Ro = 1.02–3.43% (R
2 = 0.72). Overall, the total oil window can be extended up to Ro = ~1.25–1.95%. Finally, in the cross-plots of S1 versus S2,
shale or C-shale exhibits a higher and slowly decreased slope, compared with a lower and then sharply increased slope of coal
samples, which is attributable to their compositional difference in organic material. 相似文献