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1.
V. Palchik 《Rock Mechanics and Rock Engineering》2006,39(3):215-232
Summary. This paper presents a model created by the author to predict stress–strain relationships for weak to strong carbonate rocks
(σc < 100 MPa) exhibiting axial strains up to 1%. The stress–strain model based on Haldane’s distribution function (Haldane,
1919) relates the axial stress (or normalized axial stress) to the square of an exponential function where the exponent is
axial strain. To obtain accurate stress–strain relationship over the whole pre-failure strain with the proposed stress–strain
model, it is necessary to have only one datum point (peak axial stress and maximum axial strain at this peak stress). It is
shown that the stress–strain relationships observed in laboratory compression tests on samples collected from six carbonate
rock formations (chalk, dolomites and limestones) from different parts of Israel, agree well with the stress–strain prediction
model proposed by the author. 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.
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
4.
James M. D. Day Colin G. Macpherson David Lowry D. Graham Pearson 《Contributions to Mineralogy and Petrology》2012,164(1):177-183
Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) report laser-assisted fluorination (LF) and secondary ionization mass spectrometry (SIMS) 18O/16O datasets for olivine grains from the Canary Islands of Gran Canaria, Tenerife, La Gomera, La Palma and El Hierro. As with prior studies of oxygen isotopes in Canary Island lavas (e.g. Thirlwall et al. Chem Geol 135:233–262, 1997; Day et al. Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010), these authors find variations in δ18Ool (~4.6–6.0 ‰) beyond that measured for mantle peridotite olivine (Mattey et al. Earth Planet Sci Lett 128:231–241, 1994) and interpret this variation to reflect contributions from pyroxenite-peridotite mantle sources. Furthermore, Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) speculate that δ18Ool values for La Palma olivine grains measured by LF (Day et al. Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010) may be biased to low values due to the presence of altered silicate, possibly serpentine. The range in δ18Ool values for Canary Island lavas are of importance for constraining their origin. Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) took a subset (39 SIMS analyses from 13 grains from a single El Hierro lava; EH4) of a more extensive dataset (321 SIMS analyses from 110 grains from 16 Canary Island lavas) to suggest that δ18Ool is weakly correlated (R 2 = 0.291) with the parameter used by Gurenko et al. (Earth Planet Sci Lett 277:514–524, 2009) to describe the estimated weight fraction of pyroxenite-derived melt (Xpx). With this relationship, end-member δ18O values for HIMU-peridotite (δ18O = 5.3 ± 0.3 ‰) and depleted pyroxenite (δ18O = 5.9 ± 0.3 ‰) were defined. Although the model proposed by Gurenko et al. (Contrib Mineral Petrol 162:349–363, 2011) implicates similar pyroxenite-peridotite mantle sources to those proposed by Day et al. (Geology 37:555–558, 2009, Geochim Cosmochim Acta 74:6565–6589, 2010) and Day and Hilton (Earth Planet Sci Lett 305:226–234, 2011), there are significant differences in the predicted δ18O values of end member components in the two models. In particular, Day et al. (Geochim Cosmochim Acta 74:6565–6589, 2010) proposed a mantle source for La Palma lavas with low-δ18O (<5 ‰), rather than higher-δ18O (c.f. the HIMU-peridotite composition of Gurenko et al. in Contrib Mineral Petrol 162:349–363, 2011). Here we question the approach of using weakly correlated variations in δ18Ool and the Xpx parameter to define mantle source oxygen isotope compositions, and provide examples of why this approach appears flawed. We also provide reasons why the LF datasets previously published for Canary Island lavas remain robust and discuss why LF and SIMS data may provide complementary information on oxygen isotope variations in ocean island basalts (OIB), despite unresolved small-scale uncertainties associated with both techniques. 相似文献
5.
The petrogenetic potential of in situ laser ablation Hf isotope data from melt precipitated zircons was explored through the
analyses of about 700 individual crystals derived from about 20 different granitic intrusions covering the Variscan basement
segment of eastern Bavaria, SE Germany. In combination with geochemical features, four major suites of granitic rocks can
be distinguished: (1) NE Bavarian redwitzites (52–57 wt% SiO2, intrusion ages around 323 Ma) have chondritic εHf(t) values (+0.8 to –0.4). The redwitzites are hybrid rocks and the Hf
data are permissive of mixing of a mantle progenitor and crustal melts. (2) Various intermediate rock types (dioritic dyke,
granodiorite, palite, 59–63 wt% SiO2, 334–320 Ma) from the Bavarian Forest yield negative εHf(t) values between –3.4 and –5.1. These values which apparently contradict
a mantle contribution fingerprint an enriched (metasomatized) mantle component that was mixed with crustal material. (3) Voluminous,
major crust forming granites sensu stricto (67–75 wt% SiO2, 328–298 Ma) are characterized by a range in εHf(t) values from –0.5 to –5.6. Different crustal sources and/or modification
of crustal melts by various input of juvenile material can explain this variation. (4) Post-plutonic (c. 299 Ma) porphyritic dykes of dacitic composition (64–67 wt% SiO2) from the southern Bavarian Forest have chondritic εHf(t) values (+0.6 to –1.1) and display large intergrain Hf isotope variation.
The dykes form a separate petrogenetic group and the Hf data suggest that the zircons crystallized when a pristine mantle-derived
parental melt was modified by infiltration of crustal material. The zircon Hf data form a largely coherent positive array
with the whole-rock Nd data and both systems yield similar two-stage depleted mantle model ages (1.1–1.7 Ga). 相似文献
6.
Petrogenesis of early cretaceous carbonatite and ultramafic lamprophyres in a diatreme in the Batain Nappes,Eastern Oman continental margin 总被引:1,自引:0,他引:1
S. Nasir S. Al-Khirbash H. Rollinson A. Al-Harthy A. Al-Sayigh A. Al-Lazki T. Theye H.-J. Massonne E. Belousova 《Contributions to Mineralogy and Petrology》2011,161(1):47-74
Allochthonous carbonatite and ultramafic lamprophyre occur in a diatreme at the beach of the Asseelah village, northeastern
Oman. The diatreme consists of heterogeneous deposits dominated by ‘diatreme facies’ pyroclastic rocks. These include aillikite
and carbonatite, which intrude late Jurassic to early Cretaceous cherts and shales of the Wahra Formation within the Batain
nappes. Both rock types are dominated by carbonate, altered olivine, Ti–Al–phlogopite and Cr–Al–spinel and contain varying
amounts of apatite and rutile. The carbonatite occur as fine-grained heterolithic breccias with abundant rounded carbonatite
xenoliths, glimmerite and crustal xenoliths. The aillikite consists of pelletal lapilli tuff with abundant fine-grained carbonatite
autoliths and crustal xenoliths, which resemble those in the carbonatite breccia. The aillikite and carbonatite are characterized
by low SiO2 (11–24 wt%), MgO (9.5–12.4 wt%) and K2O (<0.3 wt%), but high CaO (18–22 wt%), Al2O3 (4.75–7.04 wt%), Fe2O3tot (8.7–13.8 wt%) and loss-on-ignition (24–30 wt%). Higher CaO, Fe2O3total, Al2O3, MnO, TiO2, P2O5 and lower SiO2 and MgO content distinguish carbonatite from the aillikite. The associated carbonatite xenoliths and autoliths have intermediate
composition between the aillikite and carbonatite. Mg number is variable and ranges between 58 and 66 in the carbonatite,
66 and 72 in the aillikite and between 48 to 64 in the carbonatite autoliths and xenoliths. The Asseelah aillikite, carbonatite,
carbonatite xenoliths and autoliths overlap in most of their mineral parageneses, mineral composition and major and trace
element chemistry and have variable but overlapping Sr, Nd and Pb isotopic composition, implying that these rocks are related
to a common type of parental magma with variable isotopic characteristics. The Asseelah aillikite, carbonatite and carbonatites
xenoliths are LREE-enriched and significantly depleted in HREE. They exhibit similar smooth, subparallel REE pattern and steep
slopes with (La/Sm)
n
of 6–10 and relative depletion in heavy rare earth elements (Lu = 3–10 chondrite). Initial 87Sr/86Sr ratios vary from 0.70409 to 0.70787, whereas initial 143Nd/144Nd ratios vary between 0.512603 and 0.512716 (εNd
i
between 2.8 and 3.6). 206Pb/204Pb
i
ratios vary between 18.4 and 18.76, 207Pb/204Pb
i
ratios vary between 15.34 and 15.63, whereas 208Pb/204Pb
i
varies between 38.42 and 39.05. Zircons grains extracted from the carbonatite have a mean age of 137 ± 1 Ma (95% confidence,
MSWD = 0.49). This age correlates with large-scale tectonic events recorded in the early Indian Ocean at 140–160 Ma. Geochemical
and isotopic signatures displayed by the Asseelah rocks can be accounted for by vein-plus-wall-rock model of Foley (1992) wherein veins are represented by phlogopite, carbonate and apatite and depleted peridotite constitutes the wall-rock. The
carbonatite and aillikite magmatism is probably a distal effect of the breaking up of Gondwana, during and/or after the rift-to-drift
transition that led to the opening of the Indian Ocean. 相似文献
7.
Isotope and trace element evidence for depleted lithosphere in the source of enriched Ko’olau basalts 总被引:1,自引:0,他引:1
Vincent J. M. Salters Janne Blichert-Toft Zuzana Fekiacova Afi Sachi-Kocher Michael Bizimis 《Contributions to Mineralogy and Petrology》2006,151(3):297-312
We have measured the Hf and Nd isotopic compositions of 38 basalts from the Ko’olau drill hole, Hawai’i. The basalts show
limited variations in both 176Hf/177Hf and 143Nd/144Nd (ε
Nd varies from +4.2 to +7.3 and ε
Hf from +8.0 to +12.3). Their correlated variation has an R
2 of 0.86. The data form an array with a slope of 1.2 on an ε
Hf–ε
Nd isotope correlation diagram, while the slope of all Hawai’ian basalt data is 0.98. Both slopes are significantly shallower
than that of the mantle array of 1.4 defined by ocean island basalts. Previous studies have shown that a shallow slope in
Hf–Nd isotope space can be related to ancient pelagic sediments in the mantle source (Blichert-Toft et al. 1999; Salters and White 1998). However, the combined variations in Ko’olau basalts of Hf–Nd–Pb–Os isotopic compositions and trace element ratios, such
as La/Nb, Th/La and Sr/Nd, are not consistent with the simple addition of a sediment component to the mantle. We instead propose
that the shallow slope on the Hf–Nd isotope correlation diagram for Ko’olau shield stage basalts can be better explained if
the enriched endmember contains either an ancient oceanic lithosphere component or the high-176Hf/177Hf component observed in the Salt Lake Crater (SLC) peridotite xenoliths (which also have a depleted lithosphere origin).
Since Ko’olau basalts have high 187Os/188Os (0.135–0.160) and the SLC xenoliths have 187Os/188Os up to 0.13 (Lassiter et al. 2000) Os-isotopes are consistent with the latter being a component in the enriched Ko’olau source.
相似文献
Vincent J. M. SaltersEmail: |
8.
The thermoelastic behaviour of anthophyllite has been determined for a natural crystal with crystal-chemical formula ANa0.01
B(Mg1.30Mn0.57Ca0.09Na0.04) C(Mg4.95Fe0.02Al0.03) T(Si8.00)O22
W(OH)2 using single-crystal X-ray diffraction to 973 K. The best model for fitting the thermal expansion data is that of Berman
(J Petrol 29:445–522, 1988) in which the coefficient of volume thermal expansion varies linearly with T as α
V,T
= a
1 + 2a
2 (T − T
0): α298 = a
1 = 3.40(6) × 10−5 K−1, a
2 = 5.1(1.0) × 10−9 K−2. The corresponding axial thermal expansion coefficients for this linear model are: α
a
,298 = 1.21(2) × 10−5 K−1, a
2,a
= 5.2(4) × 10−9 K−2; α
b
,298 = 9.2(1) × 10−6 K−1, a
2,b
= 7(2) × 10−10 K−2. α
c
,298 = 1.26(3) × 10−5 K−1, a
2,c
= 1.3(6) × 10−9 K−2. The thermoelastic behaviour of anthophyllite differs from that of most monoclinic (C2/m) amphiboles: (a) the ε
1 − ε
2 plane of the unit-strain ellipsoid, which is normal to b in anthophyllite but usually at a high angle to c in monoclinic amphiboles; (b) the strain components are ε
1 ≫ ε
2 > ε
3 in anthophyllite, but ε
1 ~ ε
2 ≫ ε
3 in monoclinic amphiboles. The strain behaviour of anthophyllite is similar to that of synthetic C2/m
ANa B(LiMg) CMg5
TSi8 O22
W(OH)2, suggesting that high contents of small cations at the B-site may be primarily responsible for the much higher thermal expansion
⊥(100). Refined values for site-scattering at M4 decrease from 31.64 epfu at 298 K to 30.81 epfu at 973 K, which couples with similar increases of those of M1 and M2 sites. These changes in site scattering are interpreted in terms of Mn ↔ Mg exchange involving M1,2 ↔ M4, which was first detected at 673 K. 相似文献
9.
Mengist Teklay Erik E. Scherer Klaus Mezger Leonid Danyushevsky 《Contributions to Mineralogy and Petrology》2010,159(5):731-751
The Afar Depression offers a rare opportunity to study the geodynamic evolution of a rift system from continental rifting
to sea floor spreading. This study presents geochemical data for crustal and mantle xenoliths and their alkaline host basalts
from the region. The basalts have enriched REE patterns, OIB-like trace element characteristics, and a limited range in isotopic
composition (87Sr/86Sr = 0.70336–0.70356, ε
Nd = +6.6 to +7.0, and ε
Hf = +10.0 to +10.7). In terms of trace elements and Sr–Nd isotopes, they are similar to basalts from the Hanish and Zubair
islands in the southern Red Sea and are thus interpreted to be melts from the Afar mantle. The gabbroic crustal xenoliths
vary widely in isotope composition (87Sr/86Sr = 0.70437–0.70791, ε
Nd = −8.1 to +2.5, and ε
Hf = −10.5 to +4.9), and their trace element characteristics match those of Neoproterozoic rocks from the Arabian–Nubian Shield
and modern arc rocks, suggesting that the lower crust beneath the Afar Depression contains Neoproterozoic mafic igneous rocks.
Ultramafic mantle xenoliths from Assab contain primary assemblages of fresh ol + opx + cpx + sp ± pl, with no alteration or
hydrous minerals. They equilibrated at 870–1,040°C and follow a steep geothermal gradient consistent with the tectonic environment
of the Afar Depression. The systematic variations in major and trace elements among the Assab mantle xenoliths together with
their isotopic compositions suggest that these rocks are not mantle residues but rather series of layered cumulate sills that
crystallized from a relatively enriched picritic melt related to the Afar plume that was emplaced before the eruption of the
host basalts. 相似文献
10.
Probabilistic seismic hazard of Pakistan, Azad-Jammu and Kashmir 总被引:2,自引:2,他引:0
The seismic hazard study for Pakistan and Azad Jammu and Kashmir has been conducted by using probabilistic approach in terms
of peak ground acceleration (PGA) in m/s2 and also seismic hazard response spectra for different cities. A new version of Ambraseys et al. (Bull Earthq Eng 3:1–53,
2005) ground acceleration model is used, and parameterization is based on most recent updated earthquake catalogs that consisted
of 14,000 events. The threshold magnitude was fixed at M
w 4.8, but seismic zones like northern Pakistan–Tajikistan, Hindukush and northern Afghanistan–Tajikistan border had M
w 5.2. The average normalized ‘a’ and ‘b’ values for all zones are 6.15 and 0.95, respectively. Seismicity of study area was modeled, and ground motion was computed
for eight frequencies (0.025, 0.1, 0.2, 0.5, 1.0, 1.5, 2.0, 2.5 s) for different annual exceedance rates of 0.02, 0.01, 0.005,
0.002 and 0.001 (return periods 50, 100, 200, 500 and 1,000 years) for stiff rocks at the gridding of 0.1° × 0.1°. Seismic
hazard maps based on computed PGA for 0.02, 0.01 and 0.002 annual exceedance are prepared. These maps indicate the earthquake
hazard of Pakistan and surrounding areas in the form of acceleration contour lines, which are in agreement with geological
and seismotectonic characteristics of the study area. The maximum seismic hazard values are found at Muzaffarabad, Gilgit
and Quetta areas. 相似文献
11.
Feng Guo Weiming Fan Chaowen Li Xiaofen Gao Laicheng Miao 《International Journal of Earth Sciences》2009,98(6):1395-1411
An early Cretaceous (135 ± 2 Ma) felsic volcanic suite of dacite and rhyolite from Huolinhe, NE China is characterized by
large ion lithophile element and light REE enrichment and high field strength element (HFSE, e.g., Nb and Ta) and Ti–P depletion,
and bulk silicate earth-like Sr [87Sr/86Sr(i) = 0.70409–0.70481], quite radiogenic Nd [ε
Nd(t) = +3.98 to +5.88], Pb [e.g., 206Pb/204Pb(i) = 18.46–18.55] and Hf [ε
Hf(t) ~+9.2] isotope compositions. Compared with contemporaneous mafic rocks in the region, these felsic rocks have even higher
Nd and Hf isotopic ratios, precluding an origin through differentiation of coeval mantle-derived magmas. Isotope calculation
results suggest that these magmas were derived from a preexistent mixture composed of mainly juvenile crust (70–80%), and
a subordinate recycled crustal component (20–30%) having highly radiogenic Sr and Pb and unradiogenic Nd and Hf. About 25–30%
melting of such a mixed source produced the primary dacitic magma. The rhyolites, which have relatively low MgO, FeO*, Al2O3, CaO, TiO2, P2O5, Na2O, Ba, Sr, REE, HFSE and Y, were differentiates of the dacites after removal of a fractional assemblage of hornblende + plagioclase + K-feldspar + apatite + zircon.
Considering the prolonged events (from 262 to 130 Ma) that produced such highly positive ε
Nd felsic igneous rocks in the region, we prefer a pre-Mesozoic crustal growth model related to arc accretion associated with
the Paleo-Asian Ocean subduction. 相似文献
12.
Xiaoyu Zhang Jibamitra Ganguly Motoo Ito 《Contributions to Mineralogy and Petrology》2010,159(2):175-186
We have experimentally determined the tracer diffusion coefficients (D*) of 44Ca and 26Mg in a natural diopside (~Di96) as function of crystallographic direction and temperature in the range of 950–1,150 °C at 1 bar and f(O2) corresponding to those of the WI buffer. The experimental data parallel to the a*, b, and c crystallographic directions show significant diffusion anisotropy in the a–c and b–c planes, with the fastest diffusion being parallel to the c axis. With the exception of logD*(26Mg) parallel to the a* axis, the experimental data conform to the empirical diffusion “compensation relation”, converging to logD ~ −19.3 m2/s and T ~ 1,155 °C. Our data do not show any change of diffusion mechanism within the temperature range of the experiments. Assuming
that D* varies roughly linearly as a function of angle with respect to the c axis in the a–c plane, at least within a limited domain of ~20° from the c-axis, our data do not suggest any significant difference between D*(//c) and D*(⊥(001)), the latter being the diffusion data required to model compositional zoning in the (001) augite exsolution lamellae
in natural clinopyroxenes. Since the thermodynamic mixing property of Ca and Mg is highly nonideal, calculation of chemical
diffusion coefficient of Ca and Mg must take into account the effect of thermodynamic factor (TF) on diffusion coefficient.
We calculate the dependence of the TF and the chemical interdiffusion coefficient, D(Ca–Mg), on composition in the diopside–clinoenstatite mixture, using the available data on mixing property in this binary
system. Our D*(Ca) values parallel to the c axis are about 1–1.5 log units larger than those Dimanov et al. (1996). Incorporating the effect of TF, the D(Ca–Mg) values calculated from our data at 1,100–1,200 °C is ~0.6–0.7 log unit greater than the experimental quasibinary D((Ca–Mg + Fe)) data of Fujino et al. (1990) at 1 bar, and ~0.6 log unit smaller than that of Brady and McCallister (1983) at 25 kb, 1,150 °C, if our data are normalized to 25 kb using activation volume (~4 and ~6 cm3/mol for Mg and Ca diffusion, respectively) calculated from theoretical considerations. 相似文献
13.
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
14.
The low-temperature heat capacity (C
P) of stishovite (SiO2) synthesized with a multi-anvil device was measured over the range of 5–303 K using the heat capacity option of a physical
properties measurement system (PPMS) and around ambient temperature using a differential scanning calorimeter (DSC). The entropy
of stishovite at standard temperature and pressure calculated from DSC-corrected PPMS data is 24.94 J mol−1 K−1, which is considerably smaller (by 2.86 J mol−1 K−1) than that determined from adiabatic calorimetry (Holm et al. in Geochimica et Cosmochimica Acta 31:2289–2307, 1967) and about 4% larger than the recently reported value (Akaogi et al. in Am Mineral 96:1325–1330, 2011). The coesite–stishovite phase transition boundary calculated using the newly determined entropy value of stishovite agrees
reasonably well with the previous experimental results by Zhang et al. (Phys Chem Miner 23:1–10, 1996). The calculated phase boundary of kyanite decomposition reaction is most comparable with the experimental study by Irifune
et al. (Earth Planet Sci Lett 77:245–256, 1995) at low temperatures around 1,400 K, and the calculated slope in this temperature range is mostly consistent with that determined
by in situ X-ray diffraction experiments (Ono et al. in Am Mineral 92:1624–1629, 2007). 相似文献
15.
Three-step continental-crust growth from subduction accretion and underplating,through intermediary differentiation,to granitoid production 总被引:2,自引:0,他引:2
Wei Liu Xiao-Fei Pan Dun-Yi Liu Zhen-Yu Chen 《International Journal of Earth Sciences》2009,98(6):1413-1439
Sensitive high-resolution ion microprobe (SHRIMP) U–Pb dating, laser-ablation multi-collector ICPMS Hf isotope and electron
microprobe element analyses of inherited/antecrystal and magmatic zircons from five granitoid intrusions of Linxi area, in
the southern segment of the Great Xing’an Range of China were integrated to solve continental crustal growth mechanisms. These
intrusions were divided into two suites. Suites 1 and 2 are mainly granodiorite and syenogranite and correspond to magnesian
and ferroan granites, respectively. SHRIMP dating establishes an Early Cretaceous (135–125 Ma) age for most Linxi granitoids
and a time of ∼146 Ma when their source rocks were generated or re-melted. However, some granitoids were generated in Early
Triassic (241 Ma) and Late Jurassic (146 Ma), after their source rock experienced precursory melting episodes at 263 Ma and
165 Ma, respectively. All zircon 206Pb/238U ages (<300 Ma, n = 100), and high positive zircon εHf(t) values (n = 175) suggest juvenile source materials with an absence of Precambrian basement. Hf–Nd isotopic decoupling of Linxi granitoids
suggests a source component of pelagic sediments, i.e. Paleozoic subduction accretion complexes. Zircon εHf(t) values (t = 263–165 Ma) form a trend sub-parallel to the depleted mantle Hf isotope evolution curve, whilst those with t = 146–125 Ma fall markedly below the latter. The first trend indicates a provenance from essentially subducted oceanic slabs.
However, the abrupt εHf(t) decrease, together with extensive Early Cretaceous magmatism, is interpreted as reflecting mantle upwelling and resultant
underplating, and exhumation of subducted oceanic slabs. Suite 1 granitoids derive mainly from subducted oceanic slabs or
Paleozoic subduction accretion complex, whereas Suite 2 from underplated mafic rock and, subordinately, Paleozoic subduction
accretion complex. Compositions of Suites 1 and 2 depend on the hydrous, oxidized or relatively anhydrous, reduced nature
of source rocks. Among each of these five intrusions, magmatic zircons have systematically lower 176Hf/177Hf than inherited/antecrystal zircons. Hf isotopic and substituting element profiles through inherited/antecrystal zircons
(t = 263 to ∼146 Ma) indicate repeated low melt-fraction melting in the source region. In contrast, profiles through inherited/antecrystal
and magmatic zircons (t = 146–125 Ma) reveal melting region expansion with a widening range of source compositions and increasing melt fractions.
These results lead to the conclusion that continental growth in this region involved a three-step process. This included subduction
accretion and repeated underplating, intermediary differentiation of juvenile rocks, and granitoid production from these differentiated
rocks. 相似文献
16.
M. Cai 《Rock Mechanics and Rock Engineering》2010,43(2):167-184
By applying the Griffith stress criterion of brittle failure, one can find that the uniaxial compressive strength (σc) of rocks is eight times the value of the uniaxial tensile strength (σt). The Griffith strength ratio is smaller than what is normally measured for rocks, even with the consideration of crack closure.
The reason is that Griffith’s theories address only the initiation of failure. Under tensile conditions, the crack propagation
is unstable so that the tensile crack propagation stress (σcd)t and the peak tensile strength σt are almost identical to the tensile crack initiation stress (σci)t. On the other hand, the crack growth after crack initiation is stable under a predominantly compressive condition. Additional
loading is required in compression to bring the stress from the crack initiation stress σci to the peak strength σc. It is proposed to estimate the tensile strength of strong brittle rocks from the strength ratio of
R = \fracs\textc | s\textt | = 8\fracs\textc s\textci . R = {\frac{{\sigma_{\text{c}} }}{{\left| {\sigma_{\text{t}} } \right|}}} = 8{\frac{{\sigma_{\text{c}} }}{{\sigma_{\text{ci}} }}}. The term
\fracs\textc s\textci {\frac{{\sigma_{\text{c}} }}{{\sigma_{\text{ci}} }}} accounts for the difference of crack growth or propagation in tension and compression in uniaxial compression tests.
\fracsc sci {\frac{{\sigma_{c} }}{{\sigma_{ci} }}} depends on rock heterogeneity and is larger for coarse grained rocks than for fine grained rocks. σci can be obtained from volumetric strain measurement or acoustic emission (AE) monitoring. With the strength ratio R determined, the tensile strength can be indirectly obtained from
| s\textt | = \fracs\textc R = \fracs\textci 8. \left| {\sigma_{\text{t}} } \right| = {\frac{{\sigma_{\text{c}} }}{R}} = {\frac{{\sigma_{\text{ci}} }}{8}}. It is found that the predicted tensile strengths using this method are in good agreement with test data. Finally, a practical
estimate of the Hoek–Brown strength parameter m
i is presented and a bi-segmental or multi-segmental representation of the Hoek–Brown strength envelope is suggested for some
brittle rocks. In this fashion, the rock strength parameters like σt and m
i, which require specialty tests such as direct tensile (or Brazilian) and triaxial compression tests for their determination,
can be reasonably estimated from uniaxial compression tests. 相似文献
17.
Viktor A. Kurepin 《Contributions to Mineralogy and Petrology》2010,160(3):391-406
A refined thermodynamic model of H2O and CO2 bearing cordierite based on recent data on volatile incorporation into cordierite (Thompson et al. in Contrib Mineral Petrol
142:107–118, 2001; Harley and Carrington in J Petrol 42:1595–1620, 2001) reflects non-ideality of channel H2O and CO2 mixing. The dependence of cordierite H2O and CO2 contents on P, T and equilibrium fluid composition has been calculated for the range 600–800°C and 200–800 MPa. It has been used for establishing
thermodynamic conditions of cordierite formation and the following retrograde P–T paths of cordierite rocks from many localities. Estimates of the H2O and CO2 activities have shown that cordierites in granites, pegmatites and high-pressure granulites were formed in fluid-saturated
conditions and wide range of H2O/CO2 relations. Very low cordierite H2O contents in many migmatites may be caused not only by fluid-undersaturated conditions at rock formation and H2O leakage on retrograde P–T paths but also by the presence of additional volatile components like CH4 and N2. The pressure dependence of cordierite-bearing mineral equilibria on fluid H2O/CO2 relations has been evaluated. 相似文献
18.
Dmytro M. Trots Alexander Kurnosov Leonid Vasylechko Marek Berkowski Tiziana Boffa Ballaran Daniel J. Frost 《Physics and Chemistry of Minerals》2011,38(7):561-567
A single crystal X-ray diffraction study on lithium tetraborate Li2B4O7 (diomignite, space group I41
cd) has been performed under pressure up to 8.3 GPa. No phase transitions were found in the pressure range investigated, and
hence the pressure evolution of the unit-cell volume of the I41
cd structure has been described using a third-order Birch–Murnaghan equation of state (BM-EoS) with the following parameters:
V
0
= 923.21(6) Å3, K
0
= 45.6(6) GPa, and K′ = 7.3(3). A linearized BM-EoS was fitted to the axial compressibilities resulting in the following parameters a
0
= 9.4747(3) Å, K
0a
= 73.3(9) GPa, K′
a
= 5.1(3) and c
0
= 10.2838(4) Å, K
0c
= 24.6(3) GPa, K′
c
= 7.5(2) for the a and c axes, respectively. The elastic anisotropy of Li2B4O7 is very large with the zero-pressure compressibility ratio β
0c
/β
0a
= 3.0(1). The large elastic anisotropy is consistent with the crystal structure: A three-dimensional arrangement of relatively
rigid tetraborate groups [B4O7]2− forms channels occupied by lithium along the polar c–axis, and hence compression along the c axis requires the shrinkage of the lithium channels, whereas compression in the a direction depends mainly on the contraction of the most rigid [B4O7]2− units. Finally, the isothermal bulk modulus obtained in this work is in general agreement with that derived from ultrasonic
(Adachi et al. in Proceedings-IEEE Ultrasonic Symposium, 228–232, 1985; Shorrocks et al. in Proceedings-IEEE Ultrasonic Symposium, 337–340, 1981) and Brillouin scattering measurements (Takagi et al. in Ferroelectrics, 137:337–342, 1992). 相似文献
19.
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
20.
Victor Kress 《Contributions to Mineralogy and Petrology》2007,154(2):191-204
Experiments were performed in the system O–S–Fe–Ni designed to extend our understanding of the chemistry of sulfide liquids.
Results indicate that adding nickel to Fe-rich sulfide liquids in equilibrium with silicate liquids extends their stability
field to much higher oxygen fugacities and lower sulfur fugacities. Increasing Ni/Fe at a given temperature and sulfur and
oxygen fugacity is accompanied by a significant decrease in the oxygen content of the sulfide liquid. Results of these experiments
are combined with data from the literature to calibrate an associated regular solution model for O–S–Fe–Ni liquids. This model
represents a complete refit of the associated regular solution model of Kress (Contrib Mineral Petrol 139:316–325, 2000). The resulting model is combined with the olivine solution model of Hirschmann (Am Mineral 76:1232–1248, 1991) to explore the effect of variations in oxygen and sulfur fugacities on the distribution of Fe and Ni between olivine and
sulfide liquid. Predicted olivine–sulfide distribution trends parallel those observed by Gaetani and Grove (Geochim Cosmochim
Acta 61:1829–1846, 1997), Gaetani and Grove (Earth Planet Sci Lett 169:147–163, 1999), Brenan and Caciagli (Geochim Cosmochim Acta 64:307–320, 2000) and Brenan (Geochim Cosmochim Acta 67:2663–2681, 2003), but are systematically offset toward lower predicted Ni in the sulfide. Nevertheless our results are consistent with the
assertion that low K
D
os
values in magmatic ore deposits such as the J-M Reef reflect high iron contents in the sulfides combined with relatively
high oxygen fugacities.
相似文献
Victor KressEmail: |