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1.
Tibor Gasparik 《Contributions to Mineralogy and Petrology》1996,124(2):139-153
Melting relations on the enstatite−diopside (En, Mg2Si2O6−Di, CaMgSi2O6) join, including the compositions of crystalline phases and melts coexisting along the solidi, were experimentally determined
in the pressure range 70–224 kbar with a split-sphere anvil apparatus (USSA-2000). Melting is peritectic in enstatite-rich
compositions at 70–124 kbar (1840–2100° C) and eutectic at higher pressures, while the diopside-rich clinopyroxene melts azeotropically
at 70–165 kbar and up to 300° C lower temperatures than the eutectic. Orthopyroxene is replaced with enstatite-rich clinopyroxene
at 120 kbar and 2090°C. First garnet with 17 mol% Di forms on the solidus at 158 kbar and 2100° C. Two garnets coexist on
the solidus at 165–183 kbar and 2100° C, garnet coexists with CaSiO3 perovskite at 183–224 kbar (2100–2230° C) and two coexisting perovskites are stable at higher pressures. The melting curve
of diopside was determined at 80–170 kbar; the slope becomes negative at 140 kbar and 2155° C. At 170 kbar and 2100° C, diopside
with 96% Di breaks down to garnet with 89% Di and CaSiO3 perovskite. The new data were used to calculate an improved temperature-pressure phase diagram for the CMAS system, which
can be useful for estimating the mineralogy of the Earth's upper mantle.
Received: 15 October 1994 / Accepted: 15 October 1995 相似文献
2.
Garnet + liquid equilibrium 总被引:1,自引:0,他引:1
Keith Putirka 《Contributions to Mineralogy and Petrology》1998,131(2-3):273-288
New experiments were performed to determine saturation conditions for garnet and silicate liquid. Starting compositions were
natural basalt powders ranging from komatiite to nephelinite, which were partially melted at pressures between 25 and 100
kbar. Rounded grains of natural pyrope or grossular were added to some experiments to induce garnet saturation, and to aid
the segregation of liquid pools for microprobe analysis. Simple expressions describing K
eq as a function of P, T and liquid composition were calibrated by linear least squares analysis of the data from this, and other, studies. Since
garnets do not often occur as phenocrysts, equations were designed to predict garnet compositions when P, T and a silicate liquid composition are given. The regression data have a pressure range of 20–270 kbar, and compositions as
diverse as nephelinite and komatiite. These models should thus apply to a broad range of geological problems. The majorite
component in garnet was found to increase with increasing P, but compositional effects are also important. A garnet saturation surface applied to liquids with chondritic compositions
shows that such liquids crystallize garnet with Mj contents of 0.27–0.42 at 200 kbar. Models of Earth differentiation thus
need to account not only for fractionation of majorite, but also for Fe-, Ca-, Na- and Ti-bearing garnet components, which
occur in non-trivial quantities at high pressure. Since many models of igneous petrogenesis rely on mineral-melt partition
coefficients for the minor elements Na, Ti, and Cr, partition coefficients for these elements were also examined. The K
d
gar/liq for Na was found to be P-sensitive; Na contents of basalts may thus potentially yield information regarding depths of partial melting.
Received : 28 May 1997 / 25 November 1997 相似文献
3.
Xiao-Long Huang Yi-Gang Xu Ching-Hua Lo Ru-Cheng Wang Chuan-Yong Lin 《Contributions to Mineralogy and Petrology》2007,154(6):691-705
Petrographic investigations and electron microprobe analyses have been performed on a rare aggregate of clinopyroxene megacrysts
collected from Cenozoic basalts in Yinfengling, Leizhou Peninsula of South China. The aggregate, composed of several clinopyroxene
megacrysts, shows abundant exsolution lamellae of garnet (Grt) and orthopyroxene (Opx), and granular texture. Cr- and Ti-poor
spinels are also present in this sample. They occur predominantly as Sp–Opx–Grt clusters (Cr# = 0.025–0.034) at the interspace
between different megacrysts, and subordinately as bleb-shaped (Cr# = 0.025–0.034) or thin-lamella crystals (Cr# = 0.006–0.021)
in clinopyroxene. Three different assemblages of exsolution are identified, namely (1) Sp (high Cr/Al) and Opx; (2) Grt–Opx;
(3) Sp (low Cr/Al) and Opx. In addition, some garnets were likely developed as response to breakdown of the high-Cr/Al Sp.
The homogeneous compositions in all constituent minerals and the good agreement between calculated Cpx/Grt partition coefficients
(K
d’s) for trace elements and reference data strongly suggest a chemical equilibrium among coexisting minerals, probably attained
by diffusion after the exsolution. Thermobarometric calculation based on exsolved assemblage yields a temperature of 900 ± 30°C
and a pressure of 12 ± 2.2 kbar, corresponding to the present-day thermal gradient in the region. Much higher P–T estimates
(T = 1,210 ± 30°C, P = 16.2 ± 3.5 kbar) are obtained for the reconstructed composition of cpx prior to exsolution. The contrast in thermal state
before and after the exsolution might reflect the thermal evolution of the lithosphere beneath South China during the Cenozoic.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
4.
The Lherz orogenic lherzolite massif (Eastern French Pyrenees) displays one of the best exposures of subcontinental lithospheric
mantle containing veins of amphibole pyroxenites and hornblendites. A reappraisal of the petrogenesis of these rocks has been
attempted from a comprehensive study of their mutual structural relationships, their petrography and their mineral compositions.
Amphibole pyroxenites comprise clinopyroxene, orthopyroxene and spinel as early cumulus phases, with garnet and late-magmatic
K2O-poor pargasite replacing clinopyroxene, and subsolidus exsolution products (olivine, spinel II, garnet II, plagioclase).
The original magmatic mineralogy and rock compositions were partly obscured by late-intrusive hornblendites and over a few
centimetres by vein–wallrock exchange reactions which continued down to subsolidus temperatures for Mg–Fe. Thermobarometric
data and liquidus parageneses indicate that amphibole pyroxenites started to crystallize at P ≥ 13 kbar and recrystallized at P < 12 kbar. The high AlVI/AlIV ratio (>1) of clinopyroxenes, the early precipitation of orthopyroxene and the late-magmatic amphibole are arguments for
parental melts richer in silica but poorer in water than alkali basalts. Their modelled major element compositions are similar
to transitional alkali basalt with about 1–3 wt% H2O. In contrast to amphibole pyroxenites, hornblendites only show kaersutite as liquidus phase, and phlogopite as intercumulus
phase. They are interpreted as crystalline segregates from primary basanitic magmas (mg=0.6; 4–6 wt% H2O). These latter cannot be related to the parental liquids of amphibole pyroxenites by a fractional crystallization process.
Rather, basanitic liquids mostly reused pre-existing pyroxenite vein conduits at a higher structural level (P ≤ 10 kbar). A continuous process of redox melting and/or alkali melt/peridotite interaction in a veined lithospheric mantle
is proposed to account for the origin of the Lherz hydrous veins. The transitional basalt composition is interpreted in terms
of extensive dissolution of olivine and orthopyroxene from wallrock peridotite by alkaline melts produced at the mechanical
boundary layer/thermal boundary layer transition (about 45–50 km deep). Continuous fluid ingress allowed remelting of the
deeper veined mantle to produce the basanitic, strongly volatiles enriched, melts that precipitated hornblendites. A similar
model could be valid for the few orthopyroxene-rich hydrous pyroxenites described in basalt-hosted mantle xenoliths.
Received: 15 September 1999 / Accepted: 31 January 2000 相似文献
5.
F. Zeb Page Lora S. Armstrong Eric J. Essene Samuel B. Mukasa 《Contributions to Mineralogy and Petrology》2007,153(5):533-555
Quantitative thermobarometry of inclusions in zoned garnet from a Franciscan eclogite block record a counter-clockwise P–T path from blueschist to eclogite and back. Garnet retains prograde zoning from inclusion-rich Alm52Grs30Pyp6Sps12 cores to inclusion-poor Alm62Grs25Pyp12Sps1 mantles, with overgrowths of highly variable composition. Barometry using the Waters–Martin version of the garnet–phengite–omphacite
thermobarometer yields conditions of 7–15 kbar, 400–500°C (garnet cores), 18–22 kbar, ∼550°C (mantles), and 10–14 kbar, 350–450°C
(overgrowths), in agreement with clinozoisite–sphene–rutile–garnet–quartz barometry. These pressures are ∼10–15 kbar less
than those obtained using more recent, fully thermodynamic calibrations of the phengite–omphacite–garnet thermobarometer.
Low early temperatures suggest that the block was subducted in a thermally mature subduction zone and not at the inception
of subduction when prograde temperature is expected to be higher. Franciscan high-grade blocks likely represent crust subducted
throughout the history of this convergent margin, rather than only at the inception of the subduction zone. 相似文献
6.
Ling-Ling Xiao Chun-Ming Wu Guo-Chun Zhao Jing-Hui Guo Liu-Dong Ren 《International Journal of Earth Sciences》2011,100(4):717-739
Garnet-bearing metapelites and amphibolites are exposed in the south and middle parts of the Zanhuang complex, which is located
in the central segment of the nearly NS-striking Trans-North China Orogen. These rocks preserve three metamorphic mineral
assemblages forming at the prograde, peak and post-peak decompression stages. The prograde metamorphic stage (M1) is represented by mineral inclusions within garnet porphyroblasts, the peak metamorphic stage (M2) is represented by garnet rims and matrix minerals, whereas the retrograde stage (M3) is represented by amphibole + plagioclase symplectite rimming garnet porphyroblasts in the amphibolites and biotite + plagioclase
symplectite rimming garnet porphyroblasts in the metapelites. All garnet porphyroblasts in the metapelites preserve prograde
chemical zoning except for the ubiquitous, quite narrow zones from the underwent post-peak decompression. It has been determined
through thermobarometric computation that the metamorphic conditions are 650–710°C at 8.2−9.2 kbar for the M1 (inclusion) assemblages, >810°C at >12.5 kbar for the metamorphic peak M2 (matrix) assemblages, and 660–680°C at 4.4–4.5 kbar for the retrograde M3 (symplectite) assemblages. These rocks are thus determined to have undergone metamorphism with clockwise P–T paths involving nearly isothermal decompression (ITD) segments, which is inferred to be related to the amalgamation of the
Eastern and Western Blocks to form the coherent basement of the North China Craton along the Trans-North China Orogen in the
late Paleoproterozoic (1.88–1.85 Ga). 相似文献
7.
Dehydration melting of tonalitic compositions (phlogopite or biotite-plagioclase-quartz assemblages) is investigated within
a temperature range of 700–1000°C and pressure range of 2–15 kbar. The solid reaction products in the case of the phlogopite-plagioclase(An45)-quartz starting material are enstatite, clinopyroxene and potassium feldspar, with amphiboles occurring occasionally. At
12 kbar, zoisite is observed below 800°C, and garnet at 900°C. The reaction products of dehydration melting of the biotite
(Ann50)-plagioclase (An45)-quartz assemblage are melt, orthopyroxene, clinopyroxene, amphibole and potassium feldspar. At pressures > 8 kbar and temperatures
below 800°C, epidote is also formed. Almandine-rich garnet appears above 10 kbar at temperatures ≥ 750°C. The composition
of melts is granitic to granodioritic, hence showing the importance of dehydration melting of tonalites for the formation
of granitic melts and granulitic restites at pressure-temperature conditions within the continental crust. The melt compositions
plot close to the cotectic line dividing the liquidus surfaces between quartz and potassium feldspar in the haplogranite system
at 5 kbar and a
H
2O = 1. The composition of the melts changes with the composition of the starting material, temperature and pressure. With increasing
temperature, the melt becomes enriched in Al2O3 and FeO+MgO. Potash in the melt is highest just when biotite disappears. The amount of CaO decreases up to 900°C at 5 kbar
whereas at higher temperatures it increases as amphibole, clinopyroxene and more An-component dissolve in the melt. The Na2O content of the melt increases slightly with increase in temperature. The composition of the melt at temperatures > 900°C
approaches that of the starting assemblage. The melt fraction varies with composition and proportion of hydrous phases in
the starting composition as well as temperature and pressure. With increasing modal biotite from 20 to 30 wt%, the melt proportion
increases from 19.8 to 22.3 vol.% (850°C and 5 kbar). With increasing temperature from 800 to 950°C (at 5 kbar), the increase
in melt fraction is from 11 to 25.8 vol.%. The effect of pressure on the melt fraction is observed to be relatively small
and the melt proportion in the same assemblage decreases at 850°C from 19.8 vol.% at 5 kbar to 15.3 vol.% at 15 kbar. Selected
experiments were reversed at 2 and 5 kbar to demonstrate that near equilibrium compositions were obtained in runs of longer
duration.
Received: 27 December 1995 / Accepted: 7 May 1996 相似文献
8.
James G. Brophy Carla S. Whittington Young-Rok Park 《Contributions to Mineralogy and Petrology》1999,135(2-3):277-290
Several high alumina basalts from the Aleutian volcanic centers of Cold Bay and Kanaga Island contain large (up to 1.5 cm
diameter) megacrysts of sector-zoned augite. The megacrysts are invariably euhedral with well developed {001}, {010} and {111}
forms. All crystals display concentric bands that are rich in mineral and glass inclusions. The sector zonation typically
occurs as well developed (010), (100), (111) and (110) sectors which grew at different rates. A comparison of the width of
synchronous growth bands indicates that following relative growth rates: (111) ≫ (100) ∼ (110) > (010). Compositionally, SiO2 and MgO abundances decrease, and TiO2, Al2O3, FeO and Na2O abundances increase in the different sectors in the order (111), (100) ∼ (110), (010). This order is identical to that deduced
for the relative growth rates, implying that growth rate clearly had a role in the development of the sector zonation. Calculated
pre-eruption H2O contents of the basalts range from 1 to 3 wt% but actual (measured) post-eruption H2O contents range from 0.01 to 0.3 wt%. Deteurium isotopic values are heavily depleted and range from −110 to −141‰ . Together
these indicate significant vapor (H2O) exsolution prior to eruption. Maximum H2O abundances in primitive glass inclusions, thought to be most representative of the host liquid reservoir at the time of
melt entrapment, systematically decrease from the core to the rim of one augite megacryst studied in detail. We conclude that
the presence of sector-zoned augite is due to augite supersaturation and rapid crystallization brought about by magma decompression
and volatile (H2O) exsolution. The calculated pre-eruption H2O contents of 1–3 wt% limit vapor exsolution and basalt crystallization to depths of less than 3 and more likely 1.5 km. Very
rapid crystallization at very shallow depths makes it unlikely that the time scales between initial crystallization and final
eruption are sufficient to permit appreciable amounts of fractional crystallization. Given that high alumina basalt fractionation
is the dominant process for generating more evolved andesite, dacite and rhyolite magmas of the calc-alkaline suite, the inability
of parental high alumina basalt to yield such derivative magmas in the low pressure environment places the likely site of
fractionation in the high pressure environment, at or near the base of the crust.
Received: 1 December 1997 / Accepted: 23 December 1998 相似文献
9.
Garnet-bearing tonalitic porphyry from East Kunlun,Northeast Tibetan Plateau: implications for adakite and magmas from the MASH Zone 总被引:7,自引:0,他引:7
Chao Yuan Min Sun Wenjiao Xiao Simon Wilde Xianhua Li Xiaohan Liu Xiaoping Long Xiaoping Xia Kai Ye Jiliang Li 《International Journal of Earth Sciences》2009,98(6):1489-1510
A garnet-bearing tonalitic porphyry from the Achiq Kol area, northeast Tibetan Plateau has been dated by SHRIMP U-Pb zircon
techniques and gives a Late Triassic age of 213 ± 3 Ma. The porphyry contains phenocrysts of Ca-rich, Mn-poor garnet (CaO > 5 wt%;
MnO < 3 wt%), Al-rich hornblende (Al2O3 ~ 15.9 wt%), plagioclase and quartz, and pressure estimates for hornblende enclosing the garnet phenocrysts yield values
of 8–10 kbar, indicating a minimum pressure for the garnet. The rock has SiO2 of 60–63 wt%, low MgO (<2.0 wt%), K2O (<1.3 wt%), but high Al2O3 (>17 wt%) contents, and is metaluminous to slightly peraluminous (ACNK = 0.89–1.05). The rock samples are enriched in LILE
and LREE but depleted in Nb and Ti, showing typical features of subduction-related magmas. The relatively high Sr/Y (~38)
ratios and low HREE (Yb < 0.8 ppm) contents suggest that garnet is a residual phase, while suppressed crystallization of plagioclase
and lack of negative Eu anomalies indicate a high water fugacity in the magma. Nd–Sr isotope compositions of the rock (εNdT = −1.38 to −2.33; 87Sr/86Sri = 0.7065–0.7067) suggest that both mantle- and crust-derived materials were involved in the petrogenesis, which is consistent
with the reverse compositional zoning of plagioclase, interpreted to indicate magma mixing. Both garnet phenocrysts and their
ilmenite inclusions contain low MgO contents which, in combination with the oxygen isotope composition of garnet separates
(+6.23‰), suggests that these minerals formed in a lower crust-derived felsic melt probably in the MASH zone. Although the
rock samples are similar to adakitic rocks in many aspects, their moderate Sr contents (<260 ppm) and La/Yb ratios (mostly
16–21) are significantly lower than those of adakitic rocks. Because of high partition coefficients for Sr and LREE, fractionation
of apatite at an early stage in the evolution of the magma may have effectively decreased both Sr and LREE in the residual
melt. It is suggested that extensive crystallization of apatite as an early phase may prevent some arc magmas from evolving
into adakitic rocks even under high water fugacity. 相似文献
10.
Ca-(Fe,Mg) interdiffusion experiments between natural single crystals of grossular (Ca2.74Mg0.15 Fe0.23Al1.76Cr0.04Si3.05O12) and almandine (Ca0.21Mg0.40 Fe2.23Mn0.13Al2.00Cr0.08Si2.99O12 or Ca0.43Mg0.36Fe2.11 Al1.95Si3.04O12), were undertaken at 900–1100 °C and 30 kbar, and pressures of 15.0–32.5 kbar at 1000 °C. Samples were buffered by Fe/FeO
in most cases. Diffusion profiles were determined by electron microprobe. Across the experimental couples the interdiffusion
coefficients (D˜) were almost independent of composition. The diffusion rates in an unbuffered sample were significantly faster than in buffered
samples. The temperature dependence of the D˜ (Ca-Fe,Mg) interdiffusion coefficients may be described by
at 30 kbar and 900–1100 °C. This activation energy is marginally higher than previous experimental studies involving Ca-free
garnets; the interdiffusion coefficients are higher than previous studies for Fe-Mg and Fe-Mn exchange in garnet. The pressure
dependence of D˜ (Ca-Fe,Mg) at 1000 °C yielded an activation volume of 11.2 cm3 mol−1, which is higher than previous results from studies involving garnet and olivine. Comparison with simulation studies suggests
a vacancy mechanism for divalent ion migration in garnet, with extrinsic processes being dominant up to very high temperatures.
Received: 15 December 1996 / Accepted: 3 November 1998 相似文献