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1.
Experimental data on amphibole crystallization in water-saturated high-Mg andesite from Shiveluch volcano, Kamchatka, at 2, 3, and 5 kbar were used to calibrate a new geobarometer. The main parameters chosen to indicate the crystallization pressure of equilibrium amphibole is the ratio of tetrahedrally coordinated Al to the sum (Ti4+ + Fe3+), which is calculated by the 13eCNK technique with regard for crystal chemical considerations. The newly derived geobarometer is designed to evaluate pressure in the range of 2–12 kbar using amphibole from high-Mg andesite and basalt. The accuracy and reliability of the pressure estimates by the new geobarometer were tested by applying this geobarometer in studying amphibolized ultramafic xenoliths from the Dish Hill dike, California; magmatic amphibole hosted in cortlandite from the Shanuch intrusion, Kamchatka; and magmatic amphibole in the Pekul’ney Bay area, Chukotka. All estimates made with the newly developed geobarometer were reasonably close to values obtained by independent techniques.  相似文献   

2.
A new phase equilibria geobarometer determines magmatic storage and crystallization conditions, including pressure, temperature, oxygen fugacity (\({f_{{{\text{o}}_2}}}\)), and the presence of a fluid phase for glass-bearing rocks containing the assemblage plagioclase?+?pyroxene(s). This newly developed geobarometer can better constrain crystallization conditions of shallow (<?500 MPa; <~?20 km), glass-bearing andesites to dacites. The geobarometer utilizes rhyolite-MELTS to determine crystallization conditions in natural pumice and scoria samples. The validity of the geobarometer is tested by comparing it to results from experiments. Uncertainties are assessed using Monte Carlo simulations. We apply the geobarometer to the plag?+?opx?+?cpx-bearing system of Mt. Ruapehu, in the southern Taupo Volcanic Zone, New Zealand. The samples from Mt. Ruapehu are tested from ~?5 to ~?400 MPa and from super-liquidus to 90% crystalline (~ 1200 to ~ 700 °C). Mt. Ruapehu serves as a methodological testing ground for the geobarometer, and results from our geobarometer agree with recent Mt. Ruapehu studies. Results show a distribution of crystallization pressures ranging from 50 to 150 MPa (~?2.0 to 5.9 km) for different eruptions, with modes of 110 MPa (~ 4.3 km) and 130 MPa (~ 5.1 km). These are consistent with field interpretations of different eruptive styles based on juvenile clast textures and previous knowledge of the magma plumbing system. Mt. Ruapehu magmas are fluid saturated, with \({f_{{{\text{o}}_2}}}\) of ΔQFM ~ + 1 (NNO).  相似文献   

3.
刘福来 《矿物学报》1997,17(1):50-55
根据反应：2石榴子石（Gt）＋3石英（Q2）=2斜方辉石（Opx）＋堇青石（Cord），采用最新热力学资料，在平衡热力学原理的基础上，建立该反应Mg、Fe端员组分压力计表达式：经世界典型孔兹岩系地区的验证以及与其它石榴子石一墓青石压力计对比，计算结果基本合理，表明这一新的压力计具有较好的应用价值。  相似文献   

4.
A garnet–biotite–Al2SiO5–quartz (GBAQ) geobarometer was empirically calibrated using more than 700 natural metapelites with a broad compositional range of garnet and biotite under P–T conditions of 450–950°C and 1–17 kbar. In the calibration, activity models of garnet and biotite identical to those in the garnet–biotite (GB) geothermometer of Holdaway [American Mineralogist 2000, 85: 881–892] were used. Therefore, the GBAQ geobarometer and the GB geothermometer can be simultaneously applied to iteratively estimate metamorphic P–T conditions. Successful applications of the GBAQ geobarometer to natural metapelites certify its validity. Most importantly, when plagioclase is absent or CaO components in garnet and/or plagioclase are deficient, this geobarometer may prove useful for estimating metamorphic pressures. The random error of the present GBAQ geobarometer is inferred to be around ±1.8 kbar. An electronic spreadsheet is available as Table S4 to apply the GBAQ geobarometer in combination with the GB geothermometer.  相似文献   

5.
Massonne (1981) reported experiments on the composition of muscovite in the assemblage phlogopite-muscovite-K-feldspar-quart. The experimental data have been used to recalculate the equilibrium conditions for the chlorite-muscovite-biotite-quartz assemblage which has been proposed as a new geobarometer by Powell and Evans (1983).The recalculated equilibrium shows much steeperdp/dT slopes than those calculated by Powell and Evans (1983). Nevertheless, with the necessary precautions it is suggested that the barometer may provide the critical user with valuable pressure estimates.  相似文献   

6.
根据超高压岩石的退变质反应20Jd 3Di H2O=12Ab 2An Tar 3Na2O和18Jd 3Di 2Aeg H2O=12Ab 2An Fe-Tar 3Na2O,利用拟合的绿闪石和铁质绿闪石的热力学数据,在平衡热力学原理的基础上,建立了两个反应的压力计表达式:p=0.001 6(t 273)-0.028lnK 0.321K = (aPlNaAlSi3O8)12·(aPlCaAl2Si2O8)2·(aTarNa2CaMg3Al2[Si6Al2O22](OH)2·(aSodNa2O)3/aNCpxNaAlSi2O6)20·(aCpxCaMgSi2O6)3·aWatH2O经中国安徽省潜山县双河和西阿尔卑斯高压超高压变质带的验证及与角闪石-斜长石温度计的对比,其计算结果基本合理,表明这一新的压力计具有较好的应用价值.  相似文献   

7.
Abstract Paragonite in textural equilibrium with garnet, omphacite and kyanite is found in two eclogites in the ultrahigh-pressure metamorphic terrane in Dabie Shan, China. Equilibrium reactions between paragonite, omphacite and kyanite indicate a pressure of about 19 kbar at c . 700° C. However, one of the paragonite eclogites also contains clear quartz pseudomorphs after coesite as inclusions in garnet, suggesting minimum pressures of 27 kbar at the same temperature. The disparate pressure estimates from the same rock suggest that the matrix minerals in the ultrahigh-pressure eclogites have recrystallized at lower pressures and do not represent the peak ultrahigh-pressure assemblages. This hypothesis is tested by calibrating a garnet + zoisite/clinozoisite + kyanite + quartz/coesite geobarometer and applying it to the appropriate eclogite facies rocks from ultrahigh- and high-pressure terranes. These four minerals coexist from 10 to 60 kbar and in this wide pressure range the grossular content of garnet reflects the equilibrium pressure on the basis of the reaction zoisite/clinozoisite = grossular + kyanite + quartz/coesite + H2O. The results of the geobarometer agree well with independent pressure estimates from eclogites from other orogenic belts. For the paragonite eclogites in Dabie Shan the geobarometer indicates pressures in the quartz stability field, confirming that the former coesite-bearing paragonite-eclogite has re-equilibrated at lower pressures. On the other hand, garnets from other coesite-bearing but paragonite-free kyanite-zoisite eclogites show a very wide variation in grossular content, corresponding to a pressure variation from coesite into the quartz field. This wide variation, partly due to a rimward decrease in grossular component in garnet, is caused by partial equilibration of the mineral assemblage during the exhumation.  相似文献   

8.
正确测定尖晶石相橄榄岩的Ｔ－Ｐ关系，对于了解岩石圈地幔的许多基本性质和过程具有重要意义。介绍了根据Ｃａ在共存的橄榄石和辉石之间的分配而建立的适用于尖晶石相橄榄岩的第一个定量地质压力计，叙述了该地质压力计的研究历史、现状和使用中的注意事项。  相似文献   

9.
根据对东昆仑地区东段哈拉郭勒—哈图一带不同高度基岩的系列锆石裂变径迹年龄分析，结合磷灰石裂变径迹年龄分析和中酸性侵入岩角闪石压力计分析揭示了东昆仑东段中生代的岩石隆升剥露冷却历史．巴隆哈图一带中酸性侵入岩角闪石压力计分析结果反映晚海西—印支期以来的总体剥露幅度约8～9km，早二叠世至晚三叠世初剥蚀作用极为缓慢，大约为20～40m／Ma．不同高程样品的锆石裂变径迹年龄分析结果揭示了东昆仑地区东段在中晚侏罗世处于缓慢的岩石隆升剥露阶段，其中中侏罗世相对较快，抬升速率77～88m／Ma，晚侏罗世相对较慢，抬升速率小于37m／Ma，且呈减慢趋势，这种减慢趋势反映了早中侏罗世之交强构造抬升期后的逐渐衰退．锆石裂变径迹—磷灰石裂变径迹年龄分析结果反映了中侏罗世以来的剥蚀速率一般不超过55m／Ma，岩石的剥蚀速率与岩石的抬升速率基本为同一量级，中侏罗世—白垩纪剥蚀作用与岩石抬升作用基本处于平衡状态。  相似文献   

10.
秦巴北部的商县-卢氏县地区广泛分布有区域变质的方解石-白云石共生矿物对,它们对于估计变质作用和断裂构造作用的温压条件,有着重要的意义。本文着重就该地区Fe~(2+)在方解石-白云石中的X_(Fe)~(Co)>X_(Fe)~(Dol)分配情况,提出新的计压方法。  相似文献   

11.
Constraining the pressure of crystallisation of large silicic magma bodies gives important insight into the depth and vertical extent of magmatic plumbing systems; however, it is notably difficult to constrain pressure at the level of detail necessary to understand shallow magmatic systems. In this study, we use the recently developed rhyolite-MELTS geobarometer to constrain the crystallisation pressures of rhyolites from the Taupo Volcanic Zone (TVZ). As sanidine is absent from the studied deposits, we calculate the pressures at which quartz and feldspar are found to be in equilibrium with melt now preserved as glass (the quartz +1 feldspar constraint of Gualda and Ghiorso, Contrib Mineral Petrol 168:1033. doi: 10.1007/s00410-014-1033-3. 2014). We use glass compositions (matrix glass and melt inclusions) from seven eruptive deposits dated between ~320 and 0.7 ka from four distinct calderas in the central TVZ, and we discuss advantages and limitations of the rhyolite-MELTS geobarometer in comparison with other geobarometers applied to the same eruptive deposits. Overall, there is good agreement with other pressure estimates from the literature (amphibole geobarometry and H2O–CO2 solubility models). One of the main advantages of this new geobarometer is that it can be applied to both matrix glass and melt inclusions—regardless of volatile saturation. The examples presented also emphasise the utility of this method to filter out spurious glass compositions. Pressure estimates obtained with the new rhyolite-MELTS geobarometer range between ~250 to ~50 MPa, with a large majority at ~100 MPa. These results confirm that the TVZ hosts some of the shallowest rhyolitic magma bodies on the planet, resulting from the extensional tectonic regime and thinning of the crust. Distinct populations with different equilibration pressures are also recognised, which is consistent with the idea that multiple batches of eruptible magma can be present in the crust at the same time and can be tapped simultaneously by large eruptive events.  相似文献   

12.
Refined geothermobarometers are presented for cordierite granulites. The refinement was achieved by using internally consistent thermodynamic datasets. Improved calibrations have been demonstrated for a number of granulite areas. Also, the usefulness of the improved geobarometer in identifying decompression paths has been discussed.  相似文献   

13.
The applicability of the GRIPS geobarometry in metapelitic assemblages   总被引：5，自引：0，他引：5  
Although the garnet-rutile-ilmenite-plagioclase-silica (quartz) (GRIPS) geobarometer has been experimentally calibrated and widely applied, its applicability to metapelitic rocks has not yet been discussed carefully. In this paper, this barometer was recalibrated by fitting the available reversed-phase equilibrium data incorporating different combinations of activity models of garnet, plagioclase and ilmenite. The resultant GRIPS barometer formalisms reproduce the experimental pressures well within ±0.2 kbar. The GRIPS and garnet-aluminium silicate-plagioclase-quartz (GASP) barometer values are concordant within ±1 kbar for pressures above ∼6 kbar for natural metapelites, but the difference of pressure determinations between these two barometers becomes larger when pressure and/or the grossular content of garnet decrease. However, the pressure difference is independent of either temperature, or almandine in garnet, or anorthite in plagioclase, or iron content in ilmenite. After testing and application of the GRIPS barometer to aluminosilicate-bearing metapelites and metapelitic assemblages within limited geographical areas as well as within contact thermal aureoles, it is concluded that this barometer may be applied to low- to high-grade, medium- to high-pressure metapelites. The application of the GRIPS barometer to metapelites is not advocated in situations where calcium is deficient in garnet (      < 0.05) or plagioclase (      < 0.17), or for pressures below ∼6 kbar.  相似文献   

14.
Phengite is a common metamorphic mineral stable in a wide pressure range. The dependence of pressure on silicon content established in the mid-20th century allowed us to propose a phengite-based geobarometer. Recently, the phengite geobarometer was calibrated by Caddik and Thompson (2008) but in the narrow pressure range. However, there attempts have been made to extend this range. We have analyzed the large number of published datasets on phengite composition. These data included both natural and experimental specimens of well defined P–T-conditions. For moderate temperatures (T < 750°C), two groups of phengite are identified. These groups are divided by silicon content value of 3.25 apfu. Different geobarometer equations were suggested for both groups. The precision of these geobarometers is ±0.34 GPa and ±0.56 GPa, respectively. There is no evidence of phengite used as a geobarometer at high temperatures (T > 750°C). The derived dependences were applied to study the conditions of gneiss and schist metamorphism of the Blyb metamorphic complex in the Northern Caucasus. This study shows that the peak pressure of gneiss and schist metamorphism is 2.0–2.2 ± 0.56 GPa. The latter agrees with previous data on the Blyb metamorphic complex.  相似文献   

15.
The pressure-temperature curve for the equilibrium anorthite+2enstatite=pyrope+diopside+quartz has been determined in the system CaO-MgO-Al2O2-SiO2 to be between 13.4 and 14.0 kbars at 900° C. The slope up to 1,240° C is 8.5 bar/K. The entropy change at 1,200 K is 20 kJ. These data, combined with data from the literature, lead to a geobarometer equation which, when applied to rocks from the Agto area (West Greenland), gives pressure estimates of 6–10 kbars at 800° C. The results are consistent for rocks of differing Fe/Mg ratios and are consistent with independent pressure estimates.  相似文献   

16.
Six equilibria among quartz, plagioclase, biotite, muscovite, and garnet were empirically calibrated using mineral composition data from 43 samples having the assemblage quartz+muscovite+biotite+garnet+plagioclase+Al2SiO5 (sillimanite or kyanite). Pressures and temperatures in the data set used for calibration were determined through the simultaneous application of garnet-biotite geothermometry and garnet-quartz-plagioclase-Al2SiO5 geobarometry. Thermodynamic expressions for four of the six equilibria incorporate interaction parameters that model non-ideality in the mixing of cations in the octahedral sites of both muscovite and biotite. With pressure chosen as the dependent variable, multiple regression was used to solve for unknowns in the equilibrium thermodynamic expressions. The regressions yielded multiple correlation coefficients ranging from 0.983 to 0.999, with corresponding standard deviations of 338 and 92 bars in the residuals. The standard deviations in the residuals may be explained largely or entirely by the propagation of errors associated with electron microprobe analysis. These equilibria enable the determination of pressures from equilibrium assemblages of quartz+garnet+plagioclase+muscovite+biotite, and give results closely comparable to the experimentally calibrated garnet-quartz-plagioclase-Al2SiO5 geobarometer. Geobarometric applications should be restricted to rocks in which equilibrium constants and compositional variables fall within the same ranges as those used for calibration.  相似文献   

17.
冀东早太古代迁西群是由火山-沉积岩系变质生成的一套变质杂岩。它的主体是麻粒岩类以及退变质生成的斜长角闪岩类的岩石。该套变质岩系的下部夹有层状和透镜状变质超镁铁质岩(变橄辉岩、变辉橄岩、变辉石岩及变闪辉岩),而上部为变质的含铁岩系。以石渣子山和娄子山为例,它们的含铁岩层分别为辉石磁铁石英岩和英榴易熔岩。 本区的麻粒岩和斜长角闪岩在岩相学上呈渐变关系。绝对不含角闪石和/或富钛黑云母的麻粒岩是很少的。本文将以角闪石和斜长石为主要组成矿物的岩石归为斜长角闪岩类。在斜长角闪岩类岩石中,角闪石含量大大超过辉石,另外常见被角闪石交代的辉石残晶。  相似文献   

18.
The equilibrium between spinel lherzolite and garnet lherzolite has been experimentally determined in the CaO-MgO-Al2O3-SiO2 system between 800° and 1,100° C. In confirmation of earlier work and predictions from thermodynamic data, it was found that theP-T slope of the reaction was close to zero, the equilibrium ranging from 16.1 kb at 800° C to 18.7 kb at 1,100° C (±0.3 kb). The addition of Cr2O3 to the system raised the stability field of spinel to higher pressures. It was found that the pressure at which both garnet and spinel could exist with olivine+orthopyroxene+clinopyroxene in the system CMAS ?Cr2O3 could best be described by the empirical relationship: $$P = P^{\text{O}} + \alpha X_{{\text{Cr}}}^{s{\text{p}}} $$ whereP 0 is the equilibrium pressure for the univariant reaction in the Cr2O3-free system,α is a constant apparently independent of temperature with a value of 27.9 kilobars, andX Cr sp is the mole fraction of chromium in spinel. Use was made of the extensive literature on Mg-Fe2+ solid solutions to quantitatively derive the effect of Fe2+ on the equilibrium. The effect of other components (Fe3+, Na) was also considered. The equilibrium can be used as a sensitive geobarometer for rocks containing the five phases ol+opx+cpx+gt+sp, and thus provides the only independent check presently available for the more widely applicable geobarometer which uses the alumina content of orthopyroxene in equilibrium with garnet.  相似文献   

19.
The historic development of the first geobarometer for spinel lherzolite based on the distribution of calcium between existing olivine and clinopyroxene is reported here.
Kohler and Brey(1990) suggested the geobarometer as follows:
P(108Pa)=(−TlnDCa−11982+361T)/56.2 for T≥ (1275.25+2.827P) (K),
P(108Pa)=( −TlnDCa−5792−1.25T)/42.5 for T≤(1275.25+2.827P) (K).
Based on their calibrated experiments for calcium exchange between olivine and clinopyroxene from wide temperature-pressure range.  相似文献   

20.
区域的隆升与剥蚀是影响成矿岩体形成后变化与保存的主要因素,矿物压力计能定量获取花岗质岩浆初始结晶时的压力条件,是研究花岗岩体形成深度及隆升剥蚀历史的有效手段之一。应用黑云母的TAl地质压力计,计算了云南格咱岛弧岩浆岩带印支期典型成矿斑岩体侵位的深度,并估算了格咱岛弧地区地壳的隆升与剥蚀速率,探讨了矿床形成后变化及保存的情况,结果表明印支期以来格咱岛弧地区的成矿岩体剥蚀速率较小,平均为0.018 mm/a,这对矿床形成后的保存较为有利。研究结果为探讨滇西高原印支期以来的构造隆升—剥蚀提供了定量参考。  相似文献   

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