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1.
The high- P , medium- T  Pouébo terrane of the Pam Peninsula, northern New Caledonia includes barroisite- and glaucophane-bearing eclogite and variably rehydrated equivalents. The metamorphic evolution of the Pouébo terrane is inferred from calculated P–T  and P–T  – X H2O pseudosections for bulk compositions appropriate to these rocks in the model system CaO–Na2O–FeO–MgO–Al2O3–SiO2–H2O. The eclogites experienced a clockwise P–T  path that reached P ≈19  kbar and T  ≈600  °C. The eclogitic mineral assemblages are preserved because reaction consequent upon decompression consumed the rocks' fluid. Extensive reaction occurred only in rocks with fluid influx during decompression of the Pouébo terrane.  相似文献   

2.
变质相平衡的研究进展   总被引：18，自引：3，他引：18  
魏春景  周喜文 《地学前缘》2003,10(4):341-351
变质相平衡是变质岩石学中最核心的问题之一,20世纪90年代以来,国外在这一领域取得了重要进展,即利用内洽性热力学数据库、THERMOCALC程序以及合理的矿物相活度模型定量计算模式体系中的岩石成因格子(P-T投影图)和有关的各种剖面图,如共生图解和针对特定岩石组分的p-T、p-x和T-x视剖面图等。尤其是在p-T视剖面图解上,可以定量计算矿物成分、矿物摩尔含量及岩石饱和水含量等值线,从而可以定量地阐述天然岩石在p-T-x空间内的相平衡关系、确定岩石形成的p-T条件和p-T-t轨迹。  相似文献   

3.
High-pressure metamorphic rocks exposed in the Bantimala area, c . 40  km north-east of Ujung Pandang, were formed as a Cretaceous subduction complex with fault-bounded slices of melange, chert, basalt, turbidite, shallow-marine sedimentary rocks and ultrabasic rocks. Eclogites, garnet–glaucophane rocks and schists of the Bantimala complex have estimated peak temperatures of T  =580–630 °C at 18  kbar and T  =590–640 °C at 24  kbar, using the garnet–clinopyroxene geothermometer. The garnet–omphacite–phengite equilibrium is used to estimate pressures. The distribution coefficient K D1=[( X pyr)3( X grs)6/( X di)6]/[(Al/Mg)M2,wm (Al/Si)T2,wm]3 among omphacite, garnet and phengite is a good index for metamorphic pressures. The K D1values of the Bantimala eclogites were compared with those of eclogites with reliable P–T  estimates. This comparison suggests that peak pressures of the Bantimala eclogites were P =18–24  kbar at T  =580–640 °C. These results are consistent with the P–T  range calculated using garnet–rutile–epidote–quartz and lawsonite–omphacite–glaucophane–epidote equilibria.  相似文献   

4.
The upper pressure limit of pyrophyllite is given by the equilibria (i) pyrophyllite=diaspore+quartz and (ii) pyrophyllite=diaspore+coesite. High- P experimental investigations carried out to locate equilibrium (i) yield brackets between 497 °C/24.8  kbar and 535 °C/25.1  kbar, and between 500 °C/23  kbar and 540 °C/23  kbar. Equilibrium (ii) was bracketed at 550 °C between 26.0 and 28.3  kbar. In the experimental P–T  range, equilibria (i) and (ii) are metastable with respect to kyanite. A stable P–T  grid is calculated using thermodynamic data derived under consideration of the present experimental results. According to these data, the lower pressure limit of the assemblage diaspore+quartz according to equilibrium (i) range from about 12  kbar/300 °C to 20  kbar/430 °C (in the presence of pure water). The upper stability of diaspore+quartz is limited by the reaction diaspore+quartz=kyanite+H2O at about 450 °C (nearly independent of pressure) and, to higher pressure, by the quartz=coesite transition. Equilibrium (ii) is metastable over the whole P–T  range.
Natural occurrences600.S of the diaspore–quartz assemblage in metamorphic rocks in Sulawesi, New Caledonia, Amorgos and the Vanoise are characterized by minerals indicative of high- P such as ferro-magnesiocarpholite, glaucophane, sodic pyroxene and lawsonite. The metamorphic P–T  conditions of these rocks are estimated to be in the range 300–400 °C, >8  kbar. These data are compatible with the derived P–T  stability field of the diaspore+quartz assemblage. We conclude that, in metamorphic rocks, diaspore+quartz is, as ferrocarpholite, an indicator for unusual low- T  /very high- P settings.  相似文献   

5.
The Tormes Gneissic Dome (TGD, NW sector of the Iberian Massif, Spain) is a high-grade metamorphic complex affected by a major episode of extensional deformation (D2). The syn-D2 P–T  path of the Lower Unit of the TGD was deduced from the analysis of reaction textures related to superimposed fabrics developed during exhumation, analysis of mineral zoning and thermobarometric calculations. It comprises an initial phase of decompression, determined using the tweequ thermobarometric technique, from 6.4–8.1 kbar at 735–750 °C (upper structural levels) and 7.2 kbar at 770 °C (lower structural levels) to 3.3–3.9 kbar and 645–680 °C. This evolution is consistent with the observed sequence of melting reactions and the generation of garnet- and cordierite-bearing anatectic granitoids. The later part of the syn-D2 P–T  path consisted of almost isobaric cooling associated with the thermal re-equilibration of the unit in the new structural position. This segment of the P–T  path is recorded by assemblages with And +Bt+Ms and Ms+ Chl +Ab related to the later mylonitic S2 fabrics, which indicate retrogression to low-amphibolite and greenschist facies conditions.  相似文献   

6.
Metamorphic field gradients in the Central Alps   总被引：8，自引：0，他引：8  
Metamorphic field gradients were determined across the entire amphibolite grade Central Alps ( c . 50×100 km). P – T  were calculated from 116 samples acquired from our own field work, from samples provided to us by others, and from rocks with mineral compositions described in the literature. Only fluid-conserved equilibria were used to determine P – T  . The use of an internally consistent thermodynamic database and mineral solid solution models makes the results robust and reduces relative errors. The results are presented in contour maps. Temperature increases from 500 to 550 °C along the limit of amphibolite grade metamorphism in the north and west, to c . 675 °C toward the south at the Insubric line near the town of Bellinzona. Maximum recorded pressures of c . 7 kbar are in a central region c . 20 km north of the Insubric line, and decrease both to the north (5.5 kbar) and south (4.5 kbar). The P–T  results indicate that there is a relatively large area that reached conditions in the sillimanite stability field but developed neither sillimanite nor fibrolite; this is interpreted as a result of kinetic constraints on nucleation and growth because of the small amounts of thermal overstep (<40 °C) of the kyanite-sillimanite phase boundary. Comparison of P–T  conditions with carbonate isograds in the region indicate that fluids present during metamorphism were not dominated by a homogeneous external source. Examination of the two-dimensional distribution of pressure and temperature in the context of thermal and tectonic models indicates that two thermal pulses affected the Central Alps during the Tertiary. In the second, heat affected only the southern parts of the area and overprinted the previously established P–T  gradients.  相似文献   

7.
Garnet–orthopyroxene geothermometry and geobarometry are widely used in high-grade metamorphic terranes. These techniques may provide an insight into pressure–temperature ( P–T   ) paths followed by such terranes, provided various sources of uncertainty are taken into consideration. Analytical uncertainties, particularly with regard to their effect on ferric iron estimation in orthopyroxene, can contribute to the overall uncertainty on the calculated P–T  . Additionally, retrograde cation diffusion can affect the Fe–Mg distribution between coexisting garnet and orthopyroxene, consequently affecting P–T  estimates. Recognizing the importance of these effects, and care with both the choice of the grains analysed and analytical techniques, may lead to more reliable P–T  estimation.  相似文献   

8.
Chemical disequilibrium exists between all phases of the Alpe Arami garnet-peridotite body (Ticino, Switzerland) which hampers the evaluation of P–T  conditions of origin, yet disequilibrium offers the inherent possibility to derive a P–T–t path for this mantle slice. We tried to tackle this problem by carrying out new mineral analyses and taking diffusion rates and bulk-rock compositional effects into consideration. Peak metamorphic conditions from mineral core compositions were estimated as 1120±50 °C/5±0.2 GPa. These values are significantly higher than previously published results and were determined from a combination of the O'Neill & Wood (1979) Fe/Mg garnet–olivine exchange thermometer and the Al-in-orthopyroxene barometer (Brey & Köhler, 1990), and are supported by the Ca/Cr ratios in garnet, which are in accord with these conditions. Details of the exhumation path were derived from (1) rim compositions of minerals that yield a first retrograde stage of 720±50 °C/2±0.25 GPa (2) a spinel lherzolite assemblage in narrow shear zones (tectonic phase F0', after Möckel, 1969) which documents a second retrograde stage at 500–600 °C/0.8–1.5 GPa. The Ca content in olivine (Köhler & Brey, 1989) can be used to evaluate further P–T  conditions along the retrograde path. We measured very low values (30–40  ppm Ca) in the cores of olivine and a remarkable increase towards the rim (120  ppm). The low core values may reflect an equilibrium stage during the main Alpine metamorphism. The increasing values towards the olivine rims probably represent a late-stage heating event. The initial cooling rates for the peridotite body are between 2700 and 5100 °C Ma−1, depending on which diffusion data are used.  相似文献   

9.
When graphite is present, carbon‐bearing species dissolve in the C‐O‐H fluid and lower the activity of water (). Accordingly, metamorphic reactions that involve water, namely dehydration and partial melting reactions, adjust their P–T positions to accommodate the change of . In this modelling study, pseudosections are calculated for graphite‐bearing systems that are either closed or that progressively lose fluid and/or melt. The diagrams incorporate a new model of CO2 solubility in felsic melts that we derived to be compatible with a recently published melt model. As the result of the lowered in the carbon‐bearing systems, the temperature displacements of the solidus can be as large as 50 °C at low pressures in cordierite‐bearing zones (<4 kbar), but are smaller than 15 °C at mid‐pressure P–T conditions (4–9 kbar). In the supersolidus region, the phase relations among silicate minerals + melt are very close to those in carbon‐free systems. The fluid CO2 content increases as temperature increases in the supersolidus assemblages. The CO2‐rich fluid can be stable in granulite facies conditions in an oxidized system. In graphitic systems, melt and/or cordierite dominate the CO2 budget of high‐grade rocks. During cooling, the fluid that exsolves from such crystalizing melt is CO2‐rich. In addition to the phase relations, the pseudosections presented in this study enable researchers to quantitatively investigate the evolution of phase modes, including graphite, along specific metamorphic P–T paths. At low pressures in the cordierite stability field, graphite is predicted to precipitate as the pressure increases or temperature decreases in the subsolidus assemblages, or temperature increases in the region of melt + fluid coexistence. On the other hand, the graphite abundance remains nearly constant along the mid‐pressure P–T series, but the graphite mode in the supersolidus region may increase due to residual enrichment if the melt is extracted. The modelling results show that metamorphic processes in closed systems lead to only small changes in graphite mode (a few tenths of a per cent). This strongly suggests that open‐system behaviours are required for large amounts of graphite deposition, including fluid infiltration and mixing or residual enrichment processes in high‐grade rocks. In addition to P–T pseudosections, P/T–XO diagrams (XO = O/(H + O) in the fluid) illustrate the thermodynamic features of internal buffering from another perspective, and explore the dependence of phase relations on the externally imposed redox state. If the system is equilibrated with CO2 or CH4‐rich infiltrating fluid, the temperature displacements of metamorphic reactions can be larger than 50 °C, compared with carbon‐free systems.  相似文献   

10.
The Okiep Copper District, part of the 1.2–1.0 Ga high-grade terrane in western Namaqualand, is composed of a mid-Proterozoic supracrustal sequence and several pre- to post-orogenic intrusive suites affected by two high-grade events (M2a/M2b, M3) of Kibaran and one low-grade event (M4) of Pan-African age. Peak assemblages in quartz-bearing pelites are characterized either by garnet+cordierite coexisting with sillimanite/biotite, or by biotite+sillimanite±garnet; a difference controlled by bulk composition and variation in water activities (0.1–0.7) during dehydration melting. Maximum P–T conditions were reached during M2a coevally with the major deformational event (D2a) and are estimated at 750–820  °C and 5–6  kbar. A counterclockwise P–T  path is indicated by regionally occurring pseudomorphs of sillimanite after andalusite and by prograde reaction textures preserved as relics in M2a porphyroblasts. Two stages of retrograde metamorphism are distinguished: M2a garnet+cordierite-bearing assemblages were retrogressed to biotite+sillimanite+quartz (M2b) along discontinuous foliation planes and shear zones (D2b). Retrograde M3 corona assemblages formed at similar P–T  conditions (580–660  °C and 5.8±0.5  kbar) to the M2b assemblages but M3 crystallization postdates penetrative D2 deformation, intrusion of 1.06 Ga granitoids and formation of associated W–Mo deposits. It is concluded that: (a) Kibaran high-grade metamorphism in the Okiep Copper District is thermally punctuated and (b) reaction textures documenting apparent isobaric cooling of this low- P high- T  terrane must be interpreted with caution.  相似文献   

11.
Using an internally consistent thermodynamic dataset and updatedmodels of activity–composition relation for solid solutions,petrogenetic grids in the system NKFMASH (Na2O–K2O–FeO–MgO–Al2O3–SiO2–H2O)and the subsystems NKMASH and NKFASH have been calculated withthe software THERMOCALC 3.1 in the P–T range 5–36kbar and 400–810°C, involving garnet, chloritoid,biotite, carpholite, talc, chlorite, kyanite/sillimanite, staurolite,phengite, paragonite, albite, glaucophane, jadeite, with quartz/coesiteand H2O in excess. These grids, together with calculated AFMcompatibility diagrams and P–T pseudosections, are shownto be powerful tools for delineating the phase equilibria andP–T conditions of Na-bearing pelitic assemblages for avariety of bulk compositions from high-P terranes around theworld. These calculated equilibria are in good agreement withpetrological studies. Moreover, contours of the calculated phengiteSi isopleths in P–T pseudosections for different bulkcompositions confirm that phengite barometry is highly dependenton mineral assemblage. KEY WORDS: phase relations; HP metapelite; NKFMASH; THERMOCALC; phengite geobarometry  相似文献   

12.
Hydration of eclogite, Pam Peninsula, New Caledonia   总被引：2，自引：0，他引：2  
Garnet glaucophanite and greenschist facies assemblages were formed by the recrystallization of barroisite-bearing eclogite facies metabasites in northern New Caledonia. The mineralogical evolution can be modelled by calculated P–T and P–X H2O diagrams for appropriate bulk rock compositions in the model system CaO–Na2O–FeO–MgO–Al2O3–SiO2–H2O. The eclogites, having developed in a clockwise P–T path that reached P ≈19 kbar and T  ≈590 °C, underwent decompression with the consumption of free H2O as the volume of hydrous minerals increased. Eclogite is preserved in domains that experienced no fluid influx following the loss of this fluid. Garnet glaucophanite formed at P ≈16 kbar during semi-pervasive fluid influx. Fluid influx, after further isothermal decompression, was focused in shear zones, and resulted in chlorite–albite-bearing greenschist facies mineral assemblages that reflect P ≈9 kbar.  相似文献   

13.
The Mallee Bore area in the northern Harts Range of central Australia underwent high-temperature, medium- to high-pressure granulite facies metamorphism. Individual geothermometers and geobarometers and average P–T  calculations using the program Thermocalc suggest that peak metamorphic conditions were 705–810 °C and 8–12 kbar. Partial melting of both metasedimentary and meta-igneous rocks, forming garnet-bearing restites, occurred under peak metamorphic conditions. Comparison with partial melting experiments suggests that vapour-absent melting in metabasic and metapelitic rocks with compositions close to those of rocks in the Mallee Bore area occurs at 800–875 °C and >9–10 kbar. The lower temperatures obtained from geothermometry imply that mineral compositions were reset during cooling. Following the metamorphic peak, the rocks underwent local mylonitization at 680–730 °C and 5.8–7.7 kbar. After mylonitization ceased, garnet retrogressed locally to biotite, which was probably caused by fluids exsolving from crystallizing melts. These three events are interpreted as different stages of a single, continuous, clockwise P–T  path. The metamorphism at Mallee Bore probably occurred during the 1745–1730 Ma Late Strangways Orogeny, and the area escaped significant crustal reworking during the Anmatjira and Alice Springs events that locally reached amphibolite facies conditions elsewhere in the Harts Ranges.  相似文献   

14.
Using a previously published, internally consistent thermodynamic dataset and updated models of activity–composition relations for solid solutions, petrogenetic grids in the model system KFMASH (K2O–FeO–MgO–Al2O3–SiO2–H2O) and the subsystems KMASH and KFASH have been calculated with the software THERMOCALC 3.1 in the P–T range 5–36 kbar and 400–810 °C, involving garnet, chloritoid, biotite, carpholite, talc, chlorite, staurolite and kyanite/sillimanite with phengite, quartz/coesite and H2O in excess. These grids, together with calculated AFM compatibility diagrams and pseudosections, are shown to be powerful tools for delineating the phase equilibria and P–T conditions of pelitic high-P assemblages for a variety of bulk compositions. The calculated equilibria and mineral compositions are in good agreement with petrological observation. The calculation indicates that the typical whiteschist assemblage kyanite–talc is restricted to the rocks with extremely high XMg values, decreasing XMg in a bulk composition favoring the stability of chloritoid and garnet. Also, the chloritoid–talc paragenesis is stable over 19–20 kbar in a temperature range of ca. 520–620 °C, being more petrologically important than the previously highlighted assemblage talc–phengite. Moreover, contours of the calculated Si isopleths in phengite in P–T and P–X pseudosections for different bulk compositions extend the experimentally derived phengite geobarometers to various KFMASH assemblages.  相似文献   

15.
P–T  paths based on parageneses in the immediate vicinity of former high-temperature contact zones between mantle peridotites and granulitic country rocks of the Central Vosges (NE France) were derived by applying several conventional thermometers and thermobarometric calculations with an internally consistent dataset. The results indicate that former garnet peridotites and garnet–spinel peridotites were welded together with crustal rocks at depths corresponding to 1–1.2 GPa. The temperature of the crustal rocks was about 650–700 °C at this stage, whereas values of 1100 °C (garnet peridotites) and 800–900 °C (garnet–spinel peridotites) were calculated for the ultramafic rocks. After emplacement of the mantle rocks, exhumation of the lower crust took place to a depth corresponding to 0.2–0.3 GPa. The temperatures of the incorporated peridotite slices were still high (900–1000 °C) at this stage. This is indicated by the presence of high- T  /low- P parageneses ( c . 800 °C, 0.2–0.3 GPa) in a small (1–10 m) contact aureole around a former garnet peridotite. Crustal rocks distant to the peridotites equilibrated in the same pressure range at lower temperature (650–700 °C). High cooling rates (102–103 °C Ma−1) were calculated for a garnet–biotite rock inclusion in the peridotites and for the crustal rocks at the contact by applying garnet–biotite diffusion modelling. Minimum rates of 0.75–7.5 cm a−1 are required for vertical ascent of rock units (30 km vertical distance) derived from the crust–mantle boundary, resulting in a late Variscan (340 Ma) high- T  /low- P event.  相似文献   

16.
Two high-grade gneissic complexes of the Western Sudetes, the Góry Sowie Block and the Śnieżnik area complex, contain small, predominantly felsic granulitic inliers with minor Cpx-bearing intercalations. The P–T  conditions of the granulite facies events and of the subsequent re-equilibration are estimated using the ternary feldspar thermometer and the Geo-Calc computer program (version TWQ, Jan 92).
In the Góry Sowie granulites, the peak granulitic event occurred at c . 18–20 kbar and 900 °C, and the late decompressive re-equilibration within a range of 4–10 kbar and temperatures decreasing to 600–700 °C. The latter event is thought to have coincided with the main metamorphic phase in the surrounding gneisses.
The P–T  estimates are more scattered in the Śnieżnik granulites, but the peak conditions for the granulitic event are estimated at pressure over 22 kbar (possibly around 30 kbar) and temperature exceeding 900 °C. The analysed samples from the Śnieżnik area bear no significant evidence of lower-pressure re-equilibration.
Integrating the thermobarometric data and some age constraints indicates that the Góry Sowie granulites belong to the early stage 'type I' granulites of the Variscan Belt ( c . 400 Ma old), which are interpreted as fragments of continental crustal materials subducted to mantle depths in the earliest stages of the Variscan orogeny. The Śnieżnik granulites are more problematic; they may belong to a 'younger high- P suite' ( c . 350 Ma old), widespread in the southern and eastern parts of the Bohemian Massif, and possibly related to the climax of the Variscan continent–continent collision.  相似文献   

17.
Ultra-high pressure eclogites and granulites both occur in the Dabie Mountains, central China. A garnet porphyroblast from felsic granulite in the Dabie Mountains has been analysed for compositional zoning by electron microprobe. Two segments of the porphyroblast have opposite compositional variations. Segment I (from centre outward 9  mm to analytical point 18) has decreasing XSps and increasing XPyr, while Segment II (from analytical point 18, 1  mm outward to the rim) has increasing XSps and XAlm and decreasing XPyr and XGrs. The compositional zoning in segment I is considered as growth zoning and that in Segment II as diffusive retrograde zoning. Garnet growth zoning records a P–T  path prior to the peak granulite metamorphism. The minimum P – T  conditions are estimated to be 1.35  GPa and 850  °C for peak metamorphism, based on the highest Mg/(Fe+Mg) composition in the garnet (analytical point 18) and matrix hypersthene, biotite and plagioclase. A symplectitic corona surrounds the porphyroblast and appears to have formed at 0.6  GPa and 700  °C. The well-preserved growth zoning in garnet suggests a short residence time for the granulite at peak metamorphism and thus rapid tectonic uplift history. The P–T  path is consistent with that of ultra-high-pressure eclogite in the area. Tectonic movements during a collisional event could have brought both the granulite and the eclogite to their present positions.  相似文献   

18.
The pressure-sensitive equilibrium among anorthite, quartz and the Ca-tschermak component in clinopyroxene (CaAl2SiO6; CaTs), CaAl2SiOCpx6+SiOQtz2=CaAl2Si2OPl8 (SCAn) ,can be used as a geobarometer in granulites with the proper assemblage, and has been calibrated using mineral composition data from partial melting experiments of natural assemblages and from phase equilibrium experiments on the end-member CMAS system. The experimental data cover the P – T  range 4–32  kbar and 900–1400  °C. Linear least-squares regression analysis of the experimental data resulted in the following empirical expressions for pressure in terms of composition and temperature: P = 5.066 [±0.760]+ 1300 [±800] T  −ln K 276 [±16] · T  [±2.5  kbar]or P = 6.330 [±0.116]−ln K 301 [±9]· T  [±1.0  kbar] ,where K = a PlAn a CpxCaTs  .The first equation incorporates an enthalpy term, but is less accurate than the second equation, in which the enthalpy of reaction is ignored. Application of these expressions to natural and experimental equilibrium mineral assemblages demonstrates that the empirical barometers are applicable over a wide range of pressures (≥4  kbar), temperatures (≥700  °C) and bulk compositions (Mg#≥32.5).  相似文献   

19.
Microstructural evidence commonly is used to infer metamorphic reactions, which are used to infer pressure–temperature–time ( P–T–t ) paths. However, this approach in low- P /high- T  (LPHT) granulite facies metamorphic terranes has two main problems. (1) Microstructural evidence may be inconclusive, so that reactions cannot be inferred with confidence. In particular, relative timing of mineral growth inferred from inclusions, moulding relationships and foliation–porphyroblast relationships is commonly ambiguous or invalid. The most reliable indicators of metamorphic reactions are partial pseudomorphs and corona structures, especially if symplectic intergrowths (indicating simultaneous growth of two or more minerals) are involved. (2) Even reactions that can be inferred with confidence do not indicate unique P–T  trends, owing to P–T  slopes of reaction curves. Where successive reactions can be shown to have occurred in the same rock, a line or curve joining reaction-curve intersections gives an apparent single-event path. However, isotopic evidence is needed to prove that polymetamorphism (involving more complex paths making fortuitous intersections with the apparent single-event path) did not occur. Although these problems are well known, their importance is not always emphasized in metamorphic investigations.
The difficulties are illustrated by published work on P–T–t paths for Proterozoic LPHT granulite facies rocks of central Australia and Antarctica. Recent work in Antarctica has shown that P–T–t paths may be episodic and more complex than the simple, single-event paths commonly inferred from microstructural evidence alone.  相似文献   

20.
利用最新的内洽性热力学数据库和THERMOCALC3.21程序对胶北地块高压与低压泥质麻粒岩的相平衡关系进行了定量分析。计算了胶北地块高压泥质麻粒岩、低压泥质麻粒岩和夕线石榴黑云片岩等代表性富铝岩石KFMASH(K2O-FeO-MgO-Al2O3-SiO2-H2O)体系的p-T视剖面图,再现了这些岩石随温压条件变化可能出现的各种矿物组合与矿物成分变化,发现原岩成分不同的变质岩石,尽管变质演化过程有所差异,但在麻粒岩相变质条件下所形成的矿物组合一致。通过计算泥质岩石在高压(p=1.0GPa)和低压(p=0.5GPa)条件下的T-X视剖面图,发现极度富铁、贫镁的岩石,在高压麻粒岩相条件下并不会生成含蓝晶石的特征矿物组合,在低压麻粒岩相条件下也不会生成含堇青石的特征矿物组合。将样品实际观测结果与p-T视剖面图的计算结果对比,确定胶北地块高压泥质麻粒岩变质峰期的温压条件为830~860℃,1.25~1.4GPa,峰期后呈现顺时针样式的p-T演化轨迹,反映陆壳先碰撞增厚、后又快速减薄的地质动力学过程;确定胶北地块低压泥质麻粒岩变质峰期的温压条件为790~820℃,0.62~0.68GPa,峰期后呈现近等压冷却的p-T演化轨迹。  相似文献   

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