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1.
Oxygen bulk diffusion rates were experimentally determined in a natural ultramylonite sample ( c . 5   μ m grain size; 15–20% biotite, 20% quartz, 60–65% feldspars, and minor Fe-oxides) from the Gerrish Island shear zone, SE Maine, USA. The diffusion experiments were performed at 250–550  °C and 100  MPa water pressure. Oxygen bulk diffusion rates were determined both parallel and perpendicular to the strong foliation of the sample. The Arrhenius parameters for transport parallel to the foliation are: D bulk0=2.0×10−11 m2 s−1 and Q =30±6 kJ mol−1. The bulk diffusivity perpendicular to the foliation is about a factor of 3.5 less than that parallel to the foliation with the same activation energy. The values of bulk diffusivity and activation energy obtained are consistent with ionic diffusion through a static aqueous fluid, suggesting that an interconnected fluid exists in the ultramylonite even under hydrostatic conditions. The microstructure of the ultramylonite was characterized using transmission electron microscopy (TEM). The nature and distribution of the interconnected fluid cannot be completely resolved from the TEM analysis; however, the low percentage of three-grain channels and open grain/interphase boundaries suggests that the fluid resides as a thin film on the grain surfaces. The results of this study have direct applications in many important geological settings and provide valuable insights into the observed rapid diffusion rates, strong lithological control and pervasive nature of fluid transport in mica-bearing rocks.  相似文献   

2.
Metamorphic reactions commonly accompany ductile deformation of crustal rocks. We performed an experimental study to determine: (i) the effect of syn-deformation reaction on strain weakening and localization, and (ii) the effect of crystal plastic deformation on reaction extent and distribution. Experiments were conducted on a fine-grained gneiss (58 vol.% quartz, forming the interconnected matrix, 13 vol.% biotite, 28 vol.% plagioclase and 1 vol.% garnet/Fe-Ti oxides). General shear experiments were performed at 745 and 800 °C, 1.5 GPa, two strain rates, and shear strain ( γ ) from 0.6 to 5, yielding three suites with initial phase strength contrast between the matrix quartz and weak biotite of 45×, 25× and 10×; hydrostatic experiments were performed on cores and powders at 750 and 800 °C and 1.5–2 GPa for the same times. At these conditions, biotite reacts with plagioclase and quartz to form garnet, K-feldspar and water (no melt was observed). Greater reaction extent was observed in deformed samples than in equivalent hydrostatic samples, because of the increased surface area and internal strain energy. In all of the deformed samples, reaction contributes to strain weakening, due principally to a switch to grain boundary sliding in the fine-grained reaction products. The degree to which syn-deformational reaction causes strain weakening and localization in this polyphase aggregate depends on the phase strength contrast and how it evolves. In samples with low-phase strength contrast, strain and reaction are homogeneously distributed; however, in samples with high-phase strength contrast, ductile strain and reaction interact positively to produce a narrow ductile shear zone. Similar concentration of reaction is observed in some natural ductile shear zones.  相似文献   

3.
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4.
Diffusion modelling is applied to layered garnet–pyroxene–quartz coronas, formed by a pressure-induced reaction between plagioclase and primary pyroxene in a metabasic granulite. The reconstructed reaction involves some change in composition of reactant minerals. The distribution of minerals between layers is satisfactorily explained by diffusion-controlled reaction with local equilibrium, in which the diffusion coefficient for Al was smaller than those for Fe, Mg and Ca by a factor of approximately four. Diffusion of Mg towards plagioclase implies a chemical-potential gradient for MgO component in a direction opposite to the changing Mg content of garnet; this is explained by the influence of Al2O3 on the chemical potential of the pyrope end-member. Grain-boundary diffusion is suggested to have operated, possibly with composition gradients different from those in the bulk minerals. Chemical-potential differences across the corona are estimated from the variation in garnet composition, enabling affinity (the free energy change driving the reaction) to be estimated as 6.9±1.8  kJ per 24-oxygen mole of garnet produced. This implies that the pressure for equilibrium among the minerals was overstepped by 1.4±0.4  kbar. The probable P–T conditions of reaction were in the range 650–790  °C, 8–10  kbar. Assuming a timescale of reaction between 106 and 108 years, estimated diffusion coefficients for Fe, Mg and Ca are in the range 9×10−23 to 5×10−20 m2 s−1. These are consistent with experimental values in the literature for solid-state diffusion, including grain-boundary diffusion.  相似文献   

5.
Abstract Deformed quartz veins in garnet-zone schist adjacent to the active Alpine Fault, New Zealand, have fluid inclusions trapped along quartz grain boundaries. Textures suggest that the inclusions formed in their present shapes during annealing of the deformed veins. Many of the inclusions are empty, but some contain carbon dioxide with densities that range from 0.16 to 0.80 g cm−3. No water, nitrogen or methane was detected. The inclusions are considerably more CO2-rich than either the primary metamorphic fluid (<5% CO2) or fluids trapped in fracture-related situations in the same, or related, rocks (<50% CO2). Enrichment of CO2 is inferred to have resulted from selective migration (wicking) of saline water from the inclusions along water-wet grain boundaries after cooling-induced immiscibility of a water-CO2 mixture. Inclusion volumes changed after loss of water. Non-wetting CO2 remained trapped in the inclusions until further percolation progressively removed CO2 in solution. This mechanism of fluid migration dominated in ductile quartz-rich rocks near, but below, the brittle-ductile transition. At deeper levels, hydraulic fracturing is also an important mechanism for fluid migration, whereas at shallower levels advection through open fractures dominates the fluid flow regime.  相似文献   

6.
The 5-km deep Chinese Continental Scientific Drilling Main Hole penetrated a sequence of ultrahigh pressure (UHP)-metamorphic rocks consisting mainly of eclogite, gneiss and garnet-peridotite with minor schist and quartzite. Zircon separates taken from thin layers of schist and gneiss within eclogite were investigated. Cathodoluminescence images of zircon grains show that they have oscillatory zoned magmatic cores and unzoned to patchy zoned metamorphic rims. Zircon rims contain rare coesite and calcite inclusions whereas cores contain inclusions of both low- P minerals (e.g. feldspar, biotite and quartz) and coesite and other eclogite-facies minerals such as phengite and jadeite. The zircon cores give highly variable 206Pb/238U ages ranging from 760 to 431 Ma for schist and from 698 to 285 Ma for gneiss, and relatively high but variable Th/U ratios (0.16–1.91). We suggest that the coesite and other eclogite facies mineral inclusions in zircon cores were not magmatic but formed through metasomatic processes caused by fluids during UHP metamorphism, and that the fluids contain components of SiO2, Al2O3, K2O, FeO, MgO, Na2O and H2O. Metasomatism of the Sulu UHP rocks during continental subduction to mantle depths has partly altered magmatic zircon cores and reset isotopic systems. This study provides key evidence that mineral inclusions within magmatic zircon domains are not unequivocal indicators of the formation conditions of the respective domain. This finding leads us to conclude that the routine procedure for dating of metamorphic events solely based on the occurrence of mineral inclusions in zoned zircon could be misleading and the data should be treated with caution.  相似文献   

7.
In the Austroalpine Mont Mary nappe (Italian Western Alps) discrete zones of mylonites–ultramylonites developed from coarse-grained, upper amphibolite facies metapelites of pre-Alpine age. The syn–mylonitic mineral assemblage is quartz–biotite–muscovite–plagioclase–garnet–sillimanite–ilmenite–graphite, and formed via the model hydration reaction: Grt1+Kfs+H2O=Bt2+Ilm2+Qtz+Ms± Sil .Grain-size reduction of about three orders of magnitude was accompanied by extensive recrystallization of all minerals except sillimanite, and by compositional changes of garnet and biotite. Deformation took place at temperatures of 510–580  °C under low-pressure conditions (0.25–0.45 GPa) and corresponds to the latest stages of pre-Alpine metamorphic evolution. The pre-Alpine mylonitization conditions were close to the brittle-ductile transition, as indicated by syn–mylonitic generation of pseudotachylytes and high differential stress inferred from quartz grain-size piezometry. The brittle-ductile behaviour at a relatively high temperature, and the absence of annealing textures in quartz aggregates, are suggestive of water-deficient conditions during mylonitization. These were accomplished through progressive consumption of water by syn–kinematic hydration reaction and by adsorption onto the greatly increased grain boundary area resulting from dynamic recrystallization.  相似文献   

8.
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   

9.
The south-east Reynolds Range, central Australia, is cut by steep north-west-trending Alice Springs age ( c. 334  Ma) shear zones that are up to hundreds of metres wide and several kilometres long with reverse senses of movement. Amphibolite facies (550–600  °C, 500–600  MPa) shear zones cut metapelites, while greenschist facies shear zones (420–535  °C, 400–650  MPa) cut metagranites. The sheared rocks commonly underwent metasomatism implying that the shear zones were the pathways of significant fluid flow. Altered granites within greenschist facies shear zones have gained Si and K but lost Ca and Na relative to their unsheared counterparts, suggesting that the fluid flowed down-temperature (and hence probably upward) through the shear zones. Time-integrated fluid fluxes calculated from silica addition are up to 2.1×1010 mol  m−2 ( c. 4.2×105  m3  m−2). Similar time-integrated fluid fluxes are also estimated from changes in K and Na. The sheared granitic rocks locally have δ18O values as low as 0 which is much lower than the δ18O values of the adjacent unsheared granites (7 to 9), implying that the fluid which flowed through these shear zones was derived from the surface. For the estimated time-integrated fluid fluxes, the fluids would be able to retain their isotopic signature for many tens to hundreds of kilometres. The flow of surface-derived fluids into the ductile middle crust, with subsequent expulsion upwards through the shear zones, may have been driven by seismic activity accompanying the Alice Springs deformation.  相似文献   

10.
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   

11.
Garnet from a kinzigite, a high-grade gneiss from the central Black Forest (Germany), displays a prominent and regular retrograde diffusion zoning in Fe, Mn and particularly Mg. The Mg diffusion profiles are suitable to derive cooling rates using recent datasets for cation diffusion in garnet. This information, together with textural relationships, thermobarometry and thermochronology, is used to constrain the pressure–temperature–time history of the high-grade gneisses. The garnet–biotite thermometer indicates peak metamorphic temperatures for the garnet cores of 730–810  °C. The temperatures for the outer rims are 600–650  °C. Garnet–Al2SiO5–plagioclase–quartz (GASP) barometry, garnet–rutile–Al2SiO5–ilmenite (GRAIL) and garnet–rutile–ilmenite–plagioclase–quartz (GRIPS) barometry yield pressures from 6–9  kbar. U–Pb ages of monazite of 341±2  Ma date the low- P high- T metamorphism in the central Black Forest. A Rb/Sr biotite–whole rock pair defines a cooling age of 321±2  Ma. The two mineral ages yield a cooling rate of about 15±2  °C Ma−1. The petrologic cooling rates, with particular consideration of the f O2 conditions for modelling retrograde diffusion profiles, agree with the geochronological cooling rate. The oldest sediments overlying the crystalline basement indicate a minimum cooling rate of 10  °C Ma−1.  相似文献   

12.
Calcsilicate granulites of probable Middle Proterozoic age ( c .1000–1100  Ma) in the vicinity of Battye Glacier, northern Prince Charles Mountains, East Antarctica, contain prograde metamorphic assemblages comprising various combinations of wollastonite, scapolite, clinopyroxene, An-rich plagioclase, calcite, quartz, titanite and, rarely, orthoclase, ilmenite, phlogopite and graphite. Comparison of the prograde assemblages with calculated and experimentally determined phase relations in the simple CaO–Al2O3–SiO2–CO2–H2O system suggests peak metamorphism at ≥835 °C in the presence (in wollastonite-bearing assemblages at least) of a CO2-bearing fluid ( X CO≥0.3) at a probable pressure of 6–7  kbar.
Well-preserved retrograde reaction textures represent: (1) breakdown of scapolite to anorthite+calcite±quartz; (2) formation of grossular–andradite garnet and, locally, (3) epidote, both principally by reactions involving scapolite breakdown products and clinopyroxene; (4) local coupled replacement of clinopyroxene and ilmenite by hornblende and titanite, respectively; and finally (5) local sericitization of prograde and retrograde plagioclase. These retrograde reactions are interpreted to be the result of cooling and variable infiltration by H2O-rich fluids, possibly derived from crystallizing pegmatitic intrusions and segregations that may be partial melts, which are common throughout the area.  相似文献   

13.
The size and distribution of zircon within a garnet-mica-schist from the Scottish Highlands were assessed using scanning electron microscopy. The study reveals that abundant 0.2–3.0 μm sized zircon is preferentially concentrated within garnet and biotite porphyroblasts. The micro-zircon has grown during regional metamorphism and represents >90% of the total number of zircon in the schist. It is texturally distinct from a few larger detrital zircon grains in the schist that commonly preserve evidence of dissolution, and more rarely, small metamorphic outgrowths. The sequential incorporation of zircon in porphyroblasts allows prograde changes in the morphology of the zircon population to be identified. Zircon is reactive and soluble, and responds to medium-grade metamorphism in a series of dissolution and crystallization events, linked to possible changes in fluid composition. Deformation also has a significant influence on the distribution of zircon, allowing inclusions previously trapped within biotite to react. About 8 × 106 micro-zircon occur as inclusions within a typical individual 5-mm garnet porphyroblast and their presence must be considered prior to trace-element or isotopic analysis of such metamorphic phases.  相似文献   

14.
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   

15.
The rim-forming reaction quartz + olivine = orthopyroxene is used to investigate the effect of matrix rheology on rim growth rates. Orthopyroxene rim growth around olivine grains in quartz matrix is compared to rim growth around quartz grains in an olivine matrix. At constant P–T , within one single capsule, orthopyroxene rims grow faster around quartz clasts in olivine matrix than around olivine clasts in quartz matrix. Fourier transform infra-red spectra indicate that the entire samples are water saturated because of water adsorption on the reactant grain surfaces. The increased orthopyroxene growth rates in olivine matrix as opposed to quartz matrix are interpreted in terms of matrix rheology, where in the two different matrix-inclusion arrangements the olivine matrix behaves 'softer' and the quartz matrix 'more rigid'. The strain energy associated with accommodation of the negative reaction volume is higher for the quartz than the olivine matrix and reduces the free energy that drives orthopyroxene rim growth. Growth textures in both kinds of orthopyroxene rims indicate that the diffusivity of MgO slightly exceeds the diffusivity of SiO2. The relative mobility of MgO and SiO2 at given P , T , f H2O seems to be controlled by energy minimization during orthopyroxene growth at the compressive Ol/Opx interface. Our experiments provide evidence for two previously overlooked effects relevant to rim growth reactions in metamorphic rocks: (i) diffusivity along chemical potential gradients to reaction sites is a function of rheology and (ii) the relative diffusivity of components during reaction rim or corona growth is a function of local volume changes at the rim's interfaces.  相似文献   

16.
Magnesian metapelites of probable Archaean age from Forefinger Point, SW Enderby Land, East Antarctica, contain very-high-temperature granulite facies mineral assemblages, which include orthopyroxene (8–9.5 wt% Al2O3)–sillimanite ± garnet ± quartz ± K-feldspar, that formed at 10 ± 1.5 kbar and 950 ± 50°C. These assemblages are overprinted by symplectite and corona reaction textures involving sapphirine, orthopyroxene (6–7 wt% Al2O3), cordierite and sometimes spinel at the expense of porphyroblastic garnet or earlier orthopyroxene–sillimanite. These textures mainly pre-date the development of coarse biotite at the expense of initial mesoperthite, and the subsequent formation of orthopyroxene (4–6 wt% Al2O3)–cordierite–plagioclase rinds on late biotite.
The early reaction textures indicate a period of near-isothermal decompression at temperatures above 900°C. Decompression from 10 ± 1.5 kbar to 7–8 kbar was succeeded by biotite formation at significantly lower temperatures (800–850°C) and further decompression to 4.5 ± 1 kbar at 700–800°C.
The later parts of this P–T evolution can be ascribed to the overprinting and reworking of the Forefinger Point granulites by the Late-Proterozoic ( c . 1000 Ma) Rayner Complex metamorphism, but the age and timing of the early high-temperature decompression is not known. It is speculated that this initial decompression is of Archaean age and therefore records thinning of the crust of the Napier Complex following crustal thickening by tectonic or magmatic mechanisms and preceding the generally wellpreserved post-deformational near-isobaric cooling history of this terrain.  相似文献   

17.
Tectonic slices and lenses of eclogite within mafic and ultramafic rocks of the Early Cretaceous–Eocene Naga Hills ophiolite were studied to constrain the physical conditions of eastward subduction of the Indian plate under the Burma microplate and convergence rate prior to the India–Eurasia collision. Some of the lenses are composed of eclogite, garnet-blueschist, glaucophanite and greenschist from core to margin, representing a retrograde hydrothermal alteration sequence. Barroisite, garnet, omphacite and epidote with minor chlorite, phengite, rutile and quartz constitute the peak metamorphic assemblage. In eclogite and garnet-blueschist, garnet shows an increase in Mg and Fe and decrease in Mn from core to rim. In chlorite in eclogite, Mg increases from core to rim. Inclusions of epidote, glaucophane, omphacite and quartz in garnet represent the pre-peak assemblage. Glaucophane also occurs profusely at the rims of barroisite. The matrix glaucophane and epidote represent the post-peak assemblage. The Fe3+ content of garnet-hosted omphacite is higher than that of matrix omphacite, and Fe3+ increases from core to rim in matrix glaucophane. Albite occurs in late stage veins. P – T pseudosection analysis indicates that the Naga Hills eclogites followed a clockwise P – T path with prograde metamorphism beginning at ∼1.3 GPa/525 °C and peaking at 1.7–2.0 GPa/580–610 °C, and subsequent retrogression to ∼1.1 GPa/540 °C. A comparison of these P – T conditions with numerical thermal models of plate subduction indicates that the Naga Hills eclogites probably formed near the top of the subducting crust with convergence rates of ∼ 55–100 km Myr−1, consistent with high pre-collision convergence rates between India and Eurasia.  相似文献   

18.
Calculated results using thermocalc for melting of pelitic compositions are compared with the results of experimental melting of pelite from Morton Pass, Wyoming, USA. The experiments were carried out at 1, 2 and 3.5 kbar, dominantly at 2 kbar. For experimental charges with ('wet') and without ('dry') added H2O, the agreement is good. This is true for the compositions without added H2O, in which liquid first appears with the production of orthopyroxene at ∼800 °C, and for the runs with added H2O, in which melting begins at ∼700 °C, and continues, with the appearance of orthopyroxene between 780 and 800 °C at 2 kbar. The compositions of melts are also compared: the comparison is generally good, except in the modelling of wet runs below ∼780 °C, where the calculated values for FeO and MgO are about one-tenth of the already low analytical values, and in somewhat low calculated values of Al2O3 compared to the analytical data. A quantitative model to illustrate melting of pelite at Morton Pass is calculated, giving T – X (H2O) conditions for the observed sets of natural assemblages, along with the reactions at and near the beginning of melting.  相似文献   

19.
ABSTRACT Volume diffusion and dislocation creep at T  ∼ 800 °C led to high finite strain in granulite and orthogneiss of the Ohře crystalline complex (North Bohemian shear zone). Intragranular creep by volume diffusion is indicated by (i) lobate phase boundaries between feldspar and quartz, and (ii) removal of perthite lamellae and precipitation of tiny, aluminium-rich needles at the margins of K-feldspar. The striking diffusional-creep structures imply high interfacial free energy that has been preserved from equilibration as a result of rapid cooling. U–Pb dating of monazite (342 ± 1 Ma) and 40Ar–39Ar dating of muscovite (341 ± 4 Ma) of Kadaň orthogneiss result in a cooling rate of 50 + 25/−17 °C Myr−1. This high value is attributed to collapse-related 'elevator-style' movements along the North Bohemian shear zone, resulting in the juxtaposition of upper crustal rocks of the Tepla–Barrandian unit against lower crustal rocks of the Erzgebirge crystalline complex.  相似文献   

20.
New 40Ar/39Ar ages are presented from the giant Sulu ultrahigh-pressure (UHP) terrane and surrounding areas. Combined with U-Pb ages, Sm-Nd ages, Rb-Sr ages, inclusion relationships, and geological relationships, they help define the orogenic events before, during and after the Triassic collision between the Sino–Korean and Yangtze Cratons. In the Qinling microcontinent, tectonism occurred between 2.0 and 1.4 Ga. The UHP metamorphism occurred in the Yangtze Craton between 240 and 222 Ma; its thermal effect on the Qinling microcontinent was limited to partial resetting of K-feldspar 40Ar/39Ar ages. Subsequent unroofing at rates of 5–25 km Myr−1 brought the UHP terrane to crustal levels where it underwent a relatively short amphibolite facies metamorphism. The end of that metamorphism is marked by 40Ar/39Ar ages in the 219–210 Ma range, implying cooling at crustal depths at rates of 50–200 °C Myr−1. Ages in the 210–170 Ma range may reflect protracted cooling or partial resetting by Jurassic or Cretaceous magmatism. Jurassic 166–149 Ma plutonism was followed by cooling at rates of c. 15 °C Myr−1, suggesting relatively deep crustal conditions, whereas Cretaceous 129–118 Ma plutonism was succeeded by cooling at rates of c. 50 C Myr−1, suggesting relatively shallow crustal depths.  相似文献   

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