Based upon fluid effects, retrograde metamorphism of eclogites in the Dabie region can be divided into the fluid-poor, fluid-bearing and fluid-rich stages. The fluid-poor stage is marked by polymorphic inversion, recrystallization and exsolution of solid solutions, and is thought to represent eclogite-facies retrograde environments. The fluid-bearing stage is likely to have occurred at the late stage of ecologite-facies diaphthorosis and is represented by kyanite porphyroblasts, rutile, and sodic pyroxene in association with high-pressure hydrous minerals such as phengite and zoisite (clinozoisite) without significant amount of hydrous minerals such as amphibole, epidote and biotite. The fluid-rich stage might have commenced concomitantly with lower amphibolite-facies diaphthoresis and persisted all the way towards the near-surface environment. The product of this stage is characterized by plentiful hydrous and volatile-bearing phases.The dissemination-type rutile mineralizations in eclogites might have formed by preferential shearing-induced pressure solution of gangue minerals at the fluid-bearing stage. The accompanying vein rutile was precipitated from fluids of this stage after local transport and concentration, and may hence represent proximal mobilization of titanium from the eclogite. Therefore, rutile veins can be used as an exploration indicator for dissemination-type rutile deposits.
Carbonate rocks are one of the major hosts to eclogite in the Mt.Dabie region.Eclogite bodies enclosed in the carbonate rocks occur mostly as knobs,ovoids and lenses measuring centimeters to tens of centimeters in size.The bodies have been intensely carbonatized and usually have transitional contacts with their carbonate hosts.The carbonate rocks have abundant relics of eclogite minerals and their tetrogressive derivatives.The REE patterns of the carbonate rocks are characterized by the absence of negative Ce anomaly.These features suggest that a considerable portion of the eclogite-bearing carbonate rocks in the Mt .Dabie region was produced by carbonatization of eclogites and their retrogressive derivatives.These carbonate rocks suffered deformation and recrystllization after their formation.
Phengites in ecologites of the Dabieshan region can be divided into three generations:primary phengite formed during ecologite-facies prograde metamorphism (Phe1), phengite formed during the late stage of eclogite-facies retrograde metamorphism (Phe2) and phengite formedduring amphibolite- to greenschist-facies diaphthoresis (Phe3). Electron microprobe analyses show that the Si and Fe2 + + Mg contents of Phe1 are unexpectedly lower than those of Phe3. Therefore, much caution should be exercised while using the Si content of phengite to estimate the pressure of a retrograde process.
The crystal structure and Raman spectra of quartz are calculated by using first-principles method in a pressure range from 0 to 5 GPa. The results show that the lattice constants(a, c, and V) decrease with increasing pressure and the a-axis is more compressible than the c axis. The Si–O bond distance decreases with increasing pressure, which is in contrast to experimental results reported by Hazen et al. [Hazen R M, Finger L W, Hemley R J and Mao H K 1989 Solid State Communications 725 507–511], and Glinnemann et al. [Glinnemann J, King H E Jr, Schulz H, Hahn T, La Placa S J and Dacol F 1992 Z. Kristallogr. 198 177–212]. The most striking changes are of inter-tetrahedral O–O distances and Si–O–Si angles. The volume of the Si O4-4tetrahedron decreased by 0.9%(from 0 to 5 GPa), which suggests that it is relatively rigid.Vibrational models of the quartz modes are identified by visualizing the associated atomic motions. Raman vibrations are mainly controlled by the deformation of the Si O4-4tetrahedron and the changes in the Si–O–Si bonds. Vibrational directions and intensities of atoms in all Raman modes just show little deviations when pressure increases from 0 to 5 GPa.The pressure derivatives(dνi/d P) of the 12 Raman frequencies are obtained at 0 GPa–5 GPa. The calculated results show that first-principles methods can well describe the high-pressure structural properties and Raman spectra of quartz. The combination of first-principles simulations of the Raman frequencies of minerals and Raman spectroscopy experiments is a useful tool for exploring the stress conditions within the Earth.
The occurrence,mineralogy and geochemistry of eclogites in the Mt.Dabie area show that they were subjected to a high-pressure metamorphism together with the country rocks,but their petrochemistry and REE geochemistry show some difference from those of the country rocks.The geochemical characteristics of the eclogites are similar to those of bot continental tholeiitic basalt and oceanic tholeiitic basalt.The rocks probably subducted to the upper mantle with the Dabie metamorphic complex.When elevated to the surface,they were subjected to different staes of retrogressive metamorphism.
Spinel lhezolite found in Damaping,northern Zhangjiakou,Hebei Province occurs as xenoliths in the Hannuoba basalts that consist of alkali basalt and tholeiite.Spinel lherzolites contain50%-70% olivine(Fo:90%),10%-20% clinopyroxene(predominantly Di),10%-30% orthopyroxene(predominantly En),and less than 5%spinl ,^3He/^4He and ^40Ar/^38Ar ratios in the olivine are 7.56×10^-7and 299.1 respectively,^3He/^4He and ^40Ar/^38Ar ratios in the orthopyroxene(enstatite)are 9.1×10^-7and 307,respectively,Olivine grains are fractured irregularly,and pyroxene grains characterized by well developed cleavages,which would have resulted from explosion during the rapid eruption of lava from the deep interior to the surface.The lower isotope ratios of helium and argon may indicate that the spinel lherzolite xenoliths were derived from the strongly degassed and depleted upper mantle,and that the mantle is inhomogeneous.^3He losses to some extent might affect the helium isotope ratios.
Elastic wave velocity measurement in rocks at high pressures and high temperatures plays a key role in researching the state, properties and movement of the earth interior materials.
He found in atmosphere are considered to be produced byradioactive elements（e. g. U, Th）in the inner earth. Isotope composition of no-ble gases and ratios of their components are important geochemical indicators for thetheory of earth degassing and geochemical evolution of the mantle. The continuousand catastrophic models of earth degassing have been suggested. The mantledegassing would be actually catastrophic during geohistory and heterogeneous in dif-
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