Abstract:The forsterite mineral inclusions in chromite of podiform chromitite occur in mantle peridotite of Luobusa ophiolite in the Indo-Yarlung Zangbo tectonic unit. The forsterite inclusions from chromite grains have Fo number of 97~99 and assume the form of colorless, transparent and euhedral grains with abundant small faces. The crystal of forsterite used for X-ray analysis was measured to be approximately 0.15 mm×0.15 mm×0.15 mm. Crystal system of this forsterite is orthorhombic, space groupPbnm,α,βandγis 90°,a=4.7597°A,b=10.205°A,c=5.9831°A.The unit cell parameters of forsterite,a,b,cas well as M1—O and M2—O bond lengths are smaller than those of some olivines from mantle xenolith and mantle peridotites.The unit cell parameters of the forsterite in the study area are the same as those of the synthetic forsterite.According to experimental study cited in the literature, the small unit cell andcation-oxygen bond distances of olivine suggest a high pressure of its crystallization.

Abstract:The study of garnet pyroxenite reveals that the ultramafic block in Raobazhai within the Dabie Mountains is of metamorphic origin rather than a slice of primitive mantle. It underwent an evolutional process from spinal_Al_rich pyroxene facies (750℃, 1.1 GPa) through spinalgarnet facies (850℃, 1.5 GPa) to granulite facies (800℃, 0.85 GPa). The metamorphic history of the block is obviously different from that of ultrahigh_pressure complex in the southern Dabie Mountains. It may represent the upper rock of subducting continental crust of the south- ern Dabie Mountains characterized by a high geothermal gradient. The relationships of the granulitization of Raobazhai and other ultramafic blocks to regional granulite facies metamorphism suggests that the Dabie basement has been thoroughly reformed, and the high_grade metamorphism of the northern Dabie Mountains in Anhui Province is only a mirror of the postIndosinian granulite facies event.

Abstract:Decomposition of kyanite and omphacite occurred during the decompression of kyanite_ bearing eclogite at Rongcheng County, forming coronas around kyanite and symplectite afteromphacite. The coronas are composed of intergrowth of anorthite and radial vermicular Fe-Mg spinel in the inner part (inner corona) and anorthite along the rim (outer corona). The symplectite is made up of intergrowth of myrmekitic diopside and plagioclase (An30). Textural criteria suggest that the corona and the symplectite are coupled. The quantification of material transfer indicates that the formation of the corona gained Ca, Mg and Fe from the breakdown of the omphacite but provided no silica for the symplectization of the omphacite. The formation of the corona included two reactions, which took place simultaneously at different sites: reaction 1: 1Kyanite + 0.096Mg + 0.128Fe + 0.275Ca= 0.275An + 0.224Sp + 0.395Si +0.979Al + 1.778O; reaction 2: 0.451Si + 0.434Al + 0.212Ca + 0.013Na + 1.778O =0.225An. The silica, Al and O in reaction 2 were part of the products of the reaction 1. Two reactions between end_members of the omphacite are assumed, which provided Ca, Fe and Mg for the coronazition of the kyanite, and produced symplectite after omphacite: Na2O·Al2O3·4SiO2+CaO·MgO·2SiO2=2NaAlSi3O8+MgO+CaO (jadeite） (diopside) (Ab) 　 2CaO·2Al2O3·2SiO2+CaO·FeO·2SiO2)=2CaAl2Si2O8+FeO+CaO 　 Ca-Tsch (hedenbergite） （An） These two coupled-decomposed minerals do not constitute a closed system. The decomposition of both omphacite and kyanite obtained silica from their surroundings.

Abstract:Based on an investigation of the texture relationships between cordierite and other minerals of the Quartzofeldspathic gneisses in the Larsemann Hills, East Antarctica, especially the corrosion and crosscutting relationships between cordierite and other minerals, the authors discerned two distinct assemblages, viz., the felsic assemblage Pl+Kfs+Qtz(Grt) and the mafic assemblageCrd + Opq + Spl±Qtz . Texture and composition analysissuggeststhat cordierite might have been derived from the media quite likely in the melt state. That is, during the transformation from high_grade metamorphism to anatexis of the high grade rocks in the study area, the melt appeared first: Bt+Sil+Qtz→Grt+Melt, followed by the segregation of felsic and mafic components. The two components in the melt were immiscible and differentiated into two parts, Melt1and Melt2, which crystallized separately and formed the felsic and mafic mineral assemblages, respectively. Cordierite was not formed as a cotectic magmatic phase relatively late in peraluminous melts and the presence of the mineral had no direct relation with the felsic melt. The mafic components rich in Mg and Fe but poor in Si and Ca may have been concentrated to form cordierite. Although the mafic component was substantially derived from biotite, the contact of biotite and cordierite can rarely be found due to the face that there existed a time gap between biotite decomposition and the final crystallization of cordierite. Temporally the cordierite crystallized at the late stage of anatexis essentially brought about in the decompression process.

Abstract:Grain shapes of dynamically recrystallized quartz in ductile deformed rocks, characterized by fractal dimension, are statistically self-similar. The fractal dimensions of dynamically recrystallized quartz grains, decreasing with deformation temperature and rising with strain rate, can be an indictor for the deformation condition. Two methods of polygon and area-perimeter are applicable to calculate the fractal dimension of dynamically recrystallized quartz grains. Grain shapes of dynamically recrystallized quartz in mylonites within Qingyi ductile shear zone show statistical self-similarity, in which numbers of fractal dimension are from 1.228 to 1.326 and paleo-strain rates vary from 10-7.6 to 10-8.7 s -1 . Qingyi ductile shear zone experienced deformation under the conditions of green_schist facies and medium strain_rate.

Abstract:Late Devonian (D3) silicate and Early Carboniferous (C1) silicate in Ailao Mountain belt, Three-River" area, are quite different from each other in mode of occurence, Radiolaria association, Si isotope and REE character. The former was formed in a deep_sea environment,i.e., in an intracontinental rift, whereas the latter is a component unit of Ailao Mountain ophiolite suite formed in a bathyal environment, indicating that Ailao Mountain was a small oceanic basin at that time.

Abstract:The intermediate_basic and intermediate_acid dykes existent in the gold fields of Jiaodong peninsula, China, belong to a suite of intermediate-basic and intermediate-acid carbonate minerals-rich rocks consisting of lamprophyres and andesite porphyrites. Detailed studies of carbon and oxygen isotopes of carbonate minerals of the dykes and oxygen isotopes of the dykes in the gold fields (i. e. Linglong, Rushan and Sanjia gold deposits) show thatδ13CPDB, calcite,δ18OSMOW calciteandδ18OSMOW,whole-rockvalues of the intermediate_basic and intermediate_acid dykes in the gold fields are in the range of -3.6‰~-0.9‰, 6.9‰~11.6‰and 5.8‰~ 7.4‰respectively. These data were used to determine theδ18OSMOW,whole-rock,δ18OSMOW calcite andδ13CPDB,calcitevalues of the magmas in the source region and to study the isotope exchange of the magmas with the country rocks. Combined with the study of the geological setting for emplacement of the dykes, it is suggested that the magmas forming the intermediate-basic and intermediate_acid dykes in the gold fields are products of the evolution of the cognate magmas.The parent magmas originated from an enriched mantle (δ18OSMOW,carbonate: 9. 2‰、δ13CPDB,carbonate:-4.4‰andδ18OSMOW, magma: 5.8‰), which experienced metasomatism of the lithosphere mantle with the fluids that were generated during the subduction of the oceanic plate and then infiltrated into the lithosphere. Different isotopic effects in the evolution of magma seem to have been the main factors leading to the distinctive features of carbon and oxygen isotopes in the gold fields.

Abstract:Mesozoic volcanic activities experienced three stages, namely the Late Triassic-Late Jurassic initial stage, the Late Jurassic flourishing stage and the Cretaceous weakening-withering stage. The three stages, controlled by the same tectonic mechanism, show remarkable differences and also transitional characteristics in such aspects as volcanic activities, rock assemblages, petrochemistry and geochemistry. Studies show that the formation of Mesozoic volcanic rocks was intimately related to the subduction of the Pacific plate towards the Eurasian plate, and these volcanic rocks can be called Zhejiang_Fujian type volcanic rocks.

Abstract:The silver content of ores from the Xinrong manganese deposit in western Guangdong is higher than 100×10-6on average. According to the electron probe analyses and other data,some conclusions have been reached as follows: The modes of occurrence of associated silver include minerals of stephanite,bromargyrite,Ag-Sb-tetrahedrite,electrum etc., which occur as small grains among or between Fe-Mn minerals. Slight amounts of silver exist in Fe_Mn minerals as adsorbed ions.

Abstract:Chrysanthemum-shaped celestite is a diagenetic nodule widely distributed in the Permian Chihsia Formation of South China. As precipitated in the very early diagenesis and replaced by subsequent diagenesis, most of the celestite nodules are pseudomorphs dominantly composed of calcite, chalcedony and minor dolomite. This paper deals with the establishment of a replacement succession in the pseudomorph and the evolution of related diagenetic environments. The replacement initiated in very early diagenesis by fine cloudy calcite, followed by length_slow chalcedony and fine granular calcite. The last two components originated respectively from an episode of chalcedony veining and a calcite veining. Celestite was also noted replaced directly by chalcedony. These replacements took place in fluids rich in silica and Mg2 , revealed by microprobe analyses on the replacement calcite and the occurrence of length-slow chalcedony. Chert nodules and sepiolite in the host rock were contemporary. Late replacements include euhedral calcite crystals in the chalcedony and coarse granular calcite that stemmed from an episode of calcite veining, resulting from diagenetic fluids with relative low Mg2+ /Ca2+ ratio.