Abstract:In this paper, the ultramafic rocks distributed within underthrust collision orogenic belts are divided into two groups, namely, ophiolites and ultramatic rocks (UM) of volcanic arc type; and the latter is subdivided into Yidun type,Alaska type and peridotitediorite type. If both ophiolites and UM of volcanic arc type appear in parallel distribution in the same orogen, and are emplaced in nearly the same period, they may form a pair of ultramafic belts. The ophiolites represent the remaining traces of a closed oceanic basin，while the UM，which are usually emp,laced in the late stage of the orogenic movement, indicate an island arc or active continental marginal setting on the obducted side of the plate above the subduction zone. Recent work in the Hengduan Mts region has led the authors to conclude that there are a pair of ultramafic belts in the region; the eastern belt is composed of ophiolites(including Yushu一Litang belt and Ailaoshan belt)，while the western belt aonists of UM of volcanic arc type (including the three subtypes)·These two belts are roughly parallel in distribution and both were emplaced in almost the same period, t. e.，Late Triassic. As it is known that paired UM belts probably exist in Venezuela, the Appalachians, western U. S.,Ural and the maritime regions of U.S. S. R.，Japan and the south Island of New Zealand. Moreover, there are also clues for the existence of paired UM belts in Yinjiang and Qilian Mts region in China. Therefore, the authors think that the distribution of paired UM belts might be of worldwide significance. With the exception of some cases, if the subduction of plate occurs within an orogen paired UM belts might be formed therein. The authors also noted that the metamorphic belt might be related to the paired ultramafic belts. However, compared with the former, the paired ultramafic belts are probably more implicative.

Abstract:This paper deals with the distribution of glaucophane schists in Chinas the metamorphic conditions of glaucophane·schist facies and their tectonic positions.The glaucophane .schists appeared in various metamorphic periods since Middle·Late Proterozoic. According to their mineral assemblage, they may be divided into two groups. The first group is characterized by the association of glaucophane, crossite of magnesioriebeckite stilpnomelane, and piedmintite with the common minerals of greenschist facies, such as epidotite, actinolite, chlorite, muscovite and sometimes also biotite, almandine or sodicpyroxene. The formation conditions of these assemblages are 350-450℃C, and 500-800MPa. It is considered that they :are piobably the hig-pressure variation of greenschist facies-glaucophane gree- nschist facies. They usually occur in narrow belts that often extende into the metamorphic terrain of low-greenschist facies, and in some cases, are accompanied by ultrabasic rock belts and abyssal radiolarian siliceous sediments. Geological and petrological evidence indicates that they were formed during the closing of the local deep oceanic trough of a mobile belt, and are not directly related to plate tectonics. The rocks of another group often contain high·pressure minerals,such as lawsonite, jadeite and aragonite in addition to glaucophane, pumpellyite,stilpnomelane, phengite,piedmontite etc.They belong to high-pressure subgreenschist facies, which is referred to as glaucophane lawsonite facies. Its formation conditions are 250-350℃with pressure greater than 500-800MPa, even reaching 1200MPa. Most of the glaucophane schist belts in China belong to the first group, while that of southern Tibet (R. Yarlung Zangbo) and Ondor Sum district of Inner Mongolia may fall to the second group,which represent the ancient subduction zones of oceanic piate.

Abstract:There occur different genetic types of granitic subvolcanie rocks in nature as well as different genetic types of volcanic rocks. Corresponding to three genetic types of granites, granitic subvolcanic rocks may be divided into three types: the crust, the transitional and the mantle-type. Subvolcanic rocks of the crust type related to U, REE, W, Sn, Nb and Ta mineralization belong to the series of ore-bearing granites. Subvolcanic rocks of the transitional type related to Cu, Pb, Zn, Au,Ag and associated with W and Sn mineralization belong to the series of ore-bearing porphyry. Subvolcanic rocks of the mantle type related to Cu, Pb and Zn multi-metal mineralization of the pyrite type belong to the series of ore-bearing volcanic rocks of the marine facies.

Abstract:The Wanbaogou Group of Upper Proterozoic to Cambrian age is located in southern East Kunlun Mts, around Nachitai on the Qinghai-Tibet Highway. The volcanic sequence lies in the midlower part of the Group with a thickness of greater than 1500m. The rocks comprise mainly basaltic lava, accompanied by some basic tuff. The components of the volcanics are relatively homogeneous, sugges- ting poor differeiiciation. Vesicular and pillow structures can be observed in the lavas, but they are not widely developed; lava breccias and carbonate interlayers are present in the tuffs. The pyroxenes were replaced by amphibole and chlorite,while the plagioclases had suffered from zoisitization and argilliz}tion. In addition,there are also some cases of silisification and carbonatization. The rocks are characterized by low content of SiO2 (less than 50%)and high content of Ti02(about 3%):and low Mg0(generally 4一5%)and high TFeO (about 14 %)contents. K20+Na20. and P205 contents are 2-4%and less than 0. 4% respectiv- ely. The trace element distribution is low in Cr and Ni (69-113pprrt and 23-71ppm respectively)，corresponding to the low content of Mg0，while the high V(256-383 ppm) and Zr(116-289ppm) contents are consistent with that of TFeO.The REE normalized values show a LRE-rich pattern, and 87Sr/86Sr values range between 0.702-0.705. The above data suggest that this volcanic suite was derived from tholeiite of deep origin and formed in an intraplate environment. It is somewhat .suballcaline in character and exhibits some features of oceanic islandtype basalt, indicating in the early history of the evolution of the East Kunlun crust there existed a significant extensional period as the initial stage of the formation of the East Kunlun eugeosyncli.ne.

Abstract:Through the study of the rare earth elements in the high metamorphosed massif of the early Archaean, the granite-greenstone massif of the late Archaean and various metamorphic rocks in the eugeosyncline and volcano-island arc of the late Archaean-early Proterozoic in the east section of the north margin of the North China Platform, the authors conclude that the rare-earth elements in the above three geological periods possess approximately similar evolutionary characteristics and that the partition patterns of the rare-earth elements in similar rock types in different geological periods are about the same, indicating that they were derived from the same source rocks(genesis). However, there are some differences in abundance, Eu-anormaly and degree of fractionation of light and heavy rare earth elements, indicating the heterogeneity of the crustal composition in different geological periods and structural environments in the early Pre-cambrian in the area. The variety of the partition pattern of the rare earth elements in different rock types suggests that there are at least three different magmatic sources, namely, the ultramafic, mafic and the andesitic or the tonalitic-trondhjemitic magmatic sources.

Abstract:Since the formation of different granitic rocks involves their material sources and forming mechanism and reflect different kinds of minerallization, it is. necessary to first determine the genetic type of the granite when studing the mineral deposits related to it. In South China, the granites are mainly transformed and syntectic granitic rocks. Three late Yanshanian granite masses exposed in Wubu lead-zinc ore dis· trict are all ultra-hypabyssal subvolcanic rocks. According to their geological,petrological, mineralogical, petrochemical characters, trace-element distribution,and formation temperature, they are considered to belong to syntectic granites. After analysing large amounts of data of the circum Pacific area (including Wubu and Nanjing-Wuhu districts)，it is found that the lead isotopic composition, of granitic rocks may reflect the evolution of the geospheres and represent diff- event sources of materials. Therefore, the author suggests that lead isotopic composition may be used as new markers for distinguishing the genetic type of granites. With the change from mantle-derived granite to syntectic and then totransformed-type granite, the mantle material in granite decreases, while that from the crust gradually increases together with the content of radiogenic lead.

Abstract:The granitoids in central and southern Xizang can be divided fro m north to south into three belts, i. e.the Gangdisi belt, the Lhagoi-Gangri belt and the Himalayan belt. Though belonging unexceptionally to the talc-alkaline series, the granitoids are characterized by different rock types in different belts with gre- nodiorite occurring m ainly in G ang disi, gneissic two-mica granite in Lhagio-Gangri and muscovite granite and tourmaline granite in Himalayan. In addition, zircons from granitoids have diverse typomorphic characteristics in different belts: (1)the content of zircon in granitoids gradually decreases fro m north to south: (2) the Zr/Hf ratio of zircon decreases as the acidity of the rocks grows higher and the age of the rocks becomes younger: (3) the elongation coefficient of zir- con rises with the increasing Si一K+Na contents of the granitoids; (4) (100) and. (111) crystal faces of zircon are m uch developed where Si, K and Na contents of granitoids are relatively low in the Gangdisi belt, while (110)，(311)and(131) faces of zircon aie extensively seen in the Lhagio.Gangri and the Himalayan belt whose granites have higher contents of Si, K and Na: (5) As for REE, the zircon is dominated by HREE, with a HREE/ REE proportion of more than 80%。

Abstract:Scawtite，a rare carbonated calcium silicate hydrate mineral，was discovered at the Fushan mine, Hebei Province in 1982. It occurs in cavities of the magnesian skarn near the contact zone, coexisting with calcite, scolecite, tobermorite,gyrolite and thaumasite. Its colorless and transparent crystals look like rectan gular tablets with such forms as谧100}，{010}，谧101}.{120}，{201}，{301}，{211}，{311} and{611}.Its optical constants are Ng=1.629，Nm=1.615, Np=1.609，(+)2V=67º.c∧Ng=30~35º,and its specific gravity is 2.76. The structural parameters, determined on a Nicolet-R 3 four-circle diffracto- meter, are as follows: space group I2/m. ao=10.1206 A,bo=15.2058A,co=6.6345A， β=100º37′and Z=2. The data obtained from microprobe analysis and loss in weight on ignition give a structural formula of (Ca7.03Fe0.01Mn0.01K0.002) (Si6018)0.98(CO3)1.06·2.1H20. X-ray diffraction shows the spacings and intensities of the five stronger lines to be 3.02A(100)，2.99A(80)，2. 78A(35)，2. 49A(40)，and 1.896A(40) respectively. There are 21 abs6rption bands in the infrared spectra corresponding with the structure of scawtite. The stretch vibration of the CO3 group splits into two bands with wavenumber being 1486 and 1448cm-1 respectively.The explanation is that the CO3 triangles are horizontal isosceles ones with the length of one C-0 bond different from that of the other two C-0 bonds, thus reducing the symmetry from Dge to C2h and resulting in the disappearance of the degeneration and the split of the absorption band. The DTA curve shows two endothermic troughs at 240℃ and 7570 ℃ and an exothermic crest at 895℃, resulting respectively from loss of crystallizationwater, escape of CO2 and formation of wollastonite as a new phase. Scawtite is a typical low-temperature hydrothermal mineral formed at about 1000℃.

Abstract:A sort of clay mineral bearing resemblance to rectorite is found in Chanling area, Suixian County, Hubei, Province. It occurs at the contact zone between metaholyokeite and albit-sericite phyllite as a product of alteration. It has irregular scaled shape, with G=2.79, H=2-3, Ng'=1.5494, and Np'=1.5436. The data obtained from such means as chemical analysis, X-ray diffraction，infrared absorption, thermal analysis and electron microscopy all indicate that this mineral is made up of alternate dioctahedral mica and dioctahedral smectite layers, having do60=1.503A，a0=5.20A，b0=9.02A and c0Sin β=24.70A。A good integral sequence of 001 diffraction obtained at room temperature suggests a regular interstratification, with δ=0.059 and VC=0. 239. Following are the formulae of dehydrated chemical structures: Mica-like layer: (K1.64Na0.41)2.05AL4[(Si6.08Al1.92)8O20]O2 smectite-like layer: (Ca0.53Mg0.16Na0.01K0.01H0.09)0.8(Al1.86Fe3+0.87Fe2+0.51Mg0.40Ti0.14)3.78[Si8O20]O2 The following experimental data of this mineral distinguish it from rectorite: 1. X.ray diffraction of the K-saturated sample shows d001=9.96A. 2. After being heated at 300℃, d001=9.83A. 3. Its water-saturated sample has d001=25.26A，showing only negligible eXPansion. 4. Its expanded layer has layer charge of 0.75, higher than that of recto- rite (0.3-0.6). It is thus tentatively considered that this mineral must be a muscovite/highly charged smectite (1:1) reg ularly,interstratified mineral.

Abstract:Mossbauer spectroscopy was used in study paragenetic troilite and pyrrhotite from Panxi basic rock. The formula of troilite is Fe1.009S, and the unit cell parameters are 0=5.96A and c0=11.74A·The troilite studied is refered to LB, 2C type according to Wuensch method. The formula of paragenous pyrrhotite Mossbauer was determined to be Fe0.892S, belonging to hexagonal pyrrhotite. Mossbauer parameters of the paragenetic troilite and pyrrhotite were determined and the spectra of the troilite and pyrrhotite consist of one set of magnetic six lines and three sets of magnetic six lines, respectively. By comparing the troilite from Panxi basic rock with synthetic and meteoric troilite, it can be concluded that there are no significant differences among themo.

Abstract:In recent years, the study of cosmic dust has been a very active field in cosmochemistry and astronomical geology in that it can provide valuable information about the origin and evolution of the solar system and Galaxy. Those spherules, however, are too small to be analyzed by the normal chemical analytical techniques. The aim of our work is to use INAA for determining the trace elements in the siliceous and vitreous spherules picked up from deep-sea sediments. The experimental results demonstrate that the spherules of different origins have different chemical compositions. In our work REE in siliceous and vitreous spherules were analyzed, and their REE patterns normalized to C1 chondrite were made. It can be seen through the work that the crustal samples have undergone chemical fractionation while some siliceous and vitreous spherules have obviously not, which favors their extraterrestrial origin.

Abstract:In the petrofabric study，generally only after the rake direction and rake angle of the optic axis of quartz in thin section of rock and mineral are determined on the universal stage, a stereographic . projection diagram of the optic axis of quartz can be made. However, our method is put forward on the principle that the extinction directions of the same optic axis of quartz on a succession of two different planes result in the intersection of these planes, and the intersecting line must be the optic axis. This method, therefore, requires only determining two extinction directions and a rotation angle of I·axis of each quartz grain on dif f erent planes，a projection diagram of the optic axis can be made. The projection is made on our designed projection net for the extinction direction method according to the readings of N·ring，I-axis and M-ring. It has been proved from practice for several years that this determination Ineth,od is an easy, ready and accurate one in the petrofabric work.