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2011, Volume 18 Issue 2
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Approaches and advancement of the study of metamorphic pTt paths. 2011, 18(2): 1-16.  Abstract ( 2429 )   PDF (2789KB) ( 3395 )   Development of the metamorphic pTt path has completely modified the understanding of metamorphic processes. The regional metamorphism in a thickened crustal region (orogenic belt) is considered to occur in a dynamic process from a tectonic perturbation to subsequent thermal relaxation. Thus, a pTt path for a rock is a function of models and mechanism of crustal thickening, of the rate of thermal relaxation and the rate of rock exhumation. Results from onedimensional thermal modeling suggest that the tectonic perturbation would occur almost instantaneously and metamorphism starts to evolve during exhumation of rock. Twodimensional thermal modeling indicates that there is pronounced heating during the crustal thickening (burial stage) and a rock reaches the maximum temperature during its exhumation as a result of a slight heating. The reverse modeling of metamorphic pTt paths involves three approaches:the conventional geothermobarometry, Gibbs/differential thermodynamics and metamorphic phase diagram. Modeling of a pTt path for a rock using any of the three approaches should be on the basis of detailed petrographic observations, for instance, recognizing at least two stages of mineral assemblage. The conventional geothermobarometry approach has been widely used, but there are uncertainties in the determination of equilibrium domain and pT conditions for different stages of mineral assemblage. The Gibbs/differential thermodynamics approach, that is to calculate a pTt path based on a growth zoning of mineral (garnet), has been considered to be perfect theoretically. However, this approach is difficult to be used because:(i) it is hard to determine the evolvement of mineral assemblage during the growth of zoned minerals; and (ii) there is the lack of available activity models for complicated solid solutions. At present, the metamorphic phase diagram approach is the best one to model the pTt path. With this approach, a pTt path recorded in mineral generations and growth zoning can be well determined by isopleththermobarometry of mineral composition in a pT pseudosection. Moreover, evolvement of mineral assemblage, metamorphic reaction and fluid flowing during a metamorphic process can also be quantitatively modeled. The pTt paths reversely modeled from several mediumpressure metamorphic belts and ultrahighpressure terranes indicate that during tectonic burial, there is pronounced heating, coupled with a series of metamorphic evolvements, and the maximum pressure in a rock is reached almost simultaneously as the maximum temperature. The exhumation of rock is characterized by isothermal decompression(ITD). These are distinct from the results by onedimensional thermal modeling, and approximate to those from twodimensional thermal modeling except for the rate of exhumations being much faster. Related Articles | Metrics

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The impact of highgrade metamorphism on the UThPb system of zircons：A case study of zircon dating of metadiorite in Qixia Area， eastern Shandong. 2011, 18(2): 17-25.  Abstract ( 2987 )   PDF (1943KB) ( 1671 )   This paper presents a study of the UThPb behavior of zircons in a “dry” rock system during highgrade metamorphism in the Archean basement of eastern Shandong. The studied sample has a mineral assemblage of plagioclase+Kfeldspar+clinopyroxene+biotite+quartz and its protolith is considered to be diorite. The zircons are stubby， equant or irregular in shape and show firleaf， sector， banded or oscillatory zoning. They contain inclusions， including the mineral assemblages of clinopyroxene+orthopyroxene+hornblende+quartz and plagioclase+Kfeldspar+biotite+quartz. Fifty SHRIMP analyses were carried out on 34 zircon grains and commonly yielded high Th/U ratios(mostly>05). Most analyses are distributed along a concordia from 254 to 225 Ga， with the youngest age of about 195 Ga. Compositions and ages show large variations even in an individual zircon grain. Combined with early studies， conclusions have been drawn as follows： （1) the diorite underwent two episodes of highgrade metamorphism both at the end of the Neoarchean and the Paleoproterozoic(about 250 Ga and about 195 Ga or slightly later)； （2) highgrade metamorphism in a “dry” rock system may partially reset the UThPb system of zircons， and in this case， the ages between the oldest and youngest are chronologically meaningless； （3) high Th/U ratios may be common features of the zircons formed during highgrade metamorphic conditions. Related Articles | Metrics

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The progress and some problems in the study of rutile in metamorphic rocks. 2011, 18(2): 26-32.  Abstract ( 1963 )   PDF (1119KB) ( 1511 )   Rutile is a very common accessary mineral in metamorphic rocks. Its geochemical characteristics attract more and more researchers along with the development of insitu analysis method. This paper aims to provide an overview of the applications of rutile in metamorphic petrology， based on a review of data published in recent years. The focus lies on the following progress and some problems in the study of rutile in metamorphic rocks： (1) rutile occurrences and the reactions by which rutile grew in metamorphic rocks; (2) Zrinrutile applications in metamorphic rocks; (3) the role of rutile in arc volcanic process and subduction metamorphism; and (4) rutile UPb geochronology application in metamorphic rocks. Combined with the study of unique paleosubduction zones in China，great interest will be focused on the research of rutile application in metamorphic petrology. Related Articles | Metrics

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Insitu UPb dating of zircons from highpressure granulites in Shandong Peninsula， Eastern China and its geological significance. 2011, 18(2): 33-54.  Abstract ( 2010 )   PDF (5769KB) ( 1333 )   Highpressure(HP)granulites as enclaves and irregular veinlike blocks are widely distributed in TTG gneisses of the Early Precambrian metamorphic basement of Shandong Peninsula, in the southeast of the North China Craton. Zircon grains separated from HP granulites are subdivided into three main types based on cathodoluminescence(CL), Laser Raman spectroscopy and insitu UPb dating； they are inherited(magmatic)zircon, HP metamorphic zircon and retrogressive zircon. The obviously or weakly zoned, dark luminescent inherited(magmatic)zircon with mineral inclusions of apatite(Ap) records two group 207Pb/206Pb ages of 2890-2915 Ma and 2510-2763 Ma, indicating two magmatic events occurring at Mesoarchean and Neoarchean epoches. In contrast, the homogeneous, HP metamorphic zircon with index HP mineral inclusions of garnet(Grt)+clinopyroxene(Cpx)+plagioclase(Pl)+quartz(Qtz)+rutile(Rt)+apatite(Ap) records younger 207Pb/206Pb ages ranging from 1850 Ma to 1900 Ma, which represent peak HP granulitefacies metamorphic times. The retrogressive zircon with mineral inclusions of orthopyroxene(Opx)+plagioclase(Pl)+quartz(Qtz)+apatite(Ap)±amphibole(Amp), however, records the youngest 207Pb/206Pb ages of 1820-1840 Ma, which represents late medium and lowgranulitesfacies retrograde metamorphic times. This result indicates that Mesoarchean and Neoarchean igneous protoliths of mafic HP granulites, together with their TTG country rocks and metasedimentary rocks are subducted to coeval Paleoproterozoic HP metamorphism(1850-1900 Ma), followed by late medium and lowgranulitesfacies retrogression(1820-1840 Ma). This new result is of very important significance for deeply discussing the genetic mechanism and geodynamic model of the HP granulites distributed in the southeast part of the North China Craton. Related Articles | Metrics

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Characteristics of melt lineation of highgrade metamorphic rocks at Daqingshan region of Inner Mongolia. 2011, 18(2): 55-62.  Abstract ( 2205 )   PDF (1783KB) ( 1121 )   Melt lineation is a special linear structural element of highgrade metamorphic rocks, which is composed of long lens or rodlike aggregates of melted leucoveins distributed along Xaxis direction of strain ellipsoid. Melt lineation developed in ductile deformation zones of deep structural levels of crust and may indicate the moving direction as the mineral stretching lineation does. Melt lineation is controlled by deformation, metamorphism and partial melting in an extensional tectonic environment. The main mechanism of melt lineation is extensional deformation which led to partial melting of highgrade metamorphic rock. Melt lineation keeps a lot of rock rheological information of deep crust, which is of great scientific significance for probing into rock rheological mechanism of deep crust and the formation and evolution of early crust. Related Articles | Metrics

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Petrogenesis and geodynamic setting of Jiandeng potassic granite at the end of the Neoarchean in Zanhuang Complex, North China Craton. 2011, 18(2): 62-78.  Abstract ( 2455 )   PDF (4024KB) ( 1477 )   Jiandeng granite in the Zanhuang Complex is located in the northwestern Lincheng County, Hebei Province. The pluton consists mainly of Kfeldspar granite and monzogranite with few quartz diorite enclaves. SHRIMP dating of zircon from the granite yielded an age of (2490±13)Ma. The rocks have high contents of SiO2 (743%—754%), K2O (576%—937%) and alkali with K2O+Na2O=616%—951%, and low contents of CaO (014%—081%), TiO2(004%—015%), MgO (002%—049%) and total FeO(026%—105%), belonging to shoshonitic series with slightly peraluminous feature. They have lower REE contents((1207—16038)×10-6), with relative enrichment of the LREE and variational Eu anomaly (Eu/Eu*=046—197). The rocks are rich in largeion lithophile elements (LILE) Rb, Ba and Th, and poor in Sr, Zr, Nb, Y and Yb, with high Rb/Sr and Rb/Ba ratios. They have positive εNd (t) value ranging from 285 to 366, with TDM2 ages between 255 and 264 Ga. SHRIMP dating of zircon from the quartz diorite enclave yielded an age of （2506±13）Ma. The quartz diorite is high in Al2O3(1716%), Na2O(447%), CaO(434%) and TFeO (526%), and shows higher total REE content of 21282×10-6, with a small Eu anomaly (Eu/Eu*=083). This rock is rich in Rb, Sr and Zr, and has an εNd (t) value of 305 and a TDM2 age of 263 Ga. The geochemical data show that the Jiandeng granite is similar to the Stype granite formed by anatexis of the juvenile crust in a tectonic transition setting from compression to extension, and the quartz diorite may represent a residue of the source rock. The formation of Jiandeng granite marks a tectonomagmatic event resulting in stabilization of the North China Craton at the end of the Neoarchean. Related Articles | Metrics

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Mineral evolution and zircon geochronology of mafic enclave in granitic gneiss of the Quanji Block and implications for Paleoproterozoic regional metamorphism. 2011, 18(2): 79-84.  Abstract ( 2535 )   PDF (2405KB) ( 1787 )   A wallrockderived metamafic enclave was discovered in the EarlyPaleoproterozoic Delingha monzogranitic gneiss in the middle part of the Quanji Block. The enclave includes three rocks, from the margin to the center, being hornblende plagioclase pyroxenite, amphibolite, and garnethornblende schist. Three generations of mineral assemblages have been identified from petrological evidence and microtextural relationship in the hornblende plagioclase pyroxenite. The generation I is of clinopyroxene+brownish greenhornblende+plagioclase+quartz+ilmenite, the generation II is of bluish greenhornblende+plagioclase+garnet and the generation III is of actinolite+albite+zoisite. The generation I assemblage indicates the peak metamorphic condition of upper amphibolitefacies. Zircons from the hornblende plagioclasepyroxenite all display multifaced crystals; their CL images are characterized by hightemperature recrystallization. LAICPMS dating of the zircons yielded an upper intercept age of 1 913±38 Ma (MSWD=0.15), suggesting peak metamorphism in the Late Paleoproterozoic. It is suggested that all regionally developed monzogranitic gneisses in the Quanji Block underwent regional metamorphism with the Dakendaban Group, in response to the global assembly event of the Columbia supercontinent. Related Articles | Metrics

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Geochemistry, zircon geochronology and Hf isotopes of Lujiazhai granites from the Dabie Orogen: Evidence for the Neoproterozoic magmatism along the northeastern margin of Yangtze Block. 2011, 18(2): 85-99.  Abstract ( 2729 )   PDF (2157KB) ( 1346 )   The Lujiazhai granitic pluton located in the southern Dabie Orogen was studied by zircon LAICPMS UPb dating, zircon Hf isotope and bulk geochemistry analyses. LAICPMS zircon UPb dating gave the age of 816±17 Ma for the Lujiazhai granites, revealing that the pluton was emplaced in the Neoproterozoic. All bulk samples are high in SiO2 (6913%—7547%), with moderate A/CNK values (098—101, averaged at 10), inferring an Itype granite affinity. The concentration of total rare earth elements (REEs) varies in the range of 2743×10-6 to 16066×10-6. The Lujiazhai granites are characterized by an enriched LREE pattern with slightly negative to positive Eu anomalies. They are enriched in large ion lithophile elements (e.g. K, Ba, Sr), but depleted in high field strength elements (e.g. P, Nb, Ti). Zircon Hf isotopic data indicate that the Lujiazhai Neoproterozoic granitic pluton in the southern Dabie Orogen was likely formed by magmas derived from partial melting of Early Precambrian metamorphic complex, accompanied by the heating and possible assimilation of mantlederived magmas. By combining studies of the paleogeographic reconstruction of the Rodinia supercontinent, we propose that since the early Neoproterozoic, the northeastern margin of the Yangtze block might have been under an active continental margin setting induced by subduction of an oceanic plate. In this tectonic regime, the Lujiazhai granites were derived by partial melting of ancient crustal materials induced by the underplating or intracrustal heating of hot mantlederived magmas. After the cease of subduction and consequent continentarc collision, this area was then likely dominated by postcollisional extension or rifting tectonically, related to the breakup of the Rodinia supercontinent. Related Articles | Metrics

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Pseudosection modelling of garnet blueschist from Rongma Area, central  Qiangtang, North Tibet: Implications to the tectonic evolution of central Qiangtang. 2011, 18(2): 100-115.  Abstract ( 1793 )   PDF (6536KB) ( 801 )    Within Qiangtang basin, northern Tibet, a metamorphic belt divides the Qiangtang basin into the northern and southern blocks and was designated as the central Qiangtang metamorphic belt. Although blueschist and eclogite were distinguished within this belt, the tectonic evolution of this metamorphic belt still remains largely debatable. One interpretation is that the central Qiangtang metamorphic belt marks an insitu palaeoTethyan suture zone between northern Qiangtang terrane of Cathaysian affinity and southern Qiangtang terrane of Gondwana affinity. The alternative argument suggests that the central Qiangtang metamorphic belt was underthrust southward beneath the Qiangtang terrane along the Jinsha suture zone about 200 km in the north. Therefore, the central Qiangtang metamorphic belt did not mark an insitu suture zone within Qiangtang terrane. Here we investigate the garnetbearing blueschists from Rongma area of central Qiangtang in northern Tibet, where is critical to understanding the tectonic evolution of the central Qiangtang metamorphic belt. The mineral assemblage in these rocks is characterized by porphyroblastic garnet set within a matrix of finegrained amphibole, white mica, epidote, chlorite, albite and quartz with accessory rutile, titanite and apatite. The Mn content of the garnet porphyroblasts decreases from core to rim, whereas the Fe and Mg contents show an increasing trend, respectively. Finegrained rhombshaped inclusions of paragonite and epidote in association with quartz occurring within the core of the garnet porphyroblasts are interpreted as pseudomorphs after lawsonite. Large grains of epidote with inclusions of Na amphibole, rutile and quartz occur in the matrix in contact with the rims of the garnet grains. In the matrix, we identified two stages of Na amphibole rimmed by NaCa amphibole and albite. Retrograde chlorite is rimmed by finegrained biotite. On the basis of microstructural observations and pseudosection modelling, we trace the pT path for the Rongma garnet blueschist from 2.0 GPa and 470 ℃ (lawsonitestability field) to about 17 GPa and 530—540 ℃ (epidote eclogite field), marking an initial increase in temperature and decrease in pressure. This stage is followed by a decrease of pressure through the blueschist facies down to pT conditions of about 0.6 GPa and 530 ℃. In combination with previous work including the available isotopic age data, the pT path obtained in the present study suggests deep subduction of palaeoTethyan oceanic crust between southern and northern Qiangtang blocks, supporting the model that the blueschist belt defines the location of the palaeoTethyan suture zone within northern Tibet. Since the transformation of lawsonite to epidote is known to release water along the subduction channel, our results also provide clues to a better understanding of the subductionrelated Late Permian to early Triassic andesitic magmas in northern Tibet. Furthermore, TO pseudosection has revealed that the epidote was formed during high O fugacity, implying that the new formation of fluid was also of high O fugacity. The free fluid with high O fugacity moving upward triggered off the partial melting of mantle wedge to form high oxidation magmas. This implies that gold rich porphyry copper deposits occurred within Qiangtang terrane. Related Articles | Metrics

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A study of metamorphism of Sumdo eclogite in Tibet, China. 2011, 18(2): 116-126.  Abstract ( 1870 )   PDF (7625KB) ( 1451 )   A new eclogite belt, more than 100 km long and 2—3 km wide, was discovered in Sumdo in Lhasa terrain of Tibet. The studies show that the metamorphism of Sumdo eclogites has undergone three stages,i.e., the prograde episodeeclogite facies, peak eclogite facies and retrograde amphibolite facies. According to geothermobarometry of garnetomphacitephengiterutile, the pT estimations of peak metamorphic stage are 760—800 ℃，33—39 GPa, which implies that the Sumdo eclogites may have undergone UHP metamorphism. The pT paths are characterized by the clockwise hairpinlike shape, which indicates that the Sumdo eclogites have undergone fast subduction and exhumation. The discovery of Sumdo eclogites suggests that there may be a new suture zone in the Lhasa terrain, which would be very important for understanding the tectonic evolution of the Lhasa terrain and the PaleoTethys. Related Articles | Metrics

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Zircon SHRIMP UPb ages, Hf isotopic features and their geological significance of the Greater Himalayan Crystalline Complex augen gneiss in Gyirong Area, south Tibet. 2011, 18(2): 127-139.  Abstract ( 2798 )   PDF (2427KB) ( 1379 )   The augen gneiss in the Gyirong Area of south Tibet belongs to the Greater Himalayan Crystalline Complex. It consists of quartz, plagioclase, Kfeldspar, biotite and minor muscovite. Zircons of the augen gneiss have corerim structures with inherited cores and magmatic rims indicated by concentric oscillatory zoning. The zircon rims gave a weighted mean age of 4989±44 Ma, hinting that the protoliths of the gneiss was early Paleozoic granite. The εHf ranges between -136 and -46 with a weighted mean value of -83±095. It implies that the source of granite came from crust, possibly resulted from partial melting of the crust in the northernmost margin of the India Craton. The zircon SHRIMP UPb ages,  combined with the published geochronological data, demonstrate that the Himalaya is a composite orogenic belt, which underwent an early Paleozoic orogenesis. The early Paleozoic Himalaya was an Andeantype orogen after the Gondwana assemblying, which resulted from the subduction of the protoTethys ocean beneath the India Plate, rather than a PanAfrican orogen that was formed by the continentcontinent collision during the Gondwana assembly. Related Articles | Metrics

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Zrinrutile thermometry in HP/UHT granulite in the Bashiwake area of the South Altun and its geological implications. 2011, 18(2): 140-150.  Abstract ( 1830 )   PDF (3406KB) ( 1096 )   The trace element content in rutile was analyzed by both electron microprobe (EMP) and laser ablation inductively coupled plasma mass spectrometry (LAICPMS) for HP granulite in the Bashiwake area of the South Altun HPUHP metamorphic belt. Results indicate that Zr content in rutile from HP granulite measured by EMP coincides with these measured by LAICPMS within experimental error. Zrinrutile thermometry of Thomkins et al. (2007) yields temperatures that agree with previous results by traditional thermometry calibrations， and thus it is more suitable for temperature estimation for HP granulite in Bashiwake area， whereas the other two calibrations developed by Zack et al. (2004) and Watson et al. (2006) give systematically higher or lower temperatures. Calculated Zrinrutile temperatures in fresh HP granulite range from 890 ℃ to 962 ℃ at 20 GPa， representing the peak metamorphic temperature of high pressure granulite. Zrinrutile temperatures in retrogressed HP granulite yielded temperatures between 764 ℃ and 822 ℃. These results further show that HP granulites in the Bashiwake area of the South Altun HPUHP metamorphic belt experienced peak conditions at ultrahigh temperature and high pressure， followed by medium temperature granulite facies conditions related to retrogression. Related Articles | Metrics

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Rodingite from oceanic lithology of Shaliuhe terrane in North Qaidam UHPM belt and its geological implication 2011, 18(2): 151-157.  Abstract ( 2099 )   PDF (1775KB) ( 1155 )   Rodingite, coexisting with serpentinized harzburgite, was found in the Shaliuhe ophiolite sequence, North Qaidam UHPM belt. It is mainly composed of grossular, dioposide, chlorite, carbonate and minor prehnite, zoisite. Rodingite is a typical product of oceanfloor metamorphism. The Shaliuhe rodingite is the second evidence for the oceanic subduction in North Qaidam UHPM belt. Related Articles | Metrics

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New data on the chronology of eclogite and associated rock from Guanpo Area, North Qinling orogeny and its constraint on nature of North Qinling HPUHP eclogite terrane. 2011, 18(2): 158-169.  Abstract ( 2547 )   PDF (1667KB) ( 1404 )   Based on the investigation of petrography and zircon CL imaging, LAICPMS trace elements and UThPb isotope analyses were carried out on zircon grains of UHP eclogite and associated garnet amphibolite from Guanpo area, the North Qinling orogeny. Zircon LAICPMS dating yields metamorphic age of (502±11)Ma, protolith age of>(657±18)Ma for the eclogite, and protolith age of (791±6)Ma, metamorphic age of (487—503)Ma and amphibolite facies retrograde metamorphic age of (366±4)Ma for the garnet amphibolite. Geochemical studies show that the garnet amphibolite from the Guanpo area have characteristics of low Si (SiO249.16%—50.78%) and high Ti (TiO2 ranging from 2.28% to 2.83%), rich in LREE, LILE, most HFSE and without any depletion of Nb and Ta, showing the feature of within plate basalts (WPB). These geochemical characteristics are the same as those of the adjacent UHP eclogite in this area. Combined the geochemical data with the field occurrence, petrographic features and chronological results, it suggests that the garnet amphibolite resulted from the recrystallization of the UHP eclogite under amphibolte facies during exhumation. Therefore, the ages of (502±11)Ma, (791±6)Ma and (366±4)Ma obtained from eclogite and garnet amphibolite should represent the metamorphic, the protolith and the retrograde metamorphic age of Qinling UHP eclogite, respectively. The metamorphic age of (502±11)Ma of eclogite is consistent with that of its country rock pelitic gneiss (（507±38）Ma)and UHP felsic gneiss in Songshugou area (485—514 Ma)of the North Qinling. These nearly identical metamorphic ages suggest that the Guanpo eclogite and their host gneisses as well as the Songshugou UHP felsic gneiss underwent the same metamorphism during the Early Paleozoic. Additionally, the metamorphic age of (502±11)Ma is nearly 300 Ma younger than that of the protolith age of (791±6)Ma for eclogite； these age data together with the WPB characters of the protolith of eclogite suggest that the North Qinling UHP eclogite may not be the product of Paleozoic oceanic crust deep subduction but the Neoproterozoic oceanic crust or rift igneous rocks subducted with country rocks into deep mantle during the Paleozoic. Related Articles | Metrics

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Geological characteristics and tectonic significance of Paleozoic intrusive rocks in Western Tianshan of Xinjiang Province. 2011, 18(2): 170-179.  Abstract ( 2709 )   PDF (2070KB) ( 3551 )    Western Tianshan orogenic belt of Xinjiang is in the central and southern part of ancient Asian tectonic region where magmatic activities were very intense in the Paleozoic and intrusive rocks extensively developed. This paper sums up the spacetime distribution, geological characteristics and geochemical features of Paleozoic intrusive rocks in Western Tianshan, and they are considered as the products of the South and North Tianshan oceanic basin evolution. In the Early Carboniferous and before, Paleozoic intrusive rocks are zonally distributed in the mountains and they are mainly a set of calcalkaline intrusive rocks related to convergence and subduction of oceanic basins. In the Late Carboniferous and after, Paleozoic intrusive rocks presents planar distribution, and they are mainly a set of Alrich granite related to collision and a set of postorogenic Krich granite. Related Articles | Metrics

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Petrologic and geochemical research of Xiaohalajunshan gabbro in Southwest Tianshan Mts., Xinjiang. 2011, 18(2): 180-190.  Abstract ( 2604 )   PDF (2858KB) ( 1192 )   Xiaohalajunshan gabbro, consisting of hornblende gabbro and magnetitebearing gabbro, intruded into Carboniferous volcanicsedimentary rocks in southeast Tekesi city. The hornblende gabrro comprises clinopyroxene, hornblende and plagioclase. The magnetitebearing gabbro mainly comprises plagioclase and magnetite. All these rocks contain magmatic calcite, which is in equilibrium with plagioclase, clinopyroxene and/or biotite. The studied gabbro samples show enrichments of light rare earth elements and depletions of heavy rare earth elements without obvious Eu anomalies. These rocks are also enriched in large ion lithophile elements and depleted in high strength field elements. Petrology and geochemical characteristics suggest that the magma was produced by the partial melting of carbonated mantle in very low degree. Related Articles | Metrics

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Petrogenesis of Karamay plutons in the west Junggar： Constraints from geochronology， petrology and geochemistry. 2011, 18(2): 180-191.  Abstract ( 1940 )   PDF (5816KB) ( 2541 )   The Karamay plutons from the west Junggar are mainly made up of dioritic to granitic rocks. UPb dating of zircons from a quartz diorite suggests that the pluton was emplaced at 3155±28 Ma (late Carboniferous)，based on the SHRIMP method. The Karamay plutons show geochemical features reminiscent of arc magmas: Narich，A/CNK=057-084，enrichment of LREE((La/Yb)N=47-61) and LILEs with minor negative Eu anomalies (δEu=076-091)，depletion of HFSEs such as Nb and Ta，and being typical of Itype granitoids. Linear trends of SiO2 versus other major elements were observed，suggesting that mixing between mantlederived magma and crustal melts and/or fractional crystallization have played an important role in forming different rock types of the plutons. Microgranular mafic enclaves (MMEs) are common in the plutons. Compositional and textural disequilibrium of plagioclase and hornblende in the MMEs and host rocks was observed，suggesting a mechanical and chemical exchange between the two rock units and also a mixing origin for the MMEs. The host rocks and MMEs are similar in terms of Nd and Sr isotopic compositions，with ISr(t)=070352-070388，εNd(t)=69-74，typical of that of depleted mantle. Isotopic modeling suggests no signs of old continental crust beneath the west Junggar. The petrogenesis of the Karamay plutons can be summarized as below: postcollisional lithospheric extension caused the upwelling of asthenosphere and partial fusion of lithospheric mantle，producing voluminous basaltic magmas，which underplated in，and thus caused the partial melting of the juvenile lower crust(Paleozoic arc series and oceanic crust) and resulted in the formation of granitic magmas;subsequent mixing between the granitic and basaltic magmas gave birth to a hybrid magma，from which the Karamay plutons were formed through significant fractionation of calcic plagioclase and ferromagnesian phases such as pyroxene and hornblende. Related Articles | Metrics

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Petrology and SHRIMP zircon ages of intrusive body Ⅲ in Baogutu Area, Xinjiang. 2011, 18(2): 212-222.  Abstract ( 2345 )   PDF (3097KB) ( 2322 )   The intrusive body Ⅲ in the Baogutu area is composed of two separate parts (Ⅲ1 in north and Ⅲ2 in south). The lithologic units in Ⅲ1 are granodiorite and quartz diorite and those in Ⅲ2 are quartz diorite, diorite and a small amount of pyroxene diorite. A fresh quartz diorite sample from the central part of Ⅲ1 was dated to 313±3 Ma by zircon SHRIMP. Intrusive body Ⅰ, Ⅱ, Ⅲ1, Ⅳ and Ⅴ were formed during 310325 Ma. The copper mineralization occurred in 316310 Ma. Related Articles | Metrics

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A study of contact metamorphism of Late Paleozoic strata in the Middle of Inner Mongolia. 2011, 18(2): 223-230.  Abstract ( 1802 )   PDF (1550KB) ( 1139 )   Some of the Late Paleozoic strata in the middle Inner Mongolia developed zeoliteand/or prehnitepumpellyite facies contact metamorphism due to the intrusion of Mesozoic magmas. Studies of clay minerals, illite crystallinity and vitrinite reflectance of typical profile indicate that (1) illite and chlorite are the dominant clay minerals, interlayered illite and smectite (I/S) or smectite are present in very few samples, and in most cases interlayered illite and chlorite (I/C) are rare; that (2) illite crystallinity ranges from 0.22 to 0.40; and that (3) the vitrinite reflectance values (Ro) are in the range of 1.5—4.0. The results suggest that only very lowgrade contact metamorphism rather than largescale greenschist facies regional metamorphism developed in the limited areas affected by the magmatic intrusion, and this lowgrade metamorphism affected only sedimentary strata and oil resources formed before the Late Permian. Related Articles | Metrics

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A study of the connection of faults and metallogenic belts between Erenhot Region， China and South Gobi， Mongolia. 2011, 18(2): 231-241.  Abstract ( 1938 )   PDF (5957KB) ( 1278 )    Since many porphyry copper deposits have been discovered in South Gobi of Mongolia， recently a series of research and exploration work has been done in the ErenhotDongwuqi region. However， no breakthrough has been made in the exploration of copper deposits. Hence， it is of great significance for exploration to determine whether the ErenhotDongwuqi region and South Gobi belong to one polymetallic metallogenic belt or not. According to the comparative study of aeromagnetic characteristics， remote sensing images and some bouguer gravity anomaly in some areas， here we demonstrate that ErenhotDongwuqi region and South Gobi form different and independent tectonic units. The northwestern border of ErenhotDongwuqi region is the NEstrike ZongbayinToudaoqiaoElunchun fault. The South Gobi polymetallic metallogenic belt controlled by the Zongbayin fault extends in the direction of northeast， which  not belongs to the same metallogenic belt as ErenhotDongwuqi region. Therefore， ErenhotDongwuqi region should have unique metallogenic regularity and conditions. Related Articles | Metrics

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Development of Li Siguangs thought on oil search as discussed from the course of petroleum exploration in the Ordos Basin. 2011, 18(2): 242-257.  Abstract ( 2476 )   PDF (3660KB) ( 1366 )   The Ordos Basin is being constructed into Chinas second Daqing oil field—“ShaanMeng Daqing”—based on the large Sulige gas field. The petroleum exploration in the Ordos Basin has experienced a complex and tortuous course. People have had doubts about petroleum prospects in this basin many times. No major advances had been made until a Triassic oil field was found in Qingyang in 1970 after nearly 30 years of probe. In 1988 the Lower Paleozoic Jingbian gas field was found and in 2000 the Su No. 6 well revealed the large Sugeli gas field; then great breakthroughs in petroleum exploration in the basin have been made step by step. This paper deals with the exploration course in Ordos and the relationship between the guiding ideas in various stages of the exploration and breakthroughs in the oil field, as well as their key links. The basic experience put forward is as follows: (1) we should continuously sum up and deepen our knowledge in practice, overcome the trammels of the idea of search for structural oil/gas reservoirs and understand the importance of lithologic oil/gas reservoirs; (2) at first Li Siguang emphasized the determination of the work direction on the basis of an allround study of the basin but then he emphasized search for oil/gas in areas without structures in the central part of the basin, implying that his analysis of the oil/gas reservoirforming conditions in the Ordos Basin overstepped the view of structural expulsion of oil and structural accumulation of oil and that he had got the new idea of looking for lithologic oil/gas reservoirs; and (3) three techniques should be stressed, i.e.，the highresolution seismic technique used to outline channel sand bodies, fracture pressure technique and advance water injection used for lowpermeability oil/gas reservoirs and the “five plus one” management model. The paper also proposes the work direction of expanding resources in the future. Related Articles | Metrics

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Multiplestage evolution of mantle plume and its control of mineralization：  Taking ZhangjiakouXuanhua mantle branch as an example. 2011, 18(2): 258-267.  Abstract ( 4309 )   PDF (2050KB) ( 5008 )   ZhangjiakouXuanhua area is a gold, silver and polymetallic mineralization concentration area in Hebei. It can be divided into a gold deposit concentration area around the XuanhuaChongliChicheng magmaticmetamorphic core complex and a silver and polymetallic deposit distribution area in surrounding cover rocks. Studies indicate that the metallogenetic material of gold, silver and polymetallic deposits mainly came from deep Earth. In the process of multiplestage evolution of mantle plume, they moved up and concentrated as deposits in the favorable structures of mantle branch. This study takes the Dongping gold deposit in the core of mantle branch, the Huangtuliang gold deposit in detachment zone and the Wanquansi silvergold deposit in surrounding fault depression basin as examples to make analyses on their metallogenesis. It is considered that, horizontally from core to surroundings and vertically from deep to top, there exists zoning character of Au→Ag→PbZn deposits in ZhangjiakouXuanhua mantle branch, which has been confirmed by mining engineering and drilling engineering in many mines. This is significant for ore prospecting in deep. So it is proved that there is a great potential in the deep of ZhangjiakouXuanhua mantle branch. This approach may also  be applied to other mantle branch area with similar geological condition. Related Articles | Metrics

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Research on diagenetic environmental changes of deep reservoir in Minfeng Area, Dongying Sag. 2011, 18(2): 268-276.  Abstract ( 2106 )   PDF (5253KB) ( 1005 )   Based on thinsection observation, Raman analysis of minerals, rock and clay minerals analysis, and fluid inclusion analysis, and combined with burial history analysis, this paper discusses the diagenetic characteristics of deep reservoir in Minfeng Area, Dongying Sag. It was recognized that the deep reservoir had abundant diagenetic appearances and the characteristics of superimposed multiple diagenetic environments, such as acidic environment, alkaline environment, and alternating acidic and alkaline environments. The fluid inclusions represented different diagenetic environments were used to analyze the changes of diagenetic environments. The results showed that the depth ranging from 3000 m to 3200 m was a very important interval of alkaline fluid action. From shallow to deep, the diagenetic environments of deep reservoir in Mingfeng Area underwent a process from alkaline or alkalescent (shallower than 1750 m) to acidic (1750-3200 m), to alternating of acidic and alkaline (3200-4000 m), to alkaline (4000-5000m), and to alkalescent or weak acidic (deeper than 5000 m). The process of diagenetic environmental changes resulted in current complex diagenetic appearances. Depth and temperature were the macro dominant factors for the diagenetic environmental changes, but not the absolute control factors. The alternation of fluid property in local area might have caused the changes of diagenetic environments more directly. Related Articles | Metrics

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Discussion on the extension law of structural fracture in sandmud interbed formation. 2011, 18(2): 277-283.  Abstract ( 1745 )   PDF (1525KB) ( 4938 )    In contrast to the present backdrop of fracture prediction mainly centering on the aperture, density and development of fracture with semiquantitative and quantitative methods and less on extension law and penetrability, the paper, taking X oilfield as an example, adopts the stress field simulation to establish relationship between stress field and fracture parameters, then to research the extension law and penetrability of sandstone fractures into mudstone. Simulated result shows that the sandstone with thin thickness is easy to produce fractures, but the thickness of sandstone has little impact on extension distance and porosity of fractures in mudstone, which even can be neglected; that is to say, whatever the thickness of sandstone above or below the mudstone is, the porosity of fractures stretching into mudstone changes little, at about 0.38%. At the same time, fracture extension length at point of contact between sandstone and mudstone falls between 15—2 m; as mudstone thickness reaches 4 m, the fracture just can not penetrate through the mudstone， here the mudstone is thick enough to act as an effective cap formation. Related Articles | Metrics

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Research on seismic sedimentology of He3 Formation in Biyang Sag. 2011, 18(2): 284-293.  Abstract ( 2148 )   PDF (5482KB) ( 893 )   Braided delta, slump turbidite fans and nearshore subaqueous fan are developed in the sand group III of He3 Formation in depression area of Biyang Sag. Restricted by the research techniques and methods, the distribution of these facies is unclear yet, especially that of the slump turbidite fans. Under the guidance of the theory of seismic sedimentology, and by using the technique of enhancing the resolution and phase shift, the 3D poststack seismic data were adjusted to the optimal states. Then by using the technique of strata slicing, the sliced cubes were made to display the distribution of sedimentary microfacies and reflect the evolutionary history. Finally, on the basis of comprehensive analysis of core, lithology and welllogging data, the sandbodies of the typical slices were interpreted subtly, and the distribution of sedimentary facies was predicted. This study provides a reliable approach in exploration of latent traps. Related Articles | Metrics

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Multiple sets of information synthesized to describe fractures of volcanic reservoir： Taking volcanic reservoir of the Member 1 of Yingcheng Formation in Xudong Area of Xushen Gas Field as an example. 2011, 18(2): 294-303.  Abstract ( 2228 )   PDF (3767KB) ( 1409 )    The volcanic reservoir fractures of the Member 1 of Yingcheng Formation in Xudong Area of Xushen Gas Field are divided according to their origins into tectonic fractures, condensation contracted fractures, exploded fractures, corrosion fractures, stitched fractures and weathering fractures. Synthesizing multiple sets of information from cores, microsections and FMI logging data and using seismic variance and ant tracking technology, we described the characteristics of all kinds of fractures in detail. The results indicated that fractures developed along Xuzhong Faults and Xudong Faults in NS direction in macroscopic view. And many fractures developed along EW direction in microcosmic view at the same time. The analysis of genetic mechanisms of fractures suggested that the fractures of volcanic reservoir of the Member 1 of Yingcheng in Xudong Area of Xushen Gas Field were affected by tectonic processes, volcanic lithology, volcanic bodies, volcanic lithofacies and diagenesis, among which tectonic processes and diagenesis played the leading role. Related Articles | Metrics

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Highprecision measurement of lithium isotopes using MCICPMS. 2011, 18(2): 304-314.  Abstract ( 1867 )   PDF (1529KB) ( 1050 )    A highyield lithium separation technique for rock samples has been established together with precise Li isotope analysis by MCICPMS. The solutions with different concentration of lithium element standard reference materials and single element standard samples of potassium, calcium, sodium, magnesium and iron were used to evaluate the analytical methods applied. Three separate stages of ionexchange chromatography were carried out using organic cation exchange resin (AG 50WX8,200—400 mesh). Lithium was enriched in different eluants for the different stages. 28 mol/L HCl, 015 mol/L HCl and 05 mol/L HCl in 30% ethanol were used for the different three stages. Two kinds of columns which are made of polypropylene for the first and second stages and quartz for the third stage were used, which is different from those used abroad. Total reagent volume for the entire chemical process was reduced to 38 mL for the rock samples and the recovery is more than 976%. The precision of this technique is conservatively estimated to be ±060‰—094‰ (2σ population), which is similar to the precision of other methods used abroad. The δ7Li value (7Li/6Li relative to the IRMM016 standard) determined for AGV2 is 513‰. The δ7Li values determined for BHVO2 (7Li/6Li relative to the IRMM016 standard) and IRMM016 (7Li/6Li relative to the LSVEC standard) are 408‰ and 0038‰, respectively. In addition, the results for the same kinds of samples analyzed by my lab are the same as those by isotope lab of Maryland University. All the analytical results are consistent with those reported by others. Moreover, the δ7Li value (7Li/6Li relative to the IRMM016 standard) determined for substandard NKT1 nephelinite obtained from the United States Geological Survey (USGS) is 871‰ and its precision is ±046‰. According to the experiments, it is concluded that this proposed procedure is a suitable method for determining the lithium isotopic composition of natural samples. Related Articles | Metrics

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The application of radon measurement method and highdensity electrical method in the exploration of the fault location. 2011, 18(2): 315-320.  Abstract ( 1762 )   PDF (1156KB) ( 1144 )   This paper discusses how to apply the radon measurement and highdensity electrical method as an integrated geophysical method to fault location. Through the test of fault location in the same and different lithology, and   comparing the results with the geological sections， it is concluded that the two geophysical methods of fault location are feasible. Finally， the experimental results are applied in engineering geology to infer fault and satisfactory results have been obtained. Related Articles | Metrics

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Characteristics of sulfide minerals， genetic type  and metallogenic epoch of the Caijiaping leadzinc deposit， 2011, 18(2): 321-338.  Abstract ( 2358 )   PDF (5340KB) ( 1422 )   The Caijiaping leadzinc deposit, located in north Wuyi area, Jiangxi Province, is a newfound mediumsized deposit. Sandstones of the Jurassic Shuibei Formation（J1s） and Zhangping Formation(J2z) are wall rocks of orebodies. The leadzinc orebodies usually occur in the crush belts beside the fractures, and often exist in boundary surfaces of rhyolite porphyries and sandstones. On the basis of field work, by means of observation of microscope and analysis of electron probe, this paper researches main sulfide minerals of the deposit at great length. Oreforming process is preliminarily divided into sedimentary mineralization period, magmatic hydrothermal period and hypergene period. Magmatic hydrothermal period consists of mediumhigh temperature pyritesphalerite stage, mediumlow temperature quartzpolymetallic sulfide stage and carbonate stage. Mediumhigh temperature pyritesphalerite stage is characterized by medium and largegrained hypautomorphicautomorphic pyrite+christophite, which can reflect higher formation temperature. The alteration of this stage is epidotization. Mediumlow temperature quartzpolymetallic sulfide stage, which is a major metallogenetic stage, has a major ore mineral association consisting of pyrite+sphalerite+chalcopyrite+galena. The major alteration of this stage is silification, chloritization and sericitization. The data of electron probe indicate that following the mineralization, sulfur was more and more deficient. According to the trace element geochemistry of galena and sphalerite, mineralization mainly resulted from magmatic hydrothermal process superimposed on layercontrolling action and sedimentationmetamorphism, which indicates that the mineralization of this deposit is polygenous. The bedding and incision orebodies we found in the field imply that the origin and the type of the leadzinc orebodies are not single. Sulfur isotopic analysis indicates that sulfur of the Caijiaping deposit is mainly magmatic sulfur in origin, possibly mixed with mantlederived magma, and the sulfur isotope was approximately on balance when metallogenic materials were precipitated. The geologic thermometers of chlorite, cadmium and sulfur isotope show that the temperature of mineralization is 2923—4906 ℃, which is mediumhigh temperature and is consistent with the result of the trace element analysis. Additionally, it is found that the fault F4 cuts orebodies in the field, and the potash feldspar selected from felsic vein within F4 yields a 40Ar/39Ar age of 120±4 Ma, implying the mineralization of the Caijiaping deposit should occur before （120±4） Ma. Combining with previous studies, the authors speculate the age of mineralization was 120138 Ma, corresponding with extensional mineralization stage of the South China area. According to the researches above, the Caijiaping leadzinc deposit, a medium temperature hydrothermal deposit, mainly resulted from magmatic hydrothermal process. In addition, layercontrolling action and sedimentationmetamorphism also controlled the formation of the deposit. Related Articles | Metrics

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The structure and composition of ferrihydrite and its environmental geochemical behaviors. 2011, 18(2): 339-347.  Abstract ( 4077 )   PDF (1195KB) ( 4050 )   Ferrihydrite occurs widely in nature, such as in water body, soils, sediments and organisms. It has large surface area and high surface activity, controlling and influencing the morphology, migration and transformation of some contaminations and nutrient elements in the environment. It is also the important precursor form of many crystalloid iron (hydr)oxides. However, environmental geochemical behaviors of ferrihydrite and its implications for environments are not fully understood, which mainly presents in following aspects: (1)Ferrihydrite is always confused with amorphous iron (hydr)oxides or hydrate iron oxides and it is difficult to obtain experimental ferrihydrite samples in the environment and make quantitative analyses for them, whose contents are always underestimated. (2)Ferrihydrite is poorly crystallized, which makes the determination of its structure more difficult. The distribution, composition, structure and nature are not yet very clear. The XRD diffraction lines of ferrihydrite are wide, few and weak in intensity. Based on the number of diffraction lines, ferrihydrite can be classified into 2LFh with poorer crystallization and 6LFh with better crystallization. At present, generally accepted chemical formula of ferrihydrite is Fe5HO8·4H2O. However, lots of experiments have shown that H2O is not necessarily in its structure and it is easy to be replaced by external adsorbed matters. Some people think that ferrihydrite has a dualistic structure, i.e.with both octahedral coordination of its central Fe and tetrahedral coordination of surface Fe, which needs to be proved. Recently, structure study with use of PDF (Pair Distribution Function) shows that ideal ferrihydrite structure contents 20% tetrahedral coordination Fe and 80% octahedral coordination Fe and the chemical formula is Fe10O14(OH)2. However, quite a few researchers are doubtful of this new structure model. In this paper, the distribution, composition, structure and environmental geochemical behaviors of ferrihydrite are reviewed. The prospective research areas on ferrihydrite are also proposed. Related Articles | Metrics