Abstract:This paper reports a syenogranite from Zhaiwa area in Xiong'er Mountain on the southern margin of North China Craton. The syenogranite yielded a SHRIMP zircon U-Pb age of 217.7±3.6 Ma and MSWD=1.6, showing Mesozoic. The syenogranite is rich in alkaline and Al, but low in Mg and Fe. The trace elements are characterized by obvious depletion of Ba, Sr, P and Ti but relative enrichment of U, Th, Zr and Hf. The REE of Zhaiwa syenogranite has obvious tetrad effect. The geochemical features of the Zhaiwa syenogranite are different from those of the alkali-rich intrusive rocks in east Qinling and the early Mesozoic granitoids in north Qinling tectonic belt and south Qinling tectonic belt. The Zhaiwa syenogranite is a high-fractional Ⅰ-type granite. The tectonic setting for the Zhaiwa syenogranite is a post-collision or post-orogenic tectonic setting.

Abstract:The Shenquan sodic volcanic rocks, outcropped in the east of Lizhuang village in Tancheng County, Shandong Province, are tectonically located in the southern parts of the Yishu deep fault zone. The volcanic rocks comprise a shield volcano, and lithologically consist mainly of trachyandensite. Zircon LA-ICP-MS U-Pb dating yields an age of 96.5±1.4 Ma, which is younger than the ages of the widespread potassic rocks within the region, indicating an evolutionary trend from potassic to sodic for the Mesozoic volcanic rocks along the Yishu deep fault zone and its adjacent areas. Chemically, the Shenquan volcanic rocks have high alkali content (Na₂O+K₂O=10.34%～11.95%) and are obviously enriched in sodium (Na₂O/K₂O=1.76～3.92); they can be assigned to typical sodic volcanic rocks on the basis of various discrimination schemes. Geochemically, the rocks contain relatively high concentrations of rare earth elements (ΣREE=411.3×10^-6～456.3×10^-6), and are enriched in LREE and LILE (e. g., Rb, Ba, Th), and depleted in HFSE (e. g., Ti, Nb, Ta). They show right-oblique chondrite-normalized REE patterns and display some negative Pb anomalies in the primitive mantle-normalized trace element spidergrams. These rocks have enriched Sr-Nd isotopic compositions [I_Sr=0.706 8～0.707 7, εNd(t)=-16.66～-16.82], similar to that of the Mesozoic mafic rocks in Shandong, indicating that they were probably derived from an enriched lithospheric mantle. Based on a synthesis of geology and geochemistry, the authors hold that the mantle source of the Shenquan sodic volcanic rocks might have undergone multiple enrichment events induced by source contamination of continental crustal materials both from deep subduction of the Yangtze Craton and from lithospheric delamination of the North China Craton. During Late Cretaceous, the continued extension of Tanlu Fault induced the upwelling of asthenospheric melts which further modified the previously enriched mantle. Decompression partial melting of these multiply-modified mantle sources and further differentiation of the magmas finally generated the Shenquan sodic volcanic rocks.

Abstract:As an important part of Carboniferous volcanic rocks in eastern Tianshan Mountains, the volcanic rocks of the Dikan'er Formation have great constraints on the tectonic evolution of the Juoluotage belt. These volcanic rocks are bounded by the southern margin of Tu-Ha basin in the north and the Shaquanzi fault in the south. The major and trace elements and Sr-Nd isotopes of the volcanic rocks are discussed in this paper to constrain the petrogenesis and tectonic settings. The volcanic rocks are composed of calc-alkali basalt, andesite and rhyodacite assemblages, which are products of partial melting of garnet-spinel lherzolite mantle. The primary magma has experienced crystallization differentiation of olivine and clinopyroxene for basalt, and that of plagioclase and magnetite for andesite and rhyodacite. They are relatively enriched in large-ion-lithophile elements and light rare-earth elements, and are depleted in high-field-strength elements. The patterns of trace elements of basalt are similar to those of arc basalt, while the trace element patterns of intermediate-acid rocks are similar to those of the upper crust. Neodymium isotopic characteristics [εNd(t)=-0.14～5.69] and trace element patterns of the volcanic rocks indicate derivation from a moderately depleted mantle source which was metasomatized by subduction-related fluid and involvement of minor crustal contamination. The trace element patterns of basalt and the plots for tectonic setting suggest that the volcanic rocks were probably formed in a back-arc basin environment.

Abstract:The Himalayan orogenic belt, caused by the subduction and collision between Indian plate and Eurasian plate, is the youngest and largest currently active orogenic belt in the world. The LA-ICP-MS U-Pb zircon age of 515.5±2.3 Ma from the gneissic biotite granodiorite that intruded into the Namche Barwa complex in eastern syntaxis of the Himalayan orogenic belt provides a geological record of Pan-African tectonic-magmatic event in this area. The SiO₂ content is 66.47%～72.42%, the average of the A/CNK indexes is 1.03 (0.98～1.03), and all samples fall into the peraluminous region in the A/NK-A/CNK index diagram. The Rittmann index σ is between 1.53 and 3.08, belonging to the calc-alkaline series. Most of the samples fall into a high-K calc-alkaline series area in the SiO₂-K₂O diagram. The values of TiO₂, MgO, FeO^T, MnO and K₂O show a good linear relationship with SiO₂ content in the Harker diagrams. The chondrite-nomalized REE patterns indicate that the samples are enriched in LREE, (La/Yb)_N values are 19.1～63.8, with slightly negative Eu anomalies (δEu=0.62～0.79). Trace elements show the depletion of Ba, Nb, Ta, Sr and Z as well as the relative enrichment of Rb, Th and U. The negative εNd(t) values(-8.67～-10.57) and Nd model ages (t_DM=1.84～3.42) of the gneissic biotite granodiorite of Tanya Township indicate that this rock had an old upper crust material source. Combined with the initial ⁸⁷Sr/⁸⁶Sr ratio features, the authors hold that the source rock of the gneissic biotite granodiorite of Tanya Township was granitic magma that partially melted in a high temperature environment. From the tectonic environment discrimination diagrams, it is inferred that metaluminous-weakly peraluminous gneissic biotite granodiorite of Tanya Township was formed in the post-collisional stage characterized by the conversion from a compressional environment to an extensional. Combined with the isotope age 513 Ma,the authors consider that the Pan-African collisional orogenic movement in the eastern Himalayan syntaxis ended and started the post-collisional tectonic evolution in Early Cambrian period.

Abstract:There are two sets of basalts in Bayingou ophiolitic mélange. One is low in TiO₂ (only 0.81% to 1.00%), and its REE content shows a slight depletion of LREE in comparison with HREE. Chondrite-normalized REE patterns and primordial mantle normalized trace elements patterns show flat distribution. Nb and Ta have a slight depletion. The basalt is therefore one of the mid-ocean ridge basalts. It is tentatively considered that the basalt was formed at the early stage of ocean formation and the source area was the mid-ocean ridge basalt which had not experienced large-scale extraction phase of magma. Another kind of basalt of this area has the characteristics of a typical oceanic island basalt. The rock has high TiO₂ content(1.89%～3.14%)and rich alkalis, LILE, LREE and HFSE, and the primitive mantle normalized trace element patterns show clear positive anomalies of Nb and Ta. Trace elements have the features of EMII type OIB.

Abstract:Located between the Yangtze massif and the Cathaysian block, the Jiangnan orogenic belt is composed of a series of Pre-Sinian low-grade meta-volcaniclastic rocks. Between the Sinian and the Pre-Sinian strata, there is a regional angular unconformity. Within the Pre-Sinian strata, there are several local unconformities, whose precise ages and tectonic affinities play a significant role in understanding the tectonic evolution of the Jiangnan orogen. Unfortunately, the tectonic models of the Jiangnan orogen based on data available fail to consider these unconformities and regard the Neoproterozoic period as a continuous tectonic evolution episode. In the Guizhou-Guangxi-Hunan border area, the unconformity within the Neo-Proterozoic Qingbaikou System defines the Wuling or Sibao Movement. A growing body of high-quality in situ zircon geochronologic data has demonstrated that the Jiangnan orogen is mainly composed of Neoproterozoic geological bodies rather than Middle Proterozoic ones, and this rules out the possibility that the Wuling/Sibao Movement is of Grenville episode. Thus, precise dating of the strata below this unconformity plays a fundamental role in tectonic reconstruction of the Jiangnan orogenic belt. The Fanjingshan area in eastern Guizhou Province lies in the southwest segment of the Jiangnan orogen, where strata with variable ages are well exposed with clear structural relationships, and hence this area is an ideal area for studying tectonic evolution of the Jiangnan orogen. The Pre-Nanhua strata in the Fanjingshan area are assigned to the Fanjingshan Group consisting of seven formations. From the bottom upwards, the grain size of the sediments decreases, suggesting a complete basin sedimentary sequence. The middle segment of the Fanjingshan Group consists of numerous volcanic rocks comprising basalt, tuff, and volcaniclastic rocks. This paper reports four in-situ zircon LA-ICP-MS U-Pb dating results to precisely constrain the sedimentation time of the Fanjingshan Group. CL images reveal that the fine-grained zircons from these samples have similar internal structures. Most zircons have well-preserved sector zoning, like those derived from a mafic rock, while the zoning of some zircons has been partially destroyed probably due to late stage fluid activity. In some zircon grains, zoning is totally absent. LA-ICP-MS U-Pb analyses indicate that all the zircons without zoning have ²⁰⁶Pb/²³⁸U ages older than 1.0 Ga; on the other hand, the zircons whose zoning has been destroyed yielded unusually low ²⁰⁶Pb/²³⁸U age value down to 50 Ma. Analyses of other grains yielded accordant ²⁰⁶Pb/²³⁸U ages, showing slightly different weighted mean ages of various samples. Two volcanic samples yielded weighted mean zircon U-Pb ages of 832 Ma (MSWD=6.5, the Tongchang Formation) and 851 Ma (MSWD=1.5, the Yujiagou Formation) respectively, whereas analyses of two fine volcaniclastic samples from the Yujiagou Formation yielded weighted mean detrital zircon U-Pb ages of 849 Ma(MSWD=8.9)and 845 Ma (MSWD=1.18), respectively. These new data, along with previously published data, demonstrate that the Fanjingshan Group was deposited during the period of 850～815 Ma, which precisely constrains the timing of the Wuling/Sibao Movement, provides critical data for geological correlation, and helps understand the possible tectonic evolution of the Jiangnan orogenic belt.

Abstract:LA-ICP-MS in situ trace element analysis was performed for minerals in eclogite from Somdo. According to the results, garnet mainly contains MREE, HREE and Y, with high concentrations of Sc, V, Cr and Co; omphacite contains high concentrations of MREE, Sr, Sc, V, Cr, Co, Ni and Ti, with certain amounts of Zr and Hf; garnet, omphacite, amphibole and epidote all exhibit LREE depletion, indicating the nonexistence of metasomatism by exotic LREE-rich fluid during the retrogressive metamorphism of the eclogite, and this accounts for somewhat different trace element characteristics between eclogite here and Su-Lu UHP eclogites that are characterized by LREE enrichment. Zoning of some trace elements(e.g., Ti and Zr)demonstrates the pressure decreasing and temperature increasing closely after peak metamorphism during the turning back to the shallow position. Trace element partitioning between rock-forming minerals is controlled by the partitioning of major elements between minerals, e.g., MgO partitioning between garnet and omphacite controls the partitioning of Ni, Co, Ti, whereas CaO partitioning controls the partitioning of Sr, Y and REE. The formation and decomposition of minerals and the change of physical-chemical conditions might result in new partitioning of trace elements between minerals during retrogressive metamorphism. Amphibole formed by omphacite retrogression would not wholly inherit the trace element distribution pattern of omphacite without any diversification, as indicated by differences in their trace element distribution patterns; nevertheless, the somewhat similar specific characteristics of trace element distribution patterns between omphacite and amphibole demonstrate their certain genetic linkage. Rutile is the main bearer of HFS elements such as Ti, Nb, Ta, Zr and Hf, which strongly effects the depletion of HFS elements in coexisting epidote.

Abstract:The Ordovician sequence stratigraphic framework has been erected in this paper on the basis of the investigation of outcrop sequence stratigraphy and sedimentology along three sections in Keping area, northwest Tarim Basin. The Ordovician strata can be divided into six third-grade sequences. Correlations shows all these six sequences can be recognized in the Sishichang section, while only the lower three ones are developed in the Subashi and Tongusibulong section. Carbonate magnetic susceptibility is negatively related to the relative sea level change, while its curve can reflect the sequence boundaries and system tracts of the third-grade sequences respectively. The results obtained by the authors indicate that carbonate magnetic susceptibility can be used as a quantitative index to assist the division of stratigraphic sequence.

Abstract:The potassium-magnesium salt deposit of Khammouan Province in Laos is located in the eastern part of Khorat Basin. The main salt minerals of the deposit are halite, sylvite, carnallite and anhydrite, and the boron minerals in the deposit are of small or even trace amounts. The identification of trace boron minerals in the lower salt layer of ZK318 borehole in the deposit was studied in order to complete the mineral assemblage type. Chemical analyses show that the content of boron is related to the type of salt minerals, and that according to the distribution characteristics of boron, the lower salt layer can be divided into five layers in upward succession, i.e., halite layer→sylvite layer→carnallite layer→thin halite layer→upper sylvite layer. According to the linear relationship between the content of boron and the salinity of brine, carnallite, as the last evaporative product of halide brine, should have the highest content of boron theoretically. However, the boron value of the upper sylvite layer is up to 890.78×10^-6 which is higher than that of the carnallite layer, indicating that boron in the upper sylvite layer came not only from sea water but also from deep hydrothermal solution and that there exist small amounts of boron minerals in this layer. Preliminary XRD analytical results of bulk rock samples show that there is a small amount of boracite in the upper sylvite layer. In order to identify the type of boron minerals accurately, the authors conducted XRD analysis of insoluble substances collected through the soluble experiment of bulk rock samples. The result shows that the boron minerals in insoluble substances are mainly boracite (55%), and subordinately anorthic hilgardite-3A (15%). Hilgardite-3A belongs to trace mineral because its content is less than the detection limit of XRD (1%) so that there is no diffractive peaks in the XRD pattern of bulk rock samples. In addition, the Chinese name of anorthic hilgardite-3A is discussed in this paper. It is pointed out that the precise Chinese naming should follow the international conventions. Therefore, the name parahilgardite is cancelled and replaced by the name hilgardite-3A so as to reflect the slight difference between the mineral structures, i.e. the difference between this mineral and another anorthic polymorph 1A. This modification is consistent with the Chinese naming norms. Therefore, small amounts of boracite and trace hilgardite-3A (anorthic) exist in the potassium-magnesium salt deposit of Khammouan Province, Laos.

Abstract:Fe (Ⅲ) hydrolysis is an important process during geochemical circulation of iron, and controls the migration and redistribution of iron in water to some extent. The existing form of Fe (Ⅲ) in supernatant and the difference of Fe isotopic composition between the supernatant and the precipitate caused by Fe (Ⅲ) hydrolysis at 20℃ and 46℃ were studied in this paper. The experimental time lasted 95 days and 130 days at 20℃. At the end of this experiment, the existing form of Fe (Ⅲ) was colloid, Fe isotopic composition in different experimental periods were the same, and the difference of Fe isotopic composition between the supernatant and the precipitate (Δ⁵⁶Fe_{Fe(Ⅲ)sup-Fe(Ⅲ)pre}) was 1.15‰. The experimental time lasted 95 days at 46℃. At the end of this experiment, the existing form of Fe(Ⅲ) was aqueous, and the difference of Fe isotopic composition between the supernatant and the precipitate (Δ⁵⁶Fe_{Fe(Ⅲ)sup-Fe(Ⅲ)pre}) was 1.37‰. The instantaneous equilibrium fractionation factor (α) of Fe(Ⅲ) hydrolysis could be calculated by Rayleigh fractionation formula, and the α of 20℃ and 46℃ were 0.999 121 and 0.999 260 respectively.

Abstract:The terms of low-SiO₂ adakite (LSA, SiO₂ <60%) and high-SiO₂ adakite (HSA, SiO₂> 60%) were put forward by Martin et al. (2005). This paper does not agree with this classification, because the low-SiO₂ adakite is sanukite rather than adakite. Sanukite is a mantle source rock, whereas adakite is a crust-derived rock. Although adakite can be mixed with the mantle to form high-Mg adakite, it is still of the crust source. Crust- and mantle-derived magmas are different types of magma, so it is not proper to confuse them.

Abstract:Tooeleite is a ferric arsenite sulfate mineral only found in acid mine drainage at present, and its chemical formula is Fe₆(AsO₃)₄(SO₄)(OH)₄·4 H₂O. Few literatures have reported this mineral, and hence some important spectroscopic and mineralogical data are lacking. The authors synthesized tooeleite using temperature-constant water batch reactor, and for the first time adopted infrared and Raman spectroscopy techniques to characterize it. The result show that: the characteristic peak at FTIR of 770 cm^-1 is attributed to stretch vibration of As—O; the characteristic peaks at Raman of 663, 609, 512, 455 and 365 cm^-1 are attributed to the stretch vibration of As—OH (υ₃), asymmetric stretch vibration (υ₅), asymmetric bending vibration (υ₄) of AsO₃^3- and bending vibration of O—As—O; the incongruent dissolution occurs when pH of solution is higher than 3. The batch experiment determined for the first time the solubility product (K_sp) and the standard Gibbs free energy of the reaction, which are 10^7.7 and -3 605 kJ/mol, respectively.

Abstract:Iron cutans coated on the surface of quartz sand were synthetized at initial pH 7 and iron mole ratio R[Fe(Ⅱ)/Fe(Ⅲ)]0.1 to investigate the influence of the temperature and the aging time of the synthetic systems on the formation of iron oxides in the cutans and further providing the formation mechanism of iron cutans. The compositions and morphologies of the minerals in the synthesized cutans were determined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The results showed that when the quartz sand amount was 10 g and the aging time was 25 d, the peak intensity of goethite in XRD patterns increased successively and the crystalline shape of iron oxide in the cutans analyzed by SEM became increasingly bigger with the increase of temperature from 30℃ to 90℃. When the quartz sand amount was 10 g and the aging temperature was 60℃, the peak intensity of goethite in XRD patterns increased successively during the first 18 days, and then decreased and tended to become stable. The crystalline shape of goethite in the cutans analyzed by SEM increased during the first 18 days and reached the maximum on the 18th day, and then decreased gradually along with the increase of aging time.