REE Geochemistry of Precambrian Metamorphic Rocks in Wutaishan Region

The metasedimentary-volcanic series of the Wutai and Hutuo groups experienced regional metamorphism and thus turned into moderate-to low-grade metamorphic rocks.REE abundances and REE distribution patterns in the Shizui and Taihuai Subgroup metasedimentary-volcanic rocks are typical of the Archean,whereas the Gaofan Subgroup and the Hutuo Group show post-Archean REE geochemical char-acteristics.Five types of REE distribution pattern are distinguished:(1)rightward inclined smooth curves with little REE anomaly(Eu/Eu*=0.73-0.95) and heavy REE depletion (e.g.the Late Archean metasedimentary rocks);(2)rightward inclined V-shaped curves with sharp Eu anoma-ly (Eu/Eu*=0.48-0.76) and slightly higher ∑REE (e.g.the post-Archean metasedimentary rocks);(3) rightward inclined steep curves with negative Eu anomaly(Eu/Eu*=0.73-0.76) and the lowest ∑REE (e.g.the post-Archean dolomites);(4)rightward inclined,nearly smooth curves with both positive Eu anomaly and unremarkable positive Eu anomaly(Eu/Eu*=0.95-1.25)(e.g.the meta-basic volcanic rocks);and (5) rightward inclined curves with Eu anomaly(Eu/Eu*=1.09-1.19)and heavy REE depletion(e.g.the meta-acid volcanic rocks).Strata of the two groups are considered to have been formed in an island-arc belt-an instable continental petrogenetic environment.     

The Distribution of Trace Elements in Granitoids in the Nanling Region of China

Granitoids are widely spread in the Nanling Region of China.Four rockbodies in the region the been studied for their REE,Rb,Sr,Ba and Sc distributions.The four rockbodies occurred in different locations and are characterized as being different in age and type.The rock types are presented as follows:Qinghu monzonite,Guangxi;Fuxi granodiorite,Guangdong;Jiufeng monzonitic granite,Hunan;Zudong K-feldspar granite,Jiangxi.From the major and trace element distributions in these granitoids it is clearly shown that Rb/Sr ratios in the rocks tend to increase with increasing SiO2 content and differentiation index(DI),but LREE/HREE,La/Yb and K/Rb ratios tend to decrease,suggesting a correlation between trace element distribution and major element composition for the granitoids.The distribution characteristics of trace elements in each of the rockbodies are described in detail.From the comparative analysis of the Qinghu monzonite and Fuxi granodiorite it is evidenced that the REE distribution is closely related to the sequence of crystallization for the minerals,and also to the petrochemical types of these granitoids in addition to their crystal chemistry.     

Rare—Earth Element Geochemistry of Elogites from the Ultra—High Pressure Metamorphic Belt in Central China

Based on their REE contents and REE patterns,eclogites from the ultra-high pressure metamorphic belt in central China may be roughly divided into xis types including LREE-rich.LREE-rich positive Eu anomaly,LREE-rich negative Eu anomaly,REE pattern-smooth,MREE-rich and HREE-rich.The LREE_rich,LREE-rich positive Eu anomaly and LREE-rich negative Eu anomaly types of eclogites are dominant .REE types of eclogites in different areas can be compared and the REE feactures of the same REE type of eclogites in different areas are similar.The results of reconstruction of the primary rocks show that the primary rocks of eclogites possibly are dominated by continental tholeiites which are the product of partial melting of relatively fertile mantle and the rocks of tholeiite crystallization-differentiation.There is perfect evolution relationship among the primary rocks of the LREE-rich, LREE-rich positive Eu anomaly and LREE-rich negative Eu anomaly types of eclogites and among those of the REE pattern smooth and MREE-rich types of eclogites,the former three types were deried from continental settings and the latter two from nearly oceanic settings.Meanwhile,it is concluded that the mantle sources of primary rocks of the eclogites are inhomogeneous and the primary rocks of eclogites in this area appear to have undergone varying degree of crustal contamination.     

REE Geochemical Indicatrices of Li—F Granite Liquid Segregation

The results of 118 REE analyses of Li-F granites from South China and other countries indicate that there are three variation types of REE pattern curves with different evolution trends from early to late stages of Li-F granite complex of from lower to upper petrofacies of the Li-F granite body;(1) the decreasing,(2) the increasing,and (3) the saltatory variation types.The first variation type is called the positive evolution type,attributed to crystallization differentiation.The second is called the reversion evolution type.which represents liquid segreation dominated by vapor-liquid distillation.The third is called the saltatory variation type,which is formed from liquid segregation dominated by immiscibilty,Therefore,the indicatices of liquid segregation dominated by immiscibility are the saltatory variation type of REE pattern evolution and the separation of the main evolution trend lines either from the sub-evolution trend lines or from the composition points of Li-F granites in the diagrams of REE-(La-Yb)N and La/Sm-La,The indicatrices of liquid segregation dominated by vapor-liquid fractional distillation are the reverstion evolution type of REE pattern curves and the main evolution trend lines of Li-F granites directing to the upper right-hand on the REE-La/Yb)N and La/Sm-La diagrams.     

REE Geochemical Characteristics of Apatite,Sphene and Zircon from Alkaline Rocks

The accessory minerals apatite and sphene are the main carriers of REE in alkaline rocks.Their chondrite-normalized REE patterns decline sharply to the right as those of the host rocks,In the patterns an obvious negative Eu anomaly and a positive Ce anomaly can be seen in apatite and sphene,respectively.Zircon from alkaline rocks is different in REE pattern,I,e,. a nearly symmetric“V“-shaped pattern with a maximum negative Eu anomaly.Compared with the equivalents from granites,apatite,sphene and zircon from alkaline rocks are all characterized by higher (La/Yb)N ratio and less Eu depletion,As to the relative contents of REE in minerals,apatite,sphene and zircon are enriched in LREE,MREE and HREE respectively,depending on their crystallochemical properties.     

The Geochemical and Zircon Trace Elements Characteristics of A-type Granitoids in Boziguoer,Baicheng County,Xinjiang

The Boziguoer A-type granitoids in Baicheng County,Xinjiang,belong to the northern margin of the Tarim platform as well as the neighboring EW-oriented alkaline intrusive rocks.The rocks comprise an aegirine or arfvedsonite quartz alkali feldspar syenite,an aegirine or arfvedsonite alkali feldspar granite,and a biotite alkali feldspar syenite.The major rock-forming minerals are albite,K-feldspar,quartz,arfvedsonite,aegirine,and siderophyllite.The accessory minerals are mainly zircon,pyrochlore,thorite,fluorite,monazite,bastnaesite,xenotime,and astrophyllite.The chemical composition of the alkaline granitoids show that SiO2 varies from 64.55％ to 72.29％ with a mean value of 67.32％,Na2O＋K2O is high （9.85％-11.87％） with a mean of 11.14％,K2O is 2.39％-5.47％ （mean =4.73％）,the K2O/Na2O ratios are 0.31-0.96,Al2O3 ranges from 12.58％ to 15.44％,and total FeOT is between 2.35％ and 5.65％.CaO,MgO,MnO,and TiO2 are low.The REE content is high and the total SREE is （263-1219） ppm （mean =776 ppm）,showing LREE enrichment and HREE depletion with strong negative Eu anomalies.In addition,the chondrite-normalized REE patterns of the alkaline granitoids belong to the ＂seagull＂ pattern of the right-type.The Zr content is （113-1246） ppm （mean =594 ppm）,Zr＋Nb＋Ce＋Y is between （478-2203） ppm with a mean of 1362 ppm.Furthermore,the alkaline granitoids have high HFSE （Ga,Nb,Ta,Zr,and Hf） content and low LILE （Ba,K,and Sr） content.The Nb/Ta ratio varies from 7.23 to 32.59 （mean =16.59） and the Zr/Hf ratio is 16.69-58.04 （mean =36.80）.The zircons are depleted in LREE and enriched in HREE.The chondrite-normalized REE patterns of the zircons are of the ＂seagull＂ pattern of the left-inclined type with strong negative Eu anomaly and without a Ce anomaly.The Boziguoer A-type granitoids share similar features with A1-type granites.The average temperature of the granitic magma was estimated at 832-839℃.The Boziguoer A-type granitoids show crust-mantle mixing and may have formed in an anorogenic intraplate tectonic setting under high-temperature,anhydrous,and low oxygen fugacity conditions.     

Geochemistry, Zircon U–Pb Dating and Hf Isotopic Characteristics of Neoproterozoic Granitoids in the Yaganbuyang Area, Altyn Tagh, NW China

The South Altyn continental block is an important geological unit of the Altyn Tagh orogenic belt, in which numerous Neoproterozoic granitoids crop out. Granitoids are mainly located in the Paxialayidang–Yaganbuyang area and can provide indispensable information on the dynamics of Rodinia supercontinent aggregation during the Neoproterozoic. Therefore, the study of granitoids can help us understand the formation and evolutionary history of the Altyn Tagh orogenic belt. In this work, we investigated the Yaganbuyang granitic pluton through petrography, geochemistry, zircon U–Pb chronology, and Hf isotope approaches. We obtained the following conclusions:(1) Yaganbuyang granitoids mainly consist of two-mica granite and granodiorite. Geochemical data suggested that these granitoids are peraluminous calc–alkaline or high-K calc–alkaline granite types. Zircon U–Pb data yielded ages of 939±7.1 Ma for granodiorite and ~954 Ma for granitoids, respectively.(2) The εHf(t) values of two–mica granite and granodiorite are in the range of-3.93 to +5.30 and-8.64 to +5.19, respectively. The Hf model ages(TDM2) of two-mica granite and granodiorite range from 1.59–.05 Ga and 1.62–2.35 Ga, respectively, indicating that the parental magma of these materials is derived from ancient crust with a portion of juvenile crust.(3) Granitoids formed in a collisional orogen setting, which may be a response to Rodinia supercontinent convergence during the Neoproterozoic.     

我国台湾浅滩海底沉积物稀土元素地球化学

REE geochemistry of sea-floor sediments from the Taiwan Shallow has been studied.∑ REE of 76 samples from the Taiwan Shallow was determined by chemical extraetion-spectrophotometry, of which 7 samples were analyzed for 15 rare earth elements by XRF. The analytical results show that ,∑ REE of the samples increases gradually with a decrease in grain size. The average REE contents are 60 ppm for coarse-grained sediments,82 ppm for medium-coarse-grained ones, 145 ppm for fine-grained ones, and 211 ppm for silt. The REE content of the samples is controlled mainly by the grain size and mineralogical composition of sediments. The ehondrite-normalized REE distribution patterns in sediments from the Taiwan Shallow are similar to those in granites in Fujian Province, China, which show a negative Eu anomaly and a positive Ce anomaly. The distribution curves are negative in slope. It is considered that based on REE geochemical characteristics, mineralogical composition and related oceanographic information, the Taiwan Shallow sediments seem to be largely residual deposits of ancient littoral facies from various types of continental rocks during Pleistocene glacial period. These sediments have also been reworked by modern sedimentatoion.     

Geochemical Characteristics of Granitoids in the Eastern Sector of the Northern Tianshan Mountains in Xinjiang

The granitioids in question are located in the geosynclinal fold belt of the Northern Tianshan Mountains.The magmas are intruded into a Carboniferous marine volcanic-sedimentary rock series. forming a contempo-raneous. intermediate-basic to acid. composite intrusion. With a whole-rock Rb-Sr isochron age of 315.7 Ma. itis considered to be of middle Heicynian age. The granitoids have a SiO_2 content of 48-78%, a calc-alkali indexof 60 and silica-alkali indices ρ=2.2-2.4 and σ=1.5-2. From basic to acid compositions, the total REE con-tent increases from 38 to 143 ppm. δEu ranges from 0.47 to 0.86 and the Eu anomalies are negative. Thenormalized curves of REE of various rock types are very similar. These coupled with the characteristics of traceelement geochemistry show that the intrusion is an island arc-continental margin, calc-alkaline one. Theδ~(18)O values range from 5.8 to 8.9‰ and the ~(87)Sr/~(86)Sr initial ratio is 0.705. The materials of the intrusion arecomposed of a mixture of the magmas at the top of the upper mantle and in the lower crust, This indicates thatthe rocks might be consanguineous. differentiated and evolved products and possess the characteristics of Ⅰtype granites.     

Rare Earth Element and Trace Element Features of Gold-bearing Pyrite in the Jinshan Gold Deposit, Jiangxi Province

<正>Jinshan gold deposit is located in northeastern Jiangxi,South China,which is related to the ductile shear zone.It has a gold reserve of more than 200 tons,with 80%of gold occurring in pyrite. The LREE of gold-bearing pyrite is as higher as 171.664 ppm on average,with relatively higher light rare earth elements(LREE;159.556 ppm) and lower HREE(12.108 ppm).TheΣLREE/ΣHREE ratio is 12.612 and(La/Yb)_N is 11.765.These indicate that pyrite is rich in LREE.The(La/Sm)_N ratio is 3.758 and that of(Gd/Yb)_N is 1.695.These are obvious LREE fractionations.The rare earth element(REE) distribution patterns show obvious Eu anomaly with averageδEu values of 0.664,andδCe anomalies of 1.044.REE characteristics are similar to those of wall rocks(regional metamorphic rocks),but different from those of the Dexing granodiorite porphyry and Damaoshan biotite granite.These features indicate that the ore-forming materials in the Jinshan gold deposit derived from the wall rocks, and the ore-forming fluids derived from metamorphic water.The Co/Ni ratio(average value 0.38) of pyrite suggests that the Jinshan gold deposit formed under a medium-low temperature.It is inferred from the values of high-field strength elements,LREE,Hf/Sm,Nb/La,and Th/La of the pyrite that the ore-forming fluids of the Jinshan gold deposit derived from metamorphic water with ClF.     

华南花岗岩的稀土元素分布模式

REE. determinations were conducted f or their fractional contents on granitoid rocks in South China, which differ in age, composition and origin by means of chemical-X-ray fluorescence spectrometry and instruments! neutron activation analysis technique. Granites under consideration can be divided into three major categories in terms of normalized REE distribution pattern of ehondrite and δEu value: 1. REE distribution pattern is approximately expressed by a smooth eurve,with unremarkable negative Eu anomaly and δEu value greater than 0.5; 2. REE distribution pattern exhibits a moderately remarkable negative Eu anomaly with δEu value in the range of 0.3---0.4; 3. REE distribution pattern gives a greatly remarkable .negative Eu anomaly,with δEu value being less than 0.2. The granites belonging to the first category are mostly older in age and closely connected with geanitization in origin, those to the second category show a number of evidences for their magmatic origin anti those to the third category are especially distinquishable for their characteristic features of later maginatio differentiation and replacement.     

REE Geochemistry of the Lead—Zinc Ores from the Jinding Lead—Zinc Deposit,Lanping,Yunnan

Nineteen volcanic and magmatic rock samples were collectecd from the Jinding leadzinc deposit and its surrounding areas in Yunnan.The ICP and AES analyses,feferred to the previous results,show that the metal minerals and altered rocks in the Jinding lead-zinc deposit display a decreasing trend of ∑REE from the early to late stages of mineralization,and similarities in REE distribution patterns,indicating that the ore fluids are characterized by high LREE enrichment,markedly negative δCe anomaly and slight δEu anomaly.These REE distribution paterns exhibit striking similarities to those of the Pliocene trachyte in the study area,both of which are similar in ∑REE,LREE/HREE ratio,δEu and δCe.The ore fluids besides the basin fluids in the deposit are also closely related to those associated with Pliocene trachyte magmas.     

Geochemistry and Genesis of the Sodium-Charnockitic Gneisses, Eastern Hebei Province, China

High in sodium and low in potassium (Na_2O/ K_2O>1), the charnockitic gneiss series in theSantunying- Taipingzhai area, eastern Hebei province, consists of hypersthene- quartz- diorite,hypersthene-granodiorite and hypersthene-plagioclase-granite. Geological, petrological and large ion lithophileelement(LILE), high field strength element (HFSE) and REE geochemical studies suggest that themedium-coarse-grained hypersthene-granodiorite is the product of crystallization of anatectic magmas of thesame composition. Under granulite facies conditions, the equilibrium crystallization differentiation of themagmas yielded the early crystallization phase-high-SiO_2, LILE-depleted, low-∑REE, positive Eu anomalyand REE- saturated hypersthene- plagioclase- granite. The residual phase, coarse- grained to pegmatitichypersthene- granodiorite, is marked by low SiO_2, LILE-enrichment, high ∑REE and REE-undersaturation.These rocks and hypersthene-quartz-diorite enclaves constitute the sodium-charnockitic gneiss series in easternHebei province. Model calculation for trace elements in the granitoids was applied. On the basis of a systematicgeological study, the equation for calculation was chosen, the source magma was determined and the partitioncoefficients were obtained. The resulting curves are entirely consistent with those observed in the patterns of ac-tual rocks. The study indicates that whole-rock REE patterns can not be used directly in the comparison of thesources and genesis of granitoids.     

Regional Tectonic Transformation in East Kunlun Orogenic Belt in Early Paleozoic: Constraints from the Geochronology and Geochemistry of Helegangnaren Alkali-feldspar Granite

The Helegangnaren feldspar granite exposed in the eastern part of East Kunlun, is characterized by high concentrations of SiO2 and alkaline, low abundances of Fe, Mg and Ca, metaluminous-weak peraluminous. Trace elements analysis shows that the granite is depleted extremely in Ba, Sr and Eu, and rich in some large-ion lithophile elements and high field strength elements. Besides, the granite has high Ga contents, the values of 104(Ga/Al) vary from 2.50 to 2.77, which is mainly greater than the lower limit of A-type granites (2.6), and is higher than the I- and S-type granites’ average (2.1 and 2.28, respectively). Rare earth element (REE) is characterized by relatively high fractionations of light REE (LREE) and heavy REE (HREE) (LREE/HREE=9.3–13.60, (La/Yb)N=10.92–18.02), pronounced negative Eu anomalies (δEu=0.08–0.13), and exhibits right-dipping gull pattern. Major elements, rare elements and trace elements features show the granite is ascribed to A-type granite and A2 subtype in tectonic genetic type. They are plotted into post-collision or within-plate area in a variety of tectonic discriminations. Geological and geochemical data comprehensively suggest that the granite is formed in a post-collision extensive tectonic setting. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) zircon U-Pb dating yields a weighted mean age of 425?Ma, belonging to Middle Silurian, which is similar to the age of the post-collision geological events in the region. The differences of magmatic rocks in formation age, rocks assemblage and rocks series systematically indicate that the regional tectonic stress regime in the East Kunlun orogenic belt experienced a major transformation from compress to extension in Middle Silurianin, and the Helegangnaren feldspar granite intruded in the early stage of tectonic transformation.     

Experimental Study on the Effects of Organic Acids on the Dissolution of REE in the Weathering Crust of Granite

The results of REE leached by some organic acids with various concentrations and water/rock ratios for different durations from a mixed samples of the weathering crust of a granite in Gonghe,Guangdong,China,showed that:1)the contents of REE leached increase with increasing concentrations of the organic acids;2) the contents of REE leached by 0.01mol/L organic acids increase with increasing water/rock ration;3) the interaction between the organic acids and the samples enhances the pH value of the medium and the contents of REE leached tend to increase with decreasing pH value;and 4) compared with those leached by ammonia sulfate,the REE leached by the organic acids are characterized by a weaker negative C e anomaly,a stronger negative Eu anomaly,and lower(La/Sm)N and (Gd/Yb)N ratios,indicating that the organic acids have made contributions to the fractionation of REE in the weathering crust.     

Discovery of the Early Paleozoic Boin Sum‐Ordor Sum Island Arc in the Hadamiao Gold Ore District,Inner Mongolia and its Significance to the Evolution of the Paleo‐Asian Ocean

Early Paleozoic granodiorite has been identified on the northern margin of the North China craton in the east section of the central-Asian orogenic belt, which was previously known as early Indosinian in age. By using the LA-ICP-MS method, the obtained zircon U-Pb age is 445.6±2.7 Ma, which represents the crystallization age of the granodiorite. The granodiorite near the east of the large-sized Bilihe gold deposit is of the tholeiite series with low potassium. It is quasi-aluminous I-type granite, enriched in sodium (Na2O/K2O=7.29-9.77) and magnesium (Mg#=0.51-0.67). The ΣREE value is relatively low, obvious differentiation is shown between LREE and HREE and within LREE, and the Eu anomaly is low and negative (δEu=0.74-0.91). In the primitive-mantle normalized spider diagrams of trace elements, the granodiorite is relatively rich in LREE and LILE (Ba, Sr, Th), and strongly depleted in HFSE (Nb, Ta, Ti and P), which shows features of subduction zone components (SZC). In the discrimination diagrams of tectonic settings of granite for Rb vs. (Nb+Y), Rb vs. (Ya+Ta), La/Nb vs. Ba/Nb and Th/Nb vs. Ba/Nb, the granodiorite exhibits typical features of island arc granite. The normalized values of K and Rb are extremely low, while the values of Sr and Eu are very high, which are similar to those of island arc magma that has undergone metasomatism of fluid from the oceanic crust. The granodiorite is relatively depleted in εHf(t) (5.1-7.1) and low in εHf(t) model ages (1089-921 Ma). In the εHf(t) vs. age (T) diagram, the distribution area of the granodiorite is accordant with the field of the Xing’anling-Mongolia orogenic belt, which indicates that the magmatic sources are mainly the mixture of partial melting of wedged mantle subjected to metasomatism of fluid from the oceanic crust and young substance from the crust. The granodiorite is similar to the felsic arc magma in the Damao Banner, Bate Obon, Boin Sum and Ordor Sum regions, and they altogether constitute an early Paleozoic accretionary island arc magmatic belt on the northern margin of the North China craton. A number of early Paleozoic zircons trapped in late Paleozoic intrusions in the Hadamiao and Bilihe regions and the discovery of the early Paleozoic island arc magmatic belt near the east of the Bilihe gold deposit suggest that the late Paleozoic volcanic-intrusive rocks have a basement of early Paleozoic arc accretionary complexes. This is just the evident of the multiphase subduction and accretion model of the Paleo-Asian Ocean (PAO). Paleozoic structures and magmas on the northern margin of the North China craton are shown from south to north as the late Paleozoic Andes-type arc magmatic belt in the Inner Mongolia plateau, the Chifeng-Bayan Obo fault and the late and early Paleozoic arc magmatic belt, which shows that after the early Paleozoic arc-continent collisional orogeny and at the stage of the late Paleozoic accretionary orogeny, the PAO plate was likely to continuously pulsate and underthrust beneath the early Paleozoic island arc accretionary complex belt and its front, i.e. the North China craton. During the early Paleozoic collisional orogeny, the PAO plate might not experience large-scale breakup or delamination. The characteristics of the early Paleozoic island arc accretionary complex basement have a significant control on late Paleozoic diagenesis and metallization in the Hadamiao and Bilihe gold concentrated areas.     

REE,Fe and Mn Contents of Calcites and Their Prospecting Signi¬ficance for the Banqi Carlin-type Gold Deposit in Southwestern ChinaEI北大核心CSCD

The Banqi gold deposit is one of the important Carlin-type gold deposits in the southwestern Guizhou Carlin-type gold district, and it is the first deposit of the type found in China. As the major gangue mineral in this deposit, calcite can be divided into four types based on their formation time: pre-mineralization, main metallogenic epoch, late stage of mineralization, and post-mineralization. All types of calcites have distinct features such as field occurrence, physical typomorphic characteristics and trace elements characteristics. The pre-mineralization calcites have the highest REE contents (∑REE=29.70-40.10 μg/g), which are characterized by the most enriched LREE (LREE/ HREE=1.96-3.03), a distinct positive Eu anomalies (δEu=3.83-5.02), and almost no Ce anomalies (δCe=1.02-1.05). The calcites of the main metallogenic epoch have relatively low REE contents (∑REE=10.76-15.53 μg/g), and are characterized by the most enriched HREE (LREE/HREE=0.11-0.23), almost no Eu (δEu=0.73-1.20) and Ce anomalies (δCe=0.88-1.25). The calcites of the late stage of mineralization have the lowest REE contents (∑REE=2.82-4.34 μg/g), and are characterized by enriched HREE (LREE/HREE=0.26-0.86), weakly negative Eu (δEu=0.67-0.83) and Ce anomalies (δCe=0.55-0.81), which are similar to those of the calcites of the main metallogenic epoch. The post-minera¬lization calcites have relatively low REE contents (∑REE=6.92-10.91 μg/g), characterized by enriched LREE (LREE/HREE=1.83-2.34), weakly negative Eu anomalies (δEu=0.72-0.74) and moderately negative Ce anomalies (δCe=0.41-0.50). In addition, the Fe and Mn contents of ore-forming stage calcites are obviously higher than that of the calcites unrelated to mineralization, and negatively correlated with LREE/HREE ratio, which illustrates that the HREE concentrations of calcites are controlled by the incorporation of Fe and Mn. Thus, it will provide an important exploration indicator for the Yunnan-Guizhou-Guangxi Carlin-type gold deposits through the study of typomorphic characteristics of calcite. © 2018, Science Press. All right reserved.     

Petrology and Geochemistry of the Huangshan Granitic Intrusion in Anhui Province, Southeast China: Implications for Petrogenesis and Geodynamics

<正>The Huangshan granitic intrusion in Anhui province,SE China,is tectonically located at the southeastern boundary of the Yangtze Block.Based on the contact relation and the petrography,the Huangshan granitic intrusion can be divided into four stages,from early to late,medium-grained monzogranite,coarse-grained porphyric granite,fine-medium grained porphyric granite,and finecoarse grained granite.All rocks from the Huangshan granitic intrusion display similar petrological and geochemical characteristics,i.e.relatively high SiO_2(75%) and alkali(7.85%-8.59%),low CaO (1%),high Fe-number(FeO_T/(MgO+FeO_T) = 0.93-0.97) and A/CNK(atomic Al/(Ca+Na+K))=1.04- 1.19.They are also enriched in rare earth elements(REE,except for Eu,with a total REE contents ranging from 116 ppm to 421 ppm),high strength field elements such as Zr,Hf,Nb,but depleted in Ba,Sr and Ni.The 10 000×Ga/Al ratios are higher than 2.6,which are consistent with the A-type granitoids.Based on the classification diagrams proposed by Eby,the Huangshan granite can be classified into the A2 group,which is usually believed to be formed under an extensional tectonic setting.Their Nd isotopic compositions suggest that the primary magmas of the Huangshan granite are predominantly derived from the Proterozoic andesitic rocks in the region,and this conclusion is also supported by REE modeling.The systemic investigations on the geochemistry of the Huangshan granitic intrusion can provide significant implications for the understanding of the petrogenesis and the geodynamic regime of southeastern China during the Late-Mesozoic.     

Post-Orogenic Granites in Pingwu Region, Northwest Sichuan: Evidence for North China Block and Yangtze Block Collision during Triassic

The Nanyili (南一里), Laohegou (老河沟), and Shaiziyan (筛子岩) granitic intrusions are located in the southern margin of the Bikou (碧口) block in Pingwu (平武) area, Northwest Sichuan (四川). The petrography and geochemical characteristics of the granitic intrusions as well as their source and tectonic settings are reported and discussed in this article. The Laohegou and Shaiziyan granites are with high SiO2 (69.89 wt.%-73.05 wt.%) and Al2O3 contents, and A/CNK=1.04-1.12. They are typi-cal strongly peraluminous granites, with supersaturation in Al and Si. The abundance of ∑REE varies in the range of (33.13-89.12)×106. The rocks show an LREE enrichment pattern and obvious Eu nega-tive anomaly. The trace element geochemistry is characterized evidently by a negative anomaly of Ta, Nb, Ti, etc. and a positive anomaly of Rb, Ba, Sr, etc.. Zircons of the Nanyili granite have higher Th/U ratios, and their CL images have internal oscillatory zoning, suggesting that the zircons of the samples are igneous in origin. The LA ICP-MS zircon U-Pb isotopic concordia diagram yields an age of 223.1±2.6 Ma (MSWD=1.4), which indicates that the granodiorite intrusions formed in the early Late Triassic. The Nanyili, Laohegou, and Shaiziyan granites have the characteristics of post-eollisional granites and are regarded as post-orogenic granites. Thus, the granite intrusions are interpreted as syn-collisional granites that resulted from the crustal thickening caused by the collisions between the North China plate and the Yangtze plate during the Indosinian. The granitic intrusions formed in a transitional environment from syn- (compres-slonal environment) to post-collision (extensionalenvironment).     

Evolution of the Mesozoic Granites in the Xiong''''ershan-Waifangshan Region,Western Henan Province,China,and Its Tectonic Implications

Based on the new data of isotopic ages and geochemical analyses, three types of Mesozoic granites have been identified for the Xiong'ershan-Waifangshan region in western Henan Province: high-Ba-SrⅠ-type granite emplaced in the early stage (～160 Ma),Ⅰ-type granite in the middle stage (～130 Ma) and anorogenic A-type granite in the late stage (～115 Ma). Geochemical characteristics of the high-Ba-SrⅠ-type granite suggest that it may have been generated from the thickened lower crust by partial melting with primary residues of amphibole and garnet. Gradual increase of negative Eu anomaly and Sr content variations reflect progressive shallowing of the source regions of these granites from the early to late stage. New 40Ar/39Ar plateau ages of the early-stage Wuzhangshan granite (156.0±1.1 Ma, amphibole) and middle-stage Heyu granite (131.8±0.7 Ma, biotite) are indistinguishable from their SHRIMP U-Pb ages previous published, indicating a rapid uplift and erosion in this region. The representative anorogenic A-type granite, Taishanmiao pluton, was emplaced at～115 Ma. The evolution of the granites in this region reveals a tectonic regime change from post-collisional to anorogenic between～160 Ma and～115 Ma. The genesis of the early- and middle-stageⅠ-type granites could be linked to delamination of subducted lithosphere of the Qiniing orogenic belt, while the late-stage A-type granites represent the onset of extension and the end of orogenic process. In fact, along the Qiniing -Dabie-Sulu belt, the Mesozoic granitoids in western Henan, Dabieshan and Jiaodong regions are comparable on the basis of these temporal evolutionary stages and their initial 87Sr/86Sr ratios, which may suggest a similar geodynamic process related to the collision between the North China and Yangtze cratons.