Geologic, petrographic and petrochemical studies of the late Mesozoic K-rich melanocratic dykes, including lamprophyres, andesite porphyrites and dacite-porphyry in the gold field system in the Jiaodong Peninsula, Chi...Geologic, petrographic and petrochemical studies of the late Mesozoic K-rich melanocratic dykes, including lamprophyres, andesite porphyrites and dacite-porphyry in the gold field system in the Jiaodong Peninsula, China, have shown that these dykes are characterized by rich potassium and alkali but poor titanium. They belong to an ultra-high potassic, shoshonitic and high potassic calc-alkaline rock series. The parental magma has relatively high initial strontium ratios ((87Sr/86Sr),=0.70895-0.71140) and low (143Nd/144Nd)1 ratios (varying from 0.51135 to 0.51231); and its δ18Osmow, whole rock values vary from +5.8%c to +10.6%c with a mean of +7.1%c. These features suggest that the source region of the magma is an enriched mantle wedge transformed from a continental lithosphere mantle which has experienced metasomatism by mantle-derived fluids with H2O-dominated fluids that were provided during the underthrusting of an ocean crust. The initial magma was generated by low-degree partial melting of the enriched mantle in its mature stage in the back-arc spreading environment. The evolution of magmas is associated with two trends, i.e., fractional crystallization and mixing with or intensive contamination by palaeo-crust materials or metamorphic rocks. The former process is evident in the gold field system of quartz-vein type, whereas the latter is dominated in the gold field system of the altered-rock type. This conclusion is very important for more detailed study of petrogenesis and mineralization through the crust-mantle interaction (exchange) in the Mesozoic in this region.展开更多
Based on a study of Neoproterozoic carbonates in the Jilin-Liaoning-Xuzhou-Huaiyang area, especially its cyclic sequence stratigraphy and Sr isotopes, two maximum sea flooding events (at 820 Ma and 835 Ma) have been i...Based on a study of Neoproterozoic carbonates in the Jilin-Liaoning-Xuzhou-Huaiyang area, especially its cyclic sequence stratigraphy and Sr isotopes, two maximum sea flooding events (at 820 Ma and 835 Ma) have been identified. The resulting isochronous stratigraphic correlation proves that these Precambrian strata were connected between the Qingbaikou and the Nanhuan systems with a time range from 750 Ma to 850 Ma. The disappearance of microsparite carbonate and coming of a glacial stage offer important evidence for worldwide stratigraphic correlation and open a window for further correlation of the stratigraphic successions across the Sino-Korean and Yangtze Plates. A new correlation scheme is therefore provided based on our work.展开更多
Hydrothermal chimney is a product of hydrothermal activity on the seabed. Chimney samples dredged from Jade hydrothermal area in Izena depression of the Okinawa Trough, are characterized by relatively enriched light r...Hydrothermal chimney is a product of hydrothermal activity on the seabed. Chimney samples dredged from Jade hydrothermal area in Izena depression of the Okinawa Trough, are characterized by relatively enriched light rare earth elements (LREE) and strongly positive Eu anomalies. 87Sr/86Sr and 143Nd/144Nd of these samples are exactly between those of seawater and of acidic pumice, averaged at 0.708928 and 0.512292, respectively. These characteristics imply that the main source of hydrothermal sulfide at Jade area is possibly the undersurface acidic rocks. The mineralizing mechanism can be summarized as follows: Large amount of mineralized material would be leached out and LREE-enriched hydrothermal solution would be subsequently produced as a result of thermo-chemical exchange reaction between acidic volcanic rocks and heated seawater that penetrated in advance from upper water mass. The spurting out from the seabed and quickly crystallizing in the seawater of hydrothermal solution are responsible for the formation of Cu-Zn sulfide and barite-amorphous SiO2 minerals that are characterized by enriched LREE and positively strong Eu anomalies.展开更多
The combined use of Hf,Nd and Sr isotopes is more useful in understanding the supercontinent cycle than the use of only Hf isotopic data from detrital zircons.Sr and Nd seawater isotopes,although not as precise as εN...The combined use of Hf,Nd and Sr isotopes is more useful in understanding the supercontinent cycle than the use of only Hf isotopic data from detrital zircons.Sr and Nd seawater isotopes,although not as precise as εNd and εHf distributions,also record input from ocean ridge systems.Unlike detrital zircons where sources cannot be precisely located because of crustal recycling,both the location and tectonic setting often can be constrained for whole-rock Nd isotopic data.Furthermore,primary zircon sources may not reside on the same continent as derivative detrital zircons due to supercontinent breakup and assembly.Common to all of the isotopic studies are geographic sampling biases reflecting outcrop distributions,river system sampling,or geologists,and these may be responsible for most of the decorrelation observed between isotopic systems.Distributions between 3.5 and 2 Ga based on εHf median values of four detrital zircon databases as well as our compiled εNd database are noisy but uniformly distributed in time,whereas data between 2 and 1 Ga data are more tightly clustered with smaller variations.Grouped age peaks suggest that both isotopic systems are sampling similar types of orogens.Only after 1 Ga and before 3.5 Ga do we see wide variations and significant disagreement between databases,which may partially reflect variations in both the number of sample locations and the number of samples per location.External and internal orogens show similar patterns in εNd and εHfwith age suggesting that both juvenile and reworked crustal components are produced in both types of orogens with similar proportions.However,both types of orogens clearly produce more juvenile isotopic signatures in retreating mode than in advancing mode.Many secular changes in εHf and εNd distributions correlate with the supercontinent cycle.Although supercontinent breakup is correlated with short-lived decreasing εHf and εNd （≤ 100 Myr） for most supercontinents,there is no isotopic evidence for the breakup of the Paleoproterozoic supercontinent Nuna.Assembly of supercontinents by extroversion is recorded by decreasing εNd in granitoids and metasediments and decreasing εHf in zircons,attesting to the role of crustal reworking in external orogens in advancing mode.As expected,seawater Sr isotopes increase and seawater Nd isotopes decrease during supercontinent assembly by extroversion.Pangea is the only supercontinent that has a clear isotopic record of introversion assembly,during which median εNd and εHf rise rapidly for ≤ 100 Myr.Although expected to increase,radiogenic seawater Sr decreases （and seawater Nd increases） during assembly of Pangea,a feature that may be caused by juvenile input into the oceans from new ocean ridges and external orogens in retreating mode.The fact that a probable onset of plate tectonics around 3 Ga is not recorded in isotopic distributions may be due the existence of widespread felsic crust formed prior to the onset of plate tectonics in a stagnant lid tectonic regime,as supported by Nd and Hf model ages.展开更多
Cretaceous volcanism in the coastal region of southeastern China was characteristized by occurrenceof bimodal volcanics consisting of basalts and rhyolites, the geneses of which are still controversial. Based on the f...Cretaceous volcanism in the coastal region of southeastern China was characteristized by occurrenceof bimodal volcanics consisting of basalts and rhyolites, the geneses of which are still controversial. Based on the factthat their isotopic compositions are similar but the Sr content of the former is much higher than that of the latter, thispaper discusses the respective sources of the two end-member rocks, and concludes that basalts were derived fromthe subduction-related enriched upper mantle wedge and their isotopic compositions had not been affected by crustalassimilation, whereas rhyolites were formed by remelting of the old metamorphic basement, but they were mixed upwith the underplating basaltic magmas to various degrees so that their Sr isotopic compositions varied significantlyfrom the sources and tended to be homogeneous to the latter.展开更多
The Guanfang large-scale W deposit is located in the W polymetallic ore concentration area of Bozhushan in southeastern Yunnan,China.Despite extensive research,the fluid evolution process of the deposit remains ambigu...The Guanfang large-scale W deposit is located in the W polymetallic ore concentration area of Bozhushan in southeastern Yunnan,China.Despite extensive research,the fluid evolution process of the deposit remains ambiguous,leading to controversy regarding its genesis.This study conducted a detailed field geological survey,with systematic sampling of the KT6 orebody,to delineate mineralization stages.Fine mineralogy work,including the use of CL images of scheelite,in-situ LA-ICP-MS trace elements,and Sr isotopes,was carried out on diff erent generations of scheelite formed in various stages.The findings identified the evolution of fluids in the mineralization process,shedding light on the genesis of the deposit.The study revealed four mineralization stages at the Guanfang W deposit:prograde skarn stage,retrograde skarn stage,quartz-sulfide stage,and carbonate-fluorite stage.Diff erent generations of scheelite(Sch I,Sch II,Sch III)were observed in the first three stages,displaying distinct chondrite-normalized REE patterns.The REE of Sch I mainly substituted into the Ca site by REE^(3+)+□_(Ca),and there may be a similar substitution of Nb for REE,whereas it is not the main substitution method.The REE of Sch II mainly enter the scheelite lattice in the form of REE 3++Na+,and there may be a substitution of Nb for REE isomorphism.In the early stage,The REE of Sch III was mainly replaced by Nb for REE isomorphism,while in the later stage,the replacement mode of REE^(3+)+□_(Ca)coexisted with it.The Mo content in scheelite,along with the corresponding Eu anomalies in both scheelite and garnet,collectively imply that the ore-forming fluids during various mineralization stages were predominantly oxidizing,with only slight reducibility observed in Sch II.The in-situ Sr isotope ratios of scheelite concentrates ranged from 0.7093 to 0.7153,resembling those of the Bozhushan granite,indicating a relationship between W mineralization and granite.In addition,the Y/Ho ratios of scheelite from various mineralization stages exhibit a narrow range(19-31),with a pronounced correlation between the contents of Y and Ho and a similar trend in their variation.This consistency suggests that the Guanfang deposit has undergone a uniform or comparable evolutionary process,implying a stable ore-forming fluid across diff erent mineralization stages.展开更多
Tengchong Cenozoic volcanics that have record key information on the tectonic evolution and mantle features of the southeast margin of the Tibetan Plateau are of great importance because of its unique eruption history...Tengchong Cenozoic volcanics that have record key information on the tectonic evolution and mantle features of the southeast margin of the Tibetan Plateau are of great importance because of its unique eruption history spanning the entire Quaternary period. Magma origin and evolution of Tengchong Cenozoic volcanic rocks were studied on the basis of Nd-Sr-Pb isotope and major and trace element data from different eruptions in the Ma＇anshan area. Different samples within one eruption show relative identical lithologies, chemical and isotopic compositions. However, the geochemical features for the five eruptions are distinct from each other. These volcanic rocks show low Mg# values （〈45）, moderate to high fractionation of LREEs and HREEs, and enrichment of Pb and Ba and depletion of Nb. Tengchong Cenozoic volcanic rocks were derived from an enriched mantle based on Nd-Sr-Pb isotopic studies. And lines of evidence show that crustal contamination should be involved before the eruption of different periods of Tengchong Cenozoic volcanic rocks. Older subducted components may be responsible for adakite recycling at various stages of evolution, which results in the origin of the enriched mantle source magma accounting for the isotopic features of Tengchong Cenozoic volcanic rocks. Segregated primitive magma pulsating injected into magma chamber, fractional crystallized and contaminated with crust component. Finally, magmas with distinct chemical and isotopic compositions for each eruption formed. The extension of the northeast segment of the Yingjiang tectonic belt triggered the pulsating eruption of the Cenozoic volcanics in the Tengchong area.展开更多
Tho Gudui geothermal field records the highest temperature at equivalent borehole depths among the lainland hydrothermal systems in China's Mainland.Located about 150 km southeast of Lhasa City,the capital of Tibe...Tho Gudui geothermal field records the highest temperature at equivalent borehole depths among the lainland hydrothermal systems in China's Mainland.Located about 150 km southeast of Lhasa City,the capital of Tibet,the Gudui geothermal field belongs to the Sangri-Cuona rift belt,also known as the Sangri-Cuona geothermal belt,and is representative of the non-volcanic geothermal systems in the Himalayas.In this study,oxygen-18 and deuterium isotope compositions as well as 87Sr/86Sr ratios of water samples collected from the Gudui geothermal field were characterized to understand the origin and mixing processes of the geothermal fluids at Gudui.Hydrogen and oxygen isotope plots show both,deep and shallow reservoirs in the Gudui geothermal field.Deep geothermal fluids are the mixing product of magmatic and infiltrating snow-melt water.Calculations show that the magma fluid component of the deep geothermal fluids account for about 21.10%-24.04%;magma fluids lay also be a contributing source of lithium.The linear relationship of the 87Sr/86Sr isotopic ratio versus the 1/Sr plot indicates that shallow geothermal fluids form from the mixing of deep geothermal fluids with cold groundwater.Using a binary mixing model with deep geothermal fluid and cold groundwater as two end-members,the nixing ratios of the latter in most surface hot springs samples were calculated to be between 5% and 10%.Combined with basic geological characteristics,hydrogen and oxygen isotope characteristics,strontium concentration,87Sr/(86)Sr ratios,and the binary mixing model,we infer the 6 th-Class Reservoirs Evolution Conceptual Model(6-CRECM) for the Gudui geothermal system.This model represents an idealized summary of the characteristics of the Gudui geothermal field based on our comprehensive understanding of the origin and mixing processes of the geothermal fluid in Gudui.This study may aid in identifying the geothermal and geochemical origin of the Gudui high-temperature hydrothermal systems in remote Tibet of China,whose potential for geothermal development and utilization is enormous and untapped.展开更多
The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has bee...The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has been widely studied by geologists because of its porphyry-related Pb-Ag-Au polymetallic deposit and geotectonic location, the material sources of this belt are still debate. Whole-rock analyses show that these rocks have high total alkali contents(3.73–11.08 wt%), and their aluminum saturation index(ASI) values widely vary from 0.82 to 3.07, which comprise a metaluminous-peraluminous magma series. These rocks are characterized by high K(K2 O/Na2 O>1) and low Ti and Mg contents; enrichment in large-ion lithophile elements, such as Rb, Ba, K and light rare earth elements; and depletion in high field strength elements, such as Ta, Nb, P, and Ti. These rocks exhibit moderate Eu(Eu/Eu*=0.86–1.04) and Ce(Ce/Ce*=0.63–0.96) anomalies. Their(87 Sr/86 Sr)i, εNd(t), zircon εHf(t) and δ18 O values range from 0.70839 to 0.71013, from-10.16 to-12.45, from-19.6 to-5.8, and from 5.69‰ to 8.54‰, respectively, and their Nd and Hf two-stage model ages(TDM2) are 1.67–1.86 Ga and 1.27–2.02 Ga, respectively. These data reflect the primary partial melting of Paleoproterozoic to Mesoproterozoic lower crust with minor residual continental lithospheric mantle and supracrustal metasediments. The lithosphere was likely thickened along the southeastern margin of the Tibetan Plateau following the Indian-Asian continentcontinent collision(65–41 Ma). During the post-collision phase(36–16 Ma), the transition from a compressional to extensional setting triggered the convective removal of the over-thickened CLM beneath the Yangtze craton, which led to the upwelling of asthenospheric materials. This process created alkali-rich and high-K magma through the partial melting of the thickened lower crust. Magma that carried Cu-Au-Pb-Ag minerals was emplaced by strike-slip motion along the E-to W-or ENE-to WSWtrending tectonically weak zone, finally forming an alkaline porphyry Cu-Au-Pb-Ag polymetallic deposit.展开更多
Shadong deposit is the first large-scale tungsten deposit found in the East Tianshan orogenic belt, and the geologic characteristics of the deposit indicate that the deeply concealed granite body is ge- netically rela...Shadong deposit is the first large-scale tungsten deposit found in the East Tianshan orogenic belt, and the geologic characteristics of the deposit indicate that the deeply concealed granite body is ge- netically related with the mineralization. The LA-ICPMS U-Pb age of zircons from the Shadong concealed granite obtained in this research is 239±2.0 Ma, belonging to the Middle Triassic. The whole rock samples are metaiuminous to slightly peraluminous （A/CNK=0.95-1.02） with low contents of SiO2 （64.0 wt.%-68.5 wt.%） and low K2O/Na2O ratios （0.73-0.96）. The samples reveal enrichment of K, Rb, Th and depletion of Nb, Ta, P, Ti and have a negative slope from La to Lu （LaN/YbN=16.29-36.8） with weak negative Eu anom- aly （Eu/Eu＊= 0.71-0.82）. Initial ^87Sr/^86Sr ratios of whole rock range of 0.706 59-0.707 75, eNd（t） values range from -1.77 to -2.53 and εnf（t） values of zircon are between 2.54 and 4.90. The lithogeochemistry and Sr-Nd-Hf isotopic characteristics revealed that the concealed granite in Shadong tungsten deposit is I-type granite, and occurs in an intraplate tectonic setting. The magma mixing during intraplating of mantle de- rived magma intruding into the crust in Indosinian Period is the major formation mechanism of the granite. Of which, the proportion of mantle derived magma ranges from 58% to 60%, and the crustal materials are mainly the metamorphic basement of Xingxingxia Group of Mesoproterozoic Changcheng System, which may orovide the main source of ore forming metals of Shadong tungsten deposit.展开更多
High-purity N2 was used to increase the mobile phase flow rate during ion purification of ion-exchange resin. This was performed to improve the efficiency of isotope separation and puri- fication, and to meet the effi...High-purity N2 was used to increase the mobile phase flow rate during ion purification of ion-exchange resin. This was performed to improve the efficiency of isotope separation and puri- fication, and to meet the efficiency requirements of rapid multiple-collector-inductively coupled plasma mass spectrometry （MC-ICPMS） analysis. For Cu isotope separation, our results indicated that at a gas flow rate 〉60 mL/min, the separation chromatographic peaks broadened and the re-covery rate decreased to 〈99.2%. On the other hand, no significant change in the Cu peaks was ob- served at a gas flow rate of 20 mL/min and the recovery rate was determined to be 〉99.9%. The Cu isotope ratio, measured by the standard-sample bracketing method, agreed with reference data within a±2 SD error range. The separation time was reduced from the traditional 10 h （without N2） to 4 h （with N2）, indicating that the efficiency was more than doubled. Moreover, Sr and Nd isotope separation in AGV-2 （US Geological Survey andesite standard sample） accelerated with a 20 mL/min gas flow, demonstrating that with the passage of N2, the purified liquid comprised Rb/Sr and Sm/Nd ratios of 〈0.000 049 and 〈0.000 001 5, respectively. This indicated an effective separation of Rb from Sr and Sm from Nd. MC-ICPMS could therefore be applied to accurately determine Sr and Nd isotope ratios. The results afforded were consistent with the reference data within a±2 SD error range and the total separation time was shortened from 2 d to 〈10 h.展开更多
Trace elemental associations and Sr-Nd isotopic compositions are of important to recognition of biogenic material from mixed marine sediments. The foraminifera shell from the Okinawa Trough strongly enriches Sr,P,Mn a...Trace elemental associations and Sr-Nd isotopic compositions are of important to recognition of biogenic material from mixed marine sediments. The foraminifera shell from the Okinawa Trough strongly enriches Sr,P,Mn and Ba, enriches Li,U,Th,Sc,Co,Cu,Pb,Zn,Cr,Rb,Y,Sb and light rare earth elements,slightly enriches V,Ga,Zr,Nb,Cd and middle rare earth elements,is short of Mo,In,Sn,Cs,Hf,Ta,W,Ti,Bi and heavy rare earth elements. The mechanism of elemental enrichment in forminifera is the concentrations of trace elements in sea water and selective absorption of trace elements during foraminifera living, as well as the geochemical affinity between major elements and trace elements.The REE (rare earth elements)partition pattern of foraminifera shell of the Okinawa Trough shows enrichment of middle rare earth elements with slightly negative Ce anomaly,which are different from those of foraminifera of the Pacific Ocean.The Sr,Nd isotopic ratios of the Okinawa Trough foraminifera are 0 709 769 and 0 512 162,respectively, which are different not only from those of oceanic water, but also from those of river water of China's Mainland, the former is slightly higher than those of oceanic water,but much lower than those of river water;the latter is slightly lower than those of oceanic water,but higher than those of river water,demonstrating that the Okinawa Trough sea water has been influenced by river water of China's Mainland.展开更多
The Shitoukengde Ni-Cu deposit, located in the Eastern Kunlun Orogen, comprises three mafic-ultramafic complexes, with the No. I complex hosting six Ni-Cu orebodies found recently. The deposit is hosted in the small u...The Shitoukengde Ni-Cu deposit, located in the Eastern Kunlun Orogen, comprises three mafic-ultramafic complexes, with the No. I complex hosting six Ni-Cu orebodies found recently. The deposit is hosted in the small ultramafic bodies intruding Proterozoic metamorphic rocks. Complexes at Shitoukengde contain all kinds of mafic-ultramafic rocks, and olivine websterite and pyroxene peridotite are the most important Ni-Cu-hosted rocks. Zircon U-Pb dating suggests that the Shitoukengde Ni-Cu deposit formed in late Silurian （426-422 Ma）, and their zircons have ~Hf（t） values of-9.4 to 5.9 with the older TDMm ages （0.80-1.42 Ga）. Mafic-ultramafic rocks from the No. I complex show the similar rare earth and trace element patterns, which are enriched in light rare earth elements and large ion iithophile elements （e.g., K, Rb, Th） and depleted in heavy rare earth elements and high field strength elements （e.g., Ta, Nb, Zr, Ti）. Sulfides from the deposit have the slightly higher ~34S values of 1.9-4.3%o than the mantle （0 ~ 2%o）. The major and trace element characteristics, and Sr-Nd-Pb and Hf, S isotopes indicate that their parental magmas originated from a metasomatised, asthenospheric mantle source which had previously been modified by subduction-related fluids, and experienced significant crustal contamination both in the magma chamber and during ascent triggering S oversaturation by addition of S and Si, that resulted in the deposition and enrichment of sulfides. Combined with the tectonic evolution, we suggest that the Shitoukengde Ni-Cu deposit formed in the post-collisional, extensional regime related to the subducted oceanic slab break-off after the Wanbaogou oceanic basalt plateau collaged northward to the Qaidam Block in late Silurian.展开更多
The Bancun diabase dyke and the Bali hornblende gabbro dyke in western Fujian Province were emplaced in the Early and Late Cretaceous periods, respectively; the former is designated to calc-alkaline series and the lat...The Bancun diabase dyke and the Bali hornblende gabbro dyke in western Fujian Province were emplaced in the Early and Late Cretaceous periods, respectively; the former is designated to calc-alkaline series and the latter to K-high-calc-alkaline rock series. Both the dykes are characterized by such geochemical characteristics as high Al and Na2O>K2O. As for the Bancun dyke, Al2O3=16.32%–17.54% and K2O/Na2O=0.65–0.77; as for the Bali dyke, Al2O3=16.89%–17.81% and K2O/Na2O=0.93–0.99. Both the Bancun and Bali mafic dykes are relatively enriched in LILE and LREE, but depleted in HSFE, displaying the geochemical characteristics of continental marginal arc, with high initial Sr isotopic ratios and low εNd (t) values. The (87Sr/86Sr)i ratios of the Bancun diabase dyke are within the range of 0.708556–0.70903 and their εNd (t) values vary between -6.8 and -6.3; those of the Bali hornblende dyke are within the range of 0.710726–0.710746 and their εNd (t) values are -4.7– -4.9, showing the characteristics of enriched mantle EM II. The isotope and trace element data showed that the mafic dykes have not experienced obvious crustal contamination, and metasomatism caused by subduction fluids is the main factor leading to LILE and LREE enrichments. The enriched mantle is the source region for the mafic dykes, and mixing of subduction fluid metasomatized enriched mantle and EM II-type mantle constituted the mantle source region of both the Bancun and Bali mafic dykes. Upwelling of the asthenosphere mantle provided sufficient heat energy for the generation of magmas. In accordance with the discrimination diagram of their tectonic settings as well as their trace element geochemical characteristics, it is considered that the dykes both at Bancun and Bali possess the characteristics of continental marginal arc, revealing the tectonic environment of formation of the mafic dykes, the continental dynamic background as an intraplate tensional belt in which the mafic dykes were emplaced. Meanwhile, it is also indicated that the tensional tectonic stress mechanism is responsible for the formation of the mafic dykes in western Fujian Province.展开更多
The in-situ Sr isotope determination of solid samples has the advantages of high spatial resolution and convenient and rapid sample preparation.However,due to the lack of column chemistry separation of matrix elements...The in-situ Sr isotope determination of solid samples has the advantages of high spatial resolution and convenient and rapid sample preparation.However,due to the lack of column chemistry separation of matrix elements from Sr,the interference correction(especially the isobaric interference from 87Rb on 87Sr)becomes a big issue for high precise in-situ Sr isotope analytical results.In this study,we evaluated the influence of isobaric interference systematically and adopted an improved strategy for isobaric interference correction of Rb.Specifically,as an external standard for data calibration,an in-house silicate standard(Rb-std)was fused from pure oxide powders.The new standard(Rb-std)shows very low contents of Sr(<1 ppm),Yb(<0.09 ppm)and Er(<0.05 ppm),which directly avoid the trouble of interference of doubly charged ions and isobar,when we determinate the mass fractionation factors of Rb(βRb).Our improved method can provide more accurate data than previous researches,in which the mass fractionation were calculated from an external reference material StHs6/80-G with high Rb(30.07 ppm),Sr(482 ppm),Yb(1.13 ppm)and Er(1.18 ppm).Then,these βRb from Rb-std were applied by linear interpolation to the unknown samples for correction of 87Rb on 87Sr.The analytical results of serial international reference materials(BIR-1G,BCR-2G,BHVO-2G,T1-G and ATHO-G)demonstrate that our improved method can raise the upper limit of Rb/Sr for in-situ Sr isotope determination and reduce the relative standard deviation of results.This improvement of the upper limit of Rb/Sr(<0.33)will expand not only range of microanalysis for silicate minerals,but also bulk Sr isotope determination of volcanic rock combining with rapid fusion technique.展开更多
Up to now, there were no systematic studies of geochemistry and isotopic age for the Yixian （义县） fluorite deposit, western Liaoning （辽宁） Province, China. Based on the analysis of metallogenic geological settin...Up to now, there were no systematic studies of geochemistry and isotopic age for the Yixian （义县） fluorite deposit, western Liaoning （辽宁） Province, China. Based on the analysis of metallogenic geological setting, we studied the REE, Rb-Sr and Sm-Nd isotopes. The chondrite-normalized REE patterns of fluorite are characterized by moderate LREE depletion （LREE/HREE=0.95-3.57, （La/Yb）N=0.08-2.84） and enrichment of Sr （146×10^-6-596×10^-6） and moderately positive Eu anomalies （δEu=1.10-1.34）, which are similar to those of the host Mesoproterozoic carbonate rocks. The fluorite display （^87Sr/^86Sr）t=-0.708 5, （^143Nd/^144Nd）t=-0.511 785, and δNd（t）=-12.8, which are similar to those of the host Mesoproterozoic carbonate rocks and volcanic rocks of Middle Jurassic Lanqi （蓝旗） Formation. The REE and Sr-Nd isotope geochemistry suggest that the source of the ore-forming material may be the volcanic rocks of Lanqi Formation and host carbonate rocks. The Sm-Nd isochron age of 154±14 Ma （MSWD=0.23） indicates that the Yixian fluorite mineralization nearly corresponds to the period of Lanqi Formation. Based on the integrated geological and geochemical studies, coupled with previous studies, we suggest that Yixian fluorite deposit formed in the extension setting of postcoilisional stage and may be attributed to the partial melting of ancient basaltic rocks in the lower crust induced by underplating of basic magma and to the reaction between the F-rich ore-forming fluids and the host carbonate rocks.展开更多
The Hashitu molybdenum deposit is located in the southern part of the Great Hinggan Range, NE China. Molybdenum mineralization is hosted by and genetically associated with monzogranite and porphyritic syenogranite. Sr...The Hashitu molybdenum deposit is located in the southern part of the Great Hinggan Range, NE China. Molybdenum mineralization is hosted by and genetically associated with monzogranite and porphyritic syenogranite. Sr-Nd-Pb isotopes of the intrusions show that the porphyritic syenogranite has initial ^87Sr/^86Sr ratios of 0.70418-0.70952, ENd（t） values of 1.3 to 2.1 （t=143 Ma）, ^206Pb/^204Pb ratios of 19.191-19.573, ^207Tpb/^204pb ratios of 15.551-15.572, and ^208Pb/^204Pb ratios of 38.826-39.143. The monzogranite has initial 87Sr/86Sr ratios of 0.70293-0.71305, εNd（t） values of 1.1 to 2.0 （t=-147 Ma）, ^206Pb/^204pb ratios of 19.507-20.075, ^207Pb/^204Pb ratios of 15.564-15.596, and ^208Pb/^204Pb ratios of 39.012-39.599. The calculated Nd model ages （TDM） for monzogranite and porphyritic syenogranite range from 866 to 1121 Ma and 795 to 1020 Ma, respectively. The granitic rocks in the Hashitu area have the same isotope range as granites in the southern parts of the Great Hinggan Range. The isotope composition indicates that these granites are derived from the partial melting of a juvenile lower crust originating from a depleted mantle with minor contamination by ancient continental crust. The integrating our results with published data and the Late Mesozoic regional tectonic setting of the region suggest that the granites in the Hashitu area formed in an intra-continent extensional setting, and they are related to the thinning of the thickened lithosphere and upwelling of the asthenosphere.展开更多
Zircon U-Pb dating by the LA-ICP-MS method was applied to determining the ages of different units of the Guposhan granite complex, among which the East Guposhan unit is 160.8±1.6 Ma, the West Guposhan unit is 165...Zircon U-Pb dating by the LA-ICP-MS method was applied to determining the ages of different units of the Guposhan granite complex, among which the East Guposhan unit is 160.8±1.6 Ma, the West Guposhan unit is 165.0±1.9 Ma, and the Lisong unit is 163.0±1.3 Ma in age. Much similarity in ages of the three units has thus proved that the whole Guposhan granite complex was formed in the same period of time. They were the products of large-scale granitic magmatism through crust-remelting in the first stage of the Middle Yanshanian in South China. However, the three units have differences both in petrology and in geochemistry. Besides the differences in major, trace and rare-earth elements, they are distinct in their Rb-Sr and Sm-Nd isotopic compositions. The East Guposhan unit and Lisong unit and its enclaves have a similar (87Sr/86Sr)i value of 0.7064 with an average of εNd(t)=-3.03, indicating that more mantle material was evolved in the magma derivation; whereas the West Guposhan unit has a higher (87Sr/86Sr)i value of 0.7173 but a lower εNd(t) value of -5.00, and is characterized by strong negative Eu anomalies and higher Rb/Sr ratios, suggesting that its source materials were composed of relatively old crust components and new mantle-derived components. In addition, an inherited zircon grain in the East Guposhan unit (GP-1) yielded a 206Pb/238U age of 806.4 Ma, which is similar to the ages of the Jiulin cordierite granite in northern Jiangxi and of the Yinqiao migmatic granite in Guangxi in the HZH granite zone. All this may provide new evidence for Late Proterozoic magmatism in the HZH granite zone.展开更多
China is in severe shortage of potash reserves,and the best way for breakthrough is to make potash exploration in marine salt basins.Erdos basin is so far the only Ordovician potash basin in the world.The Erdos basin ...China is in severe shortage of potash reserves,and the best way for breakthrough is to make potash exploration in marine salt basins.Erdos basin is so far the only Ordovician potash basin in the world.The Erdos basin is located west展开更多
文摘Geologic, petrographic and petrochemical studies of the late Mesozoic K-rich melanocratic dykes, including lamprophyres, andesite porphyrites and dacite-porphyry in the gold field system in the Jiaodong Peninsula, China, have shown that these dykes are characterized by rich potassium and alkali but poor titanium. They belong to an ultra-high potassic, shoshonitic and high potassic calc-alkaline rock series. The parental magma has relatively high initial strontium ratios ((87Sr/86Sr),=0.70895-0.71140) and low (143Nd/144Nd)1 ratios (varying from 0.51135 to 0.51231); and its δ18Osmow, whole rock values vary from +5.8%c to +10.6%c with a mean of +7.1%c. These features suggest that the source region of the magma is an enriched mantle wedge transformed from a continental lithosphere mantle which has experienced metasomatism by mantle-derived fluids with H2O-dominated fluids that were provided during the underthrusting of an ocean crust. The initial magma was generated by low-degree partial melting of the enriched mantle in its mature stage in the back-arc spreading environment. The evolution of magmas is associated with two trends, i.e., fractional crystallization and mixing with or intensive contamination by palaeo-crust materials or metamorphic rocks. The former process is evident in the gold field system of quartz-vein type, whereas the latter is dominated in the gold field system of the altered-rock type. This conclusion is very important for more detailed study of petrogenesis and mineralization through the crust-mantle interaction (exchange) in the Mesozoic in this region.
文摘Based on a study of Neoproterozoic carbonates in the Jilin-Liaoning-Xuzhou-Huaiyang area, especially its cyclic sequence stratigraphy and Sr isotopes, two maximum sea flooding events (at 820 Ma and 835 Ma) have been identified. The resulting isochronous stratigraphic correlation proves that these Precambrian strata were connected between the Qingbaikou and the Nanhuan systems with a time range from 750 Ma to 850 Ma. The disappearance of microsparite carbonate and coming of a glacial stage offer important evidence for worldwide stratigraphic correlation and open a window for further correlation of the stratigraphic successions across the Sino-Korean and Yangtze Plates. A new correlation scheme is therefore provided based on our work.
基金This study was supported by the National Natural Science Foundation of China under the contract No.40276024 and 49873015.
文摘Hydrothermal chimney is a product of hydrothermal activity on the seabed. Chimney samples dredged from Jade hydrothermal area in Izena depression of the Okinawa Trough, are characterized by relatively enriched light rare earth elements (LREE) and strongly positive Eu anomalies. 87Sr/86Sr and 143Nd/144Nd of these samples are exactly between those of seawater and of acidic pumice, averaged at 0.708928 and 0.512292, respectively. These characteristics imply that the main source of hydrothermal sulfide at Jade area is possibly the undersurface acidic rocks. The mineralizing mechanism can be summarized as follows: Large amount of mineralized material would be leached out and LREE-enriched hydrothermal solution would be subsequently produced as a result of thermo-chemical exchange reaction between acidic volcanic rocks and heated seawater that penetrated in advance from upper water mass. The spurting out from the seabed and quickly crystallizing in the seawater of hydrothermal solution are responsible for the formation of Cu-Zn sulfide and barite-amorphous SiO2 minerals that are characterized by enriched LREE and positively strong Eu anomalies.
文摘The combined use of Hf,Nd and Sr isotopes is more useful in understanding the supercontinent cycle than the use of only Hf isotopic data from detrital zircons.Sr and Nd seawater isotopes,although not as precise as εNd and εHf distributions,also record input from ocean ridge systems.Unlike detrital zircons where sources cannot be precisely located because of crustal recycling,both the location and tectonic setting often can be constrained for whole-rock Nd isotopic data.Furthermore,primary zircon sources may not reside on the same continent as derivative detrital zircons due to supercontinent breakup and assembly.Common to all of the isotopic studies are geographic sampling biases reflecting outcrop distributions,river system sampling,or geologists,and these may be responsible for most of the decorrelation observed between isotopic systems.Distributions between 3.5 and 2 Ga based on εHf median values of four detrital zircon databases as well as our compiled εNd database are noisy but uniformly distributed in time,whereas data between 2 and 1 Ga data are more tightly clustered with smaller variations.Grouped age peaks suggest that both isotopic systems are sampling similar types of orogens.Only after 1 Ga and before 3.5 Ga do we see wide variations and significant disagreement between databases,which may partially reflect variations in both the number of sample locations and the number of samples per location.External and internal orogens show similar patterns in εNd and εHfwith age suggesting that both juvenile and reworked crustal components are produced in both types of orogens with similar proportions.However,both types of orogens clearly produce more juvenile isotopic signatures in retreating mode than in advancing mode.Many secular changes in εHf and εNd distributions correlate with the supercontinent cycle.Although supercontinent breakup is correlated with short-lived decreasing εHf and εNd （≤ 100 Myr） for most supercontinents,there is no isotopic evidence for the breakup of the Paleoproterozoic supercontinent Nuna.Assembly of supercontinents by extroversion is recorded by decreasing εNd in granitoids and metasediments and decreasing εHf in zircons,attesting to the role of crustal reworking in external orogens in advancing mode.As expected,seawater Sr isotopes increase and seawater Nd isotopes decrease during supercontinent assembly by extroversion.Pangea is the only supercontinent that has a clear isotopic record of introversion assembly,during which median εNd and εHf rise rapidly for ≤ 100 Myr.Although expected to increase,radiogenic seawater Sr decreases （and seawater Nd increases） during assembly of Pangea,a feature that may be caused by juvenile input into the oceans from new ocean ridges and external orogens in retreating mode.The fact that a probable onset of plate tectonics around 3 Ga is not recorded in isotopic distributions may be due the existence of widespread felsic crust formed prior to the onset of plate tectonics in a stagnant lid tectonic regime,as supported by Nd and Hf model ages.
文摘Cretaceous volcanism in the coastal region of southeastern China was characteristized by occurrenceof bimodal volcanics consisting of basalts and rhyolites, the geneses of which are still controversial. Based on the factthat their isotopic compositions are similar but the Sr content of the former is much higher than that of the latter, thispaper discusses the respective sources of the two end-member rocks, and concludes that basalts were derived fromthe subduction-related enriched upper mantle wedge and their isotopic compositions had not been affected by crustalassimilation, whereas rhyolites were formed by remelting of the old metamorphic basement, but they were mixed upwith the underplating basaltic magmas to various degrees so that their Sr isotopic compositions varied significantlyfrom the sources and tended to be homogeneous to the latter.
基金suppor ted by Yunnan Major Scientific and Technological Projects(Grant No.202202AG050006)the Personnel Training Project of Kunming University of Science and Technology(Grant No.KKZ3202221022)。
文摘The Guanfang large-scale W deposit is located in the W polymetallic ore concentration area of Bozhushan in southeastern Yunnan,China.Despite extensive research,the fluid evolution process of the deposit remains ambiguous,leading to controversy regarding its genesis.This study conducted a detailed field geological survey,with systematic sampling of the KT6 orebody,to delineate mineralization stages.Fine mineralogy work,including the use of CL images of scheelite,in-situ LA-ICP-MS trace elements,and Sr isotopes,was carried out on diff erent generations of scheelite formed in various stages.The findings identified the evolution of fluids in the mineralization process,shedding light on the genesis of the deposit.The study revealed four mineralization stages at the Guanfang W deposit:prograde skarn stage,retrograde skarn stage,quartz-sulfide stage,and carbonate-fluorite stage.Diff erent generations of scheelite(Sch I,Sch II,Sch III)were observed in the first three stages,displaying distinct chondrite-normalized REE patterns.The REE of Sch I mainly substituted into the Ca site by REE^(3+)+□_(Ca),and there may be a similar substitution of Nb for REE,whereas it is not the main substitution method.The REE of Sch II mainly enter the scheelite lattice in the form of REE 3++Na+,and there may be a substitution of Nb for REE isomorphism.In the early stage,The REE of Sch III was mainly replaced by Nb for REE isomorphism,while in the later stage,the replacement mode of REE^(3+)+□_(Ca)coexisted with it.The Mo content in scheelite,along with the corresponding Eu anomalies in both scheelite and garnet,collectively imply that the ore-forming fluids during various mineralization stages were predominantly oxidizing,with only slight reducibility observed in Sch II.The in-situ Sr isotope ratios of scheelite concentrates ranged from 0.7093 to 0.7153,resembling those of the Bozhushan granite,indicating a relationship between W mineralization and granite.In addition,the Y/Ho ratios of scheelite from various mineralization stages exhibit a narrow range(19-31),with a pronounced correlation between the contents of Y and Ho and a similar trend in their variation.This consistency suggests that the Guanfang deposit has undergone a uniform or comparable evolutionary process,implying a stable ore-forming fluid across diff erent mineralization stages.
基金supported by the Chinese Ministry of Science and Technology(Sinoprobe-05-03)Doctoral Fund of Ministry of Education of China(20110022120003)+1 种基金the Fundamental Research Funds for the Central UniversitiesOpen Fund of State Key Laboratory of Geological Processes and Mineral Resources(GPMR2011)
文摘Tengchong Cenozoic volcanics that have record key information on the tectonic evolution and mantle features of the southeast margin of the Tibetan Plateau are of great importance because of its unique eruption history spanning the entire Quaternary period. Magma origin and evolution of Tengchong Cenozoic volcanic rocks were studied on the basis of Nd-Sr-Pb isotope and major and trace element data from different eruptions in the Ma＇anshan area. Different samples within one eruption show relative identical lithologies, chemical and isotopic compositions. However, the geochemical features for the five eruptions are distinct from each other. These volcanic rocks show low Mg# values （〈45）, moderate to high fractionation of LREEs and HREEs, and enrichment of Pb and Ba and depletion of Nb. Tengchong Cenozoic volcanic rocks were derived from an enriched mantle based on Nd-Sr-Pb isotopic studies. And lines of evidence show that crustal contamination should be involved before the eruption of different periods of Tengchong Cenozoic volcanic rocks. Older subducted components may be responsible for adakite recycling at various stages of evolution, which results in the origin of the enriched mantle source magma accounting for the isotopic features of Tengchong Cenozoic volcanic rocks. Segregated primitive magma pulsating injected into magma chamber, fractional crystallized and contaminated with crust component. Finally, magmas with distinct chemical and isotopic compositions for each eruption formed. The extension of the northeast segment of the Yingjiang tectonic belt triggered the pulsating eruption of the Cenozoic volcanics in the Tengchong area.
基金This work was financially supported by the China Geological Survey(Grant No.DD20160054)the National Natural Science Foundation of China(Grant No.U1407207)the National Key Research and Development Program of China(Grant No.2017YFC0602802).
文摘Tho Gudui geothermal field records the highest temperature at equivalent borehole depths among the lainland hydrothermal systems in China's Mainland.Located about 150 km southeast of Lhasa City,the capital of Tibet,the Gudui geothermal field belongs to the Sangri-Cuona rift belt,also known as the Sangri-Cuona geothermal belt,and is representative of the non-volcanic geothermal systems in the Himalayas.In this study,oxygen-18 and deuterium isotope compositions as well as 87Sr/86Sr ratios of water samples collected from the Gudui geothermal field were characterized to understand the origin and mixing processes of the geothermal fluids at Gudui.Hydrogen and oxygen isotope plots show both,deep and shallow reservoirs in the Gudui geothermal field.Deep geothermal fluids are the mixing product of magmatic and infiltrating snow-melt water.Calculations show that the magma fluid component of the deep geothermal fluids account for about 21.10%-24.04%;magma fluids lay also be a contributing source of lithium.The linear relationship of the 87Sr/86Sr isotopic ratio versus the 1/Sr plot indicates that shallow geothermal fluids form from the mixing of deep geothermal fluids with cold groundwater.Using a binary mixing model with deep geothermal fluid and cold groundwater as two end-members,the nixing ratios of the latter in most surface hot springs samples were calculated to be between 5% and 10%.Combined with basic geological characteristics,hydrogen and oxygen isotope characteristics,strontium concentration,87Sr/(86)Sr ratios,and the binary mixing model,we infer the 6 th-Class Reservoirs Evolution Conceptual Model(6-CRECM) for the Gudui geothermal system.This model represents an idealized summary of the characteristics of the Gudui geothermal field based on our comprehensive understanding of the origin and mixing processes of the geothermal fluid in Gudui.This study may aid in identifying the geothermal and geochemical origin of the Gudui high-temperature hydrothermal systems in remote Tibet of China,whose potential for geothermal development and utilization is enormous and untapped.
基金funded by the Open Foundation of the Beijing SHRIMP Center (DDC15-016)the Applied Basic Research Program Youth Project of Yunnan Province (2016DF031)the National Basic Research Program of China (2015CB452605)
文摘The Laojiezi alkaline volcanic rocks, which are located in the intraplate region of the Yangtze craton, coincide with the formation of the Jinshajiang-Ailaoshan-Red River alkaline rock belt. Although this belt has been widely studied by geologists because of its porphyry-related Pb-Ag-Au polymetallic deposit and geotectonic location, the material sources of this belt are still debate. Whole-rock analyses show that these rocks have high total alkali contents(3.73–11.08 wt%), and their aluminum saturation index(ASI) values widely vary from 0.82 to 3.07, which comprise a metaluminous-peraluminous magma series. These rocks are characterized by high K(K2 O/Na2 O>1) and low Ti and Mg contents; enrichment in large-ion lithophile elements, such as Rb, Ba, K and light rare earth elements; and depletion in high field strength elements, such as Ta, Nb, P, and Ti. These rocks exhibit moderate Eu(Eu/Eu*=0.86–1.04) and Ce(Ce/Ce*=0.63–0.96) anomalies. Their(87 Sr/86 Sr)i, εNd(t), zircon εHf(t) and δ18 O values range from 0.70839 to 0.71013, from-10.16 to-12.45, from-19.6 to-5.8, and from 5.69‰ to 8.54‰, respectively, and their Nd and Hf two-stage model ages(TDM2) are 1.67–1.86 Ga and 1.27–2.02 Ga, respectively. These data reflect the primary partial melting of Paleoproterozoic to Mesoproterozoic lower crust with minor residual continental lithospheric mantle and supracrustal metasediments. The lithosphere was likely thickened along the southeastern margin of the Tibetan Plateau following the Indian-Asian continentcontinent collision(65–41 Ma). During the post-collision phase(36–16 Ma), the transition from a compressional to extensional setting triggered the convective removal of the over-thickened CLM beneath the Yangtze craton, which led to the upwelling of asthenospheric materials. This process created alkali-rich and high-K magma through the partial melting of the thickened lower crust. Magma that carried Cu-Au-Pb-Ag minerals was emplaced by strike-slip motion along the E-to W-or ENE-to WSWtrending tectonically weak zone, finally forming an alkaline porphyry Cu-Au-Pb-Ag polymetallic deposit.
基金financially supported by the National Key Technology Research and Development Program of China (No. 2011BAB06B04)
文摘Shadong deposit is the first large-scale tungsten deposit found in the East Tianshan orogenic belt, and the geologic characteristics of the deposit indicate that the deeply concealed granite body is ge- netically related with the mineralization. The LA-ICPMS U-Pb age of zircons from the Shadong concealed granite obtained in this research is 239±2.0 Ma, belonging to the Middle Triassic. The whole rock samples are metaiuminous to slightly peraluminous （A/CNK=0.95-1.02） with low contents of SiO2 （64.0 wt.%-68.5 wt.%） and low K2O/Na2O ratios （0.73-0.96）. The samples reveal enrichment of K, Rb, Th and depletion of Nb, Ta, P, Ti and have a negative slope from La to Lu （LaN/YbN=16.29-36.8） with weak negative Eu anom- aly （Eu/Eu＊= 0.71-0.82）. Initial ^87Sr/^86Sr ratios of whole rock range of 0.706 59-0.707 75, eNd（t） values range from -1.77 to -2.53 and εnf（t） values of zircon are between 2.54 and 4.90. The lithogeochemistry and Sr-Nd-Hf isotopic characteristics revealed that the concealed granite in Shadong tungsten deposit is I-type granite, and occurs in an intraplate tectonic setting. The magma mixing during intraplating of mantle de- rived magma intruding into the crust in Indosinian Period is the major formation mechanism of the granite. Of which, the proportion of mantle derived magma ranges from 58% to 60%, and the crustal materials are mainly the metamorphic basement of Xingxingxia Group of Mesoproterozoic Changcheng System, which may orovide the main source of ore forming metals of Shadong tungsten deposit.
基金co-supported by the National Natural Science Foundation of China (Nos. 41427804, 41421002, 41373004)Program for Changjiang Scholars and Innovative Research Team in University of China (No. IRT1281)the MOST Research Foundation from the State Key Laboratory of Continental Dynamics
文摘High-purity N2 was used to increase the mobile phase flow rate during ion purification of ion-exchange resin. This was performed to improve the efficiency of isotope separation and puri- fication, and to meet the efficiency requirements of rapid multiple-collector-inductively coupled plasma mass spectrometry （MC-ICPMS） analysis. For Cu isotope separation, our results indicated that at a gas flow rate 〉60 mL/min, the separation chromatographic peaks broadened and the re-covery rate decreased to 〈99.2%. On the other hand, no significant change in the Cu peaks was ob- served at a gas flow rate of 20 mL/min and the recovery rate was determined to be 〉99.9%. The Cu isotope ratio, measured by the standard-sample bracketing method, agreed with reference data within a±2 SD error range. The separation time was reduced from the traditional 10 h （without N2） to 4 h （with N2）, indicating that the efficiency was more than doubled. Moreover, Sr and Nd isotope separation in AGV-2 （US Geological Survey andesite standard sample） accelerated with a 20 mL/min gas flow, demonstrating that with the passage of N2, the purified liquid comprised Rb/Sr and Sm/Nd ratios of 〈0.000 049 and 〈0.000 001 5, respectively. This indicated an effective separation of Rb from Sr and Sm from Nd. MC-ICPMS could therefore be applied to accurately determine Sr and Nd isotope ratios. The results afforded were consistent with the reference data within a±2 SD error range and the total separation time was shortened from 2 d to 〈10 h.
文摘Trace elemental associations and Sr-Nd isotopic compositions are of important to recognition of biogenic material from mixed marine sediments. The foraminifera shell from the Okinawa Trough strongly enriches Sr,P,Mn and Ba, enriches Li,U,Th,Sc,Co,Cu,Pb,Zn,Cr,Rb,Y,Sb and light rare earth elements,slightly enriches V,Ga,Zr,Nb,Cd and middle rare earth elements,is short of Mo,In,Sn,Cs,Hf,Ta,W,Ti,Bi and heavy rare earth elements. The mechanism of elemental enrichment in forminifera is the concentrations of trace elements in sea water and selective absorption of trace elements during foraminifera living, as well as the geochemical affinity between major elements and trace elements.The REE (rare earth elements)partition pattern of foraminifera shell of the Okinawa Trough shows enrichment of middle rare earth elements with slightly negative Ce anomaly,which are different from those of foraminifera of the Pacific Ocean.The Sr,Nd isotopic ratios of the Okinawa Trough foraminifera are 0 709 769 and 0 512 162,respectively, which are different not only from those of oceanic water, but also from those of river water of China's Mainland, the former is slightly higher than those of oceanic water,but much lower than those of river water;the latter is slightly lower than those of oceanic water,but higher than those of river water,demonstrating that the Okinawa Trough sea water has been influenced by river water of China's Mainland.
基金financially supported by the National Natural Science Foundation of China(No.41272093)China geological survey project(No.12120114080901)
文摘The Shitoukengde Ni-Cu deposit, located in the Eastern Kunlun Orogen, comprises three mafic-ultramafic complexes, with the No. I complex hosting six Ni-Cu orebodies found recently. The deposit is hosted in the small ultramafic bodies intruding Proterozoic metamorphic rocks. Complexes at Shitoukengde contain all kinds of mafic-ultramafic rocks, and olivine websterite and pyroxene peridotite are the most important Ni-Cu-hosted rocks. Zircon U-Pb dating suggests that the Shitoukengde Ni-Cu deposit formed in late Silurian （426-422 Ma）, and their zircons have ~Hf（t） values of-9.4 to 5.9 with the older TDMm ages （0.80-1.42 Ga）. Mafic-ultramafic rocks from the No. I complex show the similar rare earth and trace element patterns, which are enriched in light rare earth elements and large ion iithophile elements （e.g., K, Rb, Th） and depleted in heavy rare earth elements and high field strength elements （e.g., Ta, Nb, Zr, Ti）. Sulfides from the deposit have the slightly higher ~34S values of 1.9-4.3%o than the mantle （0 ~ 2%o）. The major and trace element characteristics, and Sr-Nd-Pb and Hf, S isotopes indicate that their parental magmas originated from a metasomatised, asthenospheric mantle source which had previously been modified by subduction-related fluids, and experienced significant crustal contamination both in the magma chamber and during ascent triggering S oversaturation by addition of S and Si, that resulted in the deposition and enrichment of sulfides. Combined with the tectonic evolution, we suggest that the Shitoukengde Ni-Cu deposit formed in the post-collisional, extensional regime related to the subducted oceanic slab break-off after the Wanbaogou oceanic basalt plateau collaged northward to the Qaidam Block in late Silurian.
文摘The Bancun diabase dyke and the Bali hornblende gabbro dyke in western Fujian Province were emplaced in the Early and Late Cretaceous periods, respectively; the former is designated to calc-alkaline series and the latter to K-high-calc-alkaline rock series. Both the dykes are characterized by such geochemical characteristics as high Al and Na2O>K2O. As for the Bancun dyke, Al2O3=16.32%–17.54% and K2O/Na2O=0.65–0.77; as for the Bali dyke, Al2O3=16.89%–17.81% and K2O/Na2O=0.93–0.99. Both the Bancun and Bali mafic dykes are relatively enriched in LILE and LREE, but depleted in HSFE, displaying the geochemical characteristics of continental marginal arc, with high initial Sr isotopic ratios and low εNd (t) values. The (87Sr/86Sr)i ratios of the Bancun diabase dyke are within the range of 0.708556–0.70903 and their εNd (t) values vary between -6.8 and -6.3; those of the Bali hornblende dyke are within the range of 0.710726–0.710746 and their εNd (t) values are -4.7– -4.9, showing the characteristics of enriched mantle EM II. The isotope and trace element data showed that the mafic dykes have not experienced obvious crustal contamination, and metasomatism caused by subduction fluids is the main factor leading to LILE and LREE enrichments. The enriched mantle is the source region for the mafic dykes, and mixing of subduction fluid metasomatized enriched mantle and EM II-type mantle constituted the mantle source region of both the Bancun and Bali mafic dykes. Upwelling of the asthenosphere mantle provided sufficient heat energy for the generation of magmas. In accordance with the discrimination diagram of their tectonic settings as well as their trace element geochemical characteristics, it is considered that the dykes both at Bancun and Bali possess the characteristics of continental marginal arc, revealing the tectonic environment of formation of the mafic dykes, the continental dynamic background as an intraplate tensional belt in which the mafic dykes were emplaced. Meanwhile, it is also indicated that the tensional tectonic stress mechanism is responsible for the formation of the mafic dykes in western Fujian Province.
基金This research is co-supported by the National Natural Science Foundation of China(Nos.41530211,41125013,41803012)the China Postdoctoral Science Foundation(No.2017M622546)the Most Special Funds of the State Key Laboratory of Geological Processes and Mineral Resources(No.MSFGPMR01).
文摘The in-situ Sr isotope determination of solid samples has the advantages of high spatial resolution and convenient and rapid sample preparation.However,due to the lack of column chemistry separation of matrix elements from Sr,the interference correction(especially the isobaric interference from 87Rb on 87Sr)becomes a big issue for high precise in-situ Sr isotope analytical results.In this study,we evaluated the influence of isobaric interference systematically and adopted an improved strategy for isobaric interference correction of Rb.Specifically,as an external standard for data calibration,an in-house silicate standard(Rb-std)was fused from pure oxide powders.The new standard(Rb-std)shows very low contents of Sr(<1 ppm),Yb(<0.09 ppm)and Er(<0.05 ppm),which directly avoid the trouble of interference of doubly charged ions and isobar,when we determinate the mass fractionation factors of Rb(βRb).Our improved method can provide more accurate data than previous researches,in which the mass fractionation were calculated from an external reference material StHs6/80-G with high Rb(30.07 ppm),Sr(482 ppm),Yb(1.13 ppm)and Er(1.18 ppm).Then,these βRb from Rb-std were applied by linear interpolation to the unknown samples for correction of 87Rb on 87Sr.The analytical results of serial international reference materials(BIR-1G,BCR-2G,BHVO-2G,T1-G and ATHO-G)demonstrate that our improved method can raise the upper limit of Rb/Sr for in-situ Sr isotope determination and reduce the relative standard deviation of results.This improvement of the upper limit of Rb/Sr(<0.33)will expand not only range of microanalysis for silicate minerals,but also bulk Sr isotope determination of volcanic rock combining with rapid fusion technique.
基金supported by the Program for Changjiang Scholars and Innovative Research Team in University (PCSIRT)the 111 Project (No.B07011)
文摘Up to now, there were no systematic studies of geochemistry and isotopic age for the Yixian （义县） fluorite deposit, western Liaoning （辽宁） Province, China. Based on the analysis of metallogenic geological setting, we studied the REE, Rb-Sr and Sm-Nd isotopes. The chondrite-normalized REE patterns of fluorite are characterized by moderate LREE depletion （LREE/HREE=0.95-3.57, （La/Yb）N=0.08-2.84） and enrichment of Sr （146×10^-6-596×10^-6） and moderately positive Eu anomalies （δEu=1.10-1.34）, which are similar to those of the host Mesoproterozoic carbonate rocks. The fluorite display （^87Sr/^86Sr）t=-0.708 5, （^143Nd/^144Nd）t=-0.511 785, and δNd（t）=-12.8, which are similar to those of the host Mesoproterozoic carbonate rocks and volcanic rocks of Middle Jurassic Lanqi （蓝旗） Formation. The REE and Sr-Nd isotope geochemistry suggest that the source of the ore-forming material may be the volcanic rocks of Lanqi Formation and host carbonate rocks. The Sm-Nd isochron age of 154±14 Ma （MSWD=0.23） indicates that the Yixian fluorite mineralization nearly corresponds to the period of Lanqi Formation. Based on the integrated geological and geochemical studies, coupled with previous studies, we suggest that Yixian fluorite deposit formed in the extension setting of postcoilisional stage and may be attributed to the partial melting of ancient basaltic rocks in the lower crust induced by underplating of basic magma and to the reaction between the F-rich ore-forming fluids and the host carbonate rocks.
基金part of the ongoing project "Superimposed tectonic activities and large-scale oreforming processes of the Hinggan-Mongolia Orogenic Belt"financially supported by the State Basic Research Program of China(2013CB429805)
文摘The Hashitu molybdenum deposit is located in the southern part of the Great Hinggan Range, NE China. Molybdenum mineralization is hosted by and genetically associated with monzogranite and porphyritic syenogranite. Sr-Nd-Pb isotopes of the intrusions show that the porphyritic syenogranite has initial ^87Sr/^86Sr ratios of 0.70418-0.70952, ENd（t） values of 1.3 to 2.1 （t=143 Ma）, ^206Pb/^204Pb ratios of 19.191-19.573, ^207Tpb/^204pb ratios of 15.551-15.572, and ^208Pb/^204Pb ratios of 38.826-39.143. The monzogranite has initial 87Sr/86Sr ratios of 0.70293-0.71305, εNd（t） values of 1.1 to 2.0 （t=-147 Ma）, ^206Pb/^204pb ratios of 19.507-20.075, ^207Pb/^204Pb ratios of 15.564-15.596, and ^208Pb/^204Pb ratios of 39.012-39.599. The calculated Nd model ages （TDM） for monzogranite and porphyritic syenogranite range from 866 to 1121 Ma and 795 to 1020 Ma, respectively. The granitic rocks in the Hashitu area have the same isotope range as granites in the southern parts of the Great Hinggan Range. The isotope composition indicates that these granites are derived from the partial melting of a juvenile lower crust originating from a depleted mantle with minor contamination by ancient continental crust. The integrating our results with published data and the Late Mesozoic regional tectonic setting of the region suggest that the granites in the Hashitu area formed in an intra-continent extensional setting, and they are related to the thinning of the thickened lithosphere and upwelling of the asthenosphere.
基金Granted jointly by the State Key Fundamental Research Project （Grant No. 1999CB403209） the National Natural Science Foundation of China （Grant No. 40132010）.
文摘Zircon U-Pb dating by the LA-ICP-MS method was applied to determining the ages of different units of the Guposhan granite complex, among which the East Guposhan unit is 160.8±1.6 Ma, the West Guposhan unit is 165.0±1.9 Ma, and the Lisong unit is 163.0±1.3 Ma in age. Much similarity in ages of the three units has thus proved that the whole Guposhan granite complex was formed in the same period of time. They were the products of large-scale granitic magmatism through crust-remelting in the first stage of the Middle Yanshanian in South China. However, the three units have differences both in petrology and in geochemistry. Besides the differences in major, trace and rare-earth elements, they are distinct in their Rb-Sr and Sm-Nd isotopic compositions. The East Guposhan unit and Lisong unit and its enclaves have a similar (87Sr/86Sr)i value of 0.7064 with an average of εNd(t)=-3.03, indicating that more mantle material was evolved in the magma derivation; whereas the West Guposhan unit has a higher (87Sr/86Sr)i value of 0.7173 but a lower εNd(t) value of -5.00, and is characterized by strong negative Eu anomalies and higher Rb/Sr ratios, suggesting that its source materials were composed of relatively old crust components and new mantle-derived components. In addition, an inherited zircon grain in the East Guposhan unit (GP-1) yielded a 206Pb/238U age of 806.4 Ma, which is similar to the ages of the Jiulin cordierite granite in northern Jiangxi and of the Yinqiao migmatic granite in Guangxi in the HZH granite zone. All this may provide new evidence for Late Proterozoic magmatism in the HZH granite zone.
基金funded by National Program on Key Basic Research Project of China-973 Program"Potash formation mechanism,conditionslate evolution in Ordovician ancient epicontinental sea basin,Erdos"(No.2011CB403001)China Geological survey work Program–"Potash resources investigation and evaluation in Northern Shaanxi Ordovician Salt Basin"(No.1212011085516)
文摘China is in severe shortage of potash reserves,and the best way for breakthrough is to make potash exploration in marine salt basins.Erdos basin is so far the only Ordovician potash basin in the world.The Erdos basin is located west
