Geochronology of mineralization and tectonic setting of Baishidong skarn-type iron deposit in Helong area of Yanbian,Jilin Province,NE China

The Baishidong iron deposit is the only skarn-type iron deposit discovered in the study area. According to mineral assemblage and paragenesis, the mineralization can be divided into four metallogenic stages: early garnet-diopside skarn stage, late magnetite-tremolite-epidote skarn stage, early quartz-pyrite-chalcopyrite stage and late quartz-calcite-pyrite stage. Through LA-ICP-MS zircon U-Pb dating of diorite, which is closely related to mineralization, the results show that the weighted average age is 164.6±1.4 Ma, which limits the mineralization time of Baishidong iron deposit during or slightly later than Middle Jurassic. The diorite rocks are rich in sodium(Na_2O/K_2O=1.24--1.76), aluminium(Al_2O_3=17.41%--18.76%), LREE and large-ion lithophile elements(Ba, K and Sr), depleted in HREE and high-field-strength elements(Y, Nb, Ta, P and Ti), and show strongly fractionated patterns(LREE/HREE=6.58--9.93), no apparent Eu anomalies(δEu=0.91--1.13), which shows similar characteristics to island arc or active continental margin arc magma. The zircon εHf(t) values range from-22.6 to 5.9, and the age of the two-stage model(t_(DM2)) is 836--2 633 Ma. Above data combined with the geochemical characteristics, it is indicated that the magma was a mixture of multiple sources, composed of ancient materials and newly formed crust. During the process of evolution and ascending of magma, separation and crystallization occurred, and a large amount of continental crust material was mixed at the same time. Combined with regional tectonic evolution, the formation of this deposit may be related to the westward subduction of the Paleo-Pacific Plate to the Eurasian Plate.     

Zircon U-Pb geochronology and geochemistry of diorite dikes from Nancha ore deposit in Tonghua area of Jilin and its geological significance

The authors presented geochronology and geochemical data of diorites from Nancha gold deposit in Tonghua region,with the aim to constraining its formation age,magma source and tectonic setting.LA-ICP-MS U-Pb dating results of zircons from the diorites indicate that the rocks were formed in the Middle Jurassic( 171± 2 Ma,MSWD = 1.19).Geochemically,these rocks have Si O_2 concentrations of 52.52%--54.90%,K_2 O of2.14%--3.84%,Na_2 O of 3.17%--3.35%,Mg O of 7.43%--9.34% and high Mg~# of 68.57-72.57.These rocks are characterized by enrichment in large ion lithophile elements( LILE,such as K,Ba,Rb and Sr) and light rare earth elements( LREE),relatively depletion in high field strength elements( HFSE,such as Ta,Nb,Ti and Zr),and heavy rare earth elements( HREE).These characteristics suggest that primary magma of the rocks were derived from the partial melting of mantle with miner crustal contamination,which may related to partial melting of mantle wedge by addition of sediment melt from subducting oceanic crust.Based on former and present studies,the authors consider that the Nancha ore deposit high-Mg diorites were formed in compressional structural setting which is similar to volcanic arc.It could be related to the subduction of the Paleo-Pacific plate beneath the Eurasian continent.     

新疆彩霞山铅锌矿床地质及同位素地球化学特征

对彩霞山铅锌矿床矿石矿物和围岩的硫、铅同位素及脉石矿物的氢、氧同位素地球化学特征进行了研究。分析结果显示,成矿物质来源于地壳和地幔的混合;硫来源主要为同化了海水硫酸盐的岩浆硫,并有少量生物还原硫参与。氢、氧同位素指示成矿流体早期可能有岩浆热液,主成矿期主要是地层中的建造水参与成矿。     

Geochronology,geochemistry and geological significance of Early Cretaceous volcanic rocks from Niangniangshan Formation,Ningwu Basin,middle and lower reaches of the Yangtze River

Ningwu Basin is one of the Mesozoic continental volcanic basins in the middle and lower reaches of the Yangtze River.The volcanic rocks of the Longwangshan,dawangshan,Gushan and Niangniangshan formations,as well as the homologous subvolcanic rocks or small intrusions,are developed from old to new in the Ningwu Basin.Zircon U-Pb dating results show the latialite phonolite of Niangniangshan Formation was erupted at 128±1 Ma(i.e.,Early Cretaceous).The latialite phonolite contains moderate SiO2 contents(57.28%-60.96%)with high Na 2O+K 2O contents,belonging to shoshonite series.The samples have high REE contents,and display right-inclined REE distribution pattern.They are characterized by enrichment in some large ion lithophile elements(e.g.,LILEs,Rb,K),and depletion in some high field strength elements(e.g.,HFSEs,Nb,Ta,Ti).All volcanic samples have relatively depleted Nd isotopic compositions(ISr=0.707197--0.707878;εNd(t)=-0.5--0.9),indicating no genetic relationship with the lower crust of Yangtze plate,but a drift trend towards the EMII.The geochemical data suggest that the Early Cretaceous latialite phonolite was derived from the partial melting of an enriched lithospheric mantle metasomatized by subduction-related fluids in an arc-related setting.Based on the temporal and spatial distribution and geochemical variation characteristics of the regional volcanic rocks,it is suggested that the tectonic system within the study area changed from a subduction-related compression to an extensional environment in the early Early Cretaceous,which was caused by the ridge subduction of the Paleo-Pacific Ocean.     

Geochemistry and genesis of magmatic PGE-bearing Cu-Ni sulphide deposit in Wadi Bayhan，southeastern Yemen

The Wadi Bayhan mafic-ultramafic intrusions associated with magmatic PGE-bearing Cu-Ni sulphide deposit are located in the south margin of the Arabian-Nubian Shield,SW Yemen.The intrusions consist of dunite,olivine-pyroxenite,lherzolite,hornblendite,gabbro and gabbronorite.The dunite and lherzolite are the main host rock for the Cu-Ni ores.The new data of the chemical compositions of the rocks have SiO2(50%-53.6%),Al2O3(0-32%) and MgO(4%-28%),and relatively low TiO2(0-3.2%) and K2O+Na2O(0.04%-5.2%).The geochemical characteristics indicate that the parental magma is high-magnesium tholeiitic.Sulfur had reached saturation and immiscible sulfides droplets segregated from silicate magmas before their emplacement.     

山西中条山涑水杂岩中冷口变质火山岩的地球化学及构造环境

冷口变质火山岩为较典型的双峰式火山岩，以变质基性火山岩为主，夹变质英安质岩石。依据元素地球化学和同位素地球化学分析，它应形成于大陆或大陆边缘裂谷环境。基性岩浆来源于亏损地幔，岩浆在侵位过程中受到强烈的地壳成分混杂作用改造，而英安质岩石可能是由大陆地壳部分熔融作用形成的。     

辽宁岩石地球化学分区特征

通过对辽宁区域岩石41种元素的区域分布研究,作者提出了辽宁岩石元素地球化学分区系统。依次划出1个地球化学省、2个地球化学区、12个地球化学分区及若干地球化学小区。以地球化学分区为基本单位,讨论了各分区岩石元素的浓集状况,指出了不同地球化学分区岩石元素分布的差异,分析了某些元素的富集趋势与成矿的联系。对探讨不同分区的地球化学演化历程,确定找矿方向,具有一定意义。     

章丘大葱特征元素农业地球化学研究

以章丘大葱产区生态地球化学调查为基础,采集了表层土壤、大葱、根系土及出露的代表性岩石样品,实测了大量和微量营养元素的含量,查明了研究区土壤地球化学背景。通过计算大葱对土壤营养元素的吸收率及大葱品质与营养元素的相关性分析,查明了大葱生长的特征营养元素为N,K2O,Zn,B,P,Cu,Mn。在岩石-土壤-大葱这一生态体系中,营养元素在土壤中保持一定的储备和积累,为大葱的生长提供了有利的农业地球化学环境。     

Yanji city orientation and industry development towards 21st century

1 PRESENT SITUATIONYanji City is the Capital of Yanbian Korean Autonomous Prefecture (YKAP), the center of wholeprefectllre politics, economy and culture, and it is onepolar of "the golden triangle" in the Tumen River Delta(Yanji, Chongiin, Vladivostok ). It is located in theeast of Jinn Province and to the North of ChangbaiMountain which straddles the border region betweenChina and Korea. It is a frontier city that is 60km directly away from the border between China and Russia…     

琼东南盆地北部中生代凹陷特征及油气成藏条件初探

琼东南盆地的中生代凹陷群是扩大油气勘探发现的远景区。为了实现琼东南盆地中生界的勘探突破,急需落实中生代凹陷的油气成藏条件和有利勘探领域。基于地球物理、地球化学、钻井资料及古生物资料,首次对琼东南盆地中生代凹陷开展了深入系统的分析研究。研究表明,在琼东南盆地北部崖北凹陷、崖城凸起、崖南低凸起和西南部陵南低凸起及南部隆起均存在中生代沉积地层。根据盆地构造演化分析,中生代沉积形成于燕山期太平洋板块向欧亚板块俯冲期以及其后的弧后伸展期,存在烃源岩、储层及圈闭等油气地质基本条件。琼东南盆地北部坳陷带崖城-崖北地区相比盆地其他地区中生代沉积凹陷规模大,因此本研究重点对琼东南盆地北部坳陷带崖城-崖北地区进行了系统的油气地质综合分析研究,落实了崖城-崖北地区中生界沉积地层分布,并初步评价预测了有利油气勘探区带及重点目标。研究表明,琼东南盆地崖城-崖北地区中生代凹陷发育湖相烃源岩、三角洲等储集体以及构造与地层圈闭,存在西洼南坡带和中部隆起带2个有利油气勘探区带。在这些区带加大勘探,有望获得中生界油气突破。      

Zircon U-Pb geochronology and geochemistry of syenogranites in western Niubiziliang,northwestern Qaidam,Qinghai

The study presents the results of U-Pb dating of zircons and whole-rock geochemical analyses of a syenogranite located in the western Niubiziliang area,China with the aim of determining its formation time,petrogenesis and the regional tectonic setting. Zircons within the syenogranite are euhedral-subhedral and display rhythmic growth zoning,indicating a magmatic origin. Zircon U-Pb data obtained by LA-ICP-MS indicate the syenogranite formed in the Late Permian (260.7±1.5 Ma). The w(SiO_2) of syenogranites is 70.82%--73.59%,w(Al_2O_3) is 13.49%--14.82%,and w(Na_2O + K_2O) is 7.85%--8.52%,and yield K_2O/Na_2O ratios of 1.06--1.26. Therefore,the syenogranites belong to the high-K calc-alkaline and metaluminous (A/CNK 1,A/NK 1) series which display I-type granites similarly. The syenogranites also show the geochemical characteristics of volcanic arc rocks,being enriched in large-ion lithophile elements (LILEs; K,Rb) and light rare-earth elements (LREEs; La,Ce,Sm,Nd),but depleted in high field strength elements( HFSEs; Ta,Nb,P,Ti). On the whole,trace element ratios are close to the mean of the Earth's crust,indicating a lowercrust magma source. The low Sr (161--214) ×10~(-6) and Yb (1.08--1.80)×10~(-6) concentrations indicate that plagioclase and hornblende are residual mineral phases in the source. The regional geology and whole-rock geochemistry suggest that the formation of the syenogranites was related to subduction of the Zongwulong Ocean crust,and the north margin of Qaidam Block during the Late Permian was in an active continental margin tectonic setting.     

济阳坳陷下伏石炭系—二叠系煤系烃源岩中侵入岩的地球化学特征

石炭系—二叠系沉积以剥蚀残余状分布在渤海湾盆地之下,在已发现油气的部位均发现浅层侵入岩。通过侵入岩产状、主量元素和微量元素组成等地质和地球化学分析,发现侵入岩主要为富二氧化硅、钠、钾和镁的闪长玢岩以及贫二氧化硅和钠、富钾和镁的煌斑岩,它们与鲁西隆起同层位侵入岩具有很多相似之处。研究认为它们是侏罗纪断陷形成初期上地幔物质上涌、沿深大断裂侵入形成的,以富钾偏碱性或偏中性两种岩浆侵入在煤系烃源岩中。研究还发现,煤系地层中的这些侵入体规模不大,对烃源岩的烘烤作用范围不超过侵入体的厚度,对整体的煤系生烃演化影响较小。     

辽宁省岩石地球化学研究新进展

辽宁地球化学场研究,是根据辽宁全域41种元素丰度及各种地球化学参数,论述了辽宁不同地质时代和构造分区表壳岩石元素分配特点,指出了辽宁重要成矿元素的高值时代;建立了辽宁早前寒武纪变质岩、超变质岩,全域沉积岩,火成岩不同岩类的主元素地球化学模型和元素富集型式;并对Au、Pb、Zn、B等主要成矿元素的分布、分配以及与有关元素的相关特征进行了讨论;指出了成矿元素的主要载体岩石和高值地质单元。根据大地构造分区、元素组合,将辽宁全域划分为4个地球化学省,11个地球化学区,35个地球化学分区。     

东昆仑乌妥一带超镁铁质岩-镁铁质岩地质特征及构造环境

东昆仑昆中断裂带乌妥一带分布20多个超镁铁质-镁铁质岩残块(片),在野外地质调查的基础上,结合室内岩石学、岩石地球化学研究,属非典型的蛇绿岩残块(片),是东昆中断带在漫长的地质演化过程中残留在陆块边缘的洋壳物质,形成于洋中岛弧环境。分布于东昆中断裂带内及其附近,时代上属于早古生代。     

渤海湾盆地渤中凹陷古近系烃源岩生物标志物特征及其地质意义

渤中凹陷位于渤海湾盆地中东部, 主要发育沙三、沙一和东三段烃源岩层, 具有良好的油气勘探前景, 前期对渤中凹陷有机地球化学特征的研究主要基于岩屑样品, 对岩心样品生物标志物特征的研究比较薄弱。本次研究综合利用岩心和岩屑样品, 通过有机碳、岩石热解、氯仿沥青"A"、族组分饱和烃色谱-质谱等有机地球化学分析测试, 重点对渤中凹陷古近系东营组三段和沙河街组一段、三段烃源岩的有机质丰度、类型、成熟度及母质来源与沉积环境进行研究, 明确了渤中凹陷三套泥页岩的地球化学特征及发育控制因素, 并建立了区分3套烃源岩的典型生物标志化合物组合特征, 以期望为进一步厘清该区域优质烃源岩发育模式及时空分布提供一定的理论依据, 进而有利于该区油气的勘探。研究结果表明: 3套烃源岩的生烃潜力具有显著差异, 沙三段>沙一段>东三段。沙三段烃源岩有机质丰度最高, 为好-极好烃源岩, 有机质类型为Ⅰ-Ⅱ₁型, 处于成熟阶段; 沙一段次之, 为中等-好烃源岩, 有机质类型为Ⅱ₁-Ⅱ₂型, 整体处于成熟阶段; 东三段稍差, 为中等烃源岩, 有机质类型以Ⅱ₁-Ⅱ₂型为主, 处于低熟-成熟阶段。岩心样品的生物标志化合物中姥植比(Pr/Ph)、伽马蜡烷指数(Ga/C₃₀H)、C₂₇-C₂₈-C₂₉规则甾烷含量、4-甲基甾烷指数(4-MS/C₂₉甾烷)等参数表明母质输入和沉积环境是控制3套湖相烃源岩差异的主控因素, 淡水藻源输入和良好的保存条件是沙三段优质烃源岩发育的关键, 低等水生生物输入和强还原的保存条件是沙一段优质烃源岩发育的关键, 混源输入和良好的保存条件是东三段优质烃源岩发育的关键。      

莺歌海盆地中新统海相烃源岩发育主控因素及模式

中新统海相烃源岩是中国近海莺歌海盆地主要油气供给层段，也是我国新生代海相烃源岩的典型代表。综合利用地质、地球化学和古生物等资料，在烃源岩有机地球化学特征分析的基础上，探讨了莺歌海盆地中新统海相烃源岩发育的主控因素，并建立了相应的形成模式。结果表明，莺歌海盆地发育中等-好级别的中新统海相烃源岩，并具有较强的横向与纵向非均质性；中新统海相烃源岩受古气候、古生产力、水介质条件、沉积速率及海平面变化等因素的综合影响，发育以莺东斜坡带梅山组、三亚组为代表的海相陆源型和以东方区、乐东区梅山组为代表的海相内源型2种模式，其中以海相内源型烃源岩生烃条件最为优越。      

Provenance and Tectonic Implications of Paleozoic Strata in the South Yellow Sea Basin,China–Revealed from the Borehole CSDP-2

Well CSDP-2 is a fully coring deep drilling hole, penetrating the thick Paleozoic marine strata in the South Yellow Sea Basin(SYSB) in the lower Yangtze Block(LYB). Based on the petrological and geochemical analysis of 40 sandstone samples from the core CSDP-2, the provenance and tectonic features of Paleozoic detrital rocks from SYSB are analyzed and systematically delineated in this article. The results show that the Silurian – Carboniferous sandstones are mature sublitharenite, while the Permian sandstones are unstable feldspathic litharenite. The average CIA(chemical index of alteration) is 74.61, which reflects these sediments were derived from source rocks with moderate chemical weathering. The REE(rare earth element) patterns are characterized by LREE enrichment, flat HREE and obviously negative Eu anomaly, which are similar to that of the upper continental crust. Dickinson QFL discrimination results indicate the recycled orogeny provenance. Various diagrams for the discrimination of sedimentary provenance based on major and trace element data show all the sediments were derived predominantly from quartz sedimentary rocks, of which the Permian strata contain more felsic sedimentary rocks. Geochemical data for these detrital rocks suggest they occur at the passive continental margin and island arc settings, and the Permian sandstone presents active continental margin setting.     

U-Pb-Hf isotopes and petrogenesis of Late Jurassic akakitic quartz monzodiorite in Xingcheng area,western Liaoning Province

The petrogenesis and geodynamic setting of the Late Jurassic Baita porphyry quartz monzodiorite in Xingcheng--Liaoxi area provide information for understanding the Mesozoic tectonic evolution of the northeastern North China Craton. In this paper, geochronological, whole-rock geochemical, and in-situ zircon Hf isotopic analyses of Baita porphyry quartz monzodiorite were investigated to constrain the crystallization age and petrogenesis. Zircons exhibit typical oscillatory zoning in cathodoluminescence images and show relatively high Th/U ratios(0.78--1.62), and U-Pb analyses indicate that these rocks were crystallized during the Late Jurassic(159±1 Ma). Geochemically, they are characterized by high contents of SiO_2(65.21 wt%--65.31 wt%), Al_2O_3(16.29 wt%--16.31 wt%), Sr(521×10~(-6)-539×10~(-6)), and Sr/Y ratio(45.1--47.8) but low Y(10.9×10~(-6)-12.0×10~(-6)), with obvious adakitic geochemical affinities. These above-mentioned findings, combined with their negative ε_(Hf)(t) values(-21.7 to-20.2), corresponding two-stage model age(T_(DM2)) of 2 579--2 484 Ma, as well as low MgO(1.38 wt%--1.39 wt%), Cr(18.5×10~(-6)-19.5×10~(-6)) and Ni(9.45×10~(-6)-9.46×10~(-6)) values, indicate that Baita porphyry quartz monzodiorite may be generated by partial melting of the Neoarchean-Paleoproterozoic thickened basaltic lower crust. Based on the results from this study and pre-vious regional studies, it is concluded that Baita porphyry quartz monzodiorite was spatially related to the westward subduction of the Paleo-Pacific plate.     

秦岭群裂谷岩浆建造地球化学型式及其成因探讨

秦岭群形成于早元古宙华北南缘裂谷化环境中。其下部有一套岩浆岩建造,包括基性和酸性的火山岩或侵入岩。地球化学资料表明,基性岩具有OIB型和CNB型两种地球化学型式,酸性岩具有壳幔混合型地球化学型式。这些变化起因于不同的源区和岩石成因过程,但本质上取决于岩石圈拉张程度和地幔流能量。     

胶东西北部地区花岗岩类岩石成岩的物理化学条件

胶东西北部地区发育有不同类型的花岗质岩石。研究表明,这些花岗质岩石是经胶东群在不同的物理化学条件下熔融形成。本文利用热力学计算公式及有关实验资料,说明不同花岗质岩石形成时的 T、P、fo_2、f_(H_2O)。