Application of Strontium Isotopic Stratigraphy to DatingMarine Sedimentary Units: A Case Study from the PermianStratotype Section in Southern China     

QU Hongjun  CHEN Shuo  HAN Xing  WANG Li  GUAN Liqun  FAN Yuhai 《《地质学报》英文版》2021,95(2):355-369

The calibration of sedimentary rock absolute dates is one of the difficulties in sedimentological and stratigraphic research. Since strontium(Sr) resides in seawater much longer(≈106 a) than the seawater intermixing time(≈103 a), the Sr isotopic composition of global seawater is uniform at any time and results in a stable system throughout geological history,based on which a global Sr isotope composition dating database has been established for age-calibration of marine strata.The Permian stratigraphic sections in the northern part of the Upper Yangtze block, southern China, record continuous marine sediments with clear stratigraphic boundaries and is suitable for stratigraphic dating of Sr isotopes. Based on sampling and Sr isotopic compositions of Permian carbonate strata in the northern part of the Upper Yangtze, a Permian Sr isotope evolution curve was established. According to the basic principles of Sr isotope stratigraphy, the global Strontium isotope age database can be used to calibrate the Permian stratigraphic dates in the northern Upper Yangtze. The results show that the Sr isotope evolution curves for the marine carbonate rocks in the Permian stratigraphic section of the Upper Yangtze present a decreasing trend from the mid-Qixia stage(P2) to the mid-Wujiaping stage(P3), and then rise from the middle Wujiaping stage to the end of Changxing stage(P3). When the Permian Sr-isotope evolution curve is compared with the global Sr isotope evolution curve in the northern Upper Yangtze, the two are consistent in their long-term evolutionary trend, indicating that Permian global geological events are important controlling factors for the composition and evolution of Sr isotopes. The 87 Sr/86 Sr value decreased gradually in the background of large-scale regressions at the turn of middle to late Permian period, revealing that the Emeishan basalt eruption occurred near the Maokou/Wujiaping boundary(GLB). Srisotope stratigraphy dating was performed on the boundaries of the Qixia Formation/Maokou Formation, Maokou Formation/Wujiaping Formation(GLB), Wujiaping Formation/Changxing Formation(WCB) and the Permian/Triassic(PTB) using the Global Strontium Isotope Age Database. The results are 270.4 Ma, 261.2 Ma, 254.5 Ma and 249.7 Ma,respectively. Based on this, the eruption age of the Emeishan basalts is defined at about 261.2 Ma., which is more coincident with that acquired from other previous dating methods on the eruption age of the Emeishan basalts, and therefore proves that the application of Sr isotopic stratigraphy to dating marine sedimentary units is an effective method.  相似文献   

U-Pb Zircon and Re-Os Molybdenite Geochronology of theW-Mo Mineralized Region of South Qinling,China, andtheir Tectonic Implications     

HAN Ke  YANG Xingke  CHAO Huixi  HE Hujun  RUAN Shiqi  GAO Yunfeng  ZHANG Weisheng  ZHU Wei  JIN Gang 《《地质学报》英文版》2021,95(2):500-516

A W-Mo mineralized region is located along the northern margin of the South Qinling tectonic belt of China. WMo mineralization occurs mainly in Cambrian–Ordovician clastic and carbonate rocks, and the ore bodies are structurally controlled by NW–SE-and NNE–SSW-striking faults. Evidence for magmatism in the area is widespread and is dominated by intermediate–felsic intrusives or apophyses, such as the Dongjiangkou, Yanzhiba, Lanbandeng, and Sihaiping granitic bodies. Quartz-vein-type mineralization and fault-controlled skarn-type mineralization dominate the ore systems, with additional enrichment in residual deposits. At present, there are few or insufficient studies on(1) the age of mineralization,(2) the relationship between intermediate–felsic granite and W-Mo mineralization,(3) the source of ore-forming materials,and(4) the metallogenic and tectonic setting of the mineralized area. In this paper, we present geochronology results for numerous intrusive granitic bodies in the South Qinling tectonic belt. U-Pb zircon geochronology of the Lanbandeng monzogranite and Wangjiaping biotite monzogranite yields ages of 222.7 ± 2.3 and 201.9 ± 1.8 Ma, respectively. In contrast to the Late Triassic age of the Lanbandeng monzogranite, the age of the newly discovered Wangjiaping biotite monzogranite places it at the Triassic–Jurassic boundary. Re-Os molybdenite geochronology on the Qipangou W-Mo deposit yielded a model age of 199.7 ± 3.9 Ma, indicating the deposit formed in the early Yanshanian period of the Early Jurassic. Granitoid intrusions in the mineralized area are characterized by composite granite bodies that crystallized at ca.240–190 Ma. While there were multiple stages of intrusion, most occurred at 210–220 Ma, with waning magmatic activity at 200–190 Ma. The Re-Os age of molybdenite in the region is ca. 200–190 Ma, which may represent a newly discovered period of W-Mo metallogenesis that occurred during the final stages of magmatism. The heat associated with this magmatism drove ore formation and might have provided additional ore-forming components for metallogenesis(represented by the Wangjiaping biotite monzogranite). Ore materials in the mineralized area were derived from mixed crustal and mantle sources. Enrichment of the region occurred during intracontinental orogenesis in the late Indosinian–Yanshanian, subsequent to the main Indosinian collision. At this time, the tectonic environment was dominated by extension and strike-slip motion.  相似文献   

北京平原区土壤地球化学特征及影响因素分析     

李欢  黄勇  张沁瑞  贾三满  徐国志  冶北北  韩冰 《物探与化探》2021,(2):502-516

基于北京平原区土壤地球化学调查数据,运用数理统计、因子分析、相关性分析、回归分析等方法研究了土壤元素的横向和纵向分布特征,并探讨其影响因素。结果表明:北京平原区土壤CaO、MgO、Na 2O、Hg、Cd、Sr、Ba、Sn等含量偏高,Sb、As、Th、W、Br、U、I、Mo、有机质等含量偏低。R型因子分析结果显示,F1因子为反映土壤原始背景特征的元素组合,F2、F4、F6因子为反映人类活动对土壤元素分布特征影响的元素组合,F3因子为反映成土母质基本信息的元素组合,F5因子为反映成土母岩基本特征的元素组合。利用一元非线性回归分析对部分元素的垂向分布特征进行数学建模,回归系数R 2值为0.542~0.960,拟合效果总体较好;从区域尺度上初步判断出人类活动对重金属元素Cu、Hg、Pb、Zn影响深度约150~200 cm,对养分指标N、P、S、Se、有机质影响深度约50~100 cm。一般情况下,褐土中Se、Bi、Li、有机质、Mo、W等39项元素与指标的含量高于潮土,不同土壤质地中As、Cd、Cr、Ni、N、B等29项元素含量的大小关系为:砂质壤土<砂质黏壤土<黏壤土<壤质黏土,耕地土壤中Cd、N、P、有机质含量明显高于林地,中心城区土壤中有害重金属元素、养分指标的含量普遍高于郊区。  相似文献   

Structural,Kinematic and Geochronological Study of the Main Tianshan Shear Zone in the Borohoro Ranges,NW China     

LIU Tianlun  CHEN Siyu  ZHANG Bo  CAI Ked  HAN Baofu  QU Junfeng  GUO Lei  WANG Meng 《《地质学报》英文版》2021,95(5):1431-1455

The western segment of the Main Tianshan shear zone (MTSZ) branches into three major dextral strike-slip shear zones in the Borohoro Ranges, northwestern China. Mylonitic rocks within these zones exhibit vertical foliations, subhorizontal lineations, and dextral kinematics. The microstructures and CPO patterns of calcite and quartz in the tectonites suggest shearing at temperatures of 200°C to 500°C or above. The amount of dextral displacement along the zones is less than 100 km. LA-ICP-MS U-Pb dating of zircons from some pre-kinematic granites gave ages of 364–325 Ma and 316 Ma, and zircons from a syn-kinematic leucogranite gave an age of 291 Ma. We propose that dextral shearing along the MTSZ started in the earliest Permian. Our data indicate that collision between the Yili and Junggar plates might have finished before 325 Ma or 316 Ma, with a tectonic transformation from 325 Ma to 300 Ma, resulting in intracontinental transpression from 300 Ma or 291 Ma. We suggest that the formation of the Kazakhstan orocline (KO) took place in two stages, with the early stage of bending driven by convergence related to oblique subduction, and the late stage possibly associated with lateral disarticulation as a result of the dextral strike-slip shear zones.  相似文献   

东天山觉罗塔格构造带钙碱性侵入岩角闪石矿物学特征及其对区域找矿的启示     

李季霖  陈正乐  周涛发  韩凤彬  张文高  霍海龙  刘博  赵同阳  韩琼  李平  陈贵民 《大地构造与成矿学》2021,45(3):534-552

新疆东天山觉罗塔格构造带位于吐哈盆地和中天山地块之间,区内矿产资源丰富,是我国重要的金属矿产分布区,其成矿作用与岩浆活动密切相关.本文在详细岩相学观察的基础上,对角闪石进行了电子探针(EMPA)测试分析,限定了区内8个岩体结晶的温压条件、岩浆氧逸度和含水量等要素,为解析觉罗塔格构造带内钙碱性侵入岩的构造环境、演化过程和成矿作用提供矿物学方面的制约.测试分析表明,岩体中的角闪石富镁(MgO:5.82％～18.04％)、富钙(CaO:9.91％～12.56％)、富钠(Na2O/K2O>1.0)、贫钾(K2O:0.06％～1.16％),属于钙角闪石族.角闪石化学成分特征揭示其大部分为中酸性侵入岩中的角闪石,寄主岩浆为钙碱性,岩浆物质来源具有壳幔混源的特征,是板块俯冲背景下由地幔楔与大陆地壳物质混熔形成.由角闪石温压计得出矿物的结晶温度为751.88～887.46℃,压力为62～248 MPa,相应侵位深度为2.35～9.4 km.通过角闪石成分计算出岩浆的氧逸度为ΔNNO+0.30至ΔNNO+2.48,并且在角闪石结晶时岩浆具有较高的含水量(H2Omelt>5％).通过分析可知觉罗塔格构造带中的钙碱性侵入岩具有高温、低压、高氧逸度、富水和侵位浅的特点,有利于Cu等元素在成矿流体中富集,符合区域斑岩型铜矿的成矿条件.因此推测觉罗塔格构造带内仍具有一定斑岩铜矿的找矿潜力.  相似文献   

商丹断裂带(河南段)构造变形特征及其找矿意义          下载免费PDF全文

薛艳  韩天成  陶威  易志强  马洪勇  黄向东 《地质找矿论丛》2021,36(3):257-264

商丹断裂带是一条多期次活动的大型断裂带,区域上也是大型金属矿的赋存带,对金属矿产具有重要的控制作用。文章以商丹断裂带(河南段)为研究对象,在基于孔沟至寨根一带构造剖面的宏观特征和显微构造特征解析的基础上,对研究区控矿构造和机理提出了新的认识。综合研究表明,商丹断裂带(河南段)具多期活动特征,整体呈现"正花状构造"样式。分析方解石机械双晶、矿物动态重结晶及变质矿物组合等显微构造显示,断裂带以韧性变形为主,两侧地层以韧性和脆性变形叠加为特征。区内变质变形温度以绿片岩相、中低温为主,局部可达角闪岩相。早期的韧性剪切活动控制本区金矿的总体控矿界面,晚期的构造活动形成的韧-脆性破碎带对先期形成的矿床进行改造、富集、最终定位,主断裂两侧的次级韧-脆性构造带是未来寻找金矿的有利部位。  相似文献   

辽宁本溪贾家堡子地区BIF铁矿床地球化学特征     

韩仁萍  寇林林  王筱筝 《地质与资源》2021,30(1):21

利用主量元素和稀土元素相结合的地球化学方法,对本溪贾家堡子铁矿成矿物质来源和矿床成因进行了研究.结果表明：贾家堡子地区条带状铁矿（BIF）的化学成分主要为TFe₂O₃和SiO₂,并且Al₂O₃和TiO₂含量较低,这一特征与鞍本地区及山西五台山和冀东迁安地区条带状铁矿基本一致,指示该条带状铁矿是由极少碎屑物质加入的化学沉积岩.稀土元素呈现弱轻稀土亏损、重稀土富集的特征,具有明显的Eu正异常特征,表明该BIF的稀土元素来源于火山热液和海水的混合液.贾家堡子地区条带状铁矿床成因类型为Algoma型铁矿.  相似文献   

基于外部性理论的湿地退化成因分析及对策研究     

肖红叶  房娜娜  戴慧敏  韩晓萌 《地质与资源》2021,30(5):617-622

基于生态经济学中的外部性原理,结合湿地生态系统的准公共物品属性、外部经济性、外部不经济性以及代际外部性等属性,分析湿地退化的成因.结果表明：湿地萎缩加剧、生态服务功能衰退主要是由于人类缺乏对湿地功能与效益的正确认识,以及不合理的利益分配机制导致的成本外溢现象,从事湿地保护的正外部性行为未得到应有的补偿,负外部性行为未付出应有的代价,并提出应建立因地制宜的多元化生态补偿机制.  相似文献   

冰上丝绸之路与北极油气资源     

赵越  刘建民  韩淑琴  韦利杰 《地质力学学报》2021,27(5):880-889

油气是重要的战略资源。其中天然气作为清洁能源,它曾经是,现在是,在可预期的未来——全球碳减排、中国碳达峰情景下,仍然是最重要的能源资源。能源进口渠道的多元化一直是中国缓解能源紧张的有效措施之一。北极地区油气资源丰富且以天然气为主,已发现的油气资源中绝大多数在俄罗斯,尤其是天然气。但是俄罗斯天然气生产的油气田80%以上已经进入北极圈。2012年,中俄合作开发北极亚马尔液化天然气项目正式启动,标志着中国参与北极油气资源开发利用取得重要进展,也事实上开启了中国主导的"丝绸之路经济带建设"和俄罗斯主导的"欧亚经济联盟建设"对接合作的进程。北极地区已发现的油气资源共计3289.4亿桶油当量,其中石油605.4亿桶（84.1亿吨）油当量,仅为全球已发现石油资源的2.5%;天然气41.4万亿立方米（约合2683亿桶,372.6亿吨油当量）,占全球已发现天然气资源的15.5%。北极地区已发现的油气总资源中绝大多数在俄罗斯,俄罗斯已发现的北极油气资源合计2905亿桶油当量（403.5亿吨）,占88.3%;其中天然气约39.47万亿立方米,约合2557.9亿桶（355.3亿吨）油当量,占北极地区已发现天然气总资源的95%以上。北极待发现的油气资源量也非常可观,约占世界待发现常规石油资源的15%;天然气占世界待发现常规天然气资源的30%,其分布也主要在俄罗斯。随着全球气候变暖和能源战略博弈,俄罗斯为确保其天然气出口及财政来源,必然要加大北极油气、特别是天然气的开采和开发,并通过北极航道运到中国和其他消费国。本文在概括分析北极油气资源分布特点、俄罗斯油气资源与北极战略及北方海航道通行能力的基础上,回顾了北极亚马尔液化天然气项目诞生、发展演变及其国际博弈的背景;概括介绍了中国成功介入北极油气资源项目这一标志性事件过程,并进一步提出了中国对北极油气资源利用战略举措的建议。   相似文献   

新疆尾亚—天湖地区花岗岩类剥蚀程度估算及对区域找矿的启示     

李季霖  陈正乐  周涛发  韩凤彬  张文高  霍海龙  刘博  赵同阳  韩琼  李平  郑加行  陈贵民 《地学前缘》2021,28(3):355-378

尾亚—天湖地区位于新疆中亚造山带东南部的中天山地块内,晚古生代—中生代岩浆活动强烈,产出了战略性关键矿产尾亚钒铁磁铁矿。在详细岩相学观察的基础上,对尾亚、天湖和沙泉子南岩体中的角闪石和黑云母进行了电子探针(EMPA)测试分析,限定了3个岩体结晶的温压条件、氧逸度、含水量和含铁指数等要素,为解析中天山地块的岩浆-成矿物化条件及其区域找矿勘查工作提供参考。测试结果表明,该区花岗岩类中的角闪石富镁、钙、钠,贫钾,属于钙角闪石族;黑云母有高镁、钛、铝、钾和低硅、钠的特征为镁质黑云母。角闪石和黑云母的化学成分揭示其寄主岩浆为钙碱性造山带岩系,具有壳幔混源的特征,推测可能是板块俯冲背景下由地幔楔与大陆地壳物质混熔形成。根据角闪石-黑云母矿物温压计,估算出沙泉子南石英闪长岩的结晶温度为651~753 ℃,压力为31~79 MPa,尾亚二长花岗岩和钾长花岗岩的结晶温度为762~833 ℃,压力为85~215 MPa,天湖花岗闪长岩的结晶温度为668~812 ℃,压力为31~117 MPa。3个岩体岩浆结晶时的氧逸度lgf(O₂)范围为-15.7~-9.4,而且在角闪石结晶时岩浆具有较高的含水量。综合分析,认为该区的花岗岩类具有高温、低压、高氧逸度、富水和高含铁指数的特点,有利于Fe等成矿元素在流体中富集,具有良好的铁矿成矿条件。进一步利用角闪石-黑云母压力计,计算了花岗岩类岩体的侵位深度,从而估算出岩体的剥蚀程度处于2.2~5.5 km,且区域的隆升剥蚀量差异明显;结合现有的矿产地表展布特征,推测天湖岩体一带深部仍具有较好的铁矿找矿潜力。  相似文献