Strategies towards robust interpretations of in situ zircon Lu-Hf isotope analyses     

《地学前缘(英文版)》2020,11(3):843-853

The combination of U-Pb and Lu-Hf compositions measured in zircon crystals is a remarkably powerful isotopic couplet that provides measures on both the timing of mineral growth and the radiogenic enrichment of the source from which the zircon grew.The U-Pb age documents the timing of zircon crystallization/recrystallization and Hf isotopes inform on the degree to which the host melt was derived from a radiogenic reservoir(e.g.depleted mantle) versus an unradiogenic reservoir(e.g.ancient continental crust),or some mixture of these sources.The ease of generating large quantities of zircon U-Pb and Lu-Hf data has been in large part facilitated by instrument advances.However,the dramatic increase in time constrained zircon Lu-Hf analyses in the Earth science community has brought to the fore the importance of careful data collection and reduction workflows,onto which robust geological interpretations may be based.In this work,we discuss the fundamentals of Lu-Hf isotopes in zircon,which then allows us to provide a robust,accessible,methodology for the assessment of data quality.Additionally,we discuss some novel techniques for:data visualization—that facilitates better transparency of data interpretation;integration of geographic information—that may reveal spatial trends where temporal trends were only apparent before;and some novel statistical evaluation tools—that may provide more rigorous interand intra-sample comparisons.  相似文献   

S?o Francisco-Congo Craton break-up delimited by U-Pb-Hf isotopes and trace-elements of zircon from metasediments of the Ara?uaí Belt     

Mathias Schannor  Cristiano Lana  Marco A.Fonseca 《地学前缘(英文版)》2019,10(2):611-628

Detrital zircon U-Pb geochronology combined with Hf isotopic and trace element data from metasedimentary rocks of the Aracuai Belt in southeastern Brazil provide evidence for break-up of the Congo-Sao Francisco Craton. The U-Pb age spectra of detrital zircons from metasediments of the Rio Doce Group(RDG) range from 900-650 Ma and define a maximum depositional age of ca. 650 Ma. Zircon trace element and whole rock data constrain an oceanic island arc as source for the deposition setting of the protoliths to the metasediments. Zircon ε_(Hf)(t) values from these rocks are positive between +1 and +15, supporting previous evidence of a Neoproterozoic extensional phase and oceanic crust formation in a precursor basin to the Aracuai Belt. Recrystallization of detrital zircon at ca. 630 Ma is compatible with a regional metamorphic event associated with terrane accretion to the Paleoproterozoic basement after transition from an extensional to a convergent regime. The juvenile nature, age spectra and trace element composition recorded in detrital zircons of metasediments from the Aracuai Belt correspond with zircons from metasedimentary rocks and oceanic crust remnants of other orogenic belts to its south. This suggests that rifting and oceanic crust formation of the entire orogenic system, the so-called Mantiqueira Province, was contemporaneous, most likely related to the opening of a large ocean. It further indicates that the cratonic blocks involved in the orogenic evolution of the Mantiqueira Province were spatially connected as early as 900 Ma.  相似文献   

郯庐断裂带南段继承性断裂构造控矿模式研究及其应用效果——以皖东北五河金矿整装勘查为例     

汪青松  张顺林  张金会  张家嘉  尤淼 《地质学报》2020,94(10):2965-2977

郯庐断裂带南段的皖东北地区地质构造复杂，多为厚覆盖区，找矿难度大。由于控矿条件难以调查清楚，缺乏具有区域特色的勘查理论指导，区内金矿勘查长期没有取得突破成果。笔者依托五河金矿整装勘查项目，进行了区域重磁异常特征和成矿规律分析研究，发现皖东北地区北东- 北北东向重力低异常具有弧形条带特征，并以郯庐断裂带为界，大致具有旋转对称性。重磁异常保存印支期构造格架痕迹信息，反映了郯庐断裂带南段时空演化特征，显示了北东- 北北东向主要断裂构造具有继承性，形成于印支期，燕山期继续活动，控制白垩纪“红层盆地”和燕山期成岩成矿作用。中低温热液型金多金属矿床和矽卡岩型铜金矿床是皖东北地区主要矿床类型，均受继承性断裂构造控制。结合郯庐断裂的演化特征，利用物探成果引领地质理论创新，提出了郯庐断裂带南段矿床的“继承性断裂构造控矿模式”。根据继承性断裂构造形成机理分析其空间分布规律，总结了矿化蚀变构造带的物探异常标志，解决了皖东北覆盖区成矿预测与找矿靶区圈定难题，在五河金矿整装勘查区应用取得了重要找矿成果，圈定6个金矿找矿靶区，得到了钻探验证，已发现中型规模金矿床2处、小型3处，估算潜在资源量可达特大型规模，实现了安徽省境内郯庐断裂带金矿找矿的重大突破。  相似文献   

Integration of zircon and apatite U–Pb geochronology and geochemical mapping of the Wude basalts(Emeishan large igneous province):A tool for a better understanding of the tectonothermal and geodynamic evolution of the Emeishan LIP     

Jia-Nan Fu  Franco Pirajno  Fan Yang  Espine Shivute  Yi-Zhan Sun  Ning Ai  Kun-Feng Qiu 《地学前缘(英文版)》2021,12(2):573-585

Radiogenic isotopic dating and Lu–Hf isotopic composition using laser ablation-inductively coupled plasma-mass spectrometry(LA-ICP-MS)of the Wude basalt in Yunnan province from the Emeishan large igneous province(ELIP)yielded timing of formation and post-eruption tectonothermal event.Holistic lithogeochemistry and elements mapping of basaltic rocks were further reevaluated to provide insights into crustal contamination and formation of the ELIP.A zircon U–Pb age of 251.3±2.0 Ma of the Wude basalt recorded the youngest volcanic eruption event and was consistent with the age span of 251-263 Ma for the emplacement of the ELIP.Such zircons hadε_Hf(t)values ranging from7.3 to+2.2,identical to those of magmatic zircons from the intrusive rocks of the ELIP,suggesting that crust-mantle interaction occurred during magmatic emplacement,or crust-mantle mixing existed in the deep source region prior to deep melting.The apatite U–Pb age at 53.6±3.4 Ma recorded an early Eocene magmatic superimposition of a regional tectonothermal event,corresponding to the Indian–Eurasian plate collision.Negative Nb,Ta,Ti and P anomalies of the Emeishan basalt may reflect crustal contamination.The uneven Nb/La and Th/Ta values distribution throughout the ELIP supported a mantle plume model origin.Therefore,the ELIP was formed as a result of a mantle plume which was later superimposed by a regional tectonothermal event attributed to the Indian–Eurasian plate collision during early Eocene.  相似文献   

Pre- and post-drill comparison of the Mount Elbert gas hydrate prospect, Alaska North Slope     

M.W. Lee  W.F. AgenaT.S. Collett  T.L. Inks 《Marine and Petroleum Geology》2011,28(2):578-588

In 2006, the United States Geological Survey (USGS) completed a detailed analysis and interpretation of available 2-D and 3-D seismic data, along with seismic modeling and correlation with specially processed downhole well log data for identifying potential gas hydrate accumulations on the North Slope of Alaska. A methodology was developed for identifying sub-permafrost gas hydrate prospects within the gas hydrate stability zone in the Milne Point area. The study revealed a total of 14 gas hydrate prospects in this area.In order to validate the gas hydrate prospecting protocol of the USGS and to acquire critical reservoir data needed to develop a longer-term production testing program, a stratigraphic test well was drilled at the Mount Elbert prospect in the Milne Point area in early 2007. The drilling confirmed the presence of two prominent gas-hydrate-bearing units in the Mount Elbert prospect, and high quality well logs and core data were acquired. The post-drill results indicate pre-drill predictions of the reservoir thickness and the gas-hydrate saturations based on seismic and existing well data were 90% accurate for the upper unit (hydrate unit D) and 70% accurate for the lower unit (hydrate unit C), confirming the validity of the USGS approach to gas hydrate prospecting. The Mount Elbert prospect is the first gas hydrate accumulation on the North Slope of Alaska identified primarily on the basis of seismic attribute analysis and specially processed downhole log data. Post-drill well log data enabled a better constraint of the elastic model and the development of an improved approach to the gas hydrate prospecting using seismic attributes.  相似文献   

景区依托型旅游村与核心景区耦合发展研究   总被引：3，自引：0，他引：3  

杨效忠  叶舒娟  冯立新 《云南地理环境研究》2011,23(2):1-8

旅游村作为新型乡村旅游地,是国家乡村旅游＂百千万工程＂中最基础的组成部分。从景区依托型旅游村的视角出发,选取黄山山岔村与黄山风景区作为案例地,运用多元回归分析方法,对两者之间耦合发展进行研究。结果显示：（1）黄山风景区发展大力提升了山岔村社会经济文化水平;（2）黄山风景区发展对村落环境影响较小;（3）黄山风景区发展对村落社区参与有影响,但并不显著。从景区与村落的发展特征出发,较为系统地揭示景区依托型旅游村与核心景区耦合发展的内在动力源于位差潜势、催化潜势、管理潜势和多稳定潜势,这些形成了景村耦合发展的演化机制。在此基础上,提出了景村耦合发展的4条途径。  相似文献   

秦岭主峰太白山北麓降水化学特征分析     

王少安  卢爱刚  康世昌 《冰川冻土》2015,37(3):676-684

利用太白山北麓2011年12月-2013年7月共39次降水样品数据资料,定量分析了该区域降水化学的特征和时间变化规律.结果表明:太白山北麓地区降水中,除常量离子Na+、NH4+ K+、Mg2、Ca2+、F-、C1-、SO42-、NO3-外,CO32-、HCO3-、PO43-及低分子有机酸也占有相当比例.研究区降水常量离子浓度的顺序依次为:NH4+ ＞SO42-＞Ca2+ ＞NO3-＞Na+ ＞Cl-＞Mg2+ ＞K+ ＞F-,离子总浓度表现出明显的季节变化:夏季(轻度污染)＜秋季(中等污染)＜春季(严重污染)＜冬季(极重污染).利用因子分析法得出太白山北麓地区降水组分主要有三种来源;Na+、C1-、Mg2+、Ca2+主要来自地壳源,SO42-、NO3-、NH4+主要来自人为源,K+和F-主要由海盐源和人为源共同贡献.根据Hysplit后向气流轨迹分析,得出不同路径气团降水离子组分不同:受地形等因素影响,北方路径的气团比南方路径气团离子总浓度较高;受土壤类型影响,西北方向气团降水Na+、Mg2+、Ca2+浓度较高;受人为活动影响,东北方向SO42-、NO3-、NH4+浓度较高.  相似文献   

Zircon U-Pb Geochronology and Geochemical Characteristics of the Volcanic Host Rocks from the Tongyu VHMS Copper Deposit in the Western North Qinling Orogen and Their Geological Significance     

XIONG Xiao  ZHU Laimin  LI Ben  ZHANG Guowei  GONG Hujun  ZHENG Jun  JIANG Hang 《《地质学报》英文版》2015,89(6):1926-1946

Precise in situ zircon U-Pb dating and Lu–Hf isotopic measurement using an LA-ICP-MS system, whole-rock major and trace element geochemistry and Sr–Nd isotope geochemistry were conducted on the volcanic host rocks of the Tongyu copper deposit on the basis of further understanding of its geological characteristics. Three zircon samples from the volcanic host rocks yielded 206Pb/238 U weighted average ages ranging from 436±4 Ma to 440±5 Ma, which are statistically indistinguishable and coeval with the ca. 440 Ma northward subduction event of the Paleo-Qinling oceanic slab. The volcanic host rocks were products of magmatic differentiation that evolved from basalt to andesite to dacite to rhyolite, forming an integrated tholeiitic island arc volcanic rock suite. The primitive mantle-normalized trace element patterns for most samples show characteristics of island arc volcanic rocks, such as relative enrichment of LILE(e.g. Th, U, Pb and La) and depletion of HFSE(e.g. Nb, Ta, Ti, Zr and Hf). Discrimination diagrams of Ta/Yb vs Th/Yb, Ta vs Th, Yb vs Th/Ta, Ta/Hf vs Th/Hf, Hf/3 vs Th vs Nb/16, La vs La/Nb and Nb vs Nb/Th all suggest that both the volcanic host rocks from the Tongyu copper deposit and the volcanic rocks from the regional Xieyuguan Group were formed in an island arc environment related to subduction of an oceanic slab. Values of ISr(0.703457 to 0.708218) and εNd(t)(-2 to 5.8) indicate that the source materials of volcanic rocks from the Tongyu copper deposit and the Xieyuguan Group originated from the metasomatised mantle wedge with possible crustal material assimilation. Most of the volcanic rock samples show good agreement with the values of typical island arc volcanic rocks in the ISr-εNd(t) diagram. The involvement of crustal-derived material in the magma of the volcanic rocks from the Tongyu copper deposit was also reflected in the zircon εHf(t) values, which range from-3.08 to 10.7, and the existence of inherited ancient xenocrystic zircon cores(2616±39 Ma and 1297±22 Ma). The mineralization of the Tongyu copper deposit shows syn-volcanic characteristics such as layered orebodies interbedded with the volcanic rock strata, thus, the zircon U-Pb age of the volcanic host rocks can approximately represent the mineralization age of the Tongyu copper deposit. Both the Meigou pluton and the volcanic host rocks were formed during the ca. 440 Ma northward subduction of the Paleo-Qinling Ocean when high oxygen fugacity aqueous hydrothermal fluid released by dehydration of the slab and the overlying sediments fluxed into the mantle wedge, triggered partial melting of the mantle wedge, and activated and extracted Cu and other ore-forming elements. The magma and ore-bearing fluid upwelled and erupted, and consequently formed the island arc volcanic rock suite and the Tongyu VHMS-type copper deposit.  相似文献   

潞安矿区煤储层裂隙及其与人工裂缝的关系     

李鑫  傅雪海 《煤田地质与勘探》2015,(1)

为了研究潞安矿区煤储层压裂人工裂缝与天然裂隙的关系,井下实测了矿区煤储层宏观裂隙,扫描电镜观测了煤储层显微裂隙;探讨了矿区含裂缝非均质煤岩破裂规律。对原位煤储层条件下人工裂缝沿天然裂隙扩展的最大水平主应力方向与天然裂隙走向夹角的临界值进行了计算。结果表明:矿区的漳村、司马、屯留、常村和五阳5个区块临界值分别为12.00°、9.22°、9.16°、8.56°和7.42°,当最大水平主应力方向与天然裂隙走向的夹角小于此临界角时,人工裂缝沿天然裂隙扩展,反之沿最大水平主应力方向扩展。据此,探讨了潞安矿区原位煤储层压裂裂缝沿天然裂隙扩展的3种模式。  相似文献   

History of scoria-cone eruptions on the eastern shoulder of the Kenya–Tanzania Rift revealed in the 250-ka sediment record of Lake Chala near Mount Kilimanjaro     

Catherine Martin-Jones  Christine Lane  Maarten Van Daele  Thijs Van Der Meeren  Christian Wolff  Heather Moorhouse  Emma Tomlinson  Dirk Verschuren 《第四纪科学杂志》2020,35(1-2):245-255

Reconstructions of the timing and frequency of past eruptions are important to assess the propensity for future volcanic activity, yet in volcanic areas such as the East African Rift only piecemeal eruption histories exist. Understanding the volcanic history of scoria-cone fields, where eruptions are often infrequent and deposits strongly weathered, is particularly challenging. Here we reconstruct a history of volcanism from scoria cones situated along the eastern shoulders of the Kenya–Tanzania Rift, using a sequence of tephra (volcanic ash) layers preserved in the ~250-ka sediment record of Lake Chala near Mount Kilimanjaro. Seven visible and two non-visible (crypto-) tephra layers in the Lake Chala sequence are attributed to activity from the Mt Kilimanjaro (northern Tanzania) and the Chyulu Hills (southern Kenya) volcanic fields, on the basis of their glass chemistry, textural characteristics and known eruption chronology. The Lake Chala record of eruptions from scoria cones in the Chyulu Hills volcanic field confirms geological and historical evidence of its recent activity, and provides first-order age estimates for seven previously unknown eruptions. Long and well-resolved sedimentary records such as that of Lake Chala have significant potential for resolving regional eruption chronologies spanning hundreds of thousands of years.  相似文献