滇中禄丰地区中元古代早期球颗玄武岩的锆石U-Pb年龄、地球化学特征及其大地构造意义     

刘军平  孙柏东  王晓峰  刘伟  马进华  关学卿  宋冬虎  吕勃烨 《地质论评》2020,66(1):35-51

在1∶5万区域地质调查的基础上,在禄丰地区东川群黑山组新发现了球颗玄武岩及凝灰岩夹层。采用LA-ICP-MS技术测得球颗玄武岩和凝灰质板岩中锆石U-Pb加权平均年龄分别为1678±10 Ma和1572±19 Ma,表明黑山组沉积时代为中元古代早期;其中球颗玄武岩SiO_2含量介于40.83%～52.56%,δEu正异常,大离子亲石元素Rb、Ba和高场强元素Nb、Ta、Th等强不相容元素相对富集,全岩地球化学显示为大陆板内低钛拉斑海相玄武岩,形成于伸展的构造环境,可能为Columbia超大陆裂解的产物。本次的发现,为准确地标定东川群时代、层序及大地构造属性提供新的参考依据,也为重塑整个滇中前寒武纪地层格架提供时代约束。  相似文献   

The British Palaeogene Volcanic Province - Ailsa Craig Geological Conservation Review site     

C.G. Smith  R.M.L. Wignall 《Proceedings of the Geologists' Association. Geologists' Association》2021,132(1):16-23

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The evolution of the terrestrial-terminating Irish Sea glacier during the last glaciation     

Richard Christopher Chiverrell  Geoff Stephen Powell Thomas  Matthew Burke  Alicia Medialdea  Rachel Smedley  Mark Bateman  Chris Clark  Geoffrey A. T. Duller  Derek Fabel  Geraint Jenkins  Xianjiao Ou  Helen Marie Roberts  James Scourse 《第四纪科学杂志》2021,36(5):752-779

Here we reconstruct the last advance to maximum limits and retreat of the Irish Sea Glacier (ISG), the only land-terminating ice lobe of the western British Irish Ice Sheet. A series of reverse bedrock slopes rendered proglacial lakes endemic, forming time-transgressive moraine- and bedrock-dammed basins that evolved with ice marginal retreat. Combining, for the first time on glacial sediments, optically stimulated luminescence (OSL) bleaching profiles for cobbles with single grain and small aliquot OSL measurements on sands, has produced a coherent chronology from these heterogeneously bleached samples. This chronology constrains what is globally an early build-up of ice during late Marine Isotope Stage 3 and Greenland Stadial (GS) 5, with ice margins reaching south Lancashire by 30 ± 1.2 ka, followed by a 120-km advance at 28.3 ± 1.4 ka reaching its 26.5 ± 1.1 ka maximum extent during GS-3. Early retreat during GS-3 reflects piracy of ice sources shared with the Irish-Sea Ice Stream (ISIS), starving the ISG. With ISG retreat, an opportunistic readvance of Welsh ice during GS-2 rode over the ISG moraines occupying the space vacated, with ice margins oscillating within a substantial glacial over-deepening. Our geomorphological chronosequence shows a glacial system forced by climate but mediated by piracy of ice sources shared with the ISIS, changing flow regimes and fronting environments.  相似文献   

地球科学大数据的管理与共享：以英国地质调查局为例     

文蝶  黄浩  史宇坤  杨孙容  杨娇  王媛  侯旭东  樊隽轩 《高校地质学报》2021,27(1):45-57

大数据驱动的研究范式正在引起地学领域的革命,而海量大数据的有效管理和共享是数据高效利用的前提。英国地质调查局作为最早成立的国家地质调查局,拥有海量的地学数据资源,通过近年来对数字化工作的全面推进,在数据的开放共享方面走在了世界各国的最前沿。文章对英国地质调查局的数据资源管理和数据共享方式进行了分析调研,详细介绍了他们的一站式管理平台——开放地学的主体组成,以及他们与同行合作建设的数据库。开放地学全面汇总了地调局内的数据资源,并通过一系列数据共享将所有数据集有机链接,通过数据和模型的巧妙结合,在满足用户数据需求的同时,对数据的应用进行了全方位的拓展,是地球系统科学研究框架下地球科学数字化工作的良好典范。  相似文献   

Continental growth and reworking on the edge of the Columbia and Rodinia supercontinents; 1.86–0.9 Ga accretionary orogeny in southwest Fennoscandia     

Nick M.W. Roberts  Trond Slagstad 《International Geology Review》2015,57(11-12):1582-1606

Geological history from the late Palaeoproterozoic to early Neoproterozoic is dominated by the formation of the supercontinent Columbia, and its break-up and re-amalgamation into the next supercontinent, Rodinia. On a global scale, major orogenic events have been tied to the formation of either of these supercontinents, and records of extension are commonly linked to break-up events. Presented here is a synopsis of the geological evolution of southwest Fennoscandia during the ca. 1.9–0.9 Ga period. This region records a protracted history of continental growth and reworking in a long-lived accretionary orogen. Three major periods of continental growth are defined by the Transscandinavian Igneous Belt (1.86–1.66 Ga), Gothian (1.66–1.52 Ga), and Telemarkian (1.52–1.48 Ga) domains. The 1.47–1.38 Ga Hallandian–Danopolonian period featured reorganization of the subduction zone and over-riding plates, with limited evidence for continental collision. During the subsequent 1.38–1.15 Ga interval, the region is interpreted as being located inboard of a convergent margin that is not preserved today and hosted magmatism and sedimentation related to inboard extensional events. The 1.15–0.9 Ga period is host to Sveconorwegian orogenesis that marks the end of this long-lived accretionary orogen and features significant crustal deformation, metamorphism, and magmatism. Collision of an indenter, typically Amazonia, is commonly inferred for the cause of widespread Sveconorwegian orogenesis, but this remains inconclusive. An alternative is that orogenesis merely represents subduction, terrane accretion, crustal thickening, and burial and exhumation of continental crust, along an accretionary margin. During the Mesoproterozoic, southwest Fennoscandia was part of a much larger accretionary orogen that grew on the edge of the Columbia supercontinent and included Laurentia and Amazonia amongst other cratons. The chain of convergent margins along the western Pacific is the best analogue for this setting of Proterozoic crustal growth and tectonism.  相似文献   

Linking invertebrate burrow distributions (neoichnology) to physicochemical stresses on a sandy tidal flat: implications for the rock record   总被引：1，自引：0，他引：1  

SHAHIN E. DASHTGARD 《Sedimentology》2011,58(6):1303-1325

Invertebrate burrow distributions (neoichnology) across a modern tidal flat are presented as an analogue for interpreting the ichnology of palaeo‐tidal‐flat successions. Burrow distributions are linked to physical and chemical (physicochemical) stresses to establish the main controls on the distribution of biosedimentary structures. Across the tidal flat, there is clear heterogeneity in both the diversity of traces and the intensity of burrowing. This heterogeneity reflects a myriad of physicochemical stresses, with the sedimentation rate dominating burrow distributions. Across all substrates, the total area occupied by organisms rarely exceeds 3% of the tidal‐flat surface, and is commonly <1%; this equates to a bioturbation index value of one. To reach bioturbation index values of two to six, sediments must be available to biogenic reworking and/or recolonization. With an increasing sedimentation rate, substrates are rapidly buried and re‐exposed, which limits the time when a substrate is available to colonization. For palaeo‐ichnological studies, this research presents several key results. (i) Burrow cross‐cutting relationships in tidal‐flat successions commonly reflect natural heterogeneities in the areal distribution of infaunal communities, rather than infaunal tiering. (ii) Ichnofabric analysis of palaeo‐tidal flats with a high sedimentation rate would yield fabrics that reflect heterogeneities in the areal distribution of infaunal communities rather than variability in the physicochemical stresses of the environment. (iii) The composite trace‐fossil assemblage of tidal flats cannot be attributed to a single ichnofacies, but instead comprises elements typical of multiple ichnofacies. (iv) The main controls on trace assemblages across tidal flats in fully marine settings are sedimentological and include the sedimentation rate and, to a lesser extent, grain size.  相似文献   

陕西小秦岭地区太华群的锆石U-Pb年龄和 Hf同位素组成   总被引：16，自引：10，他引：6  

时毓  于津海  徐夕生  唐红峰  邱检生  陈立辉 《岩石学报》2011,27(10):3095-3108

本文对陕西华山岩体南侧一个太华群黑云斜长片麻岩进行了地球化学、锆石U-Pb年龄和Hf同位素分析.地球化学分析显示其原岩为中酸性钙碱性花岗质岩石,稀土含量较低( ∑REE =83.13×10-6),但富集Pb和LILE元素(如Rb、Ba).锆石的176Hf/177Hf比值变化于0.281258～0.281404,具明显负的εHf(t)值(-6.86～- 11.23).锆石的Hf同位素模式年龄(2.96 ～3.24Ga)表明原岩是由中太古代地壳演化而来.对比显示小秦岭太华群黑云斜长片麻岩与鲁山地区的太华群具有相似的中太古代地壳源区,但它们的形成时代可能不同.锆石内部结构、Th/U比值以及定年结果显示小秦岭地区的太华群在～1.91Ga经历了一期重要的变质热事件,该事件与Columbia超大陆拼合时的全球性碰撞造山事件相关联.小秦岭太华群为华北克拉通块体南缘的地质单元,但各地区太华群在原岩组成、形成时代和变质时代上具有不同的特征,太华群应是一个杂岩体,至少可以解体为新太古代和古元古代两部分.  相似文献   

扬子陆块~2.0 Ga的区域变质事件对南北黄陵古元古代差异演化的启示     

陈超  苑金玲  郭盼  黎方云  孔令耀  杨金香  毛新武 《中国地质》2020,47(4):899-913

扬子陆核黄陵地区发育较为完整的太古宙—古元古代片麻岩、表壳岩组合(即崆岭杂岩),前人调查研究认为南北黄陵Ar-Pt1具有一致的物质组成和地质演化过程。笔者分别对南北黄陵太古宙花岗质片麻岩进行锆石年代学研究发现,北黄陵2件样品(HL013-1、HL013-2)均存在大量锆石发育岩浆核-变质边结构,都获得～2.8 Ga原岩结晶年龄和～2.0 Ga变质年龄;而南黄陵1件样品(HL005-3)以具振荡环带结构的岩浆锆石为主,仅获得～2.9 Ga原岩结晶年龄。结合前人研究成果发现,～2.0 Ga的变质年龄在北黄陵太古宙—古元古代的花岗片麻岩、表壳岩中广泛发育,而在南黄陵相似建造中均未获得,一定程度上说明北黄陵地区广泛遭受～2.0 Ga的区域变质作用而南黄陵不发育,南北黄陵在古元古代可能处在不同地块或者同一地块不同部位。2.1～1.6 Ga的构造岩浆事件的分布特点说明扬子陆块可能存在多条古元古代造山带,扬子陆块古元古代以多块体拼贴为特点,广泛记录2.1～1.6 Ga的构造岩浆事件说明扬子陆块是全球哥伦比亚超大陆的重要组成部分。  相似文献   

Leachable particulate iron in the Columbia River,estuary, and near-field plume     

Sherry M. Lippiatt  Matthew T. Brown  Maeve C. Lohan  Carolyn J.M. Berger  Kenneth W. Bruland 《Estuarine, Coastal and Shelf Science》2010

This study examines the distribution of leachable particulate iron (Fe) in the Columbia River, estuary, and near-field plume. Surface samples were collected during late spring and summer of 2004–2006 as part of four River Influence on Shelf Ecosystems (RISE) cruises. Tidal amplitude and river flow are the primary factors influencing the estuary leachable particulate Fe concentrations, with greater values during high flow and/or spring tides. Near the mouth of the estuary, leachable particulate Fe [defined as the particulate Fe solubilized with a 25% acetic acid (pH 2) leach containing a weak reducing agent to reduce Fe oxyhydroxides and a short heating step to access intracellular Fe] averaged 770 nM during either spring tide or high flow, compared to 320 nM during neap tide, low flow conditions. In the near-field Columbia River plume, elevated leachable particulate Fe concentrations occur during spring tides and/or higher river flow, with resuspended shelf sediment as an additional source to the plume during periods of coastal upwelling and spring tides. Near-field plume concentrations of leachable particulate Fe (at a salinity of 20) averaged 660 nM during either spring tide or high flow, compared to 300 nM during neap tide, low flow conditions. Regardless of tidal amplitude and river flow, leachable particulate Fe concentrations in both the river/estuary and near-field plume are consistently one to two orders of magnitude greater than dissolved Fe concentrations. The Columbia River is an important source of reactive Fe to the productive coastal waters off Oregon and Washington, and leachable particulate Fe is available for solubilization following biological drawdown of the dissolved phase. Elevated leachable Fe concentrations allow coastal waters influenced by the Columbia River plume to remain Fe-replete and support phytoplankton production during the spring and summer seasons.  相似文献   

Central England temperature since AD 1850: the potential of stable carbon isotopes in British oak trees to reconstruct past summer temperatures     

G. H. F. Young  R. J. Bale  N. J. Loader  D. Mccarroll  N. Nayling  N. Vousden 《第四纪科学杂志》2012,27(6):606-614

In regions with seasonal temperate climatic regimes, tree growth is rarely controlled by any single environmental factor. As a consequence, the development of robust palaeoclimate reconstructions has proved challenging. Tree‐ring stable carbon isotope ratios (δ¹³C), however, are controlled primarily by photosynthetic rate, not by net growth. Therefore, at sites where climatic controls on tree‐ring growth are not strongly expressed, a robust (isotopic) palaeoclimate signal may still potentially be preserved. This hypothesis was tested using a 160‐year record of δ¹³C measured from the pooled latewood cellulose of six Quercus petraea L. (sessile oak) trees from Allt Lan‐las in West Wales, UK. Raw δ¹³C values were corrected for changes in the isotopic ratio of atmospheric carbon dioxide and for changes in the behaviour of trees due to the increasing availability of atmospheric CO₂ since AD 1850. Strong correlations with local summer temperature and sunshine are reported, and also with the Central England Temperature record over the full length of the isotopic chronology (AD 1850–2010) (r = 0.69, P < 0.001). We conclude that tree‐ring stable isotopes can be used to extract strong palaeoclimate signals even from oak trees growing in a temperate maritime climate. This demonstrates the potential for extracting robust palaeoclimatic information from the very long and well‐replicated oak chronologies which have been developed in western and central Europe primarily for dating rather than palaeoclimatic research purposes. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献