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1.
L.L. Sloss 《地学学报》1992,4(3):320-328
Over the past one hundred years North American geologists have been influenced by concepts of Earth history based on periodic events involving marked (‘Neocatastrophic’) changes and competing concepts involving steady-state (‘Uniformitanan’) behaviour. T.C. Chamberlin, a late 19th-/early 20th-Century exponent of a nonuniformitarian scenario of earth history, proclaimed ‘diastrophism as the ultimate basis of correlation’ - meaning that geological history is punctuated by orogenic paroxysms causing retreat of epicontinental waters to oceanic basins, creating segmentation of the stratigraphic and chronological record. At mid-Century James Gilluly gained wide support for the proposition that orogeny has followed a Uniformitarian, near-steady-state course. Accordingly, episodic diastrophism is a myth and cannot be the basis for periodic eustatic sea-level change, interregional unconformities, etc. In more recent decades two powerful new influences on geological thought have emerged. The global tectonic paradigm has forced upon us the realization that rearrangements of lithospheric plates are capable of changing the freeboard of continents. At the same time technological advances in the acquisition and processing of seismic-reflection data have been seized by receptive minds to organize the newly available stratigraphic imagery for application to the discipline of seismic stratigraphy which emphasizes the identification and correlation of unconformity-bounded successions of strata. Expansion of the methodology to the outcrop, beyond the limitations of seismic resolution, has brought about the flowering of the New Sequence Stratigraphy, doctrine that has deservedlyachieved wide application and acclaim. Practitioners of sequence stratigraphy, impressed by the distances over which unconformity-bounded stratal units can be correlated, hew to the belief that eustatic (commonly glacially engendered) sea-level change is the control. This paper examines evidence of tectonic episodes affecting cratons and their margins. These offer promise of a more satisfactory understanding of stratigraphic sequences and of the Earth history they represent. Consideration of these matters makes it inescapable that the elevation and subsidence of cratons (and their component basins and arches) reflect tectonic phenomena of the continental lithosphere quite independent of eustatic events. 相似文献
2.
Mark A. Woods Jonathan R. Lee 《Proceedings of the Geologists' Association. Geologists' Association》2018,129(3):255-263
Over the past one billion years, England has experienced a remarkable geological journey. At times it has formed part of ancient volcanic island arcs, mountain ranges and arid deserts; lain beneath deep oceans, shallow tropical seas, extensive coal swamps and vast ice sheets; been inhabited by the earliest complex life forms, dinosaurs, and finally, witnessed the evolution of humans to a level where they now utilise and change the natural environment to meet their societal and economic needs. Evidence of this journey is recorded in the landscape and the rocks and sediments beneath our feet, and this article provides an overview of these events and the themed contributions to this Special Issue of Proceedings of the Geologists’ Association, which focuses on ‘The Geology of England – critical examples of Earth History’. Rather than being a stratigraphic account of English geology, this paper and the Special Issue attempts to place the Geology of England within the broader context of key ‘shifts’ and ‘tipping points’ that have occurred during Earth History. 相似文献
3.
A multi‐system geochronology in the Ad‐3 borehole,Pannonian Basin (Hungary) with implications for dating volcanic rocks by low‐temperature thermochronology and for interpretation of (U–Th)/He data 
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下载免费PDF全文 Martin Danišík László Fodor István Dunkl Axel Gerdes János Csizmeg Mária Hámor‐Vidó Noreen J. Evans 《地学学报》2015,27(4):258-269
Independent geochronological and thermal modelling approaches are applied to a biostratigraphically exceptionally well‐controlled borehole, Alcsútdoboz‐3 (Ad‐3), in order to constrain the age of Cenozoic geodynamic events in the western Pannonian Basin and to test the efficacy of the methods for dating volcanic rocks. Apatite fission track and zircon U–Pb data show two volcanic phases of Middle Eocene (43.4–39.0 Ma) and Early Oligocene (32.72 ± 0.15 Ma) age respectively. Apatite (U–Th)/He ages (23.8–14.8 Ma) and independent thermal and subsidence history models reveal a brief period of heating to 55–70 °C at ~17 Ma caused by an increased heat‐flow related to crustal thinning and mantle upwelling. Our results demonstrate that, contrary to common perception, the apatite (U–Th)/He method is likely to record ‘apparent’ or ‘mixed’ ages resulting from subsequent thermal events rather than ‘cooling’ or ‘eruption’ ages directly related to distinct geological events. It follows that a direct conversion of ‘apparent’ or ‘mixed’ (U‐Th)/He ages into cooling, exhumation or erosion rates is incorrect. 相似文献
4.
Syenogranitic dykes in the north of Egypt’s Eastern Desert are of geological and economic interest because of the presence of magmatic and supergene enrichment of radioactive mineralization. Zircon crystal morphology within the syenogranitic dykes allows precise definition of sub-alkaline series granites and crystallized at mean temperature of about 637 °C. The growth pattern of the zircons suggest magmatic and hydrothermal origins of radioactive mineralization. Hydrothermal processes are responsible for the formation of significant zircon overgrowth; high U-zircon margins might have occurred contemporaneously with the emplacement of syenogranitic dykes which show anomalous uranium (eU) and thorium (eTh) contents of up to 1386 and 7330 ppm, respectively. Zircon chemistry revealed a relative increase of Hf consistent with decreasing Zr content, suggesting the replacement of Zr by Hf during hydrothermal activity. Visible uranium mineralization is present and recognized by the presence of uranophane and autunite. 相似文献
5.
A. W. G. Whittle 《Australian Journal of Earth Sciences》2013,60(2):21-46
Abstract Recent geological work in South Australia has resulted in the discovery of a wide range of radioactive minerals, some of which are of economic value. Nearly all known groups of radioactive mineral have been found. Those, including both thorium and uranium rich varieties, are restricted to the Pre-Cambrian provinces and mostly to the Archaean. The minerals are discussed on the basis of both field mode of occurrence and chemical composition. Special mention is made of several minerals which are very rare and which, it is believed, are recorded herein for the first time in Australia. Extensive petrological and related mineragraphic investigation, coupled with field geological work during the past few years, has led to the discovery of an important genetic relationship between soda metasomatism and uranium-titanium metallization in South Australia. The reality of the so-called metamict state and of the mineral davidite is discussed and alternative suggestions are made. The inability of the mineralogist, with present equipment, to cope with many primary radioactive minerals is pointed out. 相似文献
6.
锆石的U-Pb测年、Hf和O同位素及稀土、微量元素的研究与应用已获得诸多进展,但锆石中铀含量所蕴藏的地质意义却较少被关注。华南花岗岩型铀矿床的铀源一直存在争议,不同观点认为其分别来自早期已固结地质体、分异岩浆、地幔柱或热点以及U、Th、K富集圈。为尝试利用锆石中的铀含量来追索铀源,本文通过搜集诸广山南体花岗岩锆石U-Pb同位素测年文献,掌握了该花岗岩中14个岩体、37件样品、3种岩性,共467个锆石定年数据。通过数据分析发现印支期(253Ma、244Ma)和燕山期(139Ma、124Ma)具高分异特征的4件酸性岩脉(小岩体)样品中锆石的铀含量明显高于同期岩体。依据铀矿床中高分异酸性岩脉(小岩体)侵位期、基性岩脉侵位期、铀成矿早期(140~90Ma)三者的良好对应关系,结合这一锆石铀含量指示,初步认为华南花岗岩型铀矿床中铀可能主要来自高分异花岗岩浆;推测花岗岩型铀成矿可能属壳幔混合作用结果,即铀源来自地壳分异岩浆,成矿流体和矿化剂主要来自地幔,而成矿空间受断裂系统控制。岩体锆石铀含量或可在铀源丰度、矿床品位判别等方面发挥积极作用。 相似文献
7.
《地学前缘(英文版)》2023,14(2):101523
Oxygen isotopes are a versatile tool to address a wide range of questions in the Earth sciences. Applications include geothermometry, paleoclimatology, tracing of geochemical reservoirs, fluid-rock interaction, magmatic petrogenesis, and identification of extra-terrestrial materials. Zircon arguably provides one of the most robust records of primary magmatic O isotope ratio due to low diffusion rates in crystalline grains. The ability to correlate zircon O isotopes with temporal and petrogenetic information (e.g. U-Pb geochronology, Lu-Hf isotopes, and trace elements) makes this mineral a key archive for understanding Earth’s crustal evolution. Consequently, zircon O isotope geochemistry has found widespread usage to address fundamental questions across the earth and planetary sciences. The general apparent ease of O isotopic acquisition through the advancement of rapid in situ techniques (i.e. secondary ion mass spectrometry; SIMS) and associated dedicated national laboratories has led to the generation of large O isotopic data sets of variable quality, highlighting the importance of a coherent workflow for data collection, reduction, and presentation. This paper presents a set of approaches for measurement, assessment, and reporting of zircon O isotope data. The focus in this contribution is on in situ analysis via secondary ion mass spectrometry using large geometry instruments, but other commonly used techniques are briefly reviewed for context. This work aims to provide an analytical framework necessary for geologically meaningful interpretation of O isotope data. In addition, we describe inherent geological (e.g. radiation-induced disturbance of the zircon O isotopic system) and analytical (e.g. fractionation due to sample topography effects) challenges and outline means to identify and avoid such issues as a prerequisite to the generation of robust primary O isotopic signatures for geological interpretation. 相似文献
8.
This paper reviews critical features of basin-related uranium mineral systems in Australia. These mineral systems include Proterozoic unconformity-related uranium systems formed predominantly from diagenetic fluids expelled from sandstones overlying the unconformity, sandstone-hosted uranium systems formed from the influx of oxidised groundwaters through sandstone aquifers, and calcrete uranium systems formed from oxidised groundwaters flowing through palaeochannel aquifers (sand and calcrete). The review uses the so-called ‘source-pathway-trap’ paradigm to summarise critical features of fertile mineral systems. However, the scheme is expanded to include information on the geological setting, age and relative timing of mineralisation, and preservation of mineral systems. The critical features are also summarised in three separate tables. These features can provide the basis to conduct mineral potential and prospectivity analysis in an area. Such analysis requires identification of mappable signatures of above-mentioned critical features in geological, geophysical and geochemical datasets. The review of fertile basin-related systems shows that these systems require the presence of at least four ingredients: a source of leachable uranium (and vanadium and potassium for calcrete-uranium deposits); suitable hydrological architecture enabling connection between the source and the sink (site of accumulation); physical and chemical sinks or traps; and a post-mineralisation setting favourable for preservation. The review also discusses factors that may control the efficiency of mineral systems, assuming that world-class deposits result from more efficient mineral systems. The review presents a brief discussion of factors which may have controlled the formation of large deposits in the Lake Frome region in South Australia, the Chu-Sarysu and Syrdarya Basins in Kazakhstan and calcrete uranium deposits in the Yilgarn region, Western Australia. 相似文献
9.
俯冲物质深地幔循环——地球动力学研究的一个新方向 总被引：1，自引：0，他引：1
地球上发生的各种地壳运动,大规模的火山喷发,不同深度不同规模的地震活动,规模宏大的山脉和高原的形成,以及地球历史上发生的大陆漂移运动,都被认为与板块构造活动密切相关。但这些运动的动力源究竟来自何方?如何去发现和证明它们的存在以及从理论上去认识和解释,是当今地球科学面临的巨大挑战,也是今后很长一段时间内地球科学的前沿和热点问题。近些年,人们通过各种方法,试图从更深部寻找板块作用动力学的证据。首先是地震层析研究取得了很大进展,获得了许多区域性和全球的高分辨率3-D地震地幔波速结构,使得我们得以认识地球深部的结构,探讨地幔的物质组成,流体的作用和动力学过程。证据显示,板块俯冲不仅可以到达地幔过渡带深度,而且可达到下地幔底部,堆积在核幔边界的上部,成为核幔边界产生的地幔柱的重要物质组成。其次是开展了大量的实验岩石学研究,模拟了一系列地球深部的高温高压矿物组合,被认为可能代表了地幔过渡带和下地幔的矿物组合,甚至核幔边界的含水矿物组合。另一方面,计算机模拟实验揭示了冷的大洋岩石圈发生深俯冲是可行的。尤为重要的是,许多来自地幔过渡带甚至下地幔深度的高压矿物已经在自然界陆续被发现,证明其中一些矿物是源自深俯冲的洋壳物质,记录了俯冲洋壳再循环的历史,如产在巴西、南非和加拿大等金伯利岩中的超深金刚石矿物包裹体。此外,洋岛玄武岩和大陆板内玄武岩的研究,也找到了早期俯冲下去的壳源岩石的同位素证据。近些年发现的蛇绿岩型金刚石是另一实证,其金刚石碳同位素和包裹体研究表明它们源自早期俯冲下去的壳源物质,被认为是研究俯冲物质深部再循环的一个新窗口。这些俯冲再循环的物质,被认为是通过地幔柱的活动从深部带至浅表。本文综述了地球深部物质循环的研究现状,强调了该研究的重要性,并认为俯冲物质深部循环是地球动力学研究的一个新方向。 相似文献
10.
Gregory J. Clark Brian L. Gulson John A. Cookson 《Geochimica et cosmochimica acta》1979,43(6):905-918
A proton microprobe has been used to determine Pb, Tl, Hf and Zr distributions across four single zircon crystals separated from a ‘rapakivi’ granite. The Pb and Zr data are quantitative: Pb and Tl concentrations were below the measurable limits for determinations in situ by most other techniques. The distribution of U in the same crystals was determined by the fission track technique. Limits on precision of U allow only a qualitative correlation of U and Pb, whereas the Tl and Pb correlation is more exactly determined.Zircons with distinct cores and overgrowths exhibited uniform Zr and Hf concentrations across the crystals, whereas the high U rims and ‘inclusions’ (domains) also had high Tl and Pb contents. Since almost all the Pb in these zircons is derived by radioactive decay of U, the Tl substitution has paralleled that of U. The results indicate that the high U domains are ‘hot spots’ rather than a separate mineral phase. The strong positive correlation of U and Pb indicates that there is little U daughter product migration relative to U, within the crystal. However, for the zircon population investigated here, the data are equivocal on the question of whether U addition to zircon crystals is associated with new zircon growth or not. In either case, the heterogeneous U and Pb distributions complicate any interpretations of U-Pb isotopic analysis for such zircon populations. 相似文献
11.
G.P. Glasby 《Geology Today》2012,28(6):214-216
If we consider the solar system, our closest neighbour in terms of similarity is undoubtedly Mars. The planet has many features in common with the Earth, first discovered by the space probe Mariner in 1971. Since then, Mars has been subject to increasing interest by astronomers and geologists alike, and new data will start arriving when the six‐wheeled car‐sized rover named Curiosity begins rolling across the surface of Mars in August 2012. But how much do we already know about the ‘Red Planet?’ The aim of this article is to make information on Mars more available to the lay reader at a time when the ‘Red Planet’ is under the spotlight. 相似文献
12.
The principal aspects of reconstruction of conditions and paths of fluid migration in massifs of crystalline rocks are considered. The spatiotemporal relationships between stress fields, brittle failure, and migration of radionuclides are discussed. The main attention is focused on the staged character of tectonic events, fluid circulation conditions, and the sequence of uranium mineral formation as determined with structural, geological, tectonophysical, petrophysical, petrographic, mineralogical and geochemical, microstructural, microthermometric, and radiographic methods. As is exemplified in uranium deposits and massifs of silicic igneous rocks, the comprehensive consideration of the tectonodynamics of fluid-conducting structural elements and radionuclide migration is necessary for providing insights into the localization and redistribution of uranium, the PT conditions of uranium ore formation, and the forecast for long-term safety of disposal of radioactive wastes in crystalline rocks. 相似文献
13.
14.
Decoding Neoarchaean to Palaeoproterozoic tectonothermal events in the Rangnim Massif,North Korea: regional correlation and broader implications 总被引：1，自引：0，他引：1
Xiaohui Zhang Yanbin Zhang Mingguo Zhai Fuyuan Wu Quanlin Hou Lingling Yuan 《International Geology Review》2017,59(1):16-28
Any knowledge about Archaean to Palaeoproterozoic magmatic and metamorphic events in North Korea has the potential to make a significant difference to our understanding of the early tectonic configuration and evolution of East Asia. This zircon U–Pb dating and Hf isotopic study documents multiple Neoarchaean to Palaeoproterozoic tectonothermal events from the meta-igneous complex in the Machollyong ‘Group’ of the Rangnim Massif. Two tonalitic-trondjemitic gneiss samples record a crystallization age of meta-igneous protoliths at ca. 2.56 Ga and multiple migmatization and metamorphism from 2.52 to 1.85 Ga. A meta-dolerite sample yields a magmatic emplacement age of ca. 1.83 Ga. In situ zircon Hf isotopic data indicate that most zircons from the gneiss samples have εHf(t) values from –16.9 to + 3.1 and crustal model ages from 2.84 to 3.73 Ga, whereas magmatic zircons from the meta-dolerite dike record εHf(t) values from –5.2 to + 5.2 and model ages of 2.05–2.44 Ga. The first-recognized Neoarchaean tonalitic-trondjemitic migmatite complex in the Rangnim Massif, together with previously identified tonalitic-trondhjemitic-granodioritic (TTG) rocks in the Rimjingang Belt and the coeval counterparts in western Gyeonggi massif, represents the oldest crustal nuclei in the Korean Peninsula. The multiple tectonothermal events in this study present reliable evidence not only for attesting to consanguinity of the basement between the Korean Peninsula and the North China Craton but also for defining the influence scope of the late Palaeoproterozoic orogeny in the Korean Peninsula. 相似文献
15.
Dustin Trail E. Bruce Watson Nicholas D. Tailby 《Journal of the Geological Society of India》2013,81(5):605-636
Geologists investigate the evolution of the atmosphere, crust, and mantle through time by direct study of the rock record. However, the Hadean eon (>3.85 Ga) has been traditionally viewed as inaccessible due to the absence of preserved rocks. The discovery of >4.0 Ga detrital zircons from Western Australia in the 1980s — coupled with the development of new micro-analytical capabilities — made possible new avenues of early Earth research. The prevailing view that emerged is that the early Earth may have contained a stable hydrosphere, water-saturated or (near watersaturated) granitic magmas, and volcanic emanations dominated by neutral gas species (e.g., CO2, H2O, and SO2). The Hadean Earth may have been capable of supporting life ～200 Ma after accretion and perhaps earlier. Many of these models are formulated — or have been subsequently supported — by laboratory experiments of zircon. Important petrological variables such as temperature, pressure, oxygen fugacity, and component activities (e.g., SiO2/TiO2-activities) can be controlled. These experiments are fundamental for extrapolation to ‘deep time’ because they provide a means to understand primary chemistry preserved in ancient zircons. This review paper specifically focuses on zircon experimental studies (oxygen isotope fractionations, Ti-thermometry, and redox sensitive element incorporation into zircon), which have influenced our view of the very early Earth. 相似文献
16.
自生泥晶,也称作原地微晶碳酸钙或原地灰泥以区分他生泥晶或异地泥晶,指的是通过无机和/或有机媒介过程作用在原地形成的泥晶碳酸钙。在前人的基础上,对自生泥晶概念的提出和发展进行了概括;对自生泥晶的矿物组成、显微结构、荧光和阴极发光特征进行了总结;对自生泥晶的形成过程和来源（包括生物矿化作用、有机矿化作用和无机沉淀三种方式）进行了探讨;对自生泥晶在不同沉积环境碳酸盐岩中的贡献及其地球化学指示进行了论述;对自生泥晶在地质历史时期的分布做了归纳;最后对自生泥晶的后续研究提出了一些展望。认为正确认识自生泥晶的性质,其形成过程和来源对碳酸盐岩的结构成因分类、地质历史时期生物礁丘的演化和地球化学指示、建筑工程和环境修复、探寻地外生命和油气地质等方面都将产生深远的影响。 相似文献
17.
Nina Kirchner Kolumban Hutter Martin Jakobsson Richard Gyllencreutz 《Quaternary Science Reviews》2011,30(25-26):3691-3704
The simulation of dynamically coupled ice sheet, ice stream, and ice shelf-systems poses a challenge to most numerical ice sheet models. Here we review present ice sheet model limitations targeting a broader audience within Earth Sciences, also those with no specific background in numerical modeling, in order to facilitate cross-disciplinary communication between especially paleoglaciologists, marine and terrestrial geologists, and numerical modelers. The ‘zero order’ (Shallow Ice Approximation, SIA)-, ‘higher order’-, and ‘full Stokes’ ice sheet models are described conceptually and complemented by an outline of their derivations. We demonstrate that higher order models are required to simulate coupled ice sheet-ice shelf and ice sheet-ice stream systems, in particular if the results are aimed to complement spatial ice flow reconstructions based on higher resolution geological and geophysical data. The zero order SIA model limitations in capturing ice stream behavior are here illustrated by conceptual simulations of a glaciation on Svalbard. The limitations are obvious from the equations comprising a zero order model. However, under certain circumstances, simulation results may falsely give the impression that ice streams indeed are simulated with a zero order SIA model. 相似文献
18.
Mineralogical assemblages are fundamental to the interpretation of geological processes. Zircon is an integral petrographic component of the mineral assemblages present in fenites (rocks formed by alkaline metasomatism) associated with the 136 Ma-aged Chilwa Island carbonatite complex, Malawi. Zircon exhibits contrasting characteristics and properties across the fenite aureole that surrounds the carbonatite stock. It shows intense grain dissolution and subsequent replacement by pyrochlore in the more intensely metasomatised ‘high-grade’ fenite of the innermost part of the aureole. By contrast, relict zircon crystals form the nucleus for the development of apatite-ilmenite-REE mineral assemblages in less altered zones. These changes in zircon properties are considered to be evidence of the diverse nature of fluids that metasomatised the Chilwa Islands fenite aureole. Although zircon is a principal component of the fenite mineral assemblages, when dated by LA-ICP-MS techniques it was found to predate the other minerals present in the mineral assemblages and thus, the age of carbonatite intrusion, by over 380 Ma. Instead of co-crystallising with the assemblage, zircon is therefore interpreted as providing a focus around which the minerals in the fenite assemblage formed. This implies that caution is needed both in the interpretation of Zr mobility in metasomatic assemblages, and also in attributing a zircon age to the assemblage as a whole in such sequences. 相似文献
19.
STEPHEN MOORBATH 《Geology Today》1985,1(3):75-79
The ages of rocks and minerals can be determined by measuring the accumulation of the products of radioactive decay within them. The results provide a time–scale for the Earth and for the major geological events which have shaped the Earth's continental crust since it first started to separate from the mantle at least 3700 million years ago. The Earth itself is about 4600 million years old. 相似文献
20.
Zircon U-Pb SIMS dating combined with in-context (in thin section) monazite and xenotime U + Th-total Pb dating was used to clarify the Palaeozoic evolution of the ‘cold’ Chopok granite (Nízke Tatry Mountains, Slovakia). Four distinct zircon, monazite and xenotime age domains testify to a prolonged evolution from igneous formation to multi-stage metasomatism and hydrothermal overprinting. The geological interpretation of age patterns from ‘cold’ granites, expected to have low zircon saturation temperatures (<800 °C) and relatively high amounts of zircon inheritance, requires special care, especially for what concerns proper attribution of zircon inheritance and igneous growth ages. These issues can be resolved using zircon saturation temperatures (TZrn) as proxy for the amount of zircon inheritance in combination with the temperature differences between TZrn and the granite solidus. In this respect, the Chopok granite is an atypical ‘cold’ granite. Due to TZrn being substantially lower (ca. 80 °C ± 50 °C) than the granite solidus temperature, practically no zircon inheritance was found. The zircon age data indicates that the Chopok granite is a product of an Early Ordovician (475.8 ± 3.3 Ma) magmatic event, corresponding with the widespread Early Palaeozoic magmatism recorded throughout the European Variscan belt. This is further corroborated by phosphate mineral ages. The post-magmatic activity recorded in the U-Pb systematics of zircon and phosphates overgrowths can be related to the different phases of the evolution of the Variscan orogen: Early Carboniferous (ca. 352 Ma) metasomatism documents the main Variscan orogenic event, whereas the Permo-Triassic age (ca. 255 Ma) reflects thermo-tectonic activity associated with large-scale crustal extension, contemporaneous with the initial continental leading to the break-up of Pangea. 相似文献