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Geochronology and geochemistry of mafic dykes in the Helanshan complex: Implications for Mesozoic tectonics in the North China Craton

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Geoscience Frontiers 2018年第6期9卷 1711-1724页

作者： Zhenghui Li Xiaoming Liu Yunpeng Dong M.Santosh Feifei Zhang Jie Xu State Key Laboratory of Continental Dynamics Department of Geology Northwest University Department of Earth Sciences Western University(Canada) School of Earth Sciences and Resources China University of Geosciences (Beijing) Department of Earth Sciences University of Adelaide

The Helanshan tectonic belt(HTB) is a major tectonic divide between the Alxa and Ordos blocks in the North China Craton. The geochronology and petrogenesis of the mafic dykes in the northern HTB are keys to understanding the tectonic evolution of this belt. The mafic dykes, intruded into the Neoarchean-Paleoproterozoic metamorphic basement, are mainly composed of diabase with a mineral assemblage of plagioclase(45%-60%), pyroxene(25%-35%), minor quartz and Fe-Ti oxides. The LA-ICPMS U-Pb analysis of zircon grains from representative dykes yield a weighted mean age of 206 ± 1.9 Ma, which represents the crystallization age of the dyke. The diabases show high contents of Fe_2 O_3~T(11.88-17.55 wt.%), low contents of SiO_2(45.65-50.95 wt.%) and MgO(3.31-5.50 wt.%) with low Mg#(=100×MgO/(MgO + FeO) atomic ration) of 33-44. They are characterized by enrichment of light rare earth elements(LREEs) and large ion lithophile elements(LILEs)(e.g., Rb, Ba and Pb), and slight depletion of high field strength elements(HFSEs). These features suggest that the magma has undergone extensive fractionation of olivine and pyroxene but only minor crustal contamination during its evolution. Their high Sm contents and La/Sm ratios, and low Sm/Yb ratios indicate that magma from which the dykes formed was derived from low degree(about 5%) partial melting of an enriched garnet + spinel lherzolite mantle source. Together with regional geology, these geochemical and geochronological data suggest that the mafic dykes in the HTB were formed in an intracontinental extensional setting during the late Triassic.

关键词： Mafic dykes Geochemistry Zircon UePb geochronology Hf isotope Helanshan Tectonic Belt North China Craton

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Spatial-temporal analysis of wetland landscape pattern under the influence of artificial dykes in the Yellow River delta

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Chinese Journal of Population,Resources and Environment 2013年第2期11卷 109-117页

作者： Xin Fu Gaohuan Liu Siyue Chai Chong Huang Fadong Li State Key Laboratory of Resources and Environmental Information System Institute of Geographic Sciences and Natural Resources ResearchCAS Graduate University of Chinese Academy of Sciences Yucheng Comprehensive Experiment Station Key Laboratory of Ecosystem Network Observation and ModelingInstitute of Geographic Sciences and Natural Resources ResearchCAS

The influence of anthropogenic activities,especially artificial dykes,on the coastal wetland landscape is now considered as a serious problem to the coastal *** is important and necessary to analyze changes of coastal landscape pattern under the influence of artificial dykes for the protection and management of coastal *** study aimed to reveal the quantitative characteristics of the coastal wetland landscape and its spatial-temporal dynamics under the influence of artificial dykes in the Yellow River delta(YRD).It was analyzed by the methods of the statistical analysis of landscape structure,five selected landscape indices and the changes of spatial centroids of three typical wetland types,including reed marshes,tidal fiats and aquaculture-salt *** results showed that:(1)Reduction of wetland area,especially the degradation of natural wetlands,had been the principal problem since the dykes were constructed in the *** dykes created conditions for the development of artificial ***,the new born artificial wetlands were still less than the vanished natural wetlands.(2)Compared with the open area,the building of artificial dykes significantly speeded up the changes of landscape patterns and the aggravation of the landscape fragmentation in the closed area.(3)The changes of area-weighted centroids of three typical wetland landscapes were greatly affected by dykes,and the movement of the centroid of the aquaculture-salt field was very sensitive to the dykes constructed in the corresponding period.

关键词： artificial dykes coastal wetland coastal zone of the Yellow River delta landscape pattern spatial-temporal analysis

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Geochemistry and Petrogenesis of Diabase dykes in the Northern Part of EDC, Karnataka, India: Implication for Sulfide Metal Exploration

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Open Journal of Geology 2018年第2期8卷 87-103页

作者： Bhimasandra Chikkanna Prabhakar Department of Geology Bangalore University Bangalore India

Northern part of Eastern Dharwar Craton (EDC) in Karnataka is essentially a granitoid country, frequently intruded by diabase dykes of varied dimensions. Compositionally, majority of them are constituted by pyroxene and plagioclase and less frequently they are olivine-bearing types. One of the major dykes near Thinthini is intensely altered and contains sulfide mineralization brought out by episodic hydrothermal process. Geochemically they are slightly on the higher side of silica content, except the olivine bearing dykes. Their sulfur endowment is also higher. Various discrimination diagrams suggest that they are broadly tholeiitic in composition formed from the less differentiated magma derived from mantle at relatively greater depth and intruded into the granitic rocks which in turn were formed in a subduction setting. The structural deformation prior to and post dating dyke intrusion as deciphered from detailed field studies, alteration of country rocks and hydrothermal activity in the area provide a good background to explore sulfide and other associated metals and also to understand the likely extension of the known mineralized zones.

关键词： Diabase dykes EDC Sulfide Mineralization Thinthini Mineral Exploration

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Structural Relationship between Brittle Deformation and Paleozoic to Mesozoic Basalt dykes in the Precambrian Basement of the Southern Continental Part of the Cameroon Volcanic Line

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International Journal of Geosciences 2017年第3期8卷 318-331页

作者： Nicole Armelle Wambo Simeni Depesquidoux Tchaptchet Tchato Rose Noel Ngo Belnoun Jean Pierre Tchouankoue Alembert Alexandre Ganwa Department of Earth Sciences University of Ngaoundere Ngaoundere Cameroon Department of Earth Sciences University of Yaoundé I Yaoundé Cameroon

The work is a vivid description of the structural relationship between brittle deformation of the Precambrian basement in the southern continental part of the Cameroon Line and intrusive Paleozoic and Mesozoic basalt dykes swarms. A multidisciplinary approach that involves a combination of remote sensing techniques and field studies show that the major trend of brittle structures correspond to well-known regional structures: N70°E (Adamawa Shear Zone), N135°E (upper Benue trend) and N30°E (Cameroon Volcanic Line) corresponding to E-W and N-S directions respectively. Basalt dykes are associated to NE-SW, E-W and NW-SE oriented fractures. An integration of the available information on brittle structures and basalt dykes directions suggest an emplacement of the Mesozoic and Paleozoic basalt dykes structurally controlled by Precambrian structures that were originated through Riedel’s fracture kinematic model with dextral strike-slip Adamawa Shear Zone as the main shear zone during late stage of the Pan-African collision. Spatially, the restriction of the basalt dykes to the corridor of the Adamawa Shear Zone indicate that a rejuvenation of Precambrian faults may very well be the origin of the dykes with possibility that they may have been reworked several times during the Phanerozoic eon.

关键词： Basalt dykes Brittle Tectonics Adamawa Shear Zone Riedel Model Western Gondwana

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New radiometric dating of the dykes from the Hurd Peninsula,Livingston Island,South Shetland Islands

New radiometric dating of the dykes from the Hurd Peninsula,...

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中国科学院地质与地球物理研究所2003学术年会

作者： B.Kamenov P.Monchev Department of Geology and Geography Sofia University St.Kliment Ohridski15 Tzar Osvoboditel Bd.1000 SofiaBalgaria

Fifteen new K-Ar ages in the range of 79-31 Ma are partially confirmed by three Ar/Ar plateaus and isochron data of 64.9±0.4, 55.5±0.1 and 52.8±0.6 *** geochronological data reveal a much more detailed picture of the subduction imprint in the Hurd *** cutting relationships,the dyke emplacement history is divided into four *** Late Cretaceous-Paleocene dykes in the range of 80-60 Ma are related to the main magmatism in Livingston Island and most likely reflect the final stages of subduction of the proto-Pacific oceanic *** Early Eocene dykes(56-52 Ma) fill the gap in volcanic activity 70-50 Ma *** are the only magmatic event manifested at this time in the *** 45-42 Ma dykes may be related to the intrusion of the Barnard Point *** samples of Oligocene age appear to represent the last igneous activities on the Hurd Peninsula prior to the opening of the Bransfield Strait.

关键词： 40Ar/39Ar dating dykes Livingston Island Antarctica

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New Radiometric Dating of the dykes from Hurd Peninsula,Livingston Island,South Shetland Islands

New Radiometric Dating of the Dykes from Hurd Peninsula,Livi...

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中国科学院地质与地球物理研究所2002学术年会

作者： B.KAMENOV P.MONCHEV Department of Geology and Geography Sofia University St.Kliment Ohridsk 15 Tzar Osvoboditel Bd.1000 Sofia-Bulgaria

15 new K-Ar ages within the range of 79-31 Ma are partially confirmed by 3 Ar/Ar plateau and isochron data of 64.9±0.4 Ma,55.5±0.1 Ma and 52.8±0.6 *** new geochronological data reveal a much more detailed picture of the subduction imprint in Hurd *** with the cutting relationship,the dyke emplacement history is divided into four *** Late Cretaceous-Palaeocene dykes in the range of 80-60 Ma are related to the main magmatism in Livingston Island and most likely reflect the final stages of the subduction of the Proto-Pacific oceanic *** Early Eocene dykes(56-52 Ma) fill the gap of the volcanic activity from 70-50 Ma *** are the only one magmatic event manifested in these times in the *** dykes of 45-42 Ma age may be related to the intrusion of the Barnard Point tonalite. The three samples of Oligocene age appear to represent one of the last igneous activities on Hurd Peninsula prior to the opening of Bransfield Strait.

关键词： K-Ar and 40Ar-39Ar dating dykes Livingston Island Antarctica

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SHRIMP U-Pb zircon age,geochemistry and Nd-Hf isotope of Neoproterozoic mafic dyke swarms in western Sichuan:Petrogenesis and tectonic significance

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Science China Earth Sciences 2007年第1期50卷 1-16页

作者： LIN GuangChun LI XianHua LI WuXian Key Laboratory of Isotope Geochronology and Geochemistry Guangzhou Institute of GeochemistryChinese Academy of SciencesGuangzhou 510640China Graduate University of the Chinese Academy of Sciences Beijing 100039China

Neoproterozoic magmatic rocks are widespread in the western margin of the Yangtze block, and their origin and genesis have significant implications for understanding the evolution of the Rodinia super- continent. However, there are currently two opposing interpretations for their petrogenesis and tectonic setting: mantle plume-related and island arc origin. To further verify these two competing models, SHRIMP U-Pb zircon age determinations and geochemical and Nd-Hf isotopic analyses are conducted on the mafic dykes in the Kangdian Rift, western Sichuan. U-Pb dating suggests that these mafic dykes were emplaced at 780―760 Ma, spatially and temporally coeval with the Kangding granitoid complex. The parental magmas of these dykes were derived from a depleted asthenosphere mantle source likely triggered by an anomalously-hot mantle plume. Despite some arc-geochemical features caused by variable degrees of contamination of young island arc crust during magma ascending and emplace- ment, they show general geochemical and Nd-Hf isotopic features similar to those of the intraplate basalts. Our results support the reconstruction model of Rodinia in which the South China block was located between Australia and Laurentia.

关键词： Neoproterozoic mafic dykes Kangdian Rift South China Rodinia

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Practical Applications with Geosynthetic Mats Reinforced with Steel Wire Meshes to Prevent Embankment Damage by Burrowing Large Rodents and Beavers

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Journal of Civil Engineering and Architecture 2017年第1期11卷 8-15页

作者： Paolo Di Pietro Officine Maccaferri SPA Zola Predosa 40069 Italy

Recent studies show an increase in the population of beavers, nutria and other rodents in vast regions of central Europe over the last 15 years. Unfortunately, this caused in many instances considerable damage on large rivers along dykes and earthworks in the floodplain areas, leading to an increased risk of bank failures. However, most of these mammals belong to protected species. This work is aimed at showing positive experience in cooperation with universities, research institutes and environmental agencies regarding measures to permanently safeguard the banks using composite erosion control systems with polymer coated steel wire net （as flexible reinforcement component） and a geosynthetic （to promote vegetation growth）. The steel mesh component works as an effective long-term barrier against the intrusion of mammals, discouraging them from digging inside the core of the dyke. An analysis of the sensitive areas to be protected led also to definition of the characteristics of these interventions （length, shape, escape ways, population areas, etc.）. The study will present several additional benefits when using polymer steel nets along dykes, such as： high and durable erosion protection in overflow areas, promotion of fast and effective vegetation growth （increasing stability）, surface protection against ice impacts （in northern regions）, ease of installation, maintenance, ability to conform to irregular shapes of the slope. This work will also present the positive outcome of research studies along dykes in Germany, Austria and in Italy.

关键词： Beavers nutria polymer coated steel net dykes erosion control.

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The Mekong Delta in Vietnam and Cambodia Is Subsiding and in Need of Remediation

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Open Journal of Soil Science 2022年第5期12卷 171-192页

作者： Kenneth R. Olson Department of Natural Resources and Environmental Sciences College of Agricultural Consumer and Environmental Sciences University of Illinois Urbana USA

Land subsidence and rising sea levels could result in 40% of the Mekong Delta being covered by the South China Sea within the next few decades. The impact of groundwater withdrawal, in the SE Asia mega deltas of Ganges-Brahmaputra Delta, Jakarta Delta, Chao Phraya Delta and Mekong Delta, is a major reason these deltas are sinking. There are lessons to be learned from both failures and successful remediation efforts in other mega deltas as Vietnam policy makers seek to address Mekong Delta subsidence. Without a significant Vietnam government remediation and mitigation efforts, land subsidence in the Mekong Delta will continue. Land subsidence has occurred in the Mekong Delta as a result of the retention of sediments behind the China and Laos dams on the main stem of the Mekong River, reduced flooding peaks, climate change, sea level rise, storm surges and flooding. In addition, subsidence has been exascerbated by compaction, groundwater extraction for shrimp ponds, rice paddies and the household and drinking water needs of approximately 20 million people living on the Mekong Delta in Vietnam and Cambodia. The Mekong Delta shorelines are eroding and significant land areas, including wetlands, are becoming open water. The wetlands and land mass are also subsiding as a result of the reduction in sediment deposition. Large dams on the mainstem of the Mekong River in China and Laos have reduced peak flows and reduced sediment loads in lower Mekong River. Population and industrial growth have increased groundwater extraction and salt water intrusion as the delta subsides leading to consolidation and reduction in the current plumes flowing into the South China Sea. The primary objective of this paper is to assess the impact of groundwater withdrawals for rice paddies, shrimp ponds, aquaculture, industry and drinking water on Mekong Delta land subsidence. The secondary objective is to identify mitigation efforts used in other Southeast Asia deltas and make remediation recomm

关键词： dykes Ho Chi Minh City Jakarta Mekong Delta Sea Walls Subsidence Sediments

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Assessment of the Internal Instability for Granular Soils Subjected to Seepage

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Journal of Geoscience and Environment Protection 2016年第6期4卷 46-55页

作者： Marx Ferdinand Ahlinhan Marius Bocco Koube Codjo Edmond Adjovi Ecole des Sciences et Techniques du Batiment et de la Route (ESTBR) Université Polytechnique d’Abomey (UPA) Abomey Benin

The knowledge of the internal stability of granular soils is a key factor for the design of granular and filter for the geotechnical infrastructures such as dykes, barrages, weirs and roads embankment. To evaluate the internal instability of granular soils different criteria are generally used in the practice. However, the results of these criteria on the same soil may lead to different evaluations of the internal instability. In this paper the common criteria used for the internal instability have been presented and compared as far as possible. It was found that the most internal instability criteria define a limit value for the secant slope of the grain size distribution curve of the granular soils. Based on this finding an own criterion for the evaluation of the internal instability of granular soil has been developed and compared to the common criteria. A very good agreement between some criteria was found. Furthermore, a site specific assessment for the evaluation of the internal instability of granular soil has been proposed in order to get more confidence in this evaluation.

关键词： Internal Instability Granular Soils Seepage Dams dykes Site Specific Assessment Instability Index

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