Geochemistry and U–Pb SHRIMP zircon chronology of granitoids and microgranular enclaves from Jhirgadandi Pluton of Mahakoshal Belt,Central India Tectonic Zone,India     

《Journal of Asian Earth Sciences》2013

The northern part of Central India Tectonic Zone (CITZ) is delineated by an arc-shaped supracrustal belt commonly referred to as Mahakoshal Belt, which is considered as a product of intense rifting of sialic crust that occurred at ca 2400–2600 Ma. Several granitoid plutons intrude the Parsoi Formation of Mahakoshal Belt. Among these, an elliptical small stock-like granitoid body trending E–W is exposed in and around Jhirgadandi region of Mahakoshal Belt, referred herein as Jhirgadandi Pluton. It is composed of minor amount of mafic rocks (diorite) and predominant granitoids. Country-rock pelitic xenoliths and microgranular enclaves (ME) are commonly hosted in granitoids but are absent in diorite. The ME exhibit typical magmatic texture with a Bt(±Cpx ± Hbl)-Pl-Kf-Qtz-Mag-Ap assemblage, similar to that in host granitoids but with contrasting mineral proportions. Whole-rock molar Al₂O₃/(CaO + Na₂O + K₂O) (A/CNK) ratios of diorite (0.63–0.72), ME (0.69–1.21) and granitoids (0.83–1.05) suggest their nature largely metaluminous (I-type) to rarely peraluminous (S-type) granitoids. On most binary plots involving silica, two distinct compositional paths can be recognized; one formed by an array of differentiating diorite and ME, and another by fractionating granitoids gradually depleting in compatible elements. It is most likely that ME were generated by progressive and concurrent mixing of coeval pristine mafic (diorite) and granitoid magmas and fractionation processes. However, coherent and identical trace elements (except for Sr, Th, Y and Ni) and REE patterns for ME-granitoid pairs most likely suggest partial to near-complete chemical equilibration through varying degrees of diffusion process across the ME – partly crystalline host granitoid boundary. High-precision U–Pb SHRIMP zircon ²⁰⁶Pb/²³⁸U ages for ME (1758 ± 19 Ma) and host granitoid (1753 ± 9.1 Ma) from Jhirgadandi Pluton further support the notion that they were coeval. The obtained age (∼1750 Ma) of Jhirgadandi Pluton also points to the existence and role of Super-Columbian continental component in the evolution of Mahakoshal Belt of the CITZ.  相似文献   

中国主要块体奥陶纪达瑞威尔期（Darriwilian）晚期—凯迪期（Katian）早期海相红层及其构造意义   总被引：2，自引：0，他引：2  

林宝玉  任纪舜  李明  武振杰 《地质学报》2018,92(10):2002-2017

根据中国主要块体奥陶纪达瑞威尔期地层学、古生物学和岩石学的特点,本文主要论述了中国9个块体,其中包括5个主要块体（扬子克拉通、中朝克拉通、塔里木克拉通、拉萨地块和喜马拉雅北坡）中达瑞威尔晚期—凯迪期早期海相红层的分布、岩性特征和古动物群。它们的岩性特征：如红色灰岩;古生物群特征：如牙形石Pygodus serra动物群,P.anserinus动物群和Hamarodus europaeus动物群,珊瑚Yohophyllum动物群,以及头足类Sinoceras chinense动物群均十分相似或相同。这就充分阐明,中华古陆块群（包括扬子、中朝和塔里木克拉通等）与冈瓦纳古陆北缘古陆块群（包括拉萨地块和喜马拉雅北坡等）之间的关系十分密切,可能在此之前它们同属于冈瓦纳古陆。这对于阐明中华古陆块群与冈瓦纳古陆之间的关系具有重要意义。此外,还将海相红层分为两类：陆棚红层和大洋红层。陆棚红层主要见于寒武纪至三叠纪,大洋红层主要见于白垩纪至现代。  相似文献   

New Framework for Evaluating Ecosystem Quality in Nature Reserves based on Ideal References and Key Indicators     

WU Zhenliang  HOU Jihua  XU Li  HE Nianpeng 《资源与生态学报(英文版)》2022,13(3):466-475

With increasing numbers and types of nature reserves (NRs), objective evaluation and comparison of the effects of different nature NRs on conservation efforts are of great importance for protecting species diversity, ensuring reasonable national economic input, and adjusting government management schemes. Developing a method for the combined assessment of flagship or umbrella species and ecosystem quality will improve the evaluation of NRs. However, it is also important to establish a new framework for rapid evaluation of ecosystem quality, supported by the advantages of scientific, economic, and regular principles. Here, we proposed a new framework that incorporates the novel concept of ideal references into evaluation systems, which will facilitate the comparison of results from different periods and regions. Furthermore, from the perspective of making the framework as objective, rapid, and economical as possible, we recommended some key ecological indicators, such as net primary productivity, soil organic matter, plant diversity, for use in the new evaluation framework. The new framework, referred to as “ideal reference and key indicators” (IRKI), can sufficiently meet the requirements for the rapid evaluation of ecosystem quality both regionally and nationally. Furthermore, IRKI can identify the restoration potential and restoration periods of NRs, thus facilitating the rational distribution of resources and enhancing the protective effect. There are many types of NRs in China, and it is necessary to partially alter the assessment methods or parameters for different types of NRs. Overall, IRKI provides a simple, clear, and comparable framework that will strongly enhance the conservation of protected areas (PAs) and facilitate the standardization of management practices.  相似文献   

Atrazine fate and transport within the coastal zone in southeastern Puerto Rico     

《Marine pollution bulletin》2013,68(1-2):36-44

Agrichemical transport to coastal waters may have adverse ecological impact. This work examined atrazine fate and transport in a field adjacent to Puerto Rico’s Jobos Bay National Estuarine Research Reserve. The herbicide’s use was linked to residue detection in shallow groundwater and movement toward the estuary; however, data indicated that transport via this pathway was small. In contrast, surface runoff as tropical storm systems moved through the area appeared to have high potential for atrazine transport. In this case, transport to the estuary was limited by runoff event timing relative to atrazine application and very rapid atrazine dissipation (DT₅₀ = 1–3 days) in field soil. Soil incubation studies showed that accelerated degradation conditions had developed in the field due to repeated atrazine treatment. To improve weed management, atrazine replacement with other herbicide(s) is recommended. Use of products that have greater soil persistence may increase runoff risk.  相似文献   

Modeling the effect of artificial flow and sediment flux on the environment and plankton of an estuary     

Yujun Yi  Yanning Gao  Xuefei Wu  Wenfei Jia  Qi Liu 《国际泥沙研究》2023,38(3):335-348

Estuarine environments are influenced by both river flows and oceanic tidal movement of water, sediment, and nutrients, often forming ecosystems that are rich in resources and biodiversity. The Yellow River once carried the world’s largest sediment load, but artificial structures have transformed its hydrodynamic processes. An annual Water-Sediment Regulation Scheme(WSRS) was introduced to flush accumulated sediment from the Xiaolangdi Reservoir, which provides flood control and water storage.Ho...  相似文献   

断裂带同震温度负异常机制分析          下载免费PDF全文

杨小秋  林為人  葉恩肇  许鹤华  徐子英 《地球物理学报》2020,63(4):1422-1430

断裂带同震温度响应,可在震后钻孔测温中获得并识别,为发震断层摩擦特性与发震机制等基础研究提供了非常独特的思路和有效手段.集集、汶川及日本东北大地震后,实施了台湾车笼埔断层钻探项目(TCDP)、汶川地震断裂带科学钻探工程(WFSD)和日本海沟快速钻探计划(JFAST).钻孔测温结果表明:滑移面上下5~20m范围内存在温度正异常,这是同震摩擦生热所致,该机制已被广泛认识和接受;同时,距滑移面20~60m范围内也存在明显的温度负异常,但其成因机制几乎还未被真正关注和认识.虽然温度负异常峰值只有正异常峰值的1/4~1/3,但温度负异常分布范围却是正异常分布范围的3~4倍,即正、负温度异常区对应的总能量基本相当.因此,断裂带震后钻孔测温中的负异常及其成因不容忽视.在详细分析几种可能的同震温度负异常机制后(如岩层热物性分布差异、流体运移、表面自由能增大及同震应力释放),发现能在理论、实验及野外观测上都得到支撑的普适性机制只有同震应力释放.这可能是断裂带震后温度负异常的主要原因.  相似文献   

The role of nonliving organic matter in the earth's carbon cycle (report of Dahlem Workshop), environmental sciences research report 16 | J. Wiley and Sons,R.G. Zepp,Ch. Sonntag (Eds.) (1995), ISBN 0-471-95463-2. Price £70     

《Applied Geochemistry》1996,11(3):495

  相似文献   

Contamination of groundwaters | Science Rev. Northwood G.B., D.C. Adriano,A.K. Iskandar,I.P. Murarka (Eds.) (1994), p. 525, 0-905927-44-3 Price £120     

《Applied Geochemistry》1996,11(3):491

  相似文献   

黄河三角洲生态保护和高质量发展面临的挑战及科技支撑对策建议          下载免费PDF全文

张杰  杨俊芳  李忠伟  马毅  任广波  张洪亮  王安东  刘艳芬  许明明  胡亚斌  郭防铭  李晓敏 《海洋科学》2023,47(5):79-89

习近平总书记多次就黄河三角洲生态保护和高质量发展作出重要指示批示。长期以来,黄河三角洲的生态保护和高质量发展面临严峻挑战,相应的科技支撑方面也存在一定的问题。本文从黄河三角洲生物多样性保护、生态系统健康和高质量发展两个方面综述了面临的挑战情况,并进一步总结了黄河三角洲生态保护和高质量发展科技支撑存在的问题,概括为“弱”、“散”、“偏”、“缺”四个方面;基于此,提出了黄河三角洲生态保护和高质量发展科技支撑的对策建议,主要是建议成立一个能够提供黄河三角洲生态保护和高质量发展相关问题全套解决方案的研究平台,更有效地为黄河三角洲应用服务单位提供支撑。  相似文献