Evolution of subcontinental lithospheric mantle beneath eastern China: Re–Os isotopic evidence from mantle xenoliths in Paleozoic kimberlites and Mesozoic basalts     

Hong-Fu Zhang  Steven L. Goldstein  Xin-Hua Zhou  Min Sun  Jian-Ping Zheng  Yue Cai 《Contributions to Mineralogy and Petrology》2008,155(3):271-293

The ages of subcontinental lithospheric mantle beneath the North China and South China cratons are less well-constrained than the overlying crust. We report Re–Os isotope systematics of mantle xenoliths entrained in Paleozoic kimberlites and Mesozoic basalts from eastern China. Peridotite xenoliths from the Fuxian and Mengyin Paleozoic diamondiferous kimberlites in the North China Craton give Archean Re depletion ages of 2.6–3.2 Ga and melt depletion ages of 2.9–3.4 Ga. No obvious differences in Re and Os abundances, Os isotopic ratios and model ages are observed between spinel-facies and garnet-facies peridotites from both kimberlite localities. The Re–Os isotopic data, together with the PGE concentrations, demonstrate that beneath the Archean continental crust of the eastern North China Craton, Archean lithospheric mantle of spinel- to diamond-facies existed without apparent compositional stratification during the Paleozoic. The Mesozoic and Cenozoic basalt-borne peridotite and pyroxenite xenoliths, on the other hand, show geochemical features indicating metasomatic enrichment, along with a large range of the Re–Os isotopic model ages from Proterozoic to Phanerozoic. These features indicate that lithospheric transformation or refertilization through melt-peridotite interaction could be the primary mechanism for compositional changes during the Phanerozoic, rather than delamination or thermal-mechanical erosion, despite the potential of these latter processes to play an important role for the loss of garnet-facies mantle. A fresh garnet lherzolite xenolith from the Yangtze Block has a Re depletion age of ∼1.04 Ga, much younger than overlying Archean crustal rocks but the same Re depletion ages as spinel lherzolite xenoliths from adjacent Mesozoic basalts, indicating Neoproterozoic resetting of the Re–Os system in the South China Craton.  相似文献   

Silicon isotope fractionation in bamboo and its significance to the biogeochemical cycle of silicon   总被引：2，自引：0，他引：2  

T.P. Ding  J.X. Zhou  Z.Y. Chen  F. Zhang 《Geochimica et cosmochimica acta》2008,72(5):1381-1395

A systematic investigation on silica contents and silicon isotope compositions of bamboos was undertaken. Seven bamboo plants and related soils were collected from seven locations in China. The roots, stem, branch and leaves for each plant were sampled and their silica contents and silicon isotope compositions were determined. The silica contents and silicon isotope compositions of bulk and water-soluble fraction of soils were also measured. The silica contents of studied bamboo organs vary from 0.30% to 9.95%. Within bamboo plant the silica contents show an increasing trend from stem, through branch, to leaves. In bamboo roots the silica is exclusively in the endodermis cells, but in stem, branch and leaves, the silica is accumulated mainly in epidermal cells. The silicon isotope compositions of bamboos exhibit significant variation, from −2.3‰ to 1.8‰, and large and systematic silicon isotope fractionation was observed within each bamboo. The δ³⁰Si values decrease from roots to stem, but then increase from stem, through branch, to leaves. The ranges of δ³⁰Si values within each bamboo vary from 1.0‰ to 3.3‰. Considering the total range of silicon isotope composition in terrestrial samples is only 7‰, the observed silicon isotope variation in single bamboo is significant and remarkable. This kind of silicon isotope variation might be caused by isotope fractionation in a Rayleigh process when SiO₂ precipitated in stem, branches and leaves gradually from plant fluid. In this process the Si isotope fractionation factor between dissolved Si and precipitated Si in bamboo (α_pre-sol) is estimated to be 0.9981. However, other factors should be considered to explain the decrease of δ³⁰Si value from roots to stem, including larger ratio of dissolved H₄SiO₄ to precipitated SiO₂ in roots than in stem. There is a positive correlation between the δ³⁰Si values of water-soluble fractions in soils and those of bulk bamboos, indicating that the dissolved silicon in pore water and phytoliths in soil is the direct sources of silicon taken up by bamboo roots. A biochemical silicon isotope fractionation exists in process of silicon uptake by bamboo roots. Its silicon isotope fractionation factor (α_bam-wa) is estimated to be 0.9988. Considering the distribution patterns of SiO₂ contents and δ³⁰Si values among different bamboo organs, evapotranspiration may be the driving force for an upward flow of a silicon-bearing fluid and silica precipitation. Passive silicon uptake and transportation may be important for bamboo, although the role of active uptake of silicic acid by roots may not be neglected. The samples with relatively high δ³⁰Si values all grew in soils showing high content of organic materials. In contrast, the samples with relatively low δ³⁰Si values all grew in soil showing low content of organic materials. The silicon isotope composition of bamboo may reflect the local soil type and growth conditions. Our study suggests that bamboos may play an important role in global silicon cycle.  相似文献   

Origin of Fe-Ti Oxide Ores in Mafic Intrusions: Evidence from the Panzhihua Intrusion, SW China   总被引：12，自引：0，他引：12  

Pang  Kwan-Nang; Zhou  Mei-Fu; Lindsley  Donald; Zhao  Donggao; Malpas  John 《Journal of Petrology》2008,49(2):295-313

Economic concentrations of Fe–Ti oxides occur as massive,conformable lenses or layers in the lower part of the Panzhihuaintrusion, Emeishan Large Igneous Province, SW China. Mineralchemistry, textures and QUILF equilibria indicate that oxidesin rocks of the intrusion were subjected to extensive subsolidusre-equilibration and exsolution. The primary oxide, reconstructedfrom compositions of titanomagnetite in the ores and associatedintergrowths, is an aluminous titanomagnetite (Usp₄₀) with 40wt % FeO, 34 wt % Fe₂O₃, 16·5 wt % TiO₂, 5·3 wt% Al₂O₃, 3·5 wt % MgO and 0·5 wt % MnO. This compositionis similar to the bulk composition of the oxide ore, as inferredfrom whole-rock data. This similarity strongly suggests thatthe ores formed from accumulation of titanomagnetite crystals,not from immiscible oxide melt as proposed in earlier studies.The occurrence of oxide ores in the lower parts of the Panzhihuaintrusion is best explained by settling and sorting of densetitanomagnetite in the ferrogabbroic parental magma. This magmamust have crystallized Fe–Ti oxides relatively early andabundantly, and is likely to have been enriched in Fe and Tibut poor in SiO₂. These features are consistent with fractionationof mantle-derived melts under relatively high pressures (10kbar), followed by emplacement of the residual magma at 5 kbar.This study provides definitive field and geochemical evidencethat Fe–Ti oxide ores can form by accumulation in ferrogabbro.We suggest that many other massive Fe–Ti oxide depositsmay have formed in a similar fashion and that high concentrationsof phosphorus or carbon, or periodic fluctuation of fO₂ in themagma, are of secondary importance in ore formation. KEY WORDS: ELIP; Fe–Ti oxide ore; layered intrusion; Panzhihua; QUILF  相似文献   

The state of land subsidence and prediction approaches due to groundwater withdrawal in China   总被引：13，自引：6，他引：7  

Ye-Shuang Xu  Shui-Long Shen  Zheng-Yin Cai  Guo-Yun Zhou 《Natural Hazards》2008,45(1):123-135

This article gives a general introduction to land subsidence with the prediction approaches due to withdrawal of groundwater in three subsided/subsiding regions in China: the deltaic plain of Yangtse River (YRDP), North China Plain (NCP), and Fenwei Plain (FP). On YRDP, Shanghai is the typical subsided/subsiding city; on NCP Tianjin is the typical subsided/subsiding city, and on FP Taiyuan is the typical subsided/subsiding city. The subsided area with subsidence over 200 mm on YRDP is about 10,000 km² and the maximum subsided value reached 2.9 m at Shanghai; on NCP the subsided area reached 60,000 km² with the maximum subsidence of 3.9 m at Tianjing; on FP the subsided area is relatively smaller than that on the other two plains and is about 1,135 km² with maximum subsidence of 3.7 m at Taiyuan city. In order to protect the civil and industrial facilities, it is necessary to predict the future development of land subsidence based on present state. Many researchers proposed several approaches to predict the land subsidence due to groundwater withdrawal according to different geological conditions and groundwater withdrawal practice. This article classifies these approaches into five categories: (i) statistical methods; (ii) 1D numerical method; (iii) quasi-3D seepage model; (iv) 3D seepage model; (v) fully coupled 3D model. In China, the former four categories are presently employed in the prediction practice and their merits and demerits are discussed. According to the prediction practice, 3D seepage model is the best method presently.  相似文献   

华南前寒武系基底变质杂岩和中-新生代地幔岩的稀有气体同位素组成及其大地构造意义          下载免费PDF全文

谢窦克  邢光福  陆志刚  陈荣  周宇章 《地质科学》2008,43(1):175-204

对华南前寒武系变质岩浆杂岩稀有气体He、Ne、Ar和Xe的系统研究表明:扬子克拉通基底为含高³He的下地壳"原始岩石层",(³He/⁴He)×10^-6比值为2.8～4.6;而华夏板块基底变质岩浆杂岩则是在缺乏³He、低(³He/⁴He)×10^-8比值(3.15～17.7)的构造环境下形成的大陆中-上地壳变质岩浆杂岩层,反映出两者基底性质迥然不同。华南中-新生代爆破岩筒He同位素组成相反,相对稳定的扬子克拉通(³He/⁴He)×10^-8比值仅0.18～4.22,而郯庐-四会-吴川断裂以东,中-新生代活动地块(太平洋构造域)(³He/⁴He)×10^-8比值高达3.7～20.5。He同位素表明郯庐-四会-吴川断裂带为切割深至地幔的边界深大断裂,是扬子克拉通与华夏板块间的边界且控制了燕山期火山-侵入岩浆向西扩展。Ar同位素组成表明华南大陆中-新生代地幔形成接近"均一"的地幔组份。¹³⁶Xe/¹³⁰Xe-¹²⁹Xe/¹³⁰Xe相关组份表明它们具有地幔柱岩石同位素组成特征。  相似文献   

辽东湾凝析气田超压成因及侧向传递机制初探   总被引：1，自引：0，他引：1       下载免费PDF全文

李潍莲  刘震  夏庆龙  周心怀 《地质科学》2008,43(2):377-388

位于辽东湾西部低凸起北端的JZ20-2超压凝析气田,离供烃中心较远,压力系数却达到1.56~1.7,这在我国东部裂谷盆地比较少见。经过综合分析,作者认为JZ20-2凝析气田异常高压的形成与其所处的特殊地质背景紧密相关,辽中凹陷沙河街组三段超压凝析油气沿不整合面、砂体输导通道向辽东湾西部低凸起的运移、充注和能量的侧向传递是JZ20-2凝析气田异常高压形成的根本原因,而上覆东营组二段下亚段-东营组三段巨厚的强超压泥岩封盖和辽西3号边界断层侧向遮挡共同构成的优越封闭环境是超压保存的必要条件。本文分析了该气田超压特征及其远距离超压侧向传递的成因机制,不仅有助于揭示辽东湾西部低凸起超压流体运移聚集的规律和成藏作用,而且可能提供了一个超压远距离侧向传递的典型实例。  相似文献   

Loess deposition in Asia： its initiation and development before and during the Quaternary   总被引：3，自引：0，他引：3  

Andrey E. Dodonov Liping Zhou 《《幕》》2008,31(2):222-225

Dust is important in the Earth environment system. However; the role of dust in climate change remains largely unknown. A better understanding of the temporal and spatial variability of the dust accumulation in Asia forms an important step towards establishing the link between dust deposition and climate change. Here, a summary is given for the timing of the onset and expansion of loess deposition in Asia beginning in the early, Miocene. Recent progress on some aspects of loess chronology and palaeoenvironmental reconstruction is also reviewed.  相似文献   

南水北调西四环暗涵工程穿越桥梁监控量测技术应用     

丁振明  刘军  靳璞  张大成  仇文顺  房彦梅 《水文地质工程地质》2008,35(5):119-123

南水北调西四环暗涵工程为京石段控制性工程,下穿北京市西四环路桥梁30余座,桥梁的安全至关重要。在暗涵施工过程中对桥梁实施了有效的监控量测技术,通过自动化监测和常规监测手段获取数据,然后对监测数据进行详细分析、对比,以研究暗涵下穿桥梁施工过程中桥梁的受力变形协调过程。结果表明:墩柱差异沉降小于允许沉降的80%;墩柱倾斜值小于允许值的30%。监控工作做到了过程预警、过程控制,规避了工程风险,对类似工程具有借鉴意义。  相似文献   

层状出溶结构导致拉长石晕彩形成——来自透射电镜的证据   总被引：1，自引：1，他引：0  

彭艳菊  何雪梅  方勤方 《岩石矿物学杂志》2008,27(5):483-488

从拉长石出溶结构的形态特征、成分差异和出溶结构的取向研究出发,采用TEM、STEM 以及SAED等手段对其进行测试,发现拉长石出溶结构层的厚度符合理论计算值,结构层的成分由富钙和贫钙两相长石组成,具备了产生干涉作用的必要条件.研究结果表明,拉长石的晕彩色是因其内部的层状出溶结构对光的干涉所致,结构层的厚度主要受富钙相长石的控制.随着钙(An)含量的增加,结构层相应地增厚,且富钙层的增大幅度大于贫钙层,从而导致晕彩色波长也随之增大.出溶结构层的取向为(153),近于平行晶体的(010)面,但不同产地的拉长石,尽管晕彩色相同,其出溶条纹中的钙含量和条纹的具体取向也不尽相同.  相似文献   

河南桐柏老湾花岗岩体锆石SHRIMP U-Pb年龄及其地质意义   总被引：5，自引：0，他引：5  

刘翼飞  江思宏  方东会  刘妍 《岩石矿物学杂志》2008,27(6):519-523

通过对河南桐柏老湾花岗岩体开展锆石SHRIMP U-Pb测年,获得了一个高精度的U-Pb年龄(132.5±2.4)Ma,比较可靠地限定了老湾花岗岩体的形成时代属于燕山中期,而不是前人所认为的燕山晚期.结合区域构造-岩浆活动时间,认为在燕山中期,桐柏及其邻区存在次比较重要的构造-岩浆事件,老湾花岗岩体是这次构造-岩浆活动事件的产物.  相似文献