三叠纪西秦岭西北部洋俯冲的记录:来自镁安山岩/高镁安山岩的证据          下载免费PDF全文

李康宁  刘伯崇  狄永军 《中国地质》2020,47(3):709-724

三叠纪以来,西秦岭地区构造-岩浆活动极为强烈,中酸性侵入岩呈北西向弧状分布,前人做了大量卓有成效的工作,但对出露较少的火山岩鲜有研究。本次工作选取青海省同仁县麦秀和甘肃省夏河县甘加、德乌鲁3个地区的安山岩,从岩石学、岩石地球化学、年代学等进行分析。结果显示安山岩均属于钙碱性系列,具有富钾火山岩的特征。其中,麦秀安山岩中既有高镁安山岩,也有镁安山岩,而甘加与德乌鲁安山岩属于镁安山岩,为洋壳俯冲作用形成的两种典型火山岩类型。西秦岭地区安山岩形成时间东早西晚,由西向东安山岩基性程度降低,K_2O、Na_2O、∑REE等含量增高,MF、FL、DI、La/Sm等值变大,SI、Mg~#等值降低,并且呈明显的线性特征,构成同仁—合作镁安山岩(镁闪长岩)岩浆弧组合,和北部隆务峡蛇绿岩带一起,组成岩性分布极性,从而判断出西秦岭西北部在三叠纪存在隆务峡蛇绿岩代表的洋壳板块向南俯冲作用。  相似文献   

Geochemical evolution of groundwater in the carbonate aquifers of Sierra de Segura (Betic Cordillera, southern Spain)   总被引：1，自引：0，他引：1  

F. Moral  J.J. Cruz-Sanjulin  M. Olías 《Journal of Hydrology》2008,360(1-4):281-296

Sierra de Segura (Betic Cordillera), with a total area of over 3000 km², is the source of the two principal rivers in southern Spain, the Guadalquivir and the Segura. Due to the orographic effect of these mountains, precipitations are considerably more abundant than in nearby lowland areas, where the climate is semi-arid. Sierra de Segura is constituted of Mesozoic and Cenozoic sedimentary rocks, among which there are thick limestone–dolomitic formations which have given rise to extensive outcrops of permeable materials. In geomorphological terms, there is a large plateau intensively karstified that constitutes the main recharge area. Discharge takes place via a large number of springs, of which the 50 most important add up to a mean spring flow of about 13,500 l/s. The active geochemical processes in aquifers of Sierra de Segura, with their corresponding time sequence, are: dissolution of CO₂, dissolution of calcite, incongruent dissolution of dolomite, dedolomitization, exsolution of CO₂, and precipitation of calcite. More evolved water has higher temperature, magnesium content and Mg/Ca ratio; therefore, these parameters can be utilised as indicators of the degree of hydrochemical evolution. In addition, a good correlation between water temperature and magnesium concentration (or Mg/Ca ratio) indicates that an increase in temperature accelerates the kinetics of the dissolution of dolomite. Finally, the distribution of the temperatures in the vadose zone, determined by atmospheric thermal gradient, implies an apparent stratification of the predominant hydrochemical processes and of the groundwater physical and chemical characteristics.  相似文献   

重庆地区石笋记录中Mg /Ca比值及古气候意义   总被引：6，自引：3，他引：3  

李清  王建力  李红春  叶明阳  王勇  李廷勇  何潇 《中国岩溶》2008,27(2):145-150

在重庆梁天湾洞石笋LT14 31. 9～ 15. 02ka. B. P.古气候重建成果已发表的此基础上,本文选取Mg / Ca比值这一新的替代指标,探讨其在重庆地区独特的水热组合模式下的古气候指示意义,从而进一步探讨了该时段的气候变化。研究结果发现,重庆地区Mg /Ca 比值与碳同位素的正相关关系较好( R2= 0. 60) ,可能与碳酸钙溶液在到达洞顶之前提前沉淀或滴率减小机制有关,它间接响应了降水的变化。运用Mg / Ca 值变化对古气候的重建结果与以前的研究基本相符,说明Mg /Ca 比值可以作为古降水的指标,但需同碳氧稳定同位素结合起来讨论,以便相互验证,提高古环境解译的准确性。   相似文献   

复合矿的矿物学特征初步研究     

彭卓伦  彭明生 《矿物岩石地球化学通报》1999,(4)

复合矿又名硅硼镁铝矿（ｇｒａｎｄｉｄｉｅｒｉｔｅ）,属硼铝硅酸盐矿物。产于细晶岩和伟晶岩中,少数产于变质沉积角页岩中的辉长岩体的捕体中［１,２］,常与黑云母、磁铁矿、红柱石、尖晶石等共生。国内少见,研究亦少。１　矿物学特征本文研究的复合矿样品长３．０ｍｍ、宽２．５ｍｍ、厚０．０３ｍｍ,淡绿色,玻璃光泽,硬度６～７,测得比重２－９７,平均折射率１－６０６（１－５９０～１－６２３）。在长短波紫外荧光灯下无荧光反应。镜下观察样品中９７％为复合矿,晶体呈板柱状,高正突起,交互生长,具明显多色性（Ｎｇ＜Ｎ…  相似文献   

Quantifying the carbon source of pedogenic calcite veins in weathered limestone: implications for the terrestrial carbon cycle     

Lin Zou  Lin Dong  Meng Ning  Kangjun Huang  Yongbo Peng  Shujian Qin  Honglin Yuan  Bing Shen 《Acta Geochimica》2019,(4):481-496

The continent is the second largest carbon sink on Earth’s surface.With the diversification of vascular land plants in the late Paleozoic,terrestrial organic carbon burial is represented by massive coal formation,while the development of soil profiles would account for both organic and inorganic carbon burial.As compared with soil organic carbon,inorganic carbon burial,collectively known as the soil carbonate,would have a greater impact on the long-term carbon cycle.Soil carbonate would have multiple carbon sources,including dissolution of host calcareous rocks,dissolved inorganic carbon from freshwater,and oxidation of organic matter,but the host calcareous rock dissolution would not cause atmospheric CO2drawdown.Thus,to evaluate the potential effect of soil carbonate formation on the atmospheric p CO2level,different carbon sources of soil carbonate should be quantitatively differentiated.In this study,we analyzed the carbon and magnesium isotopes of pedogenic calcite veins developed in a heavily weathered outcrop,consisting of limestone of the early Paleogene Guanzhuang Group in North China.Based on the C and Mg isotope data,we developed a numerical model to quantify the carbon source of calcite veins.The modeling results indicate that4–37 wt%of carbon in these calcite veins was derived from atmospheric CO2.The low contribution from atmospheric CO2might be attributed to the host limestone that might have diluted the atmospheric CO2sink.Nevertheless,taking this value into consideration,it is estimated that soil carbonate formation would lower 1 ppm atmospheric CO2within 2000 years,i.e.,soil carbonate alone would sequester all atmospheric CO2within 1 million years.Finally,our study suggests the C–Mg isotope system might be a better tool in quantifying the carbon source of soil carbonate.  相似文献   

The Formation of Li-salts from Natural Brines During Isothermal Evaporation at 25 ℃          下载免费PDF全文

宋彭生  Dong Yaping  李武 《盐湖研究》2019,27(1)

Lithium and its compounds have very important applications in the new energy sources, new materials, and information technique industries. Lithium has two types of resources in nature: hard rock, e.g. Spodumene (LiAlSi2O6), Petalite(LiAlSi4O10), Lepidolite(K(Li,Al)3(Si,Al)4O10(F,OH)2), and brines, e.g. salt lake brines, oil well brines, underground brines etc. The biggest producer of Li commodities SQM in the world produces Li compounds from brines of famous salt lake Atacama on the central Andes Mountains in Chile  相似文献   

南秦岭印支期花岗岩带的“地幔印记”   总被引：4，自引：0，他引：4       下载免费PDF全文

田伟  董申保  陈咪咪  朱文萍 《地学前缘》2009,16(2):119

南秦岭印支期花岗岩带的岩石组合包括闪长岩、二长闪长岩、英云闪长岩、花岗闪长岩和花岗岩等,岩体内广泛存在镁铁质微粒包体和脉体。大量(超过50%)样品具有高Mg#(<0.76),高Cr(>100×10-6,最高为1600×10-6)、Sr(>500×10-6)、Ba(>1000×10-6)的"地幔印记(mantle signature)"。含石榴石基性岩部分重熔模型可以解释部分样品的高LREE、低HREE和高Sr低Y特征,但无法合理解释"地幔印记"的存在。简单的地幔上涌、减压熔融模型虽然可以产生幔源岩浆并解释基性-酸性岩浆混合现象,但与具"地幔印记"样品的Sr、Nd同位素富集(ISr=0.7054～0.7085;εNd(t)=-1.52～-9.17)和区域地质特征相矛盾。具"地幔印记"样品与高Mg埃达克岩和太古宙sanukitoid岩系的相似性表明它们可以由含水富集地幔的直接熔融形成。  相似文献   

青藏高原湖泊水化学与盐度的相关性初步研究   总被引：3，自引：0，他引：3  

王海雷  郑绵平 《地质学报》2010,84(10):1517-1522

本文综合分析了青藏高原地区400多个湖泊的水化学成分(Mg2+、Ca2+、Sr2+、Sr/Ca和Mg/Ca)与湖水盐度的相关关系,以及这种关系随着湖水变化(不同采样时间和采样点以及蒸发实验)而产生的变化规律。认为:在青藏高原湖泊中,Mg2+与盐度具有较为稳定的正相关关系,而Ca2+、Sr2+、Sr/Ca以及Mg/Ca与盐度的相关性较弱且不稳定。而在特定的水化学类型的湖泊中,碳酸盐型湖泊的Mg2+、Ca2+以及Mg/Ca与盐度均没有明显的相关性。硫酸盐型湖泊中Mg2+和盐度呈现较高的正相关关系,而Ca2+以及Mg/Ca与盐度的相关性仍很弱。而在氯化物型湖泊中,Mg2+与盐度呈更强的正相关关系,Ca2+与盐度也呈一定的正相关关系,而Mg/Ca与盐度的相关性依然很弱。在特定的单个湖泊中,Ca2+以及Mg/Ca与盐度的相关性仍然不稳定或很弱,而Mg2+与盐度仍然保持明显的正相关关系。在青藏高原利用湖相沉积恢复特定湖区古环境演化序列的时候,Mg2+浓度是湖水古盐度一个较好的转换指标,而在应用Mg/Ca这一指标时应谨慎。  相似文献   

高镁安山岩/闪长岩类(HMA)和镁安山岩/闪长岩类(MA):与洋俯冲作用相关的两类典型的火成岩类   总被引：16，自引：3，他引：13       下载免费PDF全文

邓晋福  刘翠 冯艳芳  肖庆辉  苏尚国赵国春孔维琼曹文燕 《中国地质》2010,37(4):1112-1118

本文主要基于对实验岩石学成果的简要评述,讨论与洋俯冲作用有关的两类典型的火成岩类:楔形地幔在含水条件下橄榄岩局部熔融产生的高镁安山岩/闪长岩类(HMA)和俯冲洋壳局部熔融岩浆与地幔楔相互作用产生的镁安山岩/闪长岩类(MA)。提出:(1)识别HMA和MA必须同时运用两套参数系统:SiO2-MgO系统和SiO2-FeO/MgO系统;(2)区别HMA和MA是在它们均符合LF-CA(低Fe钙碱趋势)特征条件下,再用SiO2-MgO系统进一步加以鉴别;(3)识别HMA和MA的方法,或用在给定SiO2时,MgO和FeO/MgO的具体数值,或用图解法。  相似文献   

Mg/Ca比对微生物成因的碳酸盐矿物种类和形态的影响   总被引：2，自引：0，他引：2  

苏宁  李福春  马恒  李学林 《矿物学报》2010,30(1)

研究Mg/Ca比对生物成因的碳酸盐矿物种类和形态的影响是研究各种含镁方解石形成机理的关键。本文在Mg/Ca摩尔比分别为1、2、4、6和8的条件下进行了为期55d的硫酸盐还原细菌诱导碳酸盐矿物形成的实验,利用X射线衍射仪和扫描电子显微镜研究了Mg/Ca比对碳酸盐矿物种类和形态的影响。实验结果表明:①Mg/Ca比与矿物的种类之间存在密切的关系。在Mg/Ca摩尔比较低(1和2)时仅形成高镁方解石,在Mg/Ca摩尔比为4时,形成的矿物组合为含镁方解石+高镁方解石,在Mg/Ca摩尔比为6和8时,矿物组合为高镁方解石+单水碳钙石+钙白云石;②Mg/Ca比影响矿物的生长速率。Mg/Ca比越高,晶体生长速率越快;③Mg/Ca比明显影响矿物的形态。随着Mg/Ca比的增大,矿物的形态有如下发展规律:哑铃形→花菜状→光球状→刺球状。这些研究结果将有助于探讨制约含镁碳酸盐矿物种类和形态的机制。  相似文献