Calcio-carbonatite melts and metasomatism in the mantle beneath Mt. Vulture (Southern Italy)     

Gianluigi Rosatelli  Frances Wall  Francesco Stoppa 《Lithos》2007,99(3-4):229-248

At Mt. Vulture volcano (Basilicata, Italy) calcite globules (5–150 μm) are hosted by silicate glass pools or veins cross-cutting amphibole-bearing, or more common spinel-bearing mantle xenoliths and xenocrysts. The carbonate globules are rounded or elongated and are composed of a mosaic of 2–20 μm crystals, with varying optical orientation. These features are consistent with formation from a quenched calciocarbonatite melt. Where in contact with carbonate amphibole has reacted to form fassaitic pyroxene. Some of these globules contain liquid/gaseous CO₂ bubbles and sulphide inclusions, and are pierced by quench microphenocrysts of silicate phases. The carbonate composition varies from calcite to Mg-calcite (3.8–5.0 wt.% MgO) both within the carbonate globules and from globule to globule. Trace element contents of the carbonate, determined by LAICPMS, are similar to those of carbonatites worldwide including ΣREE up to 123 ppm. The Sr–Nd isotope ratios of the xenolith carbonate are similar to the extrusive carbonatite and silicate rocks of Mt. Vulture testifying to derivation from the same mantle source. Formation of immiscibile silicate–carbonatite liquids within mantle xenoliths occurred via disequilibrium immiscibility during their exhumation.  相似文献   

北京周口店豹皮灰岩的变形特征   总被引：1，自引：0，他引：1  

陈云峰吴淦国  王根厚 《地质通报》2007,26(6):69-775

周口店地区广泛分布的寒武纪地层府君山组底部灰岩因其具典型的豹斑状构造而被称为豹皮灰岩。本文主要以出露于周口店黄院地区的豹皮灰岩为研究对象。组成豹皮灰岩的物质成分有2种,一为白云质成分的豹斑,其余部分为泥灰质。在露头尺度上,豹皮灰岩中的豹斑发生了明显的旋转变形并具有一定的定向性,而泥灰质成分则具有清晰的韧性变形特征,为较典型的碳酸盐糜棱岩;在微观尺度上,构成豹斑的白云石矿物未发生韧性变形,而泥灰质成分中的方解石具有明显的细粒化、拉长和定向。豹皮灰岩变形发生时岩石所处的温度介于200～250℃之间。豹皮灰岩的形成经历了原岩形成和后期构造变形改造2个阶段,于寒武纪由沉积作用形成了岩石的物质组分和原生层状构造,在前印支期受水平剪切作用形成岩石的豹斑状构造。  相似文献   

邻二氮菲分光光度法测定碳酸盐相中微量亚铁   总被引：2，自引：2，他引：2  

潘涵香胡超涌  王红梅马仲武 《岩矿测试》2007,26(3):198-200

建立了在超声波作用下，HAc—NaAc缓冲溶液和邻二氮菲选择性溶解分光光度法直接测定碳酸盐相中微量亚铁的方法。结果表明，在适宜条件下，含2g／L邻二氮菲的HAc—NaAc缓冲溶液（pH3）可选择性溶解并络合碳酸盐相中的Fe（Ⅱ），通过加入EDTA溶液有效地抑制了Fe（Ⅲ）的光还原作用。常见含铁矿物如赤铁矿、磁铁矿及硅酸盐等均对碳酸盐中Fe（Ⅱ）的测定无干扰。样品经30％的H2O2浸泡、过滤、晾干预处理，能有效地消除黄铁矿和有机物的干扰。方法用于石灰岩国家一级标准物质的测定，结果与标准值相符。  相似文献   

青藏高原北部新生代湖相碳酸盐岩碳氧同位素特征及古环境意义   总被引：3，自引：2，他引：3  

伊海生  林金辉  周恳恳  李军鹏 《古地理学报》2007,9(3):303-312

对青藏高原北部地区新生代陆相地层中湖相碳酸盐岩进行了系统采样分析，以碳氧同位素作为古环境和古气候变化的替代指标,试图从古湖泊演化的角度，阐明高原新生代早期环境演变历史和过程。研究结果表明，该区所有分析样品中生物碎屑灰岩类样品的δ¹⁸O和δ¹³C显示最低值，反映它们沉积在一个水体滞留时间短的开放性淡水湖泊系统中。泥晶灰岩类样品的δ¹⁸O和δ¹³C之间具有正相关关系，表明它们发育在蒸发作用明显的封闭性咸水湖泊体系中，而叠层石灰岩类明显富集13C可能与微生物活动有关。从始新世到渐新世至中新世，湖相碳酸盐岩δ¹⁸O值具有逐渐增大的趋势，δ¹³C则由古近纪的负值变为新近纪的正值，反映该区古湖泊系统经历了一个由开放到封闭的过程，预示古近纪到新近纪之交高原古气候格局发生了重大变革。  相似文献   

Determination of Total Organic Carbon Content and δ¹³C in Carbonate-Rich Detrital Sediments     

Valier Galy  Julien Bouchez  Christian France-Lanord 《Geostandards and Geoanalytical Research》2007,31(3):199-207

The determination of total organic carbon content and composition in detrital sediments requires careful removal of their carbonate minerals. In detrital sediments containing large amounts of carbonates, including dolomite, this can only be achieved by liquid acid leaching that may solubilise a significant proportion of the organic carbon. For a set of detrital sediments from the Himalayan system and the Amazon River as well as five geological reference materials, we determined the proportion of organic carbon (C_org) solubilised during acid leaching. This proportion is significant for all analysed sediments and generally tends to increase with the organic carbon content. Compared to other types of sediments analysed, clay fractions extracted from river sediments and bed sediments with very low organic carbon content have high and low proportions of acid soluble C_org respectively. In Himalayan and Amazon river sediments, the proportion of C_org solubilised during acid leaching was relatively constant with average values of 14 and 19 % respectively. Thus, it is possible to correct the C_org content for the dissolved organic carbon content measured after decarbonation. Data presented here show that C_org dissolved during liquid acid leaching must be taken into account. After careful calibration, the method presented here should, therefore, be applied to any carbonate-rich detrital sediment.  相似文献   

Implications of the Precambrian Non-stromatolitic Carbonate Succession Making up the Third Member of Mesoproterozoic Gaoyuzhuang Formation in Yanshan Area of North China   总被引：4，自引：0，他引：4  

梅冥相 《中国地质大学学报(英文版)》2007,18(3):191-209

A particular non-stromatolitic carbonate succession making up the third member of the Mesoproterozoic Gaoyuzhuang (高于庄) Formation might demonstrate that a stromatolite decline of the Mesoproterozoic occurring at ca. 1 450 Ma besides other three events of the Proterozoic,respectively,occurred at ca. 2 000 Ma,ca. 1 000 Ma,and ca. 675 Ma. The forming duration of this non-stromatolitic carbonate succession can be generally correlative to that of a similar depositional succession in North America,i.e. a non-stromatolitic carbonate succession made up by the Helena Formation of the Belt Supergroup,which suggests that the stromatolite decline occurring at ca. 1 450 Ma may be a global event. This information endows the non-stromatolitic carbonate succession making up the third member of the Gaoyuzhuang Formation in the Yanshan (燕山) area with important significance for the further understanding of Precambrian sedimentology. The Mesoproterozoic Gaoyuzhuang Formation in Yanshan area is a set of more than 1 000 m thick carbonate strata that can be divided into four members (or subformations). The first member (or the Guandi (官地) subformation) is marked by a set of stromatolitic dolomites overlying a set of transgressive sandstones; the second member (or the Sangshu'an (桑树鞍) subformation) is a set of manganese dolomites with a few stromatolites; the third member (or the Zhangjiayu (张家峪) subformation) is chiefly made up of leiolite and laminite limestones and is characterized by the development of molar-tooth structures in leiolite limestone; the fourth member (or the Huanxiusi (环秀寺) subformation) is composed of a set of dolomites of stromatolitic reefs or lithoherms. Sequence-stratigraphic divisions at two sections,i.e. the Jixian (蓟县) Section in Tianjin (天津) and the Qiangou (千沟) Section of Yanqing (延庆) County in Beijing (北京),demonstrate that a particularly non-stromatolitic succession making up the third member of the Mesoproterozoic Gaoyuzhuang Formation is developed in the Yanshan area of North China,in which lots of grotesque matground structures (wrinkle structures and palimpsest ripples) are developed in beds of leiolite limestone at the Qiangou Section and lots of molar-tooth structures are developed in beds of leiolite limestone at the Jixian Section. The time scale of the Gaoyuzhuang Formation is deduced as 200 Ma (from 1 600 Ma to 1 400 Ma). The duration of an obvious hiatus between the Gaoyuzhuang Formation and the underlying Dahongyu (大红峪) Formation is deduced as 50 Ma to 100 Ma,thus the forming duration of the GaoyuzhuangFormation is thought as 100 Ma (1 500 Ma to 1 400 Ma). Furthermore,the age of the subface of the third member of the Gaoyuzhuang Formation that is just in the mid position of the Gaoyuzhuang Formation can be deduced as about 1 450 Ma,which is the basis to infer a stromatolite decline of the Mesoproterozoic occurring at ca. 1 450 Ma. Importantly,several features of both the molar-tooth structure and the stromatolite,such as the particular forming environment,the important facies-indicative meaning,and the episodic distribution in the earth history,might express the evolutionary periodicity of the surface environment of the earth and can provide meaningful clues for the understanding of the Precambrian world,although their origin and forming mechanism is highly contentious. Therefore,like other three stromatolitic declines,respectively,occurring at ca. 675 Ma,ca. 1 000 Ma,and ca. 2 000 Ma,the identification of the stromatolite decline occurring at ca. 1 450 Ma during the Golden Age of stromatolites (2 800 Ma to 1 000 Ma) has important meaning for the further understanding of the evolving carbonate world of the Precambrian.  相似文献   

Reform of Carbonate Rock Subsurface by Crustose Lichens and Its Environmental Significance   总被引：5，自引：0，他引：5  

CAO Jianhua  WANG FuxingInstitute of Karst Geology  Chinese Academy of Geological Sciences  Guilin  Guanxi Xiao Pinfang Liu Xinzhu 《《地质学报》英文版》1998,72(1):94-99

Crustose lichens are distributed extensively in karst areas in Southern China. They can be found on the surface of carbonate rocks. Through biophysical and biochemical processes, crustose lichens reform the subsurface of carbonate rocks and in the meanwhile change their physical and chemical properties: (1) the mechanical strength decreases by 17.04° on average (up to 33.2° ); (2) the chemical solution surface area increases from 28.26% to 75.36% (lichen microholes considered only); and (3) the water-holding capacity is greatly improved. Comparative field experiments between biokarst samples underneath crustose lichens and fresh rock samples with the same composition and texture show that the corrosional rate of carbonate rocks of the former is 1.264-1.643 times higher than that of the latter. Crustose lichens are considered as an activator of the surface corrosion of carbonate rocks.  相似文献   

任丘油田开发过程中油田水水质演化特征研究     

陈锁忠  余俊吉 《高校地质学报》1998,4(3):338-345

对任丘油田开发过程中油田水水质特征及演化规律进行了初步分析,探讨了人工注水对油田水质的演化影响,其结果表明,注入水对油田水泊稀释混合作用明显,破坏了油层内部水－岩作用平衡,改变了井下原来的水文地球化学环境,根据诺模图求得的一些离子含量与其实际值之间存在明显差异,表明机械混合与水－岩相互作用并存,这与实际情况是吻合的。  相似文献   

云贵高原湖泊沉积物碳酸盐和有机质的同位素组成及环境信息记录   总被引：1，自引：0，他引：1  

肖保华 《矿物岩石地球化学通报》1998,(1)

云贵高原湖泊沉积物碳酸盐和有机质的同位素组成及环境信息记录＠肖保华￥中国科学院地球化学研究所高原湖泊,碳酸盐,有机质,碳同位素,地球化学记录,环境气候信息云贵高原湖泊沉积物碳酸盐和有机质的同位素组成及环境信息记录肖保华（中国科学院地球化学研究所,贵阳５５０...  相似文献   

关于黄土碳酸盐与气候环境关系探讨   总被引：1，自引：0，他引：1  

陈忠  马海州  曹广超  周笃珺  张西营  姚远 《云南地理环境研究》2007,19(3):7-10,14

黄土中碳酸盐与气候环境密切相关。从碳酸盐的成因看，干冷的气候利于原生碳酸盐的保存，而温湿的气候使大量的次生碳酸盐产生。碳酸盐的存在形式与降水量多少有关，降水量大可形成结核层和钙板等，而降水量小则形成各种胶膜。胶膜中各种不同形态的方解石胶膜又可反映不同的气候条件。黄土一古土壤中形成的碳酸盐实际上在古土壤期形成的碳酸盐要高于黄土期形成的，只是由于古土壤期强烈的风化淋溶作用，大量的碳酸盐从古土壤中淀积到下伏的黄土层中。黄土中CaCO3的淀积可分为连续淀积和不连续淀积两类。依据淀积深度和降水量的关系，可建立二者定量的关系。从黄土碳酸盐的不同方面，得到其与气候环境关系较为全面的认识。  相似文献