Highly alkaline,high-temperature hydrothermal fluids in the early Archean ocean     

Takazo Shibuya  Tsuyoshi Komiya  Kentaro Nakamura  Ken Takai  Shigenori Maruyama 《Precambrian Research》2010

Based on the petrology of hydrothermally altered Archean basaltic greenstones, thermodynamic calculations of phase equilibria were conducted to estimate the composition of a high-temperature (∼350 °C) hydrothermal fluid in an Archean subseafloor basalt-hosted hydrothermal system. The results indicate that the hydrothermal fluid was highly alkaline attributed to the presence of calcite in the alteration minerals under a high-CO₂ condition, and predict a generation of SiO₂-rich, Fe-poor hydrothermal fluids in the Archean subseafloor hydrothermal system. The chemically reactive mixing zones between alkaline hydrothermal fluids and slightly acidic-neutral seawater are characterized by inverse pH and chemical polarity to modern hydrothermal systems, leading to extensive precipitation of silica and iron oxyhydroxides on/under the seafloor. Such processes can be responsible for the abiotic formation of voluminous chert and subseafloor silica dike, the mechanism of silicification, and the pH-controlled generation of banded iron formation that has been arising mainly from the redox chemistry in the Archean ocean. Such high-temperature alkaline fluids could have had a significant role not only in the early ocean geochemical processes but also in the early evolution of life.  相似文献   

云南鸡街碱性超基性岩铂族元素地球化学特征   总被引：1，自引：1，他引：0  

赵正  漆亮  黄智龙  严再飞  许成 《岩石学报》2010,26(3):938-946

本文首次报道了攀西裂谷南段云南省鸡街碱性超基性岩中铂族元素(PGE)的地球化学特征。采用改进的Carius管法测定了霞霓钠辉岩、霓霞岩和磷霞岩中的低含量PGE。PPGE与IPGE呈现强烈分馏,推断幔源岩在低程度部分熔融过程中Pt、Pd表现为相似的不相容性,而Ir、Ru表现为相容性,这种分馏效应随着结晶分异作用的进行而逐渐增强。3种岩石均出现Ru的负异常及Pt、Pd的解耦,说明母岩浆经历了早期的橄榄石晶出,在结晶分异过程中Pd较Pt更不相容。由于岩浆上升过程中的压力减小和结晶分异作用导致的成份变化使岩浆可以达到硫的局部饱和而熔离,表现为部分样品中Cu/Pd远高于原始地幔值。本文通过碱性超基性岩与金伯利岩、煌斑岩和邻区碱性、过碱性玄武岩PGE特征的对比,探讨了其岩浆源区及演化特征。  相似文献   

南天山川乌鲁碱性杂岩体的岩石学和地球化学特征及其岩石成因   总被引：2，自引：1，他引：1  

黄河  张东阳  张招崇  张舒  李宏波  薛春纪 《岩石学报》2010,26(3):947-962

位于中国南天山西侧阔克萨彦岭一带的川乌鲁碱性杂岩体,与该区川乌鲁铜金多金属矿床有着直接的成因联系,该杂岩体由早期的辉长岩—闪长岩岩、主期的二长岩—正长岩和晚期的正长花岗斑岩脉组成,各期岩石在矿物组成和化学成分上有明显的变化。从早到晚,SiO2含量增加,变化范围是50.52%～70.64%;全碱含量先增后减,在SiO2含量小于61.69%时,随SiO2含量增加而增加,而当SiO2含量大于61.69%时,与SiO2含量负相关。在AR-SiO2图解上,大多样品落入碱性区间,在A/CNK-A/NK图解上表现出由准铝质向过碱性演化的趋势。微量元素表现为大离子亲石元素相对高场强元素富集,Rb、Ba、Th、Sr等元素的相对富集和Nb、Ta、P、Ti等元素的负异常。稀土元素表现为轻稀土相对富集的特征,其(La/Yb)N为14.13～25.09,具有Eu的正异常或极微弱的Eu负异常。一些元素比值的线性关系暗示了该杂岩体为岩浆混合成因,基性岩浆的源区为富水的岩石圈地幔,而酸性岩浆是中下地壳中性火成岩在含饱和水条件下部分熔融的产物。这些性质指示川乌鲁杂岩体是在后碰撞拉张环境中由岩石圈地幔熔融的基性岩浆的底侵作用导致地壳的熔融以及后期的岩浆混合作用有关。  相似文献   

云南武定晚二叠世高钛辉绿岩特征及形成环境     

焦骞骞 《云南地质》2012,(3):396-400

高钛辉绿岩为富钠碱性系列,玄武岩浆有较明显的分异。稀土元素总量较高,轻稀土元素富集,无明显Eu异常或亏损。微量元素蛛网图中,Rb、Ba、Th和Hf、Zr、Sm两组元素双隆起的特征,与板内碱性玄武岩特征相似。综合多种图解判别,属于大陆裂谷环境。  相似文献   

新疆哈尔里克山二叠纪碱性花岗岩-石英正长岩组合的成因及其构造意义   总被引：2，自引：0，他引：2  

汪传胜  顾连兴  张遵忠  吴昌志  唐俊华  三金柱  黎广荣  李中华 《岩石学报》2009,25(12):3182-3196

哈尔里克奥姆尔塔格碱性花岗岩(OMAG)侵入于小铺东二长花岗岩中.该岩体岩性较均一,呈灰紫色,主要矿物组合为石英、钾长石、钠长石、碱性角闪石和霓石;化学成分上富硅、碱,贫钙、镁,低铝;富Rb、Th、U和Zr,Ga/AI比值大(3.18×10~4～3.56×10~4),贫Ba、Sr,岩石中Co、Cr、V和Ni等过渡元素显著亏损,U、Hf、Zr和Nb等高场强元素的含量高;稀土总量较高,配分模式右倾,并具有显著的负铕异常;LA-ICP-MS锆石~(206)Pb/~(238)U加权平均年龄为287.6±2.1Ma;具有正的ε_(Nd)(t)值(+4.96),较低的(~(87)>Sr/~(86)Sr);值(0.70159).同样侵入于小铺东二长花岗岩中的恰干昆多沟含角闪石石英正长岩(QGQS)也呈灰紫色,其结构和构造与OMAG非常相似.两个岩体在主量元素和REE图解上均呈现有规律的分布和一致的演化趋势.从QGQS到OMAG,SiO_2含量增加(从64.71%～64.83%到71.23%～74.31%)、全碱含量降低(从11.72%～11.79%到8.49%～9.87%)和Al_2O_3含量减少(从16.09%～16.19%到11.44%～13.34%)、稀土总量减少(从592.3×10~(-6)～656.0×10~(-6)到273.9×10~(-6)～405.9×10~(-6))、轻/重稀土比值降低(从18.2～20.1到4.4～6.0)、稀土配分曲线从平滑到Eu显著亏损.基于OMAG的岩相学、矿物学、地球化学、锆石年代学和与QGQS的对比研究,笔者认为奥姆尔塔格碱性花岗岩可能是由石英正长岩母岩浆经过分离结晶作用演化的产物,且这种石英正长岩岩浆起源于亏损地幔;根据哈尔里克造山带地质演化历史的分析,这两个岩体均形成于紧随主碰撞后的挤压-伸展转折阶段.  相似文献   

Gravity and magnetic 3D inversion of Morro do Engenho complex, Central Brazil     

Alanna C. Dutra  Yra R. Marangoni 《Journal of South American Earth Sciences》2009,28(2):193-203

In the Goiás Alkaline Province, in central Brazil, some mafic–ultramafic alkaline bodies crop out, such as Morro do Engenho Complex (ME), whereas other intrusive bodies are completely covered by Quaternary sediments, such as A2 body, and can only be defined by their magnetic and gravity responses. The bodies give rise to strong gravity and magnetic anomalies. We inverted the gravity and magnetic data to estimate 3D density and magnetic intensity contrasts. The gravity inversion reveals that ME and A2 intrusions, totally emplaced in the upper crust, have maximum depths of about 10 and 6 km, respectively. The estimated density contrast distribution indicates a NE–SW preferential direction for ME intrusive body. Since the remnant magnetization is very important in the area, we inverted the magnetic data, testing two hypotheses: only induced field and induced plus remnant magnetizations. The results of the inversion using only induced field could not explain the observed magnetic field, which was about 1000 nT larger than the calculated one. Induced plus remnant field inferred from wandering polar path fitted the observations. 3D magnetic inversions when remnant magnetization was included recover deeper and thinner bodies compared with gravity inversion. The inverted bodies have spherical shapes which are more consistent with the model of magmatic chambers instead of plug intrusions.  相似文献   

乙醇对锯缘青蟹碱性磷酸酶活力与构象的影响   总被引：4，自引：2，他引：2  

郑文竹  黄璜  刘晓丹  史渊源  陈清西 《台湾海峡》2000,19(4):489-493

应用荧光光谱、紫外吸收光谱研究锯缘青蟹碱性磷酸乙醇微扰后的分子构象变化情况。乙醇对酶分子构象有显著的影响,酶的内源荧光强度随乙醇浓度增大而增加,荧光发射峰逐渐发生红移,说明酷氨酸、色氨酸残基的微环境发生明显的变化;紫外吸收光谱在278nm吸收峰随乙醇浓度增大而增强。这些结果表明,酶蛋白分子中的生色基因残 基的微环境发生变化;酶的剩余活力随着乙醇浓度增大而迅速下降,经乙醇失活的酶在正常的测活体系中监测酶活力,发现酶活力可以回升到92％以上,说明酶的乙醇失活是可逆的,可以通过稀释复活。测定乙醇对酶的抑制动力学,表明乙醇对青蟹碱性磷酸酶的抑制作用是反竞争性机制,其抑制常数Ki为11．8％。  相似文献   

贻贝(Mytilus edulis)发育早期酸性和碱性磷酸酶活性   总被引：1，自引：0，他引：1       下载免费PDF全文

孙虎山  王宜艳  梁建光  冉镇  曾鹏  韩强 《海洋与湖沼》2008,39(1):42-48

采用组织化学和分光光度技术对贻贝卵、胚胎和早期幼虫酸性磷酸酶(ACP)和碱性磷酸酶(AKP)活性进行了定位和定量研究,以探讨贝类早期发育过程中的免疫防御机制。组织化学显示,从卵细胞到D型面盘幼虫各个时期都呈ACP和AKP阳性,卵细胞中阳性颗粒较大且分布比较均匀,受精卵中央着色较深,卵裂期核区呈强阳性且大分裂球内阳性颗粒较多,原肠胚和担轮幼虫外层细胞阳性较强,面盘幼虫外套膜边缘膜、内脏团和面盘基部呈强阳性。生化测定ACP和AKP活力,均是卵细胞最低,随着发育酶活力逐步提高,其中ACP活力在受精后和囊胚期明显提高,囊胚期达到最高峰,其后又略有下降;AKP活力在卵裂期、担轮幼虫和面盘幼虫提高较大,面盘幼虫期酶活力最高。ACP和AKP可能在贻贝的发育早期抵抗病原生物侵染方面发挥重要作用。  相似文献   

西秦岭月照 琵琶寺地区火山岩地球化学特征及地质意义          下载免费PDF全文

刘军锋  孙勇  高明  杨磊 《地质学报》2008,82(7):998-2008-01-30

月照琵琶寺地区的变质火山岩出露于甘肃武都县境内,夹在泥盆系和前震旦碧口群地层之间。按地球化学分类,火山岩可划分为双峰式和碱性两个系列。双峰式火山岩系由低K富Na拉斑玄武岩和酸性英安岩、流纹岩组成。该玄武岩具有类似MORB的微量元素特征,平坦的稀土配分模式,但富Th贫Nb显示其受到陆壳混染的影响。该套火山岩总体特征指示其为大陆裂谷向成熟洋盆转化阶段的产物,从而推测本区火山岩可能为勉略古洋盆西延的分支产物。  相似文献   

Petrogenesis of Permian alkaline lamprophyres and diabases from the Spanish Central System and their geodynamic context within western Europe   总被引：1，自引：1，他引：0  

D. Orejana  C. Villaseca  K. Billström  B. A. Paterson 《Contributions to Mineralogy and Petrology》2008,156(4):477-500

Basic to ultrabasic alkaline lamprophyres and diabases intruded within the Spanish Central System (SCS) during Upper Permian. Their high LREE, LILE and HFSE contents, together with positive Nb–Ta anomalies, link their origin with the infiltration of sublithospheric K-rich fluids. These alkaline dykes may be classified in two distinct groups according to the Sr–Nd isotope ratios: (1) a depleted PREMA-like asthenospheric component, and (2) a BSE-like lithospheric component. A slight enrichment in radiogenic ²⁰⁷Pb and ²⁰⁸Pb allows the contribution of a recycled crustal or lithospheric component in the mantle sources. The intrusion of this alkaline magmatism is likely to have occurred due to adiabatic decompression and mantle upwelling in the context of the widespread rifting developed from Carboniferous to Permian in western Europe. The clear differences in the geochemical affinity of Lower Permian basic magmas from north-western and south-western Europe might be interpreted in terms of a more extensive separation of both regions during that period, until they were assembled during Upper Permian. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.  相似文献