The effects of quartz recrystallization and reaction on weak phase interconnection,strain localization and evolution of microstructure     

《Journal of Structural Geology》2015

We conducted axial compression and general shear experiments, at T = 900 °C and P = 1.5 GPa, on samples of banded iron formation (BIF) and synthetic aggregates of quartz, hematite and magnetite to investigate how dynamic recrystallization of quartz promotes strain localization, and the role of weak second phases (oxides) on the rheology and microstructural evolution of the aggregates. Experiments showed strain localization into oxide rich layers, and that the oxide content and oxide distribution are key factors for the strength of the aggregate. Only 2–10 wt.% hematite leads to pronounced weakening and increasing hematite content above ∼10% has only a minor additional effect. Where oxide grains are dispersed, the initial strength contrast with quartz induces stress concentrations at their tips, promoting high stress recrystallization-accommodated dislocation creep of quartz. Fine recrystallized quartz reacts with oxide, forming trails of fine reaction product (ferrosilite/fayalite) leading to the interconnection/percolation of a weaker matrix. The strength contrast between the quartz framework and these fine-grained trails promotes strain localization into micro-shear zones, inducing drastic strain weakening. Thus dynamic recrystallization of quartz promotes syn-deformational reactions leading to a microstructurally-controlled evolution of phase strength contrast. It results in a rheologic transition from load-bearing framework to a matrix-controlled rheology, with transition from S–C′ to S–C fabric with increasing strain.  相似文献   

新疆若羌坡北地区镁铁-超镁铁质侵入岩含矿特征及找矿方法探讨          下载免费PDF全文

王恒王鹏李建冯京邓刚  吕新彪 《中国地质》2015,42(3):777-784

新疆若羌坡北地区因发现了众多岩浆硫化物型镍矿而受到关注,坡一镍矿为近期发现评价的超大型岩浆硫化物型铜镍矿床.但未发现有规模的高品位富矿体,不能满足矿产开发的条件.文章从坡北镁铁-超镁铁岩带地质特征出发,对坡北地区已经发现的岩浆硫化物矿床含矿特征进行了归纳总结,分析岩体就位成矿有利部位,开展了富矿成矿预测.结合已经总结出的综合地质、物探、遥感、化探等的找矿方法组合,通过地质实践,取得了很好的找矿进展,首次在坡北一带发现了深熔贯入式镍矿床——坡东镍矿.  相似文献   

寿光市水文地质特征浅析          下载免费PDF全文

于得芹  蒙永辉 《山东国土资源》2014,30(8)

寿光市位于山东半岛中部,渤海莱州湾南畔,是全国主要蔬菜生产基地。近些年来由于工农业的飞速发展及地下水开发利用程度的加大,已产生了一系列的环境地质问题,水文地质条件也发生很大的转变。在借鉴半岛蓝色经济区1∶10万区域水文地质工程地质环境地质综合调查(寿光幅)工作成果基础上,系统分析了寿光市的水文地质特征,并圈定了富水地段,预测其远景开采量,为寿光市地下水资源的可持续利用提供依据。  相似文献   

滇东北伴(共)生锗矿地质特征及成因探讨   总被引：3，自引：1，他引：2  

薛步高 《化工矿产地质》2004,26(4):210-219,227

长期以来,习惯上将伴(共)生锗矿的成因,归属于主金属矿的成因。代表性的会泽矿其主流派的成因认识是沉积一改造成因,而且是与岩浆岩无关的改造作用。通过对滇东北伴(共)生锗与酸性岩有关的地质特性、另一组与酸性岩有关的伴生元素的存在和深受二次矿化叠加富矿存在的事实的分析与研究,认为会泽矿深部存在尚未被揭露的与晚期主要叠加矿化有关的酸性岩体。提出早期的火山热液与晚期岩浆热液复式成矿的新观点。合理解释了在相关准地台构造单调,地表又无岩浆岩的会泽地区会产出一个超大型富锗-铅锌矿床的根本原因。  相似文献   

Al–Mg and Pb–Pb systematics of Allende CAIs: Canonical solar initial Al/Al ratio reinstated     

Benjamin Jacobsen  Qing-zhu Yin  Frederic Moynier  Yuri Amelin  Alexander N. Krot  Kazuhide Nagashima  Ian D. Hutcheon  Herbert Palme 《Earth and Planetary Science Letters》2008,272(1-2):353-364

The precise knowledge of the initial ²⁶Al/²⁷Al ratio [(²⁶Al/²⁷Al)₀] is crucial if we are to use the very first solid objects formed in our Solar System, calcium–aluminum-rich inclusions (CAIs) as the “time zero” age-anchor and guide future work with other short-lived radio-chronometers in the early Solar System, as well as determining the inventory of heat budgets from radioactivities for early planetary differentiation. New high-precision multi-collector inductively-coupled plasma mass spectrometry (MC-ICP-MS) measurements of ²⁷Al/²⁴Mg ratios and Mg-isotopic compositions of nine whole-rock CAIs (six mineralogically characterized fragments and three micro-drilled inclusions) from the CV carbonaceous chondrite, Allende yield a well-defined ²⁶Al–²⁶Mg fossil isochron with an (²⁶Al/²⁷Al)₀ of (5.23 ± 0.13) × 10^− 5. Internal mineral isochrons obtained for three of these CAIs (A44A, AJEF, and A43) are consistent with the whole-rock CAI isochron. The mineral isochron of AJEF with (²⁶Al/²⁷Al)₀ = (4.96 ± 0.25) × 10^− 5, anchored to our precisely determined absolute ²⁰⁷Pb–²⁰⁶Pb age of 4567.60 ± 0.36 Ma for the same mineral separates, reinstate the “canonical” (²⁶Al/²⁷Al)₀ of 5 × 10^− 5 for the early Solar System. The uncertainty in (²⁶Al/²⁷Al)₀ corresponds to a maximum time span of ± 20 Ka (thousand years), suggesting that the Allende CAI formation events were culminated within this time span. Although all Allende CAIs studied experienced multistage formation history, including melting and evaporation in the solar nebula and post-crystallization alteration likely on the asteroidal parent body, the ²⁶Al–²⁶Mg and U–Pb-isotopic systematics of the mineral separates and bulk CAIs behaved largely as closed-system since their formation. Our data do not support the “supra-canonical” ²⁶Al/²⁷Al ratio of individual minerals or their mixtures in CV CAIs, suggesting that the supra-canonical ²⁶Al/²⁷Al ratio in the CV CAIs may have resulted from post-crystallization inter-mineral redistribution of Mg isotopes within an individual inclusion. This redistribution must be volumetrically minor in order to satisfy the mass balance of the precisely defined bulk CAI and bulk mineral data obtained by MC-ICP-MS.The radiogenic ²⁰⁸Pb/²⁰⁶Pb ratio obtained as a by-product from the Pb–Pb age dating is used to estimate time-integrated ²³²Th/²³⁸U ratio (κ value) of CAIs. Limited κ variations among the minerals within a single CAI, contrasted by much larger variations among the bulk CAIs, suggest Th/U fractionation occurred prior to crystallization of igneous CAIs. If interpreted as primordial heterogeneity, the κ value can be used to calculate the mean age of the interstellar dust from which the CAIs condensed.  相似文献   

相山铀矿田特富矿成矿模式   总被引：10，自引：0，他引：10  

温志坚  杜乐天  刘正义 《地质论评》1999,45(7):763-767

相山铀矿田是我国最大的火山热液型铀矿田之一。大量的电子探针测试揭示该矿田特富铀矿体中普遍存在铀矿物与氟碳磷灰石紧密共生,对特富铀矿石的化学分析也显示铀含量与P2O5和CaO呈大体正相关关系。进一步研究表明磷、铀具有相似的地球化学特性并在热液条件下可以共迁移、共沉淀,据此作者提出：磷、铀胶体共沉淀是该区特富矿形成的主要机理。对采自相山盆地邻区地幔捕虏体研究证实地幔流体与相山矿田铀成矿热液化学成分具有相似性：即富含钾、钠离子和还原性气体。对相山铀矿田He、Ar同位素研究进一步证实该矿田铀成矿热液中有地幔流体参与。配合其他方面的研究,在本区首次提出特富矿铀成矿模式。  相似文献   

五大连池裂谷型富钾火山岩带的岩石学与地球化学   总被引：3，自引：0，他引：3  

樊祺诚  刘若新  隋建立 《地质论评》1999,45(7):358-368

以五大连池火山群为中心的小古里河—科洛—五大连池—二克山近SN向的裂谷型富钾火山岩带,除了科洛火山群的火山活动从晚第三纪持续到第四纪,其它火山主要限于第四纪的喷发活动。按照岩石学和化学成分,晚第三纪和第四纪富钾火山岩分别命名为白榴碧玄岩和白榴玄武岩。富钾火山岩的岩石学、主微量元素和SrNdPb同位素地球化学特征表明,富钾火山岩来自交代的EMI地幔。  相似文献   

等离子体发射光谱法同时测定大洋富钴结壳中硅锰铁钙镁铝钛   总被引：3，自引：0，他引：3  

吴建之  赵宏樵 《岩矿测试》2000,19(3):221-223

大洋富钴结壳试样经ＨＣｌ＋ＨＮＯ３＋ＨＦ溶解,在０．２ｍｏｌ／ＬＨＦ和０．１３ｍｏｌ／ＬＨ３ＢＯ３介质中,用感耦等离子发射光谱法同时测定Ｓｉ、Ｍｎ、Ｆｅ、Ｃａ、Ｍｇ、Ａｌ、Ｔｉ元素的含量。方法经国家标准物质ＧＢＷ０７２４９大洋多金属结核验证,其结果与标准值相符,精密度ＲＳＤ〈３．２％（ｎ＝６）;已应用于太平洋富钴结壳中多元素分析。  相似文献   

东秦岭北部富碱侵入岩钕、锶、铅同位素特征及构造意义   总被引：15，自引：0，他引：15  

张正伟  朱炳泉  常向阳 《地球化学》2000,29(5):455-461

东秦岭北部富碱侵入岩主要分布在陕西省洛南与河南省卢氏－确山一带,岩石有碱性岩、碱性花岗岩和石英正长岩三大类。岩石Ｎｄ、Ｓｒ和Ｐｂ同位素地球化学的研究表明,该区富碱侵入体的源区应是以下地壳为主,并通过碰撞造山作用带入少量地幔和上地壳物质。源区同位素组成横向与垂向的不均一性说明华北块体存在成熟的下地壳层,而北秦岭块体是造山带环境。古大陆边缘经历了多次裂解作用和多期碱性岩浆活动;碱性岩浆是在减压扩容环境  相似文献   

辽东半岛海城-大石桥菱镁矿矿床成因探讨     

胡古月  孙新胜  郑军  余旭辉  王东波  李延河  赵悦  陈翰  徐莺  Alison Ord 《地质学报》2022,96(4):1340-1355

辽东半岛古元古界辽河群大石桥组三段地层中赋存有全球最大工业储量的菱镁矿矿床.在总结和整理已发表的辽东半岛晶质菱镁矿床地质和地球化学数据的基础上,本次研究进行了Mg和B同位素测试及研究工作,获得以下认识:① 菱镁矿矿体呈北东东走向,产于大石桥组三段,但不同矿床的矿体厚度差异较大(30～300 m),菱镁矿矿体与顶、底板高...  相似文献