温湿气候区结晶岩与碎屑岩腐岩特征及其发育过程

发育于斜坡非饱和带的结晶岩与碎屑岩腐岩多夹于残坡积土层和风化岩带之间,保留有裂隙及层理等构造,但质地松软。腐岩结构体与母岩色差显著,保留原岩结构和构造特征,矿物成分以次生粘土矿物、次生石英及褐铁矿最为常见。腐岩次生微孔隙发育,具有低密度、高孔隙度、高渗透率、高容水度及高持水度特征。腐岩发育是通过低渗透岩石结构体风化前锋的渐进性扩展实现的,非饱和带高湿度空气形成的凝结水和降水入渗形成的非饱和渗流是该过程的核心动力。气态水分子能够扩散到低渗透岩石结构体表面内侧一定宽度范围内的孔隙系统之中凝结为液态水并溶蚀造岩矿物。雨季入渗降水在结构体表面形成的薄膜水流通过分子扩散机制接受其内侧结构体粒间溶液中的溶出组分并将其携入饱水带,同时恢复粒间溶液的侵蚀动力。当上述过程循环到一定程度时,结构面内侧便形成一定厚度的腐岩壳。腐岩壳在雨季直接吸收、贮存流经其表面的液态渗入水,在核心石外侧形成富水结构层并在旱季向包气带或其内侧的风化前锋提供水汽。随着时间推移,腐岩壳越来越厚,核心石最终消失;当某一范围内的岩石结构体全部演变为腐岩结构体时,该范围内的岩体也就完成了向腐岩体的转变。     

岩体化学风化的非连续性及其科学意义

岩体化学风化在空间上具有高度的非连续性,这种非连续性广泛存在于从宏观、细观到微观的所有尺度。宏观结构面是化学风化最主要的发生场所;风化岩体内,新鲜岩块被沿结构面内法线方向发育的腐蚀带包围,呈斑点状分散于腐岩中。微缝等细观损伤普遍存在于各类岩石中;化学风化从岩块内不同空间位置的水力有效空隙向三维空间扩展,决定了细观尺度上化学风化的非连续性。矿物溶解是在晶体中具有过剩表面能的缺陷位置优先发生的,因而具有显著的微观非连续性。由于非连续特性,化学风化可增大水岩界面,提升矿物溶解反应的规模及速率。通过对既有损伤的扩展及在损伤空间堆积残余物,化学风化具有分离—裂化岩体、岩块及造岩矿物的重要作用,这种作用可使以新鲜岩石为主的岩体大规模脱离母岩,而堆积于坡脚的岩石块体在化学风化的继续作用下,可裂解为更小的岩屑或矿物碎屑,为向水体搬运创造条件,从而极大地促进斜坡夷平及地貌重塑进程。     

某路基边坡化学风化机理研究

以云南省富民县某典型路基边坡为例,采用铸体薄片鉴定、岩石全分析和电子扫描电镜等分析测试方法,研究岩石结构体岩石学、矿物学及微观结构特征,并据此对该边坡化学风化机理进行探讨。试验结果表明:岩石为碳酸盐化钙质基性沉凝灰岩,经历溶解、水解、氧化等多种水岩化学作用后,岩石微观结构疏松、孔隙发育;腐岩壳与核心石存在明显界线并发育微裂纹。由此可以得出:化学风化的实质为侵蚀性地下水与岩石造岩矿物之间发生化学作用并造成岩石结构体损伤;相对实验室条件,天然斜坡水岩化学作用机理复杂并涉及诸多科学问题;水岩化学作用诱发斜坡失稳,孕育不良地质现象,促进斜坡夷平和地貌重塑,推动全球气候演化,参与成矿作用,对其研究具有重要的科学意义。     

基于结构体的峨眉山玄武岩风化程度评价（Ⅱ）：玄武岩斜坡地下水及浸泡液水文地球化学

岩石风化过程中的元素活动性评价除应考虑该元素在风化产物中残留与淋失状况及在淋滤液(地下水及室内浸泡液等)中的浓度外,还应考虑其在母岩中的相对含量.峨眉山玄武岩斜坡地下水及室内浸泡液中各元素原子个数比值与母岩中对应比值之间均存在显著差异,其造岩矿物的非全等溶解特征显著.综合考虑风化过程中的岩石成分变化、斜坡地下水及室内浸泡液化学成分确定的峨眉山玄武岩风化过程中的元素活动性顺序为Ca＞Na＞Mg≥Si＞K＞Fe.活动性强或惰性程度高、对风化程度变化响应敏感应成为岩石风化程度指示性元素的选择标准,Ca和Fe应成为峨眉山玄武岩风化程度评价的首选元素.     

斜坡非饱和带低渗透岩石结构体风化前锋扩展过程

非饱和带低渗透岩石结构体风化前锋扩展是斜坡灾害孕育过程中的关键环节之一。到目前为止,化学风化领域的研究成果主要集中在高水-岩比的饱和环境下单矿物及矿物成分单一的碳酸盐岩的风化动力学方面,非饱和环境下的岩石风化研究还主要限于风化产物的特性描述方面。斜坡非饱和带低渗透岩石结构体风化前锋扩展是一种高度复杂的THMC过程。由于在溶解对象、溶解液及溶解过程的水动力-水化学环境等方面存在的显著差异,既有的地质材料风化动力学成果为探索这一复杂过程提供了理论储备,但还不能阐明其核心机理。斜坡非饱和带低渗透岩石结构体风化前锋的扩展过程研究不仅可以加深人们对斜坡灾害孕育的理解,为灾害预报-预警及其控制提供理论依据,同时可以促进岩石-岩体力学及浅表生水文地球化学等相关学科的交叉与发展。     

基于结构体的峨眉山玄武岩风化程度评价（Ⅰ）：风化结构体地球化学

峨眉山玄武岩属典型低渗透介质,其岩体风化是通过结构体风化实现的.风化玄武岩结构体具有一层或多层腐岩壳包围核心石形成的壳状结构;从表面向内,越靠近结构体几何中心,玄武岩风化程度越低.玄武岩风化可分为初期和中后期两个阶段,第一阶段仅存在二价铁向三价铁的转变而无明显组分流失与相对富集,第二阶段二价铁氧化与活动性组分(Si、Ca、MgNa、K)淋失和惰性组分(Al、Ti、ΣFe)相对富集同时发生.风化初期,随着风化程度的提高,FeO和Fe2O3相对含量此消彼长,但∑Fe相对含量变化不大;风化中后期,随着风化程度的提高,SiO2、CaO、MgO、Na2O、K2O、FeO相对含量单调降低,Al2O3、TiO2、Fe2O3、LOI单调升高.玄武岩风化过程中,FeO和Fe2O3相对含量对风化程度变化最为敏感.贯穿整个风化过程的含铁矿物氧化引起的铁种相对含量变化应成为峨眉山玄武岩风化程度评价需要考虑的关键因素.     

根据矿物薄片颜色判估铬尖晶石类型的方法

尖晶石族矿物为AB2X4型氧化物,因其阳离子A和B元素的不同,分属Cr、Fe、Al、Zn、Mn、Ti、Ni等不同种属,并有不同的产状。其中铬尖晶石仅见于幔源超镁铁岩和镁铁岩中。对岩石中副矿物铬尖晶石的薄片颜色与其矿物化学类型对比发现,二者存在着明显的专属关系,薄片中铬尖晶石的不同颜色可做为寄生岩体可能产出铬矿床或镍矿床的判据。副矿物和造矿铬尖晶石的化学通式是相同的,其中二价阳离子为Mg和Fe,三价阳离为Cr、Al和Fe。铬尖晶石以其三价阳离子含量百分比的不同分为不同的种属。岩石薄片下,铬尖晶石类矿物除含钛磁铁矿、铬磁铁矿和高铁…     

丹霞地貌砂岩的微观化学风化作用电子探针研究

利用偏光显微镜观察、电子探针分析等手段对江西龙虎山丹霞地貌崖壁砂岩的微观化学风化作用的发展过程进行了研究,重点观测黑云母蛭石化以及长石黏土化过程中矿物组分的变化,进而探讨丹霞地貌砂岩的微观化学风化作用机理。在微观化学风化下,强风化层胶结物中的方解石迅速分解流失,从而导致黑云母大量发生蛭石化和铁的氧化物在矿物边部富集;长石则大量发生黏土化而使高岭石、石英等矿物富集。研究表明丹霞地貌砂岩在微观化学风化作用下矿物分解以及新矿物的形成都破坏原来岩石中的力学平衡,因而风化作用在宏观上表现为岩面片状剥离和重力崩塌,据此推断更大尺度的风化作用可能与岩石中矿物的微观化学风化作用存在着密切联系,是微观化学风化作用长期累积后在宏观上的综合表现。      

江西武宁县石门寺钨铜矿区风化作用过程中W、Cu等元素的表生地球化学行为(之一)

以江西省武宁县石门寺钨铜矿区燕山期和晋宁期岩体风化作用过程中W、Cu等元素的表生地球化学行为为研究对象,通过反映风化程度的化学风化指数CIA、风化作用过程中组分得失的估算、不同介质中W、Cu等成矿元素的含量变化及大离子亲石元素表生地球化学行为等方法的研究表明,石门寺钨铜矿区2个时期岩体元素淋失与风化强度有关,土壤剖面中碱金属、碱土金属元素大量淋失,而W、Cu等成矿元素在土壤B层中显著富集;从岩石到土壤、再到水系沉积物风化过程中,W、Cu等成矿元素含量逐渐升高,为此,一级水系沉积物和B层土壤是赣北九岭W、Sn、Cu、Mo多金属矿集区地球化学找矿的绝佳采样介质,是矿集区内找矿新突破的有效手段。     

江西武宁县石门寺钨铜矿区风化作用过程中W、Cu等元素的表生地球化学行为（之一）

以江西省武宁县石门寺钨铜矿区燕山期和晋宁期岩体风化作用过程中W、Cu等元素的表生地球化学行为为研究对象,通过反映风化程度的化学风化指数CIA、风化作用过程中组分得失的估算、不同介质中W、Cu等成矿元素的含量变化及大离子亲石元素表生地球化学行为等方法的研究表明,石门寺钨铜矿区2个时期岩体元素淋失与风化强度有关,土壤剖面中碱金属、碱土金属元素大量淋失,而W、Cu等成矿元素在土壤B层中显著富集;从岩石到土壤、再到水系沉积物风化过程中,W、Cu等成矿元素含量逐渐升高,为此,一级水系沉积物和B层土壤是赣北九岭W、Sn、Cu、Mo多金属矿集区地球化学找矿的绝佳采样介质,是矿集区内找矿新突破的有效手段。     

黔西北地区二叠纪玄武岩古风化壳常量元素的地球化学特征

通过对峨眉山玄武岩古风化壳进行野外调查、取样和分析测试工作,认为: ①贵州西部广泛出露峨眉山玄武岩,晚二叠世古气候温润潮湿,利于峨眉山玄武岩风化形成含Fe、Ti的黏土矿物和铝质黏土矿物的古风化壳,该风化壳受古地理环境和峨眉山玄武岩控制。②相对玄武岩而言,铝质黏土岩主量元素含量特征表现为富TiO₂、Al₂O₃,轻度亏损SiO₂,明显亏损TFe,其他主量元素大量流失; 铁质黏土岩主量元素含量特征表现为富TFe、TiO₂, 轻度富Al₂O₃,但相对于铝质黏土岩,TiO₂的富集程度偏低,SiO₂亏损明显,其他元素亦大量流失。③由于晚二叠世频繁的海侵作用,水位较高的区域,风化壳下部处于较还原的条件下,Fe被还原成易溶的二价状态或在有机质的作用下迁出风化壳,而Ti由于存在形式较为稳定,继续保存在黏土矿物中,与Fe发生分异; 局部水位较浅的氧化环境及重力分异作用下,黏土矿物与铁矿物由于比重差异而分选开来,形成Fe与Al、Ti的分异,并伴随铁矿、钛矿和铝土矿的富集。该富集规律的发现对寻找该区铁、钛和铝土矿有一定的理论指导意义。     

Weathering of a Quaternary glass-rich basalt in Bakrit,Middle Atlas Mountains,Morocco. Comparison with a glass-poor basalt

Abstract

We compared the disintegration processes and mineralogic and chemical evolution pathways of two Quaternary basalts at Bakrit and Ifrane, weathered in the same physiographic and hydrologic conditions, but differing in texture according to the quantity of glass present. At Bakrit, quite abundant glass favoured the formation of a microfissure network throughout the rock and its disintegration without any distinct weathering front. As a result, basaltic sand with polymineral grains and a clayey-silty matrix were produced. At Ifrane, weathering of a glass-poor basalt produced only a clayey-silty saprolite. In glass-rich basalts, secondary minerals formed in microfissures and were 2/1 clay-mineral rich. In glass-poor basalts, secondary minerals formed mainly within primary minerals and were 1/1 clay-mineral rich. Because glass could be easily dissolved, it protected the minerals of close chemical composition, especially the plagioclases. The order of basalt-mineral weathering (olivine, labrador, augite, Fe-Ti oxides) was modified when glass was abundant (glass, olivine, augite, labrador, Fe-Ti oxides). © Elsevier, Paris     

沉积型铝土矿的陆表淋滤成矿作用: 兼论铝土矿床的成因分类*

铝土矿是化学风化作用的细粒终极产物,与强烈的化学风化作用密切相关。根据母岩的类别及作用过程,风化作用进一步分为铝硅酸盐岩强化学风化形成的红土化作用和碳酸盐岩强化学风化形成的钙红土化作用。在强烈的化学风化过程中,地表的原始沉积物(母岩)的原生矿物发生溶蚀、水解、水化、碳酸化、氧化,破坏原始的矿物结构,形成新的细粒矿物(主要是黏土质矿物)。在适合的地质条件下,持续的强烈化学风化作用会造成大部分活动的元素(如K、Na、Ca、Mg、Si)的流失与Al的残留富集从而形成铝土矿。现在观察到的沉积型铝土矿,虽然与古风化壳具有密切联系,但沉积型铝土矿多数是由沉积过程搬运到沉积盆地中所形成的强化学风化产物的沉积层,与古风化壳的残坡积层具有显著差别,只有少数工业价值不大(品位低、品质差)的残坡积相铝土矿。铝土矿含矿岩系的沉积环境与铝土矿(尤其是高品位、高品质的铝土矿)的成矿环境不尽相同。铝土矿主要形成于暴露于大气中的陆表环境(而非水下环境),由地下水淋滤作用形成(在渗流带由活动元素流失、Al等稳定元素残留富集而成)。本研究在铝土矿成矿作用分析等基础上,提出了以铝土矿沉积物等物源和沉积、成矿作用为依据的中国铝土矿床分类方案,包括原地或准原地残坡积物成因的红土型和喀斯特型,和异地物源沉积成因的沉积型。     

亚热带小流域花岗岩化学风化及CO2消耗速率研究

文章选择深圳市的亚热带典型小流域作为研究对象,通过定期采集流域内降水、泉水、岩石及风化残积土样品,分析所有样品的常量元素和微量元素,探讨流域水体的化学成分组成和主要成分来源以及岩石化学风化程度和风化趋势,结合流域水文气象数据估算了花岗岩化学风化速率及CO2消耗速率.结果表明,研究区地下水化学类型为HCO3-Na型,主要...     

Subaerial leaching process of sedimentary bauxite and the discussion on classifications of bauxite deposits

Bauxite is the ultimate fine-grained products of chemical weathering,and thus it is closely linked with the intense chemical weathering. Based on variations of parent rock and weathering processes,the weathering products can be subdivided into laterite and terra rossa,of which the former is formed by weathering of aluminosilicates and the latter is produced by the weathering of carbonates. During the intense chemical weathering,minerals in original subaerial sediments(parent rocks)would suffer a series of processes(dissolution,hydrolyzation,hydration,carbonation,and oxidation)and be destroyed or transformed,leading to formation of new minerals. In the favorable environment,continuously intense chemical weathering would cause the loss of most mobile elements(e.g., K,Na,Ca,Mg,Si)and the enrichment of Al,resulting in the formation of bauxite. Although sedimentary bauxites are closely linked with the weathering curst,they show obvious differences in formation processes. Sedimentary bauxites are composed of intense chemical weathering products that are transported from outside of the basin and re-deposited in the basin,while most weathering crusts are transformed from saprolite and/or deluvium in-situ,and they can only form low-grade bauxites. Sedimentary environments also differ in bauxite ore layers and bauxitic claystone layers. Bauxite ore layers are formed in the subaerial environment and controlled by the leaching process of groundwater in the vadose zone. Based on the analysis of bauxitization,this study proposes to use multiple parameters,such as provenance,sedimentation and mineralization,to build the new classification of Chinese bauxite deposits. In this classification,lateritic and karstic types of bauxite deposits are autochthonous or parautochthonous saprolite and/or deluvium,while sedimentary type is dominated by heterochthonous provenance.     

真菌-玄武岩相互作用过程中真菌属种差异对元素释放行为的影响

真菌在矿物、岩石风化和元素溶解过程中发挥着重要作用。土壤中分布和生长着多种真菌,这些不同真菌在矿物和岩石风化,以及元素溶解过程中发挥的作用可能存在显著差异。为限定此差异,本研究从玄武岩风化土壤中分离获取了4种真菌(Aspergillus pesudofelis、Aspergillus viridinutans、Aspergillus undagawae和Aspergillus clavatus),设计批式溶解实验,探究了实验室条件下(28℃、30天内)4种真菌对玄武岩的风化作用,主要通过分析元素(包括Mg、Al、Si、Ca、Ti、Mn、Fe、Ni和Sr)的溶解速率和机制揭示不同属种真菌造成的玄武岩风化差异,并选取其中两种典型真菌所在的体系进行分析。实验结果显示不同属种真菌对玄武岩的风化和元素溶解的作用确实存在显著差异:1)与无机对照组相比,真菌A.pseudofelis的生长使得溶液pH值发生显著变化,元素的线性释放速率(Ril)显著升高;2)不同种真菌对体系pH值和Ril的影响差别巨大,且并非所有真菌均能加快玄武岩风化,如经过30天反应,含真菌A.pseudofelis体系溶液pH值上升了2.1,元素Mg的线性释放速率是无机对照组的22.5倍;而含真菌A.viridinutans体系溶液pH值仅上升了0.1,Mg的线性释放速率与无机对照组近似相等;3)Mg、Al、Ca、Ti元素的线性释放速率Ril最大值均出现在溶液最低pH值条件下,表明这4种元素的释放行为很大程度上受控于质子交换作用,而Fe和Ni的释放则由真菌代谢的草酸主导。由此可知,不同种真菌对有机酸代谢水平的差异影响了玄武岩中元素的释放行为。这也可能表明,在岩石早期风化过程中,具有较强有机酸(如草酸)代谢能力的真菌在Fe和Mg等生命必需元素的释放过程中起着重要作用。     

Geochemistry and mineralogy of saprolite in Finnish Lapland

An ancient saprolite has developed on the Palaeoproterozoic granulite, granite gneiss and amphibolite bedrock of the Vuotso–Tankavaara area of central Finnish Lapland. The present day climatic regime in Finnish Lapland lies within the northern boreal zone and so the saprolite there can be regarded as fossil. Cores of saprolite were collected from 4 sections (42 samples) and analyzed chemically and mineralogically. In the study area, progressive weathering of the rocks has been marked by gradual enrichment in Al, Fe and Ti; and depletion of Na, K and Ca. The higher concentration of Fe(III) and water and reduced Na and Ca in weathered bedrock in the 4 sections are indicative of oxidation, hydration and leaching processes involved during weathering. The primary minerals in the saprolite are plagioclase feldspar, K-feldspar, quartz, garnet (almandine) and hornblende; the common secondary minerals are kaolinite, halloysite, and vermiculite in addition to minor amounts of sericite. Intense weathering is indicated by: (1) the presence of kaolinite and halloysite in 4 sections of different bedrock types, and (2) the comparatively lower SiO₂/Al₂O₃ (wt.%) ratio (2.30) of weathered granulites (3 sections) as compared to fresh granulite (4.33) and that of weathered amphibolite (2.68) as compared to fresh amphibolite (3.56). In general, kaolinite and halloysite have formed through the weathering of feldspars, garnet, and biotite. Vermiculite is the most probable alteration product of biotite. The formation of kaolinite and halloysite in Finnish Lapland indicates wetter and warmer climatic conditions during the time of their formation than at present. The possible time for formation of the saprolite is early Cretaceous–early Tertiary into Middle Miocene.     

Minéralogie et bilan de matière de l''altération supergène d''un basalte alcalin du Moyen Atlas Marocain

In the Middle Atlas of Morocco, alkali basaltic flows record successive weathering phases during the Quaternary. In fresh basalt interior and intermediate external zones, the first weathering stage is characterised by glass dissolution and the formation of a Si-Al poorly-crystallised product. Advanced weathering phases are characterised by 10 Å halloysite, kaolinite and goethite, located within the primary minerals or as secondary products in fissures. Olivine and iddingsite are transformed into Si-rich goethite, plagioclase into halloysite and pyroxene into a mixture of halloysite + geothite. Dissolution of Ti-magnetite and ilmenite yielded Ti-rich products. In these conditions, the weathering of basalts and development of a soil matrix are accompanied by the elimination of certain chemical elements, such as Si, Ca, Na and K, and the concentration of Fe and Al. In the soil, clay minerals such as illite and vermiculite, do not have any genetic relationship with weathered basalt and were probably introduced externally.     

Reverse Weathering in River-dominated Marginal Seas

In estuarine regions and marginal seas, reverse weathering refers to the formation of authigenic aluminosilicate and carbonate minerals promoted by large inputs of terrestrial weathering products and intense remineralization of Sedimentary Organic Carbon (SOC), which is opposite to land weathering process. Compared with the process in open ocean, the formation of authigenic aluminosilicate and carbonate minerals caused by reverse weathering in estuarine regions and marginal seas is rather rapid, playing an important role in the maintenance of ocean acidity and elements cycles. At present, there are two research methods regarding the reverse weathering process, i.e., direct observation and chemical detection. The first method is used to study the structure and chemical composition of authigenic minerals and the second is mainly used to do quantified studies of authigenic minerals. The reverse weathering is very important to the cycles of Si, C, major ions (F^-, Li⁺, Na⁺, K⁺, Ca²⁺ and Mg²⁺), and alkali metal cations (Fe, Mn and Al) in marine environments, which promotes the burial of these elements in marine sediments. Due to large inputs of weathering products rich in Fe, Mn and Al oxides, precipitation of labile OC and biogenic silica, intense remineralization process and suboxic/anoxic conditions, estuarine and marginal seas are suitable sites for reverse weathering studies. The reverse weathering studies in sub-tropical and temperate estuaries should be emphasized in the future.     

发育完整的灰岩风化壳及其矿物学和地球化学特征

对于碳酸盐岩土覆土壤成因、尽管碳酸盐岩风化残积成土说被多数学者认同,但由于碳酸盐岩中酸不溶物含量极低,在风化成土过程中会伴随着巨大的体积缩小变化,原岩结构和半风化带无法保留,从而缺失了探索上覆土壤物质来源的重要中间环节,使得这种观点缺乏野外宏观证据的支持。最近,我们在贵州、湖南等地发现了数个以泥质灰岩和泥质白云岩为基岩的碳酸盐岩风化壳剖面,尚保留有较好的原岩结构,具有明显的风化壳分带和过渡现象。这些风化壳剖面的发现为深入研究碳酸盐岩风化成土过程提供了良好的研究场所。本文选取了较为典型的吉首泥灰岩风化壳剖面,从矿物学地球化学的角度来探讨碳酸盐岩风化壳的形成过程和发育特征,结果表明该风化壳既遵循非碳酸盐岩（主要是结晶岩类）风化壳的发育特征,也具有自己独特的地球化学演化规律。风化壳总体特点受碳酸盐中的酸不溶物矿物组合及化学成分的影响甚至控制,风化非碳酸盐风壳相似的发育特征。吉首泥灰岩风化壳剖面的发育特征和作者早先提出 的碳酸盐岩风化成土的两阶段模式是一致的,即以碳酸盐矿物大量淋失、酸不溶物逐渐堆积或残积为特征的早期阶段和残积物进一步风化成土的阶段,后一阶段的演化类似非碳酸盐岩类的风化过程。