断裂剪切带中的纳米结构与成矿作用

Nano Texture and Mineralization in Fault Shear Zones

纳米科学已涉及从信息学到地学的各个领域,成为这个时代一个标志性的关键词。近十多年来,国内外的纳米地学研究,在实践、理论和实验等诸方面都取得了迅速的进展。该文运用4F (Fact, Formation, Function and Formulation,即事实观察、形成机理、功效作用和计算模拟)研究方法,利用扫描电子显微镜(SEM)和透射电子显微镜(TEM)对断裂剪切带中的纳米结构与成矿作用进行了样品观察和综合分析。首先,作者表述了岩石剪切面上广泛分布的剪切薄壳(膜)的形成、发育和组成,一般脆性剪切的薄壳厚度(h,毫米—厘米级)要比韧性的剪切薄膜(忽米—毫米级)厚,前者是由动态摩擦粘滑滑移引起的,而后者则是由静态蠕滑滑移造成的,且两者均是由纳米矿物和纳米结构组成的。随之,作者集中探讨了作为研究主体的剪切薄壳(膜)中纳米结构的应变变形和生成演化,它们既具有弹性又有粘性的变形特征而不是单一的力学属性。纳米结构的生成—发育—演化,可依剪切变形过程划分为强化(硬化)—弱化(软化)—脆化(退化)三个变形应变阶段,和相应的纳米涂层—纳米弱化—纳米层裂三种类型纳米作用:(1)纳米涂层是一种最基本的纳米作用,在成熟的断裂剪切(带)中,只要有滑移摩擦存在,就会有纳米结构。这种作用能引起有序的纳米结构和定向结构,包括单体纳米颗粒(通常直径d=40～80 nm)—复体纳米颗粒—多重复体纳米颗粒;纳米粒—纳米线—纳米层;纳米颗粒粒化—异化—再生等。(2)纳米弱化作用是由颗粒粒度减小,瞬时温热,叶理发育和弱势矿物等所致,并可细分为滑动纳米弱化、流变纳米弱化和动力纳米弱化三种类别。(3)纳米层裂作用是一种由动力热作用到静力冷作用诱发的剥离作用,通常沿着纳米结构的劈理面、解理和滑移面开裂。进而,以江西省的金山金矿和广丰滑石矿为例讨论了纳米结构与成矿关系:(1)含金糜棱岩发育过程中的纳米涂层作用成岩,纳米弱化作用成矿和纳米层裂作用形成面理的三个阶段。其重要的是纳米弱化作用期间超糜棱岩的温度能够达到纳米金物质的熔点327℃,并在流变滑移过程中产生集中颗粒型(d=15～35 nm)和分散颗粒型(d=4～8 nm)的金颗粒;(2)滑石矿中高应变反映的纳米结构和纳米作用尤为强烈,具有局部熔融流变,纳米弱化作用阶段的纳米次分层作用非常发育,沿(001)面滑移的叶理厚度仅10～15 nm,且纳米层裂作用更是造成开放性的剥离、裂理作用。上述的研讨,揭示了实质上至少一维的"纳米小疙瘩(nano-orange)在地球物质中无处不在"。这场地学变革——"纳米科学与技术是地球科学的下一次革命(Hochell, 2000)"——大幕才刚刚开启,就促使科研工作者对一些地质现象重新认识,也激发大家去开发"纳米小疙瘩"在地球物质中的"新奇"功效。

Nowadays nanoscience is pelwasive, touching ahnost every professional field from infornmtion sciences to geosciences, consequently, it has become a buzzword in ore＂ era. Over the past one decade, studies of nanogeosciences has all obtained rapid progression on practice, theolT and experiment at home and abroad. In this article, applying research methods of the 4F （Fact, Formation,Function and Formulation）, the authors carried out specimen obsmwation and synthetic for nanotexture and mineralization under scanning electron microscope （SEM） and transmitting electron microscope （TEl）. The authors firstly described a formation, development and composition of shear shell （fihn）, which widespreadly contribute on shear slip surfaces, in general, a brittle shear thin shell is thicker （h, thickness reaching mm-cnl gx＇ade） than a ductile fihn （h, mum-ram gx＇ade）. The former is caused by a kinetic fi＇iction-stick slip sliding, hut the latter is created by a static friction-creep slip sliding, and both of the shell and fihn all consist of nanominerals and nalmtextm＇es. Then, the authors focused one＇s exploration to strain deformation and gx＇owth evolution on the nanotextm＇e and nanoaction of the shear thin shall （film） as regarding research principal part, and they are together with not only elastic feature hut also viscous one rather than single mechanic property. According to developing processes of the shear deformation, gx-owth^evelopment-evolution of the nonotexture can he classified three deformation strain stages, i.e., strengthen （harden）-weaken （soflen）-enbrittlement （degeneration）, and cmwespondlng with three kinds nanoactions, i. e., nanocoating-nanoweakening-nanodelaminating. （1）The nanocoating is a mostly basic nanoaction, and so long as shear slip remains a friction, it must bear the nanocoating in mature fault shearing （zone）. Significantly, it can give rise to order nanotextm＇e and direct fabrication, including individual nanogx＇ain （commonly, diameter d 40-80 nm）-aggx＇egate nanogx＇ain-multi aggx＇egate nanogx＇ain; nanogx＇ain-nanoline-nanolayer, as well as gx＇ain gx＇anulation-alienation-regeneration, etc. （2） The nanoweakening results from particle-size reduction, flash heating, foliation development, and weaken mineral, etc., and it may be subdivided three categories, i. e., slipping nanoweakening, rheological nanoweakening, and dynamic nanoweakening. （3）Tile nanodelaminating is a strip which is induced by control from dynamic heating to static cooling, and its fission is commonly along a parting, cleavage and slip plane. In summary, the three nanoactions with mutual fusion forcefully reflect an internal relation of a symbiosis feedback system between the shear slip friction and nanoordered texture. Furthermore, we discussed a relation between the nanotextm＇e and mineralization, taking the Jinshan gold deposit and the Guan^eng talc deposit, Jiangxi Province as examples. （1） In the three stages of the gold-bearing mylonite develop porcess, including a diagenesis, mineralization and formation foliation respectively caused by the nanocoating, nanoweakening and nanodelaminating, an important case is that temperature of the ultramylonite can reach melt point 327~C of the gold material during the nanoweakening stage, thus, in the rheological process it may produce gold gx＇ain gx＇oups both a concenll＂ated gx＇ain type （d, 15-35 nm） and discrete gx＇ain type （d, 4-8 nm）. （2）In the talc deposit, the higher sll＂ain strongly reflects the nanotexture and nanoaction much more. During the nanoweakening stage, the nanosublayering, which results in a vmT thin thickness （only 10-15 nm） along the （001） slip plane, local melt rheology and the delaminating even more creates an open stripping and parting. Through the researches mentioned above, the authors have revealed ＂Earth materials with at least one dimension in the nano-orange are essentially ubiquitous＂ from an aspect. Needless to say, a bigger curtain of the geosciences ＂nanoscience and technology： the next revolution in the earth sciences＂ exactly rises, it moves towards to impel us to recognize some geological phenomena moreover, also urges us to exploit a ＂novel （or dramatic）＂ effect of the ＂nano-orange＂ in the Earth materials.