超级喷发(超级侵入)后成矿作用  

Post-supereruption(-superintrusion) metallogenesis

作　　者：罗照华[1] 周久龙[1] 黑慧欣 刘翠[1] 苏尚国[1] 

机构地区：[1]中国地质大学地质过程与矿产资源国家重点实验室,北京100083

出　　处：《岩石学报》2014年第11期3131-3154,共24页Acta Petrologica Sinica

基　　金：中国地质调查局地质调查项目(1212011220921;1212011121266;12120113094100;1212011121075;12120114020901);973项目(2011CB808901);中俄国际合作项目(RFBR 14-05-91162-NSFC)联合资助

摘　　要：本文仿照超级喷发的概念定义了超级侵入,并将超级火山对应于大型岩基。文章聚焦于这样一个科学问题:为什么大规模成矿作用发生在紧接着超级喷发和超级侵入之后?为此,首先探讨了峨嵋山地幔柱系统的活动规律。尽管少数学者对玄武质岩浆大规模喷出之前的千米级地壳隆升提出了质疑,峨嵋山火山岩系第一旋回底部玄武岩直接覆盖在喀斯特之上的新观察支持千米级隆升的认识。这表明,峨嵋山地幔柱快速上涌之初期,岩石圈子系统在相当长一段时间没有作出伸展响应,尽管局部已经发生了地壳岩石的部分熔融。因此,岩浆通道形成之后,首先喷出了巨厚层玄武岩,并且后者裹挟了部分长英质岩浆。此后,岩浆喷发的规模振荡性减小,直至消失和地表沉降。斜长石巨斑玄武岩和苦橄岩中橄榄石斑晶与基质间的不平衡表明这些晶体属于循环晶,暗示岩浆曾经在深部岩浆房滞留了相当长的时间,这将导致岩石圈受热膨胀和再次隆升以及岩浆的冻结。因此,下一阶段岩浆活动的开始要求有一个冻结岩浆房的活化机制。依据野外地质学和岩相学观察,文章详细描述了流体活化机制,并强调了提出这种机制的必要性。虽然多数作者偏好升温活化机制,流体活化机制对长英质和镁铁质岩浆成矿系统都是必需的。进而,结合地幔名义无水矿物的H2O丰度及其对岩浆产生过程的贡献,提出岩浆产量与减压速率正相关而与流体产量反相关的观点。尽管水流体可以有效降低地幔橄榄岩的固相线温度从而有可能提高岩浆产量,新生代玄武岩中橄榄岩包体依然含有未分解的角闪石和云母且名义无水矿物依然含有较多的H2O,表明快速减压条件下含水暗色矿物的分解反应和名义无水矿物的脱水作用都是低效的。将这种认识与峨嵋山地幔柱系统的振荡性运动结合在一起,结合成矿作用的�Following the idea for proposing supereruption,a term to describe processes building up supervolcanos,we provide,in this article,a new term called as superintrusion to describe processes assembling batholiths. The article has a principal focus of why the giant ore deposits have formed immediately after supereruption or superintrusion. Accordingly,the behaviors of the Emeishan mantle plume system are discussed,firstly. Though a few authors query that a kilometre-scale domal uplift took place before onset of volcanism in the large igneous province,the new observation of that base basalt of the first cycle in the Emeishan volcanic series fills immediately in the ancient karst supports the view point about kilometre-scale domal uplift. This suggests that the lithosphere subsystem bas not an extending response for significantly long time when the Emeishan plume is rapidly ascending,despite of that the crust may be partially melted in some depth levels. Therefore,after opening the magma conduits,the plume system firstly blew out a significantly thick stratum of basaltic lava,and the later wraps some felsic lavas. Then,the volcanic eruption is characterized by oscillatory decrease of its lava volume,even till to disappear,accompanied by surface subsidence. The giant plagioclase phenocrysts in basalts and the unequilibrium relationships between the olivine phenocrysts and the host matrix in the so-called picrite show that these crystals are of antecrysts instead of that crystallized from the host lava. This suggests that the primary magma in which such crystals have grown was detained in the deep chamber for a long period. Such retention should induce the lithosphere to dilate due to conductive heating and the surface to swell up again and hence the retained magma should be frozen. Subsequently,onset of the next stage of magmatism requires a reasonable mechanism for rejuvenation and reactivation of the frozen chamber. According to the field and petrographical observations,the fluid reactivation mechanism is described in

关 键 词：岩基后成矿作用 熔体-流体强相互作用 透岩浆流体 岩浆型铁矿 峨嵋山地幔柱 四川攀枝花 

分 类 号：P588.1[天文地球—岩石学] P611[天文地球—地质学]