【摘要】 新西兰克马德克弧上发育一热液活动极为活跃的海底潜火山——兄弟火山,为了研究该地区热液成矿模式,IODP376科学家于2018年5～7月在火山口选取了5个位置进行了钻探工作,并获得数百米岩芯。其中U1530A号钻孔采样深度为453.1 mbsf(meter below sea floor),共揭露76.77 m岩芯,部分呈现出一种蓝色调,被前人称作"蓝黏土"。为了查明其致色矿物、研究呈色机理及其地质意义,笔者等利用XRD、DR-UV-Vis、SEM、TEM对16.97-309.22 mbsf的11个样品进行了分析测试。根据测试结果可以将样品的矿物组合大致分为两类:(1)伊利石+绿泥石+殴泊-C+黄铁矿+硬石膏+石英±蓝铁矿;(2)叶蜡石+伊利石+石英±蓝铁矿。SEM和TEM形貌观察结果显示,蓝铁矿并不具有完好的晶形,甚至未发现微米级及以上尺寸的单颗粒,而仅以基质或胶结物形式均匀分布在样品中,最终导致样品被染色而呈现出不同色调的蓝色。蓝铁矿在IODP样品中的发现指示着研究区热液流体具有低温及还原性特征,且在蓝铁矿形成后也仍然保持着相对还原的环境而使得蓝铁矿能够稳定存在。更多还原

【Abstract】 Objectives: Brothers submarine volcano is very hydrothermally active and sits in the Kermadec arc,New Zealand. The International Ocean Discovery Program( IODP) Expedition 376 was intended to explore the Cu,Au etc. mineralization model,they drilled five sites in caldera and recovered about hundreds of meters of cores between May and July 2018. The hole U1530 A dilled to 453.1 meter below sea floor and recovered 76.77 meter samples.Some of them show different degrees of blue color,which is usually called “blue clay”. We attempt to find out the coloration mineral and mechanism,and further discuss the geological significance.Methods: A series of analytic methods,involved X-ray powder diffraction,Diffused Reflection Spectrum-Ultra Violet-Visual( DRS-UV-VIS),Scanned Electron Microscopy( SEM) and Transmission electron microscope( TEM) were applied to 11 cores from 16.97 mbsf to 309.22 mbsf.Results: There is different amounts of vivianite in the blue samples. According to these test results,mineral assemblages can be divided into two types:(1) illite + chlorite +opal-C + pyrite + anhydrite + quartz ± vivianite;(2) pyrophyllite + quartz +illite ± vivianite. SEM and TEM images suggest that the vivianite grains in the blue samples shows ultra-fine xenomorphic crystal,or even none single grain with size of micron or bigger.Conclusions: Vivanite is the coloration mineral and it filled in the intergranular of other mineral grains as matrix or cement,which caused blue color of samples. Discovery of vivanite in the IODP drill cores suggests that brothers volcano hydrothermal fluid characterized by low temperature and reducibility,and still maintains relative reduction condition after the formation of vivanite,which makes vivianite exists stably.更多还原