海底玄武岩玻璃中蚀变微结构: 探索海洋深地生物圈的新材料

玄武岩玻璃中的生物蚀变微结构为微生物摄取玄武岩玻璃中营养成分,通过新陈代谢产生有机酸溶解玄武岩玻璃而形成的微米级孔洞或钻穴。生物蚀变微结构在现代海洋洋壳及代表古老洋壳残片的蛇绿岩和绿岩带中广泛存在。研究玄武岩玻璃中蚀变微结构的形态特征、形成机制及其时空分布,不仅对探索地球早期生命起源和演化具有重要启示意义,也为研究海洋深地生物圈的微生物组成及其时空演化提供了新材料。形态学上,生物蚀变微结构分为颗粒和管状微结构。某些非生物成因微结构与生物蚀变微结构相似,识别生物蚀变微结构还需结合元素、同位素地球化学、有机质及DNA检测等方面研究手段。对全球玄武岩中生物蚀变微结构的时空分布总结表明其在地质历史时期普遍存在,并在洋壳垂向分布上可能密切受控于岩石的孔隙度和渗透率。不同海底环境,如氧化还原条件、酸碱度、深度、温度及孔隙度等都会影响微生物群落及其代谢方式,从而形成不同类型的生物蚀变微结构。具体哪些因素对玄武岩玻璃中生物蚀变微结构起主要控制作用还需进一步探索。

Alteration microstructures in seafloor basaltic glass: New material for exploring the subseafloor deep biosphere

Bioalteration microstructures in basaltic glasses are those pits and grooves formed by microbial metabolisms. Microbes produce organic acid while absorbing nutrients within basaltic glasses, dissolving the basaltic glasses and forming bi-oalteration microstructures. Bioalteration microstructures within basalts not only occur in modern oceanic crusts, but have been discovered in ophiolites and greenstone belts representing ancient oceanic crusts. Studying the morpho-logical characteristics, formation mechanisms and spatio-temporal distributions of bioalterated microstructures within basaltic glasses is thus pivotal to exploring the origin and evolution of early lives on Earth, and provide new materials to understand the composition of microbial organisms in the sub-seafloor deep biosphere and their spatio-temporal dis-tribution characteristics. Morphologically, bioalterated microstructures within basaltic glasses can be divided into granular and tubular microstructures. However, abiotic microstructures can also occur in basalt glasses mimicking those bio-alterted microstructures. Thus, multi-disciplinary studies combining morphologies, elemental and isotopic geo-chemistry, organic and DNA detection are all significant in distinguishing bioalterated microstructures from abiotic ones. A summary of occurrences of bioalteration microstructures from geological records show that they occur more common than previously thought, and the vertical distribution of these microstructures within oceanic crusts may be closely related to the porosity and permeability of basaltic rocks. In addition, different seafloor environmental condi-tions, such as redox, pH, water depth, temperature, and porosity, can all greatly affect the composition of microbial community and their subsequently formed bioalteration microstructures. It remains to be answered, however, that which of these factors play a major control.