Bioalteration of basaltic glass in the oceanic crust
Bioalteration of basaltic glass in the oceanic crust
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DOI：
10.1029/2000gc000150
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发表时间：
2001-08
期刊：
影响因子：
3.7
通讯作者：
H. Furnes;H. Staudigel;I. Thorseth;T. Torsvik;K. Muehlenbachs;O. Tumyr
中科院分区：
文献类型：
--
作者：
H. Furnes;H. Staudigel;I. Thorseth;T. Torsvik;K. Muehlenbachs;O. Tumyr
深海钻探计划/大洋钻探计划（DSDP/ODP）从大西洋北部到中部、劳盆地和哥斯达黎加裂谷（一个广泛的海洋环境）的浅到深钻孔中采集的样品中，记录了第四纪到早白垩世玄武岩玻璃的生物蚀变。生物生成的纹理植根于裂缝中，并以两种主要类型出现，颗粒型和管状型。颗粒型火山岩常见于火山岩堆的所有深度，表现为固体条带、球状体或不规则斑块状的单个和/或合并的球体，直径大多为0.2-0.6 μm，在新鲜玻璃中有不规则突起。管型在地壳较深的层次更为常见，由细管组成，有时是分支体，大多数长20-30 μm，在较深的层次更为常见。上地壳生物蚀变与非生物蚀变的相对重要性有很大的差异，生物蚀变的程度似乎随着深度的增加而降低。因此，生物蚀变的玻璃总蚀变的分数范围从20-90%，在上部300米下降到最大值10%，在约500米的深度。这可能是由于生物蚀变玻璃丰度的自然变化，或者是由于相对年轻地壳的低钻井回收率造成的有偏见的取样。生物蚀变玻璃与非生物蚀变玻璃的比例并不随地壳年龄的变化而显示出任何系统性的变化。因此，生物改变持续的时间与非生物改变一样长，即，只要有水可供海洋地壳水合作用使用。来自热流测量的证据表明，热液循环至少持续到2.70亿年，因此深部生物圈可能至少扩展到这个年龄的地壳。
Bioalteration of Quaternary to Early Cretaceous basaltic glass from pillow lavas of the upper oceanic crust can be documented in Deep Sea Drilling Project/Ocean Drilling Program (DSDP/ODP) samples from shallow to deep drill holes from the north to central Atlantic Ocean, Lau Basin, and Costa Rica Rift, a wide range of marine settings. Biogenerated textures are rooted in fractures and occur as two main types, a granular type and a tubular type. The granular type, common at all depths within the volcanic pile, appears as solid bands, semicircles or irregular patches of individual and/or coalesced spherical bodies, mostly 0.2–0.6 μm in diameter, with irregular protrusions into the fresh glass. The tubular type is more common at deeper levels in the crust and consists of thin tubes, sometime branching bodies, mostly 20–30 μm long and are more common at deeper levels. The upper crust displays a large variability in the relative importance of biotic to abiotic alteration, and the degree of bioalteration appears to decrease with depth. Thus the fraction of bioalteration of the total alteration of the glass ranges from 20–90% in the upper 300 m down to a maximum of 10% at about 500 m depth. This might be due to a natural variability in the abundance of bioaltered glass or to biased sampling from low drilling recovery of relatively young crust. The proportion of bioaltered to abiotically altered glass does not show any systematic variations with age of the crust. Thus bioalteration lasts as long as abiotic alteration, i.e., for as long as water is available to the hydration of the oceanic crust. Evidence from heat flow measurements suggests that hydrothermal circulation lasts until at least ∼70 Ma, and thus the deep biosphere is likely to expand at least into crust of this age.