Petrography and genesis of spicular and columnar geyserite from the Whakarewarewa and Orakeikorako geothermal areas, North Island, New Zealand
Petrography and genesis of spicular and columnar geyserite from the Whakarewarewa and Orakeikorako geothermal areas, North Island, New Zealand
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新西兰北岛华卡雷瓦雷瓦和奥拉凯科拉科地热区针状和柱状间歇泉的岩相学和成因
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发表时间：
2003
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通讯作者：
R. Renaut
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作者：
B. Jones;R. Renaut
在Whakarewarewa地热区，围绕着许多间歇泉喷口的间歇泉岩穹状块体主要由针状体、针状柱体和灌木柱体构成。无分支骨针和分支骨针的分支，分别高达3厘米和1毫米直径，有一个由硅质皮层包裹的层压核心。硅化微生物在核心中很少见，但在皮层中很常见。在相邻骨针之间的缝隙中发现了硅化的微生物垫和假树突。灌木柱，高达5厘米，直径1.5厘米，形成的蛋白石A沉淀周围的三维，分支，灌木状微生物（？）结构灌木的树枝是中空的，有着扇形的壁，不包含任何形成它们的原始微生物或矿物质的证据。硅化微生物垫存在于柱之间。微生物钻孔和酸性蒸汽的侵蚀导致这些柱的局部成岩降解。在Whakarewarewa的凝灰岩土丘中，骨针和骨针柱很常见，而灌木柱很少见。然而，与灌木柱状硅灰岩的针状硅灰岩的互层和夹层表明，这些不同的形态实体可能形成在类似的环境条件下的间歇泉喷口周围的土丘。岩相学证据表明，骨针、骨针柱和灌木柱是通过生物和非生物过程相结合而生长的。
Domal masses of geyserite, which surround many geyser vents in the Whakarewarewa geothermal area, are formed largely of spicules, spicule columns, and shrub columns. The non-branching spicules and the branches of branching spicules, individually up to 3 cm high and 1 mm diameter, have a laminated core encased by siliceous cortex. Silicified microbes are rare in the core but common in the cortex. Silicified microbial mats and pseudodendrites are found in the crevices between neighbouring spicules. Shrub columns, up to 5 cm high and 1.5 cm in diameter, are formed of opal-A that was precipitated around a three-dimensional, branching, shrub-like microbial (?) structure. The shrub branches, which are hollow with scalloped walls, do not contain any evidence of the original microbes or minerals that formed them. Silicified microbial mats are present between the columns. Microbial boring and etching by acidic steam led to local diagenetic degradation of these columns. In the geyserite mounds at Whakarewarewa, spicules and spicule columns are common, whereas shrub columns are rare. Interbedding and intercalation of spicular geyserite with shrub columnar geyserite indicate, however, that these different morphologic entities probably formed under similar environmental conditions on the mounds around the geyser vents. Petrographic evidence shows that the spicules, spicule columns, and shrub columns grew through a combination of biotic and abiotic processes.