Formation of spinifex texture in komatiites: an experimental study
Formation of spinifex texture in komatiites: an experimental study
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DOI：
10.1093/petrology/egl021
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发表时间：
2006-08-01
影响因子：
3.9
通讯作者：
Libourel, Guy
中科院分区：
文献类型：
--
作者：
Faure, Francois;Arndt, Nicholas;Libourel, Guy
片状橄榄石三齿刺的形成，是科马提岩熔岩的特征结构。长期以来一直是个谜。一个主要问题是，橄榄石的枝晶形态类似于在实验室实验中以高冷却速率（> 50 摄氏度/小时）生长的晶体的枝晶形态，但在这些纹理形成的位置，在科马提石流顶部以下几米处，冷却速率不能大于 1-5 摄氏度/小时。我们进行的实验证明，三齿刺橄榄石或辉石的游戏习性是超镁铁质岩浆在热梯度（7-35 摄氏度/厘米）下缓慢冷却的结果。装料以 2 至 1428 摄氏度/小时之间的速率冷却，即使在低冷却速率下，热梯度也会导致生长受限，并导致优先取向的树枝状晶体的发展，其形态类似于天然的三齿稃纹理熔岩中的形态。在这些条件下，橄榄石在远低于平衡液相线温度（37 摄氏度 < -Delta T < 56 摄氏度）的温度下开始结晶，具体取决于起始材料的组成。当冷却速率较高时，热梯度对织构的影响可以忽略不计，晶体具有随机取向。就像科马提石流的拉链部分一样。
The formation of platy olivine spinifex, the texture that characterizes komatiite lavas. has long been enigmatic. A major problem is that the dendritic morphology, of the olivine resembles that of crystals grown in laboratory experiments at high cooling rates (> 50 degrees C/h), but at the position where these textures form, up to several meters below the komatiite flow top, the cooling rate cannot have been greater than 1-5 degrees C/h. We performed experiments that demonstrate that the play habit of spinifex olivine or pyroxene is a consequence of slow cooling of ultramafic magma in a thermal gradient (7-35 degrees C/cm). The charges were cooled at rates between 2 and 1428 degrees C/h and, even at the low cooling rates, the thermal gradient led to constrained growth and the development of preferentially oriented dendritic crystals with morphologies like those in natural play spinifex-textured lavas. Under these conditions, olivine starts to crystallize at temperatures well below the equilibrium liquidus temperature (37 degrees C < -Delta T < 56 degrees C) depending on the composition of the starting material. When the cooling rate is high, the thermal gradient has a negligible effect on the texture and the crystals have a random orientation. like that in the zipper parts of komatiite flows.