Serpentinites of the Zermatt‐Saas ophiolite complex and their texture evolution
Serpentinites of the Zermatt‐Saas ophiolite complex and their texture evolution
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DOI：
10.1111/j.1525-1314.2004.00503.x
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发表时间：
2004-04
影响因子：
3.4
通讯作者：
X. Li;M. Rahn;K. Bucher
中科院分区：
文献类型：
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作者：
X. Li;M. Rahn;K. Bucher
采尔马特-萨斯蛇纹岩杂岩是阿尔卑斯山脉中部奔尼尼克蛇绿岩的组成部分，代表了特提斯洋岩石圈的地幔部分。蛇纹岩的变质结构保留了原始深海橄榄岩通过海底水化、俯冲相关高压叠加、中阿尔卑斯绿片岩相变质和晚期热液蚀变的复杂矿物学演化。尖晶石方辉橄榄岩的早期洋底水化作用在残余的假晶碧辉长岩和局部保存的网状结构中仍然可见。原生蛇纹石矿物被叶蛇纹石完全取代。与俯冲作用有关的糜棱岩蛇纹岩的稳定组合为闪长岩-橄榄石-磁铁矿±透辉石。中第三纪绿片岩相叠加的特征是轻微的叶蛇纹石重结晶。本研究的结构和矿物成分数据证明，在高达2.5 GPa和650 °C的高压变质作用期间，水合矿物组合保持稳定。因此，采尔马特-萨斯蛇纹岩提供了一个有据可查的例子，说明地幔碎片在俯冲至75公里深度时没有脱水。
The Zermatt‐Saas serpentinite complex is an integral member of the Penninic ophiolites of the Central Alps and represents the mantle part of the oceanic lithosphere of the Tethys. Metamorphic textures of the serpentinite preserve the complex mineralogical evolution from primary abyssal peridotite through ocean‐floor hydration, subduction‐related high‐pressure overprint, meso‐Alpine greenschist facies metamorphism, and late‐stage hydrothermal alteration. The early ocean floor hydration of the spinel harzburgites is still visible in relic pseudomorphic bastite and locally preserved mesh textures. The primary serpentine minerals were completely replaced by antigorite. The stable assemblage in subduction‐related mylonitic serpentinites is antigorite–olivine–magnetite ± diopside. The mid‐Tertiary greenschist facies overprint is characterized by minor antigorite recrystallization. Textural and mineral composition data of this study prove that the hydrated mineral assemblages remained stable during high‐pressure metamorphism of up to 2.5 GPa and 650 °C. The Zermatt‐Saas serpentinites thus provide a well documented example for the lack of dehydration of a mantle fragment during subduction to 75 km depth.