The peridotite deformation cycle in cratons and the deep impact of subduction
The peridotite deformation cycle in cratons and the deep impact of subduction
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DOI：
10.1016/j.tecto.2021.229029
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发表时间：
2021-08
期刊：
影响因子：
2.9
通讯作者：
E. Chin;B. Chilson‐Parks;Y. Boneh;G. Hirth;A. Saal;B. C. Hearn;E. Hauri
中科院分区：
文献类型：
--
作者：
E. Chin;B. Chilson‐Parks;Y. Boneh;G. Hirth;A. Saal;B. C. Hearn;E. Hauri
捕虏体在解释地幔变形和地球化学方面起着至关重要的作用。Mercier和Nicolas（1975）的经典著作引入了橄榄岩变形旋回的概念，将观察到的微观结构与变形的物理序列联系起来。我们重新审视了Mercier和Nicolas的原始概念，使用大面积EBSD图和相关的微结构数据集，分析名义上无水矿物的含水量，以及辉石和石榴石的微量元素化学，引入了新的约束条件。我们将这些技术应用于怀俄明州克拉通西北部始新世Homestead和Williams金伯利岩的橄榄岩捕虏体。辉石水含量和微量元素矿物化学表明克拉通下普遍存在含水交代作用，很可能与新生代拉腊酰胺造山运动有关。Homestead捕虏体主要表现为粗糙的原颗粒和等粒结构，b型橄榄石结构，与Williams相比，矿泉水含量普遍较高。Williams捕虏体变形强烈，具有斑岩碎屑和过渡性结构，含有退火橄榄石片，多为a型橄榄石织物，一般矿物质含量较低。从整体上看，从Homestead到Williams的地幔反映了一个克拉通尺度的变形旋回，该旋回可能始于Laramide时代，一直持续到始新世造山运动结束。在威廉姆斯，在主变形旋回内的快速变形“亚旋回”的证据保存在含片的捕虏体中，与Mercier和Nicolas（1975）神秘的“过渡性”结构相对应。我们的研究结果表明，这种结构反映了主要变形周期的中断，可能与快速形成的岩石圈不稳定和金伯利岩岩浆的产生有关-为这种模糊的橄榄岩结构提供了新的解释。总的来说，我们的研究结果结合了典型的不同地球化学和包体结构数据集，为深入克拉通岩石圈中交代作用、挥发物和变形是如何联系在一起的提供了新的见解。
Xenoliths play a crucial role in interpretation of mantle deformation and geochemistry. The classic work of Mercier and Nicolas (1975) introduced the concept of the peridotite deformation cycle, which connected observed microstructures to a physical sequence of deformation. We revisit Mercier and Nicolas' original concept, bringing in new constraints using large area EBSD maps and associated microstructural datasets, analysis of water contents in nominally anhydrous minerals, and trace element chemistry of pyroxenes and garnets. We apply these techniques to a well-characterized suite of peridotite xenoliths from the Eocene-age Homestead and Williams kimberlites in the northwestern Wyoming Craton. Pyroxene water content and trace element mineral chemistries reveal ubiquitous hydrous metasomatism beneath the craton, most likely linked to the Cenozoic Laramide Orogeny. Homestead xenoliths primarily exhibit coarse protogranular and equigranular textures, B-type olivine fabrics, and generally elevated mineral water contents compared to Williams. Xenoliths from Williams are strongly deformed, with porphyroclastic and transitional textures containing annealed olivine tablets, mostly A-type olivine fabrics, and generally lower mineral water contents. As a whole, mantle from Homestead to Williams reflects a cratonic scale deformation cycle that likely initiated in Laramide times and lasted until the end of orogeny in the Eocene. At Williams, evidence for a rapid deformation “sub-cycle” within the main deformation cycle is preserved in the tablet-bearing xenoliths, corresponding to the enigmatic “transitional” texture of Mercier and Nicolas (1975). Our results suggest that this texture reflects interruption of the main deformation cycle by processes possibly related to a rapidly forming lithospheric instability and generation of the kimberlite magma – offering a new interpretation of this ambiguous peridotite texture. Collectively, our results incorporate typically disparate geochemical and textural datasets on xenoliths to shed new insights into how metasomatism, volatiles, and deformation are connected in the deep cratonic lithosphere.