Late magmatic healed fractures in granitoids and their influence on subsequent solid-state deformation
Late magmatic healed fractures in granitoids and their influence on subsequent solid-state deformation
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花岗岩中晚期岩浆愈合裂缝及其对后续固态变形的影响
DOI：
10.1016/j.jsg.2013.09.006
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发表时间：
2013
影响因子：
3.1
通讯作者：
G. Pennacchioni
中科院分区：
文献类型：
--
作者：
N. Mancktelow;G. Pennacchioni
在许多花岗岩类岩体中，岩浆结晶的最后阶段形成的晚期岩浆裂缝被岩浆黑云母和/或浅色脉的平面痕迹记录下来，但以前没有描述过。这种富含黑云母的痕迹，长度为几厘米到几十厘米，宽度为几毫米，方向可变，在内维斯地区（意大利东阿尔卑斯山陶恩窗）的变花岗岩类中普遍存在。这些前阿尔卑斯花岗岩变质到上角闪岩相和变形在阿尔卑斯造山带，使平面愈合的岩浆断裂的后续固态韧性剪切带的成核的影响，直接评估。考虑幂律粘性材料的数值模型预测，与缩短方向成45°的较弱矿物（例如黑云母）的平面阵列应该成核并局部化粘性变形。然而，没有明显的本地化的自然小规模的黑云母痕迹观察，即使当他们描绘的平面，以及定向剪切活化。相反，非均质剪切带在较大尺度（>1-10 m长）的平面成分或结构边界上成核，如节理、岩墙、石英脉、脉周围的蚀变层以及由密集的基性包体群勾勒出的岩浆混合带，而不管它们相对于强加的缩短方向的取向如何。显然，纯粘性数值模型中缺少某些关键方面。我们建议，这个缺失的方面是观察到的断裂和流动之间的相互作用，与新的裂缝发展和局部剪切体应变太低，可辨别的本地化发生在预先存在的愈合的岩浆断裂。天然花岗岩具有真正的弹塑性粘性流变学，即使在低差应力（如内维斯的例子）和高级变质条件下，被认为是典型的湿“韧性”中地壳。
Late magmatic fractures developed during final stages of magma crystallization are recorded in many granitoid plutons by planar trails of magmatic biotite and/or leucocratic veins but have not been previously described. Such biotite-rich trails, with lengths of a few centimetres to several tens of centimetres, widths of a few millimetres, and a variable orientation, are ubiquitous in meta-granitoids of the Neves area (Tauern Window, Eastern Alps, Italy). These pre-Alpine granitoids were metamorphosed to upper amphibolite facies and deformed during the Alpine orogeny, allowing the effect of planar healed magmatic fractures on the nucleation of subsequent solid-state ductile shear zones to be directly assessed. Numerical models considering power-law viscous materials predict that planar arrays of a weaker mineral (e.g. biotite) oriented at around 45° to the shortening direction should nucleate and localize viscous deformation. However, no discernible localization on the natural small-scale biotite trails is observed, even when they delineate planes that were well-oriented for shear reactivation. In contrast, heterogeneous shear zones nucleated on larger scale (>1–10 m long) planar compositional or structural boundaries such as joints, dykes, quartz veins, alteration layers surrounding veins, and zones of magma mingling outlined by densely packed clusters of basic enclaves, irrespective of their orientation relative to the imposed shortening direction. Clearly some crucial aspect is missing from purely viscous numerical models. We propose that this missing aspect is the observed interplay between fracture and flow, with new fractures developing and localizing shear at bulk strains too low for discernible localization to occur on the pre-existing healed magmatic fractures. Natural granitoids have a truly elasto-plasto-viscous rheology even at low differential stress (as in the Neves example) and for high grade metamorphic conditions considered as typical of wet “ductile” middle crust.
影响因子：
5.8
作者：
Cordonnier, B.;Caricchi, L.;Burlini, L.
通讯作者：
Burlini, L.