The nature and development of shear zone junctions

韧性剪切带通常被想象为岩石中具有简单的涡度和应变梯度的圆盘状高应变区域。然而，大多数剪切带具有更复杂的几何形状，是以复杂方式分支的不同方位的相互连接的带网络的一部分。关于脆性断层的分支和相互联系，人们已经知道了很多，这主要归功于矿产行业获得的3D信息。然而，关于韧性剪切带的分支系统及其形成和发展的方式，在这种环境下的韧性流动条件是什么，以及它们如何影响地壳强度，人们知之甚少。在某些剪切带交界处，甚至在低孔隙度的岩石(如花岗岩)中，也可能发生瞬时脆性变形和矿脉张开。剪切带交界处可以作为地壳中的流体通道，这可能导致矿藏的积累，并对花岗岩中的核废料堆积场产生影响。最大的地壳规模剪切带的交汇处可能在决定地壳碎片如何沿着走滑剪切带相互作用，以及大陆地壳如何在碰撞中组装和在伸展中解体方面发挥重要作用。此外，矿床通常以大型剪切带为界。仔细研究选定剪切带中不同类型的结合部有助于找到在所有构造背景下识别它们的工具。我们计划研究瑞士格里姆塞尔花岗岩中保存非常完好的剪切带连接的一些例子，并描述它们的3D场几何、微结构以及与脆性变形的关联。这项研究得到了正在进行的剪切带交界处的计算机模拟研究的支持。

Ductile shear zones are usually imagined as straight disc-shaped high strain domains in the rock with simple gradients of vorticity and strain. Most shear zones, however, have a more complex geometry and are part of a network of interconnected zones of variable orientation that branch in a complex manner. Much is known about branching and interconnection of brittle faults, mainly due to 3D information obtained by the minerals industry. However, little is known about the branching systems of ductile shear zones and the way in which they form and develop, what the ductile flow conditions are in such environments and how they affect the strength of the crust. Transient brittle deformation and opening of veins may possible in some shear zone junctions, even in low porosity rocks such as granites. Shear zone junctions can act as fluid pathways in the crust, which can lead to accumulation of mineral deposits and has consequences for nuclear waste deposition sites in granites. Junctions of the largest, crustal scale shear zones may play an important role in deciding how crustal fragments interact along strike slip shear zones, and how the continental crust is assembled in collision and dismembered in extension. Furthermore, mineral deposits are commonly bounded to large scale shear zones. Careful study of different types of junctions in selected shear zones can help to find tools to recognize them in all tectonic settings. We plan to study a number of exceptionally well preserved examples of shear zone junctions in the Grimsel granite, Switzerland, and characterize their 3D field geometry, microstructure, and association with brittle deformation. The study is supported by an ongoing computer modelling study of shear zone junctions.