Pulverized granite at the brittle-ductile transition: An example from the Kellyland fault zone, eastern Maine, U.S.A.
Pulverized granite at the brittle-ductile transition: An example from the Kellyland fault zone, eastern Maine, U.S.A.
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DOI：
10.1016/j.jsg.2017.07.002
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发表时间：
2017-08
影响因子：
3.1
通讯作者：
W. A. Sullivan;E. Peterman
中科院分区：
文献类型：
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作者：
W. A. Sullivan;E. Peterman
在Kellyland脆韧性断裂带附近50 - 200米宽的破坏带中，花岗岩包含愈合的裂缝网络，几乎具有动态粉碎岩石的所有特征。裂缝网络只表现出弱的优先取向，是相互交叉切割的，独立的拼图状联锁碎片，并且与可能来自普遍粉碎的材料的再结晶区域相关。原始火成岩颗粒形状样品中的断裂网络进一步表明粉碎作用。微斜层的最小裂缝密度为~ 100 mm/mm2。微斜岩和石英中较大的裂缝有时以新生细胞为标志，但大多数裂缝在光学上是连续的，只有在阴极发光图像中才能看到。斜长石中的裂缝受晶体学控制，通常由黑云母充填。岩石学观察和脆性结构与糜棱质岩石之间的横切关系表明，裂缝发生在400℃或更高的温度和200 MPa的压力下。这些限制将已知的粉碎范围扩展到比以前认为的更高的温度和压力条件。相互交叉切割的愈合裂缝也提供了粉状岩石中重复损伤的第一个记录。此外，粉碎作用对围岩孔隙度一定有显著但短暂的影响，斜长石中充满黑云母的裂缝网络形成了可以容纳未来应变局部化的薄弱带。
Granite from a 50–200-m-wide damage zone adjacent to the brittle-ductile Kellyland Fault Zone contains healed fracture networks that exhibit almost all of the characteristics of dynamically pulverized rocks. Fracture networks exhibit only weak preferred orientations, are mutually cross-cutting, separate jigsaw-like interlocking fragments, and are associated with recrystallized areas likely derived from pervasively comminuted material. Fracture networks in samples with primary igneous grain shapes further indicate pulverization. Minimum fracture densities in microcline are ∼100 mm/mm2. Larger fractures in microcline and quartz are sometimes marked by neoblasts, but most fractures are optically continuous with host grains and only visible in cathodoluminescence images. Fractures in plagioclase are crystallographically controlled and typically biotite filled. Petrologic observations and cross-cutting relationships between brittle structures and mylonitic rocks show that fracturing occurred at temperatures of 400 °C or more and pressures of 200 MPa. These constraints extend the known range of pulverization to much higher temperature and pressure conditions than previously thought possible. The mutually cross-cutting healed fractures also provide the first record of repeated damage in pulverized rocks. Furthermore, pulverization must have had a significant but transient effect on wall-rock porosity, and biotite-filled fracture networks in plagioclase form weak zones that could accommodate future strain localization.