Diverse habitats of pseudotachylytes in the Alpine Fault Zone and relationships to current seismicity

Pseudotachylytes are ubiquitous within New Zealand's Alpine Fault Zone, occurring as: (i) thin fault veins parallel to existing
hanging wall mylonitic foliation; (ii) thicker fault and injection veins around and within metabasite lenses in hanging wall
fault rocks and on the footwall–hanging wall boundary; (iii) chaotic injected masses within footwall-derived, granitoid mylonites;
and (iv) chaotic injected masses into cataclasites within the fault core.
Overall, pseudotachylytes are not volumetrically dominant enough to have formed during all increments of earthquake slip on
the Alpine Fault. We propose they were mostly generated during regular moderate magnitude events or during foreshock and aftershock
sequences to larger earthquakes. The largest volume pseudotachylytes occur in footwall-derived mylonites (type (iii)). This
may indicate that high-stress, anhydrous seismic slip is most common in the footwall. Most types (i), (ii) and (iii) pseudotachylytes
formed at or near the base of the seismogenic zone, at temperatures up to 350 °C and at depths of 7–10 km or more. Ductilely
overprinted pseudotachylytes represent the down-dip termination of large fault ruptures in a zone that would usually fail
by aseismic creep. Type (iv) pseudotachylytes were formed at shallower depths (4–7 km) in a damage zone around the fault principal
slip surface. Rare amygdules indicate that the fault zone locally contained free fluids.

伪快速岩浆体在新西兰阿尔卑斯断层带中广泛分布，其形成方式包括：(i) 与现有悬壁侧滑片平行分布的细断层脉；(ii) 围绕和位于悬壁断层岩体中及底板-悬壁侧板边界处的较厚断层和注入脉；(iii) 在底板派生的花岗质滑片内部的混乱注入岩块；以及(iv) 在断层核心内的 cataclasites 中的混乱注入岩块。总体而言，伪快速岩浆体在体积上不足以在阿尔卑斯断层所有地震滑动阶段形成。我们提出，它们主要是在常规中等强度事件期间或在大地震的前震和余震序列期间形成的。最大体积的伪快速岩浆体出现在底板派生的滑片中（类型(iii)）。这可能表明，高应力、无水地震滑动在底板处最为常见。大多数类型(i)、(ii)和(iii)的伪快速岩浆体形成于地震生成带底部或附近，温度高达350°C，深度为7-10公里或更深处。韧性叠加的伪快速岩浆体代表了大型断层破裂在通常通过无震蠕变破坏的区域的下倾终止。类型(iv)的伪快速岩浆体是在较浅的深度（4-7公里）形成的，位于断层主要滑动表面的损伤带内。稀有的杏仁体表明，断层带局部含有自由流体。