Slip on the active Mai'iu low‐angle normal fault in Papua New Guinea that dips 15–24° at the surface has exhumed in its footwall a single, continuous fault surface across a >25‐km‐wide dome. Derived from a metabasaltic protolith, the fault zone consists of a <3‐m‐thick zone of gouges and cataclasites that overprint a structurally underlying carapace of extensional mylonites. Detailed microstructural and geochemical data, combined with chlorite‐based geothermometry, reveal changing deformation processes and conditions in the Mai'iu fault rocks as they were exhumed. The microstructure of nonplastically deformed actinolite grains inherited from the fine‐grained (6–35 µm) metabasaltic protolith indicates that shearing at depth was controlled by diffusion creep accompanied by grain‐boundary sliding of these grains together with chlorite neo‐crystallization at T > 275°C–370°C. In a foliated cataclasite unit at shallower crustal levels (T ≈ 150°C–275°C), metasomatic reactions accompanied fluid‐assisted mass transfer processes that accommodated aseismic, distributed shearing; pseudotachylites and ultracataclasites in the same unit indicate that such creep was punctuated by episodes of seismic slip—after which creep resumed. At the shallowest levels (T < 150°C), gouges contain abundant saponite, a frictionally weak mineral that promotes creep on the shallowest dipping (≤24°), most poorly oriented part of the Mai'iu fault. Our field, microstructural and geochemical data of freshly exhumed fault rocks support geodetic, seismological, and geomorphic evidence for mixed seismic‐to‐aseismic slip on this active low‐angle normal fault.

中文翻译：

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巴布亚新几内亚东南部伍德拉克纵裂活动低角度正断层上的基性断层岩石中的慢速变形

在巴布亚新几内亚的活跃的迈伊低角度正断层上滑动，在地表下倾15-24°，已在其底盘中挖出了一个连续的断层面，覆盖了超过25公里的穹顶。断层带是由准玄武质原生岩衍生而来的，其断层由厚度小于3 m的凿孔和白云母覆盖，在构造上覆盖了伸展性lon石的甲壳。详细的微观结构和地球化学数据，再结合基于亚氯酸盐的地热法，揭示了在迈尤断层岩中挖掘出的不断变化的变形过程和条件。细粒（6-35 µm）变质原生质体继承的非塑性变形阳起石晶粒的微观结构表明，深度剪切受扩散蠕变控制，伴随这些晶粒的晶界滑动以及亚绿酸盐在T> 275的新结晶°C–370°C。在地壳较浅（T≈150°C–275°C）的叶状催化裂殖单元中，交代反应伴随着流体辅助的传质过程，适应了抗震性，分布式剪切作用。同一单元中的假速滑石和超催化硅酸盐表明，这种蠕变被地震滑动事件所打断，此后蠕变又恢复了。在最浅的水平（T <150°C），凿孔含有丰富的皂石，一种摩擦较弱的矿物，会在最浅的浸入（≤24°）时促进蠕变，迈尤断层的最不定向部分。我们的现场，新近发掘出的断层岩石的微观结构和地球化学数据为该活跃的低角度正断层上的地震-地震混合滑动提供了大地，地震和地貌证据。