Quantifying the strength evolution of faults that cut the lithosphere is essential to better understand seismicity in continental regions. We estimate differential stresses and principal stress orientations driving rapid slip of ∼10 mm/yr on the active Mai'iu low-angle normal fault (LANF), SE Papua New Guinea. The fault's mafic footwall hosts a well-preserved sequence of mylonite, (ultra-)cataclasite, and gouge. In these fault rocks, we combine stress inversion of fault-slip data and paleostress analysis of syntectonically emplaced calcite veins with microstructural and clumped-isotope geothermometry to constrain a syn-exhumational sequence of deformation stresses and temperatures, and to construct a stress profile through the exhumed footwall of the active Mai'iu LANF. This includes: (a) at ∼12–20 km depth (T ≈ 275–370°C), mylonites accommodated slip on the Mai'iu fault at low differential stresses (>25–135 MPa) before being overprinted by localized brittle deformation at shallower depths; (b) at ∼6–12 km depth (T ≈ 130–275°C) differential stresses in the foliated cataclasites and ultracataclasites were high enough (>150 MPa) to drive slip on a mid-crustal portion of the fault (dipping 30–40°), and to trigger brittle yielding of mafic footwall rocks in a zone of mixed-mode seismic/aseismic slip; and (c) at shallower crustal depths (T < 150°C; depth <6 km) on the most poorly oriented segment of the Mai'iu LANF (dipping ∼22°), slip occurred on frictionally weak clay-rich gouges (μ ≈ 0.15–0.38). Subvertical σ₁ and subhorizontal σ₃ parallel to the extension direction, with σ₁ ≈ σ₂ (constriction), reflect vertical unloading and 3-D bending strain during rolling-hinge style flexure of the footwall.

中文翻译：

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利用同构造方解石脉重建巴布亚新几内亚东南部伍德拉克裂谷活动低角度正断层的强度演化

量化切割岩石圈的断层的强度演化对于更好地了解大陆地区的地震活动至关重要。我们估计了巴布亚新几内亚东南部活跃的 Mai'iu 低角度正断层 (LANF) 上的微分应力和主应力方向驱动约 10 毫米/年的快速滑动。断层的镁铁质下盘有一系列保存完好的糜棱岩、（超）碎裂岩和凿岩。在这些断层岩中，我们将断层滑移数据的应力反演和同构造侵位方解石脉的古应力分析与微观结构和成簇同位素地球温度测量相结合，以约束变形应力和温度的同剥脱序列，并通过挖掘出活跃的 Mai'iu LANF 的下墙。这包括： (a) 在 ∼12–20 km 深度 ( T ≈ 275–370°C)，糜棱岩在低应力差 (>25–135 MPa) 下在 Mai'iu 断层上发生滑动，然后在较浅的深度被局部脆性变形覆盖；（B）在~6-12千米深度（Ť  ≈130-275℃）在面理化碎裂和ultracataclasites应力差分别为足够高（> 150兆帕）来驱动上的故障的一个中地壳部滑动（浸渍30 –40°），并在混合模式地震/地震滑动区触发基性下盘岩石的脆性屈服；(c) 在较浅的地壳深度 ( T  < 150°C；深度 <6 km) 的 Mai'iu LANF 最差定向段（倾角 22°），滑动发生在摩擦力较弱的富含粘土的凿（μ ≈ 0.15–0.38）。次垂直 σ ₁和次水平 σ ₃平行于延伸方向，σ ₁  ≈ σ ₂（收缩），反映了下壁滚动铰链式弯曲过程中的垂直卸载和 3-D 弯曲应变。