The fluid budget of a continental plate boundary fault: Quantification from the Alpine Fault, New Zealand
The fluid budget of a continental plate boundary fault: Quantification from the Alpine Fault, New Zealand
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DOI：
10.1016/j.epsl.2016.03.046
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发表时间：
2016-07
影响因子：
5.3
通讯作者：
C. Menzies;D. Teagle;S. Niedermann;S. Cox;D. Craw;M. Zimmer;M. Cooper;J. Erzinger
中科院分区：
文献类型：
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作者：
C. Menzies;D. Teagle;S. Niedermann;S. Cox;D. Craw;M. Zimmer;M. Cooper;J. Erzinger
流体在改变断层带的化学和物理性质方面起着关键作用，这可能会通过产生高孔隙流体压力和沉淀通常较弱的次生矿物来引发断层带的反复破裂。流体流动路径，源和通量，以及渗透率的断层带在整个地震周期的演变仍然缺乏约束，尽管它们的重要性，以了解断层带的行为。在这里，我们使用地球化学示踪剂的流体-岩石交换，以确定预算的流星，变质和地幔流体的主要挤压板块边界。阿尔卑斯山断层标志着穿越新西兰南岛的太平洋-澳大利亚板块的压扭边界，似乎在定期（329±68年）的大地震（Mw ≥ 8）中失败，最近一次发生在公元1717年。显著的会聚运动形成了南阿尔卑斯山脉，上盘地温梯度升高，驱动了地壳流体流动。沿着阿尔卑斯断层，太平洋板块的阿尔卑斯片岩被推覆在澳大利亚板块的放射成因变质沉积岩之上。在阿尔卑斯断层破坏带的一系列深度上形成的上盘热泉和热液矿物没有高放射成因（87 Sr/86 Sr> 0.7200）锶同位素比值，表明流体流动受到贯穿孕震地壳的跨断层流体流动屏障的限制。在阿尔卑斯断层附近的温泉中测得的氦同位素比值（0.15-0.81 RA）表明，该断层是一个地壳尺度的特征，充当了地幔流体的通道。岩石交换的氧，但流星水一样的热液脉的氢同位素签名表明，部分岩石交换的流星流体占主导地位的顶部的脆性到韧性过渡带在1.66公里。地球化学示踪剂运输模型表明，只有0.02%至0.05%的总降雨量西部的主要分水岭渗透到深度，但这种补给通量足以压倒其他流体的贡献。计算的地幔流体CO2和H2O通量（分别为0.2和3 ~ 13 mol/m2/yr）和变质H2O通量（4 ~ 750 mol/m2/yr）明显低于由南阿尔卑斯山> 3000 m水文水头驱动的阿尔卑斯断层上的大气降水通量（4× 103 ~ 7× 104 mol/m2/yr）。大气沃茨主要负责在流体-岩石相互作用过程中改变断层带渗透性，并可能促进产生高孔隙流体压力，这可能有助于幕式地震破裂。
Fluids play a key role in modifying the chemical and physical properties of fault zones, which may prime them for repeated rupture by the generation of high pore fluid pressures and precipitation of commonly weak, secondary minerals. Fluid flow paths, sources and fluxes, and the permeability evolution of fault zones throughout their seismic cycles remain poorly constrained, despite their importance to understanding fault zone behaviour. Here we use geochemical tracers of fluid–rock exchange to determine budgets for meteoric, metamorphic and mantle fluids on a major compressional tectonic plate boundary. The Alpine Fault marks the transpressional Pacific–Australian plate boundary through South Island, New Zealand and appears to fail in regular (329±68 yrs) large earthquakes (M w∼ 8) with the most recent event in 1717 AD. Significant convergent motion has formed the Southern Alps and elevated geothermal gradients in the hangingwall, which drive crustal fluid flow. Along the Alpine Fault the Alpine Schist of the Pacific Plate is thrust over radiogenic metasedimentary rocks on the Australian plate. The absence of highly radiogenic (87 Sr/86 Sr> 0.7200) strontium isotope ratios of hangingwall hot springs and hydrothermal minerals formed at a range of depths in the Alpine Fault damage zone indicates that the fluid flow is restricted to the hangingwall by a cross-fault fluid flow barrier throughout the seismogenic crust. Helium isotope ratios measured in hot springs near to the Alpine Fault (0.15–0.81 R A) indicate the fault is a crustal-scale feature that acts as a conduit for fluids from the mantle. Rock-exchanged oxygen, but meteoric water-like hydrogen isotope signatures of hydrothermal veins indicate that partially rock-exchanged meteoric fluids dominate down to the top of the brittle to ductile transition zone at∼ 6 km. Geochemical tracer transport modelling suggests only∼ 0.02 to 0.05% of total rainfall west of the Main Divide penetrates to depth, yet this recharge flux is sufficient to overwhelm other fluid contributions. Calculated mantle fluid fluxes of CO 2 and H 2 O (0.2 and 3 to 13 mol/m 2/yr respectively) and metamorphic H 2 O fluxes (4 to 750 mol/m 2/yr) are considerably lower than the focused meteoric water discharge flux up the Alpine Fault (4× 10 3 to 7× 10 4 mol/m 2/yr), driven by the> 3000 m hydrologic head of the Southern Alps. Meteoric waters are primarily responsible for modifying fault zone permeability during fluid–rock interactions and may facilitate the generation of high pore fluid pressures that could assist episodic earthquake rupture.