Hydrothermal alteration in an exhumed crustal fault zone: Testing geochemical mobility in the Caleta Coloso Fault, Atacama Fault System, Northern Chile
Hydrothermal alteration in an exhumed crustal fault zone: Testing geochemical mobility in the Caleta Coloso Fault, Atacama Fault System, Northern Chile
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挖出的地壳断层带的热液蚀变：测试智利北部阿塔卡马断层系卡莱塔科洛索断层的地球化学活动性
DOI：
10.1016/j.tecto.2014.03.024
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发表时间：
2014
期刊：
影响因子：
2.9
通讯作者：
Arancibia G
中科院分区：
文献类型：
--
作者：
Arancibia G
地壳尺度走滑断裂带具有复杂的非均质渗透构造，在地壳流体运移中起着重要作用。挖掘出的断层提供了对变形机制、流体-岩石相互作用和整体化学再分布之间相互作用的见解。对智利北部Caleta Coloso断裂带断层核进行了全岩地球化学和矿物化学测定，以期约束导致强烈热液蚀变的物理化学条件。走滑Caleta Coloso断核具有多核结构，由交替的低应变岩（原岩、弱变形原岩和原碎裂岩）和源自侏罗系tonalite的高应变链（碎裂岩和离散的超碎裂岩带）组成。与断层流体流动相关的热液蚀变以绿泥石、绿帘石、钠长石、石英和方解石组成的极低品位组合为特征。绿泥石测温表明t值在284 ~ 352℃之间，不同碎裂单元的矿物组成和t值没有变化。质量平衡和体积变化计算表明，原碎裂岩的化学流动性明显大于碎裂岩（和超碎裂岩）。这表明流体流动和化学蚀变受变形的强烈控制，原碎裂岩比碎裂岩更具渗透性。碎裂岩（和超碎裂岩）中绿泥石的沉淀和颗粒的减少会降低作为流体流动屏障的渗透率。在随后的和次平行的变形带合并过程中，colso断层核的化学迁移率和体积变化表明，不同的有效流体/流量比最终控制了裂缝通道，使断层相关的流体流入每个变形带。
Crustal scale strike slip fault zones have complex and heterogeneous permeability structures, playing an important role in fluid migration in the crust. Exhumed faults provide insights into the interplay among deformation mechanisms, fluid–rock interactions and bulk chemical redistributions. We determined the whole-rock geochemistry and mineral chemistry of the fault core of the Caleta Coloso Fault in Northern Chile, in order to constrain the physical and chemical conditions that lead to strong hydrothermal alteration. The strike-slip Caleta Coloso Fault core has a multiple-core architecture, consisting of alternate low strain rocks (protolith, weakly deformed protolith and protocataclasites) and high-strain strands (cataclasites and discrete band of ultracataclasite) derived from a Jurassic tonalite. Hydrothermal alteration associated with fault-related fluid flow is characterized by a very low-grade association consisting of chlorite, epidote, albite, quartz and calcite. Chlorite thermometry indicates T-values in the range of 284 to 352 °C, no variations in mineral composition or T-values were observed among different cataclastic units. Mass balance and volume change calculations show significantly larger chemical mobility in the protocataclasites than in the cataclasite (and ultracataclasite). This suggests that fluid flow and chemical alteration are strongly controlled by deformation being protocataclasite relatively more permeable than cataclasite. Chlorite precipitation and grain reduction in cataclasite (and ultracataclasite) would reduce permeability acting as a barrier for fluid flow. Chemical mobility and volume changes in the Coloso Fault core suggest different effective fluid/flow ratios during amalgamation of subsequent and subparallel deformation bands that finally control the fracture–channeling allowing fault-related fluid–flow into each of them.
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DOI：
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