Abstract The Cap de Creus peninsula in NE Spain exposes Variscan amphibolite-facies rocks, transected by greenschist-facies mylonitic shear zones accommodating displacements of up to 1 km. One of these shear zones contains pseudotachylytes with 1–4 mm thick fault veins and cm-scale high-angle injection veins and breccias. The pseudotachylyte matrix encloses mm-to μm-scale wallrock fragments and consists of ultrafine biotite and feldspar, often with a microporphyritic structure suggesting crystallization from a melt. Recent dating of the host shear zone yielded a Jurassic (170-160 Ma) age. Here we present 40Ar/39Ar dating of the pseudotachylytes yielding Early Eocene ages between 52.76 ± 1.64 Ma and 44.55 ± 0.77 Ma, indicating Alpine brittle faulting at times that Jurassic low-angle ductile shears had been tilted to their present vertical position following Alpine thrusting in the Pyrenees. The kinematics of the pseudotachylytes suggest strike-slip reactivation along the host shear zone, consistent with plate-kinematic analyses indicating coeval Iberia - Europe motion dominated by strike-slip. The dimensions of the pseudotachylyte-bearing zone and estimated brittle displacements suggest a moment magnitude of ~4.7–4.9. The average thicknesses of the fault veins indicate deformation at ≥4 km depth, an energy density of ~9.106 J/m2 and a frictional resistance of ~23 MPa.

中文翻译：

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西班牙东北部比利牛斯角 Cap de Creus 侏罗纪韧性剪切带始新世地震再活化

摘要 西班牙东北部的 Cap de Creus 半岛出露 Variscan 角闪岩相岩石，被绿片岩相糜棱质剪切带横断，可容纳长达 1 公里的位移。这些剪切带之一包含具有 1-4 毫米厚断层脉和厘米级高角度注入脉和角砾岩的拟速溶物。拟速溶岩基质包含毫米到微米级的围岩碎片，由超细黑云母和长石组成，通常具有微斑状结构，表明从熔体中结晶。最近对宿主剪切带的测年得出侏罗纪（170-160 Ma）时代。在这里，我们展示了产生早始新世年龄介于 52.76 ± 1.64 Ma 和 44.55 ± 0.77 Ma 之间的拟速溶物的 40Ar/39Ar 测年 表明高山脆性断层有时在比利牛斯山脉的高山逆冲之后侏罗纪低角度韧性剪切已经倾斜到它们现在的垂直位置。假速溶物的运动学表明沿着宿主剪切带重新激活了走滑，这与表明同期伊比利亚 - 欧洲运动以走滑为主的板块运动分析一致。含假速凝液的区域的尺寸和估计的脆性位移表明矩量级约为 4.7-4.9。断层脉的平均厚度表明在≥4 km 深度处发生变形，能量密度为~9.106 J/m2，摩擦阻力为~23 MPa。与板块运动学分析一致，表明同时期的伊比利亚 - 欧洲运动以走滑为主。含假速凝液的区域的尺寸和估计的脆性位移表明矩量级约为 4.7-4.9。断层脉的平均厚度表明在≥4 km 深度处发生变形，能量密度为~9.106 J/m2，摩擦阻力为~23 MPa。与板块运动学分析一致，表明同时期的伊比利亚 - 欧洲运动以走滑为主。含假速凝液的区域的尺寸和估计的脆性位移表明矩量级约为 4.7-4.9。断层脉的平均厚度表明在≥4 km 深度处发生变形，能量密度为~9.106 J/m2，摩擦阻力为~23 MPa。