Figure 8.

Examples of frictional-viscous deformation in a blueschist-facies shear zone on Syros Island in Greece, modified from [148]. (a) Lensoidal mafic eclogite pod (approx. 2.5 m in length) embedded in a blueschist and quartz schist matrix. (b) Zoom in on the base of the eclogite pod showing brittle shear veins filled with high pressure minerals (e.g. glaucophane). The brittle shear veins culminate in discrete ductile shear zones in the surrounding blueschist matrix, indicating coeval frictional viscous slip. (c) Zoom in on the flanks of the eclogite pod where several generations of quartz veins were emplaced and subsequently sheared in a top-right shear sense, indicating cyclical switches from brittle vein emplacement at high pore fluid pressures to viscous creep and back again (cf. figure 10a). (d) Sketch illustrating the inferred cyclical development of the quartz vein set in (c). The veins show repeated opening and precipitation parallel to Sigma3 (horizontal) followed by progressive rotation in the shear direction. (e–f ) Panoramic photo of the entire outcrop highlighting the distribution of brittle eclogite pods and their vein structures, within the dominantly viscously deformed matrix. (Online version in colour.)