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首页> 外文期刊>Geosphere >Length scales and types of heterogeneities along the deep subduction interface: Insights from exhumed rocks on Syros Island, Greece
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Length scales and types of heterogeneities along the deep subduction interface: Insights from exhumed rocks on Syros Island, Greece

机译：沿深浅界面的长度和类型的异质性：从希腊锡罗斯岛挖掘出岩石的见解

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We use structural and microstructural observations from exhumed subduction-related rocks exposed on Syros Island (Cyclades, Greece) to provide constraints on the length scales and types of heterogeneities that occupy the deep subduction interface, with possible implications for episodic tremor and slow slip. We selected three Syros localities that represent different oceanic protoliths and deformation conditions within a subduction interface shear zone, including: (1) prograde subduction of oceanic crust to eclogite facies; (2) exhumation of oceanic crust from eclogite through blueschist-greenschist facies; and (3) exhumation of mixed mafic crust and sediments from eclogite through blueschist-greenschist facies. All three localities preserve rheological heterogeneities that reflect metamorphism of primary lithological, geochemical, and/or textural variations in the subducted protoliths and that take the form of brittle pods and lenses within a viscous matrix. Microstructural observations indicate that the matrix lithologies (blueschists and quartz-rich metasediments) deformed by distributed power-law viscous flow accommodated by dislocation creep in multiple mineral phases. We estimate bulk shear zone viscosities ranging from ～10 18 to 10 20 Pa-s, depending on the relative proportion of sediments to (partially eclogitized) oceanic crust. Eclogite and coarse-grained blueschist heterogeneities within the matrix preserve multiple generations of dilational shear fractures and veins formed under high-pressure conditions. The veins commonly show coeval or overprinting viscous shear, suggesting repeated cycles of frictional and viscous strain. These geologic observations are consistent with a mechanical model of episodic tremor and slow slip (ETS), in which the deep subduction interface is a rheologically heterogeneous distributed shear zone comprising transiently brittle (potentially tremor-genic) sub-patches within a larger, viscously creeping interface patch. Based on our observations of outcrop and map areas of heterogeneous patches and the sizes, distributions, and amounts of brittle offset recorded by heterogeneities, we estimate that simultaneous brittle failure of heterogeneities could produce tremor bursts with equivalent seismic moments of 4.5 × 10 9 –4.7 × 10 14 N m, consistent with seismic moments estimated from geophysical data at active subduction zones.
机译：我们使用从锡罗斯岛（基克拉泽斯，希腊）暴露的膨胀的俯冲相关岩石的结构和微观结构观测在占据深层俯冲界面的长度和异质性的长度和类型的限制，具有对情节震颤和慢速滑动的可能影响。我们选择了三个锡罗斯地区，代表了不同海洋促果实和变形条件的俯冲界面剪切区，包括：（1）植物胶片对eClogite相的海洋外壳; （2）通过Blueschist-Greenschist相片挖出eClogite海洋地壳; （3）通过Blueschist-Greenschist相结合eClogite的混合乳头地壳和沉积物挖出。所有三个地区都保留了反映了岩体型促果实中初级岩性，地球化学和/或纹理变化的流变性异质性，并采用粘性基质内的脆荚和透镜的形式。微观结构观察表明，通过在多个矿物相中脱位蠕变的分布式电力 - 律粘性流动变形了基质岩性（BLUESCHISTS和石英的改性）。我们估算从〜10 18至10 20 pa-s的堆积剪切区粘度，这取决于（部分eNlemitized）海壳的相对比例。在基质内的欧雷加和粗粒子的黑蛋白基因异质性保留在高压条件下形成的多种膨胀剪切裂缝和静脉。静脉通常显示颈曲或叠印粘性剪切，建议反复摩擦和粘性菌株的循环。这些地质观测与诸多震颤和慢速滑动（ETS）的机械模型一致，其中深层俯冲界面是一种流变学异质的分布式剪切区，其包含瞬时脆弱（潜在的震颤）子贴片，在较大，粘性蠕变内接口补丁。基于我们对异质贴片的露头和地图区域的观察以及异质性记录的脆性偏移的尺寸，分布和数量，估计异质性的同时脆性失效可能产生4.5×10 9 -4.7的等效地震时刻产生震颤突发.7 ×10 14 n m，与主动俯冲区域的地球物理数据估计的地震矩一致。

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