Magnetic susceptibility anisotropy in deformed sediments of ODP Leg 110

The anisotropy of magnetic susceptibility documents the generation of tectonically produced fabrics in sediments that macroscopically show no evidence of this disruption. The fabric observed in initial accretion is largely produced by overprinting of the original sedimentary susceptibility anisotropy by an E-W horizontal tectonic shortening and vertical extension. The response of the sediments to stress during initial accretion is variable, particularly near the sediment surface, and appears to reflect the inhomogeneous distribution of strain rate in the overthrust sequence. The susceptibility anisotropy of sediments possessing scaly fabric is consistent with the strong orientation of Phyllosilicates seen in thin section, producing a Kmin normal to the scalyness. The slope sediments deposited on the accreted sequence are also affected by tectonic shortening. The accreted sequences at Sites 673 and 674 show a complex history of fabric modification, with previous tectonic fabrics overprinted by later fabric modifications, pointing to continued tectonic shortening during the accretion process. The form of the susceptibility anisotropy axes at Sites 673 and 674 is consistent with NESW shortening, probably reflected in the NW-SE surface expression of the out-of-sequence thrusts. The susceptibility anisotropy appears to document a downhole change in the trend of shortening from E to W at the surface to more NESW at depth, probably as a result of the obliquely trending basement ridge, the Tiburon Rise.

磁化率各向异性（anisotropy of magnetic susceptibility）可揭示宏观上未表现出构造破坏迹象的沉积物中，由构造作用形成的组构的发育过程。初始增生作用中观测到的组构，主要是东西向水平构造挤压与垂直伸展作用对原始沉积磁化率各向异性进行叠加改造的产物。沉积物在初始增生过程中对应力的响应存在差异，尤其在沉积物表层附近更为明显，这一现象反映了逆冲序列内应变速率的非均匀分布特征。发育鳞片状组构的沉积物的磁化率各向异性，与薄片观测到的层状硅酸盐（Phyllosilicates）强定向排列特征一致，其最小磁化率轴（Kmin）垂直于鳞片状构造方向。沉积在增生序列之上的斜坡沉积物同样受到构造挤压作用的影响。673与674站位的增生序列经历了复杂的组构改造历史，早期构造组构被后续的组构改造作用叠加，表明增生过程中构造挤压作用持续进行。673和674站位的磁化率各向异性轴的分布特征，与北东-南西向（NESW）构造挤压模式相符，这一特征可能通过地表出露的无序逆冲断层的北西-南东向展布得以体现。磁化率各向异性特征显示，井下的挤压方向存在变化：地表处为东西向挤压，深部则转变为更显著的北东-南西向挤压，这一变化可能由斜向展布的基底隆起——蒂伯龙海隆（Tiburon Rise）所导致。