Figure F211. Summary of magmatic and structural trends in Hole U1309D. The top boundary of the middle magmatic unit (~600–1080 mbsf) is defined by magmatically strained troctolites, and the upper half of the unit contains common noritic gabbro and more abundant oxide gabbro (D). In this part of the unit, plastic strain culminates in plastic strain shear zones (660 mbsf). The lower part of the unit displays better magmatic strain, and the lower boundary is marked by the top of olivine-rich troctolites (F). An association of plastic strain shear zones and oxide gabbros similar to that at 660 mbsf occurs at ~1300 mbsf (G), possibly the top of another magmatic unit. Magmatic units are not clearly related to the structural units (see “Definition of structural units”). Structural Unit 1 seems to be associated with the suspected detachment fault exposed at the surface and is marked by talc-tremolite schist (A), abundant late, relatively undeformed diabase, high intensity of greenschist-grade alteration, and near present-day paleomagnetic inclination orientation. Recovered core shows pervasive static alteration and largely unmodified pseudomorphs of igneous textures. The Unit 1/Unit 2 boundary is marked by a low to moderately dipping crystal-plastic shear zone within gabbroic rocks, high veining intensity, strong cataclasis (B), and a ~2 m thick interval of altered ultramafic rocks including mantle harzburgite. Structural Unit 2 is marked by a high intensity of veining including sulfides, paleomagnetic inclinations that are 10°–30° shallower than present-day values, and varied lithology. The base of Unit 2 is defined by a decrease in whole-rock Mg# of gabbros and a series of greenschist-grade cataclastic fault zones (C) below which there is an abrupt decrease in the intensity of veining and cataclastic deformation. Structural Unit 3 is characterized by overall low intensity of cataclastic deformation, veining, and plastic deformation. (Continued on next page.)
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