Progressive deformation of the Chugach accretionary complex, Alaska, during a paleogene ridge-trench encounter

摘要: Abstract The Mesozoic accretionary wedge of south-central Alaska is cut by an array faults including dextral and sinistral strike-slip faults, synthetic antithetic thrust normal faults. three fault sets are characterized quartz ± calcite chlorite prehnite slickensides, all relatively late, i.e. truncate ductile fabrics the host rocks. Cross-cutting relationships suggest that predate late sets. Together, system exhibits orthorhombic symmetry. Thrust faulting shortened subhorizontally perpendicular to strike, then extended oblique orogenic strike. Strongly curved slickenlines on some each set reveal displacement directions changed over time. On dip-slip (thrust normal), tend become steeper with younger increments slip, whereas shallower strain increments. These patterns may result from progressive exhumation while were active, curvature tracking change a non-Andersonian stress field at depth more Andersonian (σ 1 or σ 2 nearly vertical) crustal levels. We interpret this complex as deformation one response Paleocene-Eocene subduction Kula-Farallon spreading center beneath because: (1) Kenai Peninsula, ENE-striking exhibit mutually cross-cutting dikes related ridge subduction; (2) mineralized have yielded 40 Ar/ 39 Ar ages identical near-trench intrusives subduction. Both features diachronous along-strike, having formed circa 65 Ma in west 50 east. Exhumation deeper levels southern formation interpreted critical taper adjustment progressively oceanic lithosphere yielding basal de´collement dip approached prism. structures also record different kinematic regimes associated plates, before after Prior triple junction passage, Farallon plate occurred right angles trench axis, migration, Kula involved significant component transpression northward translation Chugach terrane. changes kinematics apparent sequence from: thrusting; plutonism + faulting; (3) very gouge-filled