Multistage evolution and variable motion history of Agenor Linea, Europa

Abstract

Europa, the second Galilean moon of Jupiter, is composed of a silicate mantle and an ice shell which overlies a supposed subsurface ocean. The surface of Europa is scarred with fractures varying in morphology, dimensions, and geometry. We focus on Agenor Linea: a ∼1500km bright band that extends across Europa’s antijovian to trailing southern hemisphere. Agenor Linea is morphologically a band-like strike-slip fault; however, it experienced at least three evolutionary growth phases marked by three zones of varying albedo, each with a different geological history. Structures within the band material and kinematic indicators are consistent with formation through oblique left-lateral dilation, followed by normal dilation and right-lateral strike-slip movement, or combinations thereof. These motions produced a cumulative maximum right-lateral offset of 29.5km and a maximum band width of 34km. We interpret Agenor Linea to have formed primarily in response to the combined effects of nonsynchronous rotation stress and diurnal tidal flexing. If so, its orientation is optimal for right-lateral oblique opening in the current global stress field, consistent with its most recent kinematic behavior. A small amount of offset of relatively young tension fractures that postdate cryospheric disruption by lenticulae suggest the possibility of ongoing activity along Agenor. In contrast to a previously published model in which strike-slip duplexing was the primary process of band formation, this study shows that initial dilation of three distinct morphological zones under disparate stress orientations preceded strike-slip motion that resulted in both localized and distributed deformation features within the zones across the width of the band.