ALBERT

Description: High-resolution imaging data sets were used to identify and investigate a discrete stratigraphic unit exposed in the walls of impact craters throughout Chryse and Acidalia Planitiae, Mars. The unique morphology and spectral signatures observed in this unit, which include fine-scale layering, lensing, pinching, and elevated hydration signatures, all indicate that this material was deposited in a suite of aqueous environments. Furthermore, this unit’s widespread distribution and relationship to regional topography suggests an origin from the circum-Chryse outflow channels. While earlier studies have suggested that large quantities of outflow channel effluents are located throughout this region, this analysis is the first to identify and characterize the outcrop-scale morphology and spatial distribution of this extensive unit. These observations imply that the northern plains of Mars served as a global depocenter for immense volumes of water and sediment early in martian history.

Description: The relationships between tectonics and hotspot-related magmatism in transform/transtensive settings are poorly known. The Azores archipelago, lying where the transform plate boundary between the Nubian and Eurasian plates meets the Mid-Atlantic Ridge, is a rare site to investigate these relationships. The distinct tectono-magmatic features of Faial make it the ideal island to focus the study. Here, we analyze the relationships between tectonics and magmatism, using remote-sensing, field, and paleomagnetic analyses. Dominant WNW-ESE–trending lineaments correspond to major faults with transtensive dextral motion and NE-SW opening, probably related to the nearby transtensive Terceira Rift. Most (~60%) dikes, vent elongations, and alignments are parallel to this system. The lavas forming the basement of the distinctive WNW-ESE–trending Pedro Miguel graben strike parallel to the graben axis, dipping outward with a tilt consistent with that of paleomagnetic data. These lavas are dissected by the WNW-ESE–trending transtensive faults. Therefore, the graben consists of outward-tilted fault-bounded blocks, forming two opposite-verging dominoes. Its estimated stretching factor (β = 1.35) and mean extension rate (between 3.4 and 8.2 mm/yr) are similar or slightly larger than those of Terceira Rift, to the east. Part of the graben extension may be magma induced, via diking. We suggest that: (1) Faial, along with the nearby Pico Island, is a major locus of extension within the Azores, directly above the imaged hotspot; and (2) the Faial-Pico magmatic segment constitutes the offset, westward magmatic continuation of the Terceira Rift. The segment opening highlights the importance of extensional strain along magmatic transtensive plate boundaries.