Plains Style Caldera Complexes: Evidence for Ancient, Explosive Volcanism on Mars

Abstract:

One of the mysteries of Mars’ geology is the origin of widespread, layered, friable deposits that likely formed through air fall deposition. The enigmatic chaos terrains are largely composed of such deposits, as are many of the most intriguing layered, clay- and sulfate-bearing deposits of astrobiological interest. Such deposits are most likely of volcanic origin, but lack an obvious source, based on comparison with well-known volcanic provinces [1]. We suggest that these deposits may have been sourced from previously unrecognized explosive volcanoes in Arabia Terra. While Arabia is not traditionally considered to be a volcanic region, we propose that several of the large depressions in the area are in fact calderas that formed through a combination of structural collapse and explosive volcanism. These features are characterized by the observation of sets of nested depressions, association with ridged plains, development of ring fractures and faults, the presence of interior slump blocks, and direct association, in some cases, with friable deposits, lavas and evidence for lava lakes. Eden Patera is the type example and shows evidence for three nested calderas with >4000 km³ of collapse volume. Siloe Patera also contains a set of nested collapse features that occur within a zone of demagnetized crust that might indicate the presence of a magma chamber at shallow depth [2]. It is not yet clear why explosive volcanoes may have formed in Arabia Terra, but we suggest that they might represent the rapid rise of mafic magmas through a thin crust. They might represent more silicic or volatile-rich magmas, but these scenarios do not appear to be necessary [3]. We suggest that explosive mafic volcanism was an important aspect of early Martian geological processes.

[1] Kerber, L., Head III, J., Madeleine, J. B., Forget, F. & Wilson, L. The dispersal of pyroclasts from ancient explosive volcanoes on Mars: Implications for the friable layered deposits. Icarus 219, 358-381 (2012)

[2] Morschhauser, A., V. Lesur and M. Grott. A spherical harmonic model of the lithospheric magnetic field of Mars. JGR Planets. 199 (6), 1162-1188 (2014).

[3] Gregg, T. K. P. and S. N. Williams. Explosive mafic volcanoes on Mars and Earth: Deep magma sources and rapid rise rate. Icarus 122 (2), 397-405.