Insights into pitted cones at Isidis Planitia through synthesis of interior and surface

Abstract

The Isidis Planitia impact basin on Mars is located on the
north-south dichotomy boundary, bordered by Utopia Planitia and the
Syrtis Major volcanic province. The basin records a long geological
history of global and regional events of impact-induced, volcanic and
sedimentary processes. This is evident in the presence of a high-density
subsurface mass concentration, the strongest on Mars outside the major
volcanic provinces. The nature of this interior structure remains poorly
understood despite modelling efforts (e.g., [1-3]). Isidis Planitia’s
surface also hosts the densest clustering of pitted cones [4,5]. The
formation mechanism of these landforms, characterised by a conical mound
with a central depression, remains debated as volcanic [6], sedimentary
[4] or glacial [7].

We present an integrated approach to Isidis
Planitia, showing that pitted cones are topographically constrained by
surface wrinkle ridges driven by its subsurface structure. The
subsurface is modelled using impact scaling laws combined with
geological context to formulate a multi-layered model, which is fit to
the local gravity field. Resultant structural elements are consistent
with impact theory [8-10], estimated structures below Lunar basins
[11,12], as well as mapped basins [13]. However, the gravity field
cannot be constrained using infill, scaling laws and realistic density
values. The models require mantle-like materials in the innermost parts
of the basin. This element does not reconcile with expectations of
impact theory nor basin infill, and is interpreted as significant
post-impact plutonic intrusions.

This intrusive element is linked
to a set of wrinkle ridge surface expressions with anomalous direction
and dip. Two distinct formations of ridges are identified: an initial
radial set of ridges and a latter concentric inward-dipping formation.
This anomalous concentric set is not mirrored in Lunar basins [14,15]
nor in Martian basins Utopia and Hellas [16,17]. The initial set is
likely driven by regional compressive effects. The latter formation is
driven by a stress field in the inner basin, which could be achieved
during pluton inflation.

The pitted cones are shown to correlate
with the basin topography dominated by the wrinkle ridges. The
population conforms to both sets of pre-existing wrinkle ridges in
distinct surface flow patterns. They are most consistent with volcanic
rootless cones formed by lavas interacting with near-surface volatiles.
The lava could be sourced from the intrusive magmatism, addressing the
lack of other sources [6]. Overall, this study links Isidis Planitia’s
subsurface structure to surface morphology. It could redefine the
complex and dynamic basin, offering new insights into the active
geological evolution of Mars.