Unveiling the tectonic history of Tharsis insights from wrinkle ridges: multi-stage tectonic activity and critical taper dome

Introduction

The Tharsis region on Mars has occurred over the last four billion years, as evidenced by significant volcanic activity and the continuous deposition of volcanic materials [1].  The predominant theory posits that a mantle plume located beneath the lithosphere has driven the development of this volcanic province [ 2 &3]. Alternative hypotheses suggest a superplume origin similar to terrestrial examples [4] or a combination of isostatic uplift and flexural loading, alongside the accretion of volcanic deposits above a thin lithosphere and crustal thickening due to intrusive processes [5 & 6]. Further mantle convection models have been employed to elucidate the variations in crustal thickness and volcanic activities [7 & 8]. The volcanic activities and the stress sources of the Tharsis rise have been conducted to elucidate the dynamics of plume-induced stress centers [9 & 10].

Wrinkle ridges are linear or sinuous arch-like positive landforms and serve as paleo-strain and paleo-stress indicators for the compressional history and thermal evolution of Mars [11]. Previous studies analyzed 4,554 wrinkle ridges supported by compressional faults [9] and the mapping studies performed on the global fault catalog exhibited 8,500 compressional faults [12 & 13]. Recently, studies have utilized impact craters and depression cuts to explore the subsurface and assess the dip of reverse and thrust faults associated with wrinkle ridges [14]. Although many studies have been conducted on the tectonic history of Tharsis, the specific connection between plume-induced stresses and the pattern of compressive stress regime that forms the wrinkle ridges remains to be fully elucidated. Notably, the present study has importance concerning recent studies that indicate recent tectonic and volcanic activities in Tharsis [15 & 16].

The objective of this study is to conduct a comprehensive quantitative analysis of circumferential wrinkle ridges to improve our understanding of the plume and stress history of Tharsis.

Methodology

We mapped 34,741 wrinkle ridge segments, which together span 77,294 kilometers, around the edge of the dome. We utilized data from the NASA Planetary Data System, within ESRI ArcGIS Software. High-resolution mapping was facilitated using the MOLA-HRSC blend mosaic (200 m/px) [17] and the Thermal Emission Imaging System daytime infrared mosaic (∼100 m/px) as a base map [18]. Additionally, we used the latest Mars Reconnaissance Orbiter Context Camera global image mosaics (∼6–7 m/px) [19] alongside THEMIS for detailed mapping.

We adapted the "concentric deviation" method [20] to assess the orientation of wrinkle ridge segments concerning potential stress centers. This method involves analyzing the strike of wrinkle ridge crestlines, relative to any focal point and using a great circle to calculate the least deviation from best flitting. We used the fold propagation folding kinematic model [21] to reproduce wrinkle ridge topography assuming balance iso-volumetric plane-strain deformation takes place. This approach applied each wrinkle ridge segment to quantify the degree of shortening and the depth of the detachment, based on the measurable dimensions (width and height) of wrinkle ridges for constant the dip angle of 38° [14] for the underlying fault ramp. By investigating the superposition of crosscutting wrinkle ridge sets, we reconstructed the potential activation stages of stress centers.

Results and Conclusion

Our results show systematic shifts toward five specific stress centers within the Tharsis Rise. They are located near Alba Mons' southern caldera boundary (C1), the Ceraunius Fossae area (C2), the region between Ulysses Patera and Pavonis Chasma (C3), near Phoenicis Lacus (C4), and around Claritas Rupes (C5). Our findings disclose multiple stages of activation for wrinkle ridges, with the final stage of plume-induced stress being directed towards the Phoenicia Lacus quadrangle. NASA's InSight mission suggests that Mars is still seismically and/or tectonically active [22]. Our results are consistent with the proposed source regions of seismic activity.

Kinematic modeling of wrinkle ridges enables us to infer the amount of shortening and reconstruct the depth of detachment, which ranges from approximately 8.8 km to 2.9 km. The amount of horizontal shortening was calculated for each center, with the highest horizontal shortening on a radial topographic profile being 3.8 km for C4 and the lowest being 1.5 km for C1. The gently rising basal detachments and gently outward descending topography form a wedge approximately 4500 km long with an acute shape of 1.2° to 2.2°.

The computed results for the basal friction coefficient of each detachment, from C1 to C5, are 0.077, 0.059, 0.055, 0.078, and 0.093, respectively. These values can be plausibly linked to the manifestation of fluid overpressure beneath stratigraphic units such as permafrost, salt layers, and clay layers. We propose that the reduction of the basal friction coefficient for detachments occurs in regions where liquid water, rather than ice, is the predominant stable phase. These formations may be associated with fluid overpressure beneath highly altered and/or fractured stratigraphic units, such as salt layers, clay layers, evaporites, and permafrost. The upper crust functions as a permafrost layer, demonstrating impermeability to fluid transmission. In this context, fluid overpressure is considered a highly effective mechanism for significantly reducing the basal friction coefficient along the detachment beneath the Tharsis.

 

References

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