Microcontinents are globally recognized as continental regions partially or entirely surrounded by oceanic lithosphere. Due to their positioning, they may become entangled in subduction zones and undergo either accretion or subduction. High-pressure metamorphism in subducted continental rocks support the idea that microcontinents can be subducted, regardless of their low densities. In this study, we used 2D numerical models to simulate collision of microcontinents with different sizes located at various distances from the upper plate in a subduction system characterized by different convergence velocities, in order to examine their effects on the thermo-mechanical evolution of subduction systems. Specifically, we analyzed the conditions that favor either subduction or accretion of microcontinents and investigated how their presence affects the thermal state within the mantle wedge. Our results reveal that the presence of microcontinents can lead to four styles of subduction: 1) continuous subduction; 2) continuous subduction with jump of the subduction channel; 3) interruption and restart of the subduction; 4) continental collision. We discovered that larger microcontinents and higher velocities of the subducting plate contrast a continuous subduction favoring accretion, while farther initial locations from the upper plate and higher velocities of the upper plate favor the subduction of the microcontinent. Additionally, we observed that the style of subduction has direct effects on the thermal state, with important implications for the potential metamorphic conditions recorded by subducted continental rocks. In particular, models characterized by parameters that favor the subduction of a larger amount of continental material from the microcontinent exhibit warm mantle wedges.

Venus is a terrestrial planet with dimensions similar to the Earth, but a vastly different geodynamic evolution, with recent studies debating the occurrence and extent of tectonic-like processes happening on the planet. The precious direct data that we have for Venus is very little, and there are only few numerical modeling studies concerning lithospheric-scale processes. However, the use of numerical models has proven crucial for our understanding of large-scale geodynamic processes of the Earth. Therefore, here we adapt 2D thermo-mechanical numerical models of rifting on Earth to Venus to study how the observed rifting structures on the Venusian surface could have been formed. More specifically, we aim to investigate how rifting evolves under the Venusian surface conditions and the proposed lithospheric structure. Our results show that a strong crustal rheology such as diabase is needed to localize strain and to develop a rift under the high surface temperature and pressure of Venus. The evolution of the rift formation is predominantly controlled by the crustal thickness, with a 25 km-thick diabase crust required to produce mantle upwelling and melting. The surface topography produced by our models fits well with the topography profiles of the Ganis and Devana Chasmata for different crustal thicknesses. We therefore speculate that the difference in these rift features on Venus could be due to different crustal thicknesses. Based on the estimated heat flux of Venus, our models indicate that a thin crust with a global average of 25 km is the most likely crustal thickness on Venus.