Plate Tectonics and Macrogeomorphology

The plate tectonics revolution was the most significant advance in our understanding of the Earth in the 20th century, but initially it had little impact on the discipline of geomorphology. Topography and landscape development were not considered to be important phenomena that deserved attention from the broader earth-science community in the context of the new model of global tectonics. This situation began to change from the 1980s as various technical innovations enabled landscape evolution to be modelled numerically at the regional to sub-continental scales relevant to plate tectonics, and rates of denudation to be quantified over geological time scales. These developments prompted interest amongst earth scientists from fields such as geophysics, geochemistry and geochronology in understanding the evolution of topography, the role of denudation in influencing patterns of crustal deformation, and the interactions between tectonics and surface processes. This trend was well established by the end of the century, and has become even more significant up to the present. In this chapter I review these developments and illustrate how plate tectonics has been related to landscape development, especially in the context of collisional orogens and passive continental margins. I also demonstrate how technical innovations have been pivotal to the expanding interest in macroscale landscape development in the era of plate tectonics, and to the significant enhancement of the status of the discipline of geomorphology in the earth sciences over recent decades.

Polygonal impact craters reveal a global fracture pattern on Mercury

<div> <div> <div> <p>Mercury’s surface displays a rich history in impact cratering and tectonic activity, which both provide insight into the geological evolution of the innermost planet. Global contraction, the volume decrease of the planet associated with a long, sustained period of cooling, and tidal despinning, the slowing of rotation to lock Mercury in its current 3:2 spin-orbit resonance with the sun, are both thought to have played an important role on the observed systematic variations of preferred orientations of thrust fault-related landforms across the planet. While these landforms show preferred north-south orientations in the equatorial and mid-latitudes, they show random or concentric (east-west) orientations at the poles. Other fractures, such as joints, are likely present on Mercury, too, but their expressions are too subtle to be identified unless they are utilized as crater rims during the emplacement of impact craters. Fracture sets that existed in the bedrock prior to impact are widely accepted to produce crater rims showing straight rim segments that overall result in polygonal plan-view shapes of the impact structures, with perhaps the most prominent example Meteor Crater, Arizona. To test if regional fracture sets actually governed the shape of polygonal impact craters on Mercury, we have rigorously mapped all impact craters with diameters between 20 to 400 km. A total of 7,146 impact craters were mapped using Mercury Surface Space ENvironment GEochemistry and Ranging (MESSENGER) global image and topography datasets. After analyzing the shape, lengths, and orientations of 124,671 rim segments, we assessed if these rim segments contain additional information about systematic tectonic patterns. Our results show a strong preferred east-west orientation of straight crater rims at the poles, while in the mid-latitude and equatorial regions, they only have weak north-south or random orientations. That straight crater rims to show preferred east-west orientation at the poles is consistent with observed fault orientations by previous studies. However, we observe a lack of correlation of straight crater rim orientations and mapped faults at the equatorial and mid-latitudinal regions. These results have implications for and will enable further quantitative investigations of the global tectonics and fault reactivation on Mercury.</p> </div> </div> </div>

Constraining the process of intracontinental subduction: implications from petrology and Lu-Hf geochronology of eclogites from the Austroalpine Nappes

<p>The nucleation of subduction zone remains a widely discussed topic in the global tectonics. The prevalent view is that subduction starts within an oceanic plate. However, there is strong evidence that subduction can also be initiated within a continent. To test this hypothesis, we combine petrology, isotope geochronology and thermodynamic phase equilibrium modelling on eclogites from the Austroalpine Nappes of the Eastern Alps.</p><p>The high- and ultrahigh-pressure rocks occur in a ~400 km long belt from the Texel Complex in the west to the Sieggraben Unit in the east without remnants of Mesozoic oceanic crust. Garnet growth during pressure increase was dated using Lu-Hf chronometry. The results range between c. 100 and c. 90 Ma, indicating a short period of subduction. Combined with already published data, our estimates of metamorphic conditions indicate a field gradient with increasing pressure and temperature from northwest to southeast, where the rocks experienced ultrahigh-pressure metamorphism. The oldest Cretaceous eclogites (c. 100 Ma) are found in the Saualpe-Koralpe area which comprises widespread gabbros formed during Permian to Triassic rifting. This supports the hypothesis that subduction initiation was intracontinental and localized by a Permian rift. In the Texel Complex two-phased garnets yielded a Variscan-Eoalpine mixed age indicating re-subduction of Variscan eclogite-bearing continental crust during the Eoalpine orogeny. Jurassic blueschist-facies metamorphism at Meliata in the Western Carpathians and Cretaceous eclogite-facies metamorphism in the Austroalpine are separated by a time gap of ~50 Ma and therefore do not represent a transition from oceanic to continental subduction but rather separate events.</p>

Development of a simulator of the SIMBIOSYS suite onboard the BepiColombo mission

ABSTRACT BepiColombo is the fifth cornerstone mission of the European Space Agency (ESA) dedicated to study the Mercury planet. The BepiColombo spacecraft comprises two science modules: the Mercury Planetary Orbiter (MPO) realized by ESA and the Mercury Magnetospheric Orbiter provided by the Japan Aerospace Exploration Agency. The MPO is composed by 11 instruments, including the ‘Spectrometer and Imagers for MPO BepiColombo Integrated Observatory System’ (SIMBIOSYS). The SIMBIOSYS suite includes three optical channels: a Stereoscopic Imaging Channel, a High Resolution Imaging Channel, and a Visible and near Infrared Hyperspectral Imager. SIMBIOSYS will characterize the hermean surface in terms of surface morphology, volcanism, global tectonics, and chemical composition. The aim of this work is to describe a tool for the radiometric response prediction of the three SIMBIOSYS channels. Given the spectral properties of the surface, the instrument characteristics, and the geometrical conditions of the observation, the realized SIMBIOSYS simulator is capable of estimating the expected signal and integration times for the entire mission lifetime. In the simulator the spectral radiance entering the instrument optical apertures has been modelled using a Hapke reflectance model implementing the parameters expected for the hermean surface. The instrument performances are simulated by means of calibrated optical and detectors responses. The simulator employs the SPICE (Spacecraft, Planet, Instrument, C-matrix, Environment) toolkit software, which allows us to know for each epoch the exact position of the MPO with respect to the planet surface and the Sun.