Venus: The corona conundrum

<p>Our neighbouring planet Venus holds key insights into terrestrial planet evolution. At present, there is no mosaic of mobile tectonic plates on the planet, yet Venus’ surface is scarred with many tectonic and volcanic structures. Surface deformation seems to be related to regional-scale tectonic deformation and/or mantle upwellings, but it remains questionable exactly when, and how, Venus is resurfacing. “Coronae” are ~circular crown-like structures with traces of tectonic and volcanic activity. They are commonly proposed to be surface manifestations of mantle plume upwellings and/or magmatism, and may therefore provide fundamental insights to Venus’ interior dynamics through time. The exact processes underlying their development and the reasons for their diverse morphologies have been widely debated in the past, with several key outcomes for the Venus scientific community. </p><p>In this presentation, I focus on our recent 3D numerical study<sup></sup>of plume-induced corona formation<sup> [1]</sup> and discuss what insights this study gives on the thermal evolution of Venus, as well as its present-day geological activity. The modelled corona morphologies are strongly on the lithospheric structure and the underlying dynamic processes at play. By a detailed comparison the modeling results with observed corona features (data from NASA’s Magellan mission), widespread plume activity on Venus was identified.  Moreover, I present prompting new results on the gravitational signatures of these modelled corona structures, and discuss whether we can distinguish between different stages of corona evolution in the gravity field. These outcomes may be important for future radio science experiments aboard ESA’s EnVision orbiter.</p><p>Finally, I’ll touch upon several key directions for future research on these enigmatic coronae structures, which are relevant in light of the upcoming ‘Decade(s) of Venus Science’. While I mainly formulate these key questions form a geodynamical point-of-view, I invite scientists from all disciplines of the Geo- and Planetary sciences to join the discussion on how these unique coronae can provide key information on the evolution of the interior and surface of Earth’s twin planet.<br><br><br>[1] Gülcher, A.J.P., Gerya, T.V., Montési, L.G.J., and Munch, J., (2020). Corona structures driven by plume–lithosphere interactions and evidence for ongoing plume activity on Venus. <em>Nature Geoscience,</em> 13, 547–554. </p>

Large topographic rises on Venus are regions thought to be formed in response to the presence of a mantle plume or mantle upwelling, equivalent to hot spots on Earth. In this work, we study the geology and evolution of one of these large topographic rises, Imdr Regio, based on geologic mapping and analysis of geophysical data of the area. Imdr Regio presents a complex structure with two very different areas: (a) an elevated southeast area that is dominated by volcanism associated with Idunn Mons, a large volcano that has been proposed as a site of recent or even active volcanism; (b) another elevated area in the northwest area that also has a large volcano (Arasy Mons), but that is dominated by volcanism and tectonic activity associated with the formation of the Olapa Chasma rift system. These two very differentiated topographically elevated areas also exhibit differences in their geology, volcanic and tectonic style, and geophysical characteristics, which leads us to suggest that more than the classic volcano‐dominated rise classification attributed to Imdr Regio the area could rather be considered as an intermediate or hybrid volcano‐rift dominated large topographic rise. The evaluation of the different genetic scenarios and its correspondence with the observed geology in the area suggests that the complex geology of Imdr Regio could be better explained if we consider models of hot spot evolution that involve the presence of several mantle plumes or secondary upwellings derived from a mantle plume emplaced at a deeper rheological boundary.

<p>The VenSpec instrument suite on the EnVision mission consists of three channels: VenSpec-M, VenSpec-H, VenSpec-U, and the Central Control Unit (CCU).</p> <p>VenSpec-H will be dedicated to high-resolution atmospheric measurements. The main objective of the VenSpec- H instrument is to detect and quantify SO2, H2O and HDO in both the troposphere and the mesosphere, to enable characterization of volcanic plumes and other sources of gas exchange with the surface of Venus, complementing VenSAR and VenSpec-M surface, SRS subsurface observations and VenSpec-U observations in the upper cloud layer. A nadir pointed high-resolution infrared spectrometer is the ideal instrument for these observations in different spectral windows between 1 and 2.5 microns, that permit measurements of the troposphere during the night, and of the mesosphere during the day. VenSpec-U will monitor sulphur-bearing minor species (mainly SO and SO2) and the yet unknown UV absorber in Venusian upper clouds and just above. It will therefore complement the two other channels by investigating how the upper atmosphere interacts with the lower atmosphere, and especially characterize to which extent outgassing processes such as volcanic plumes are able to disturb the atmosphere through the thick Venusian clouds. The twin channel (0.2 nm in high-resolution, 2 nm in low-resolution) spectral imager in the 190-380 nm range able to operate in nadir is ideally suited to such a task.</p> <p>VenSpec-M will provide near-global compositional data on rock types, weathering, and crustal evolution by mapping the Venus surface in five atmospheric windows. The broadest window at 1.02 μm is mapped with two filters to obtain information on the shape of the window. Additional filters are used to remove clouds, water, and stray light. VenSpec-M will use the methodology pioneered by VIRTIS on Venus Express but with more and wider spectral bands, the NASA VERITAS VIRSAR and Envision VenSAR-derived DEMs, and EnVision’s lower orbit compared to Venus Express to deliver near-global multichannel spectroscopy with wider spectral coverage and an order of magnitude improvement in sensitivity. It will obtain repeated imagery of surface thermal emission, constraining current rates of volcanic activity following earlier observations from Venus Express. In combination with the observations provided by the identical VEM instrument on the NASA VERITAS mission VenSpec-M will provide more than a decade of monitoring for volcanic activity, as well as search for surface changes.</p> <p>In combination, VenSpec spectrometers will provide unprecedented insights into the current state of Venus and its past evolution. VenSpec will perform a comprehensive search for volcanic activity by targeting atmospheric signatures, thermal signatures and compositional signatures, as well as a global map of surface composition. VenSpec will be key to studying the coupled system of surface and atmosphere on Venus following the holistic approach of Envision.</p>

Problems Statement and Purpose. Northern Tanzania Volcanic terrain has been a subject of evaluation for geothermal potential in the last four decades. The region is characterized by Neogene to Recent volcanic and tectonic activities. This preliminary study based on remote sensing, water chemistry, gravity data, geological structures and volcanic centers distribution reports the geothermal manifestations identified and discusses the implications on geothermal fluid pathways. Oxygen-hydrogen isotope data from water samples indicate that there were involved in the hydrothermal system. Tectono-Volcanic Structures. The Northern Tanzania Divergence (NTD) area characterized by Neogene to Recent volcanic and tectonic activities. Recent volcanic and tectonic activities are ash cone and lava dome eruption at the floor of Meru crater a century ago, dyke intrusion and volcanic eruption south of Gelai volcano, and Oldoinyo-Lengai volcano, respectively. Fumarolic activities and hot springs are dominant in a relatively young volcanic area to the north-eastern and northern part of the NTD. Data and Methods. Shuttle Radar Topography Mission (SRTM), Landsat 8 Operational Land Imager (OLI) image, water isotope analysis and gravity data were used to extract and analyze the surface and subsurface geological lineaments and map the hydrothermal alteration zones in the study area. The hydrothermal alteration is used to evaluate and identify the permeable structures. Analysis and interpretation of the length and trends of extracted lineaments were used to investigate the tectonic evolution. Geological map of a study area was digitized from the existing geological maps and the age of rocks to delineate volcanic activity and associated lineaments based on the age of the lithological domain. Digital image processing was applied to enhance the visual interpretation. Gravity data were used to give insight into the subsurface structure in the study area. Results and Discussion. The higher δ 18O values and large deviation from meteoric water lines suggest that is due to the interaction of fluids with host rocks at elevated temperatures. These are consistent with open structures that act as conduits for fluid flow. The potential field gravity data reveal a basin-like structure trending in the NNW direction. The gravity data show that the basement units gradually deepen towards the central part and that it is controlled by two main fault systems that trend N-S and NW-SE respectively. The gravity data presented here provides new constraints on the tectonic evolution and geothermal resources of the study area.

Geological processes and ecological adaptation are major drivers of diversification on oceanic islands. Although diversification in these islands is often interpreted as resulting from dispersal or island hopping rather than vicariance, this may not be the case in islands with complex geological histories. The island of Tenerife, in the Canary Islands, emerged in the late Miocene as 3 precursor islands that were subsequently connected and reisolated by volcanic cycles. The spider Dysdera verneaui is endemic to the island of Tenerife, where it is widely distributed throughout most island habitats, providing an excellent model to investigate the role of physical barriers and ecological adaptation in shaping within-island diversity. Here, we present evidence that the phylogeographic patterns of this species trace back to the independent emergence of the protoislands. Molecular markers (mitochondrial genes cox1, 16S, and nad1 and the nuclear genes ITS-2 and 28S) analyzed from 100 specimens (including a thorough sampling of D. verneaui populations and additional outgroups) identify 2 distinct evolutionary lineages that correspond to 2 precursor islands, each with diagnostic genital characters indicative of separate species status. Episodic introgression events between these 2 main evolutionary lineages explain the observed incongruence between mitochondrial and nuclear markers, probably as a result of the homogenization of their ITS-2 sequence types. The most widespread lineage exhibits a complex population structure, which is compatible with either secondary contact, following connection of deeply divergent lineages, or alternatively, a back colonization from 1 precursor island to another.

Volcanic and tectonic activities in the Aegean region have controlled the evolution of Santorini volcano, including changes in the shape and size of the island through time. Previous studies associate much of the island’s volcanic activity with the presence of regional faults, but a comprehensive volcanotectonic study that clarifies the relationship between dyking and faulting in the island has not been made. Here we present a detailed structural analysis focused on the northern caldera wall of Santorini, where numerous dykes and faults outcrop and can be studied in the mesoscale. To augment our discussion of dyke and fault interactions, we combine previous volcanological and geophysical observations with our structural analysis to report the volcanotectonic evolution of the northern part of the island and design a conceptual spatial-temporal model. We mapped 91 dyke segments and 15 faults and classified the latter, where possible, with respect to their observed or recorded kinematics, their size, and the active stress field under which they were formed based on prior geophysical data. We relate our observations to a mechanical unconformity within the northern caldera wall. Our field observations, coupled with previous numerical, geophysical, and volcanological studies, offer insights on the interaction between dykes and faults and indicate the conditions under which the faults facilitated magma emplacement, or not, during the volcano’s activity. Our analysis attempts to answer an essential question: under what conditions do crustal faults facilitate or inhibit magma propagation to the surface, with application to the island of Santorini.

New data are obtained on the structure, evolution, and origin of zones of nontransform offsets of adjacent segments in the Mid-Atlantic Ridge (MAR), which, in contrast to transform fracture zones, so far are studied insufficiently. The effects of deep mantle plumes developing off the crest of the MAR on the processes occurring in the spreading zone are revealed. These results are obtained from the geological investigation of the crest of the MAR between 19.8 ° and 21° S, where bottom sampling, bathymetric survey, and magnetic measurements have been carried out previously. Two segments of the rift valley displaced by 10 km relative to each other along a nontransform offset are revealed. A volcanic center of a spreading cell, which has been active over the last 2 Ma, is located in the northern part of the southern segment and distinguished by a decreased depth of the rift valley and increased thickness of the crust. Magnesian, slightly evolved basalts of the N-MORB type are detected in this center, whereas evolved and high-Fe basalts are found beyond it. The variation in the composition of the basalts indicates that the volcanic center is related to the upwelling of the asthenospheric mantle, which spread along and across the spreading ridge. In the lithosphere, the melt migrated off the volcanic center along the rift valley. In the northern segment, a vigorous volcanic center arose 2.5 Ma ago near its southern end; at present, the volcanic activity has ceased. As a result of the volcanic activity, an oval rise composed of enriched T-MORB-type basalts was formed at the western flank of the crest zone. The isotopic signatures show that the primary melts are derivatives of the chemically heterogeneous mantle. The mixing of material of the depleted mantle with the mantle material pertaining either to the Saint Helena or the Tristan da Cunha plumes is suggested; the mixture of all three sources cannot be ruled out. The conclusion is drawn that the mantle material of the Saint Helena plume was supplied to the melting zone beneath the axial rift near the oval rise along a linear permeable zone in the mantle extending at an azimuth of 225° SW. The blocks of mantle material that got to the convecting mantle from the Tristan da Cunha plume at the stage of supercontinent breakup were involved in melting as well. The nontransform offset between the two segments arose on the place of a previously existing transform fracture zone about 5 Ma ago. The nontransform offset developed in the regime of oblique spreading at the progressive propagation of the southern segment to the north. The zone of nontransform offset is characterized by recent volcanic activity. Over the last 2 Ma, spreading of the studied MAR segment was asymmetric, faster in the western direction. The rates of westward and eastward half-spreading in the northern segment are estimated at 1.88 and 1.60 cm/yr, respectively.

During the past 65 million years, the northwestern portion of the United States has experienced significant tectonic and volcanic activity, including volcanism in the Yellowstone region. The origins of volcanism in the area have been debated.To learn more about the region's tectonic activity and the underlying geologic structure, Obrebski et al. analyzed high‐resolution tomographic images of the Earth's interior created using data from the EarthScope USArray. They verified that there is a mantle plume (a column of hot rock rising upward within the mantle) beneath the Yellowstone Snake River Plain in Idaho.

Research Article| May 01, 2009 Neogene tephra correlations in eastern Idaho and Wyoming: Implications for Yellowstone hotspot-related volcanism and tectonic activity Mark H. Anders; Mark H. Anders † 1Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA †E-mail: manders@ldeo.columbia.edu Search for other works by this author on: GSW Google Scholar Janet Saltzman; Janet Saltzman ‡ 1Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA ‡Present address: Science Department, Red Hook High School, Red Hook, New York 12571, USA. Search for other works by this author on: GSW Google Scholar Sidney R. Hemming Sidney R. Hemming 1Department of Earth and Environmental Sciences and Lamont-Doherty Earth Observatory, Columbia University, Palisades, New York 10964, USA Search for other works by this author on: GSW Google Scholar GSA Bulletin (2009) 121 (5-6): 837–856. https://doi.org/10.1130/B26300.1 Article history received: 02 Aug 2007 rev-recd: 31 Jul 2008 accepted: 01 Aug 2008 first online: 03 Oct 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Mark H. Anders, Janet Saltzman, Sidney R. Hemming; Neogene tephra correlations in eastern Idaho and Wyoming: Implications for Yellowstone hotspot-related volcanism and tectonic activity. GSA Bulletin 2009;; 121 (5-6): 837–856. doi: https://doi.org/10.1130/B26300.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The explosive rhyolitic eruptions that define the track of the Snake River Plain–Yellowstone volcanism have produced a large volume of tephra found in late Miocene and younger basin-fill sediments throughout the western United States. Here we use 40Ar/39Ar isotopic dating, paleomagnetic analysis, major- and trace-element geochemistry, and standard optical techniques to establish regional tephra correlations. We focus on tephra deposits in three Neogene basins in spatially separated areas—Grand Valley, in eastern Idaho; Jackson Hole, in northwestern Wyoming; and the Granite Mountains area, in central Wyoming. These basins have experienced relatively continuous deposition from the late Miocene to the Holocene. We found tephra layers that directly tie the stratigraphy between all three basins. Using these correlations we found that basins experienced discrete pulses of extension separated by long periods of relative quiescence, the dates of which are staggered between basins. An early pulse of extension occurred in Grand Valley and Jackson Hole between 10.3 Ma and 16.33 Ma with a second pulse initiating between 4.54 Ma and 2.09 Ma. The Granite Mountains basin experienced a single pulse of extension sometime between 11.14 Ma and 6.75 Ma. These pulses of accelerated extension, along with evidence of similar pulses in other basins, present a pattern of west-to-east migration that we suggest is related to the Yellowstone hotspot. The later pulse of activity in Grand Valley and Jackson Hole corresponds to the migration of the North American Plate over the tail of the Yellowstone hotspot. We speculate that the earliest pulse in each basin is related to the more rapid movement of the sublithospheric hotspot head as it spreads out from its earliest known location, where the Columbia River Plateau Flood Basalt Province initiated in southeastern Oregon, to its outermost edge under central Wyoming. Our results are consistent with this model of a plume head, though not unique to it.The results of our study also indicate that previous suggestions that the rate of Snake River Plain explosive volcanism has decreased by a factor of 2 or 3 since emplacement of the middle Miocene Trapper Creek tuffs likely underestimate post–Trapper Creek eruption rates. We have discovered a large number of previously unidentified post–middle Miocene major eruptive events, both as ash-flow tuffs and as vitric air-fall tuffs. Recalculation to include these newly discovered events results in a rate of major eruptions that is fairly uniform until ca. 4.54 Ma. However, there is a substantial gap in major silicic eruptions in the interval between 4.54 Ma and 2.09 Ma, which we call the “post–Heise eruptive gap.” With the exception of this gap, the rate of major eruptions on the Snake River Plain has been roughly constant since inception of the eastern Snake River Plain–Yellowstone volcanic track between 16 Ma and 17 Ma. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Quaternary volcanism and tectonic history of the Suwa–Yatsugatake Volcanic Province, Central Japan

Relationship of coronae, regional plains and rift zones on Venus

This chapter reviews the conditions under which the basic landforms of Venus formed, interprets their nature, and analyzes their local, regional, and global age relationships. The strong greenhouse effect on Venus causes hyper-dry, almost stagnant near-surface environments. These conditions preclude water-driven, and suppress wind-related, geological processes; thus, the common Earth-like water-generated geological record of sedimentary materials does not currently form on Venus. Three geological processes are important on the planet: volcanism, tectonics, and impact cratering. The small number of impact craters on Venus (~1,000) indicates that their contribution to resurfacing is minor. Volcanism and tectonics are the principal geological processes operating on Venus during its observable geologic history. Landforms of the volcanic and tectonic nature have specific morphologies, which indicate different modes of formation, and their relationships permit one to establish their relative ages. Analysis of these relationships at the global scale reveals that three distinct regimes of resurfacing comprise the observable geologic history of Venus: (1) the global tectonic regime, (2) the global volcanic regime, and (3) the network rifting-volcanism regime. During the earlier global tectonic regime, tectonic resurfacing dominated. Tectonic deformation at this time caused formation of strongly tectonized terrains such as tessera, and deformational belts. Exposures of these units comprise ~20% of the surface of Venus. The apparent beginning of the global tectonic regime is related to the formation of tessera, which is among the oldest units on Venus. The age relationships among the tessera structures indicate that this terrain is the result of crustal shortening. During the global volcanic regime, volcanism overwhelmed tectonic activity and caused formation of vast volcanic plains that compose ~60% of the surface of Venus. The plains show a clear stratigraphic sequence from older shield plains to younger regional plains. The distinctly different morphologies of the plains indicate different volcanic formation styles ranging from eruption through broadly distributed local sources of shield plains to the volcanic flooding of regional plains. The density of impact craters on units of the tectonic and volcanic regimes suggests that these regimes characterized about the first one-third of the visible geologic history of Venus. During this time, ~80%–85% of the surface of the planet was renovated. The network rifting-volcanism regime characterized the last two-thirds of the visible geologic history of Venus. The major components of the regime include broadly synchronous lobate plains and rift zones. Although the network rifting-volcanism regime characterized ~2/3 of the visible geologic history of Venus, only 15%–20% of the surface was resurfaced during this time. This means that the level of endogenous activity during this time has dropped by about an order of magnitude compared with the earlier regimes.

Understanding the impact of tectonic activity and volcanism on long-term (i.e. millions years) evolution of shallow-water carbonate platforms represents a major issue for both industrial and academic perspectives. The southern central Mozambique Channel is characterized by a 100km-long volcanic ridge hosting two guyots (the Hall and Jaguar banks) and a modern atoll (Bassas da India) fringed by a large terrace. Dredge sampling, geophysical acquisitions and submarines videos carried out during recent oceanographic cruises revealed that submarine flat-top seamounts correspond to karstified and drowned shallow-water carbonate platforms largely covered by volcanic material and structured by a dense network of normal faults. Microfacies and well-constrained stratigraphic data indicate that these carbonate platforms developed in shallow-water tropical environments during Miocene times and were characterized by biological assemblages dominated by corals, larger benthic foraminifera, red and green algae. The drowning of these isolated carbonate platforms is revealed by the deposition of outer shelf sediments during the Early Pliocene and seems closely linked to (1) volcanic activity typified by the establishment of wide lava flow complexes, and (2) to extensional tectonic deformation associated with high-offset normal faults dividing the flat-top seamounts into distinctive structural blocks. Explosive volcanic activity also affected platform carbonates and was responsible for the formation of crater(s) and the deposition of tuff layers including carbonate fragments. Shallow-water carbonate sedimentation resumed during Late Neogene time with the colonization of topographic highs inherited from tectonic deformation and volcanic accretion. Latest carbonate developments ultimately led to the formation of the Bassas da India modern atoll. The geological history of isolated carbonate platforms from the southern Mozambique Channel represents a new case illustrating the major impact of tectonic and volcanic activity on the long-term evolution of shallow-water carbonate platforms.

The Mid-Atlantic Ridge between 29°N and 31°30′N in the last 10 Ma

Southeast Asia has the most complicated convergent system on the Earth. The effective elastic thickness (Te) can be a constraint on the long-term flexural strength and deformation mechanism of the lithosphere. In this study, we estimate Te over the Southeast Asia via the free-air admittance function calculated by the continuous wavelet transform. Sedimentary correction is performed to avoid the biases induced by the low density of sediments. The spatial variations of Te coincide well with the tectonic settings. The Northeast Indian Seamount Province and young oceanic basins correspond to the lowest Te (≤10 km). The Sunda Shelf displays relatively low Te (10–20 km), where Cenozoic rifting and extension weakened the lithosphere. The Molucca Sea and most continental regions show high Te (≥40 km). Overall, Te shows dependence on the oceanic crustal age in our study area, and is influenced by intensive tectonic activities. Low Te (≤10 km) in northern Sumatra and central Java subduction zone is consistent with the presence of a slab tear/window and mantle upwelling. Moreover, Te in Southeast Asia is either non-correlated with surface heat flow, or weakly correlated to Curie-point depth and seismic velocities at the 100 km depth. In some regions, e.g., the South China Sea and Sumatra-Java Trench, Te shows poor correlation with all geothermal proxies we employed. We argue that the geothermal state of lithosphere exerts very limited effects on integrated lithospheric strength in the tectonically active Southeast Asia, and apart from the temperature and composition, tectonic factors dynamically control the rigidity of the lithosphere.