The Surface of Venus

2018 ◽  
Author(s):  
M.A. Ivanov ◽  
J.W. Head
Keyword(s):  
Global Scale ◽  
Impact Craters ◽  
Tectonic Activity ◽  
Tectonic Deformation ◽  
Geologic History ◽  
Stratigraphic Sequence ◽  
Near Surface ◽  
Tectonic Regime ◽  
Geological Processes ◽  
History Of

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.

MAGMATOLOGICAL TECTONICS: ALFRED RITTMANN’S PARADIGM

2021 ◽  
Vol 40 (1) ◽  
pp. 266-281
Author(s):  
DANIELE MUSUMECI ◽  
STEFANO BRANCA ◽  
LUIGI INGALISO
Keyword(s):  
Twentieth Century ◽  
Interdisciplinary Research ◽  
Tectonic Activity ◽  
Geodynamic Model ◽  
Geological Processes ◽  
History Of ◽  
Fundamental Law ◽  
Scientific Worldview ◽  
Working Hypotheses

ABSTRACT The aim of this research is to present the life and research of Alfred Rittmann (1893–1980). He was an Earth scientist in the broadest sense: a petrographer, mineralogist, magmatologist, tectonist, geodynamicist, planetologist, volcanologist and, what is more, a philosopher of geosciences. He is considered the founder of contemporary, volcanology by combining in his interdisciplinary research the study of volcanic phenomena at the surface with tectonic activity and magmatology. In his books, Rittmann discussed the first correlations between volcanism and tectonics; his geodynamic model comprises complex studies of geology, volcanology, magmatology and geodynamics. We propose to name his scientific worldview ‘Magmatological Tectonics’ (MT) and to describe it as a Kuhnian paradigm. The leading concept of all geological processes is the fundamental law. Rittmann also made abundant use of Chamberlin’s method, the method of multiple working hypotheses. Some brief interpretations will be proposed regarding the importance of Rittmann in the history of geosciences in the twentieth century and the emergence of some philosophical problems deriving from this research.

Slope failure and mass transport processes along the Queen Charlotte Fault, southeastern Alaska

2018 ◽  
Vol 477 (1) ◽  
pp. 69-83 ◽  
Author(s):  
Daniel S. Brothers ◽  
Brian D. Andrews ◽  
Maureen A. L. Walton ◽  
H. Gary Greene ◽  
J. Vaughn Barrie ◽  
...  
Keyword(s):  
Mass Transport ◽  
Transport Processes ◽  
Tectonic Activity ◽  
Tectonic Deformation ◽  
Quaternary Sediments ◽  
Sediment Delivery ◽  
Gentle Slope ◽  
First Order ◽  
Geological Processes ◽  
Tectonic Features

AbstractThe Queen Charlotte Fault defines the Pacific–North America transform plate boundary in western Canada and southeastern Alaska for c. 900 km. The entire length of the fault is submerged along a continental margin dominated by Quaternary glacial processes, yet the geomorphology along the margin has never been systematically examined due to the absence of high-resolution seafloor mapping data. Hence the geological processes that influence the distribution, character and timing of mass transport events and their associated hazards remain poorly understood. Here we develop a classification of the first-order shape of the continental shelf, slope and rise to examine potential relationships between form and process dominance. We found that the margin can be split into six geomorphic groups that vary smoothly from north to south between two basic end-members. The northernmost group (west of Chichagof Island, Alaska) is characterized by concave-upwards slope profiles, gentle slope gradients (<6°) and relatively low along-strike variance, all features characteristic of sediment-dominated siliciclastic margins. Dendritic submarine canyon/channel networks and retrogressive failure complexes along relatively gentle slope gradients are observed throughout the region, suggesting that high rates of Quaternary sediment delivery and accumulation played a fundamental part in mass transport processes. Individual failures range in area from 0.02 to 70 km2 and display scarp heights between 10 and 250 m. Transpression along the Queen Charlotte Fault increases southwards and the slope physiography is thus progressively more influenced by regional-scale tectonic deformation. The southernmost group (west of Haida Gwaii, British Columbia) defines the tectonically dominated end-member: the continental slope is characterized by steep gradients (>20°) along the flanks of broad, margin-parallel ridges and valleys. Mass transport features in the tectonically dominated areas are mostly observed along steep escarpments and the larger slides (up to 10 km2) appear to be failures of consolidated material along the flanks of tectonic features. Overall, these observations highlight the role of first-order margin physiography on the distribution and type of submarine landslides expected to occur in particular morphological settings. The sediment-dominated end-member allows for the accumulation of under-consolidated Quaternary sediments and shows larger, more frequent slides; the rugged physiography of the tectonically dominated end-member leads to sediment bypass and the collapse of uplifted tectonic features. The maximum and average dimensions of slides are an order of magnitude smaller than those of slides observed along other (passive) glaciated margins. We propose that the general patterns observed in slide distribution are caused by the interplay between tectonic activity (long- and short-term) and sediment delivery. The recurrence (<100 years) of M > 7 earthquakes along the Queen Charlotte Fault may generate small, but frequent, failures of under-consolidated Quaternary sediments within the sediment-dominated regions. By contrast, the tectonically dominated regions are characterized by the bypass of Quaternary sediments to the continental rise and the less frequent collapse of steep, uplifted and consolidated sediments.

Volcanism on Mercury

2018 ◽  
Author(s):  
David A. Rothery
Keyword(s):  
Partial Melting ◽  
Explosive Volcanism ◽  
Impact Craters ◽  
Explosive Eruptions ◽  
Effusion Rate ◽  
Thermal Contraction ◽  
Near Surface ◽  
Radiogenic Heat ◽  
History Of ◽  
Over Time

The history of volcanism on Mercury is almost the entire history of the formation of its crust. There are no recognized tracts of intact primary crust analogous to the Moon’s highland crust, probably because the density of Mercury’s iron-poor magma ocean was insufficient to enable crystalized silicate phases to float. Mercury’s surface consists of multiple generations of lavas. These were emplaced, rather like terrestrial “large igneous provinces” or LIPs, in their greatest volumes prior to about 3.5 Ga. Subsequently, erupted volumes decreased, and sites of effusive eruption became largely confined to crater floors. Plains lava surfaces younger than about 3.7 Ga have become scarred by sufficiently few impact craters that they are mapped as “smooth plains.” The older equivalents, which experienced the inner solar system’s “late heavy bombardment,” are mapped as intercrater plains. There is no consensus over whether plains with superimposed-crater characteristics that are intermediate between the smooth plains and intercrater plains end members can be consistently mapped as “intermediate plains.” However, any subdivision of the volcanic plains for mapping purposes arbitrarily splits apart a continuum. The volcanic nature of Mercury’s smooth plains was ambiguous on the basis of the imagery returned by the first mission to Mercury, Mariner 10, which made three fly-bys in 1974–1975. Better and more complete imaging by MESSENGER (in orbit 2011–2015) removed any doubt by documenting innumerable ghost craters and wrinkle ridges. No source vents for the plains are apparent, but this is normal in LIPs where effusion rate and style characteristically flood the vent beneath its own products. However, there are good examples of broad, flat-bottomed valleys containing streamlined islands suggesting passage of fast-flowing low viscosity lava. Although the causes of the mantle partial melting events supplying surface eruptions on Mercury are unclear, secular cooling of a small, one-plate planet such as Mercury would be expected to lead to the sort of temporal decrease in volcanic activity that is observed. Factors include loss of primordial heat and declining rate of radiogenic heat production (both of which would make mantle partial melting progressively harder), and thermal contraction of the planet (closing off ascent pathways). Lava compositions, so far as can be judged from the limited X-ray spectroscopic and other geochemical measurements, appear to be akin to terrestrial komatiites but with very low iron content. Variations within this general theme may reflect heterogeneities in the mantle, or different degrees of partial melting. The cessation of flood volcanism on Mercury is hard to date, because the sizes of the youngest flows, most of which are inside <200-km craters, are too small for reliable statistics to be derived from the density of superposed craters. However, it probably continued until approximately 1 Ga ago. That was not the end of volcanism. MESSENGER images have enabled the identification of over a hundred “pits,” which are noncircular holes up to tens of km in size and up to about 4 km deep. Many pits are surrounded by spectrally red deposits, with faint outer edges tens of km from the pit, interpreted as ejecta from explosive eruptions within the pit. Many pits have complex floors, suggesting vent migration over time. Pits usually occur within impact craters, and it has been suggested that crustal fractures below these craters facilitated the ascent of magma despite the compressive regime imposed by the secular thermal contraction. These explosive eruptions must have been driven by the violent expansion of a gas. This could be either a magmatic volatile expanding near the top of a magma conduit, or result from heating of a near-surface volatile by rising magma. MESSENGER showed that Mercury’s crust is surprisingly rich in volatiles (S, Cl, Na, K, C), of which the one likely to be of most importance in driving the explosive eruptions is S. We do not know when explosive volcanism began on Mercury. Cross-cutting relationships suggest that some explosion pits are considerably less than 1 Ga old, though most could easily be more than 3 Ga. They characteristically occur on top of smooth plains (or less extensive smooth fill of impact craters), and while some pits have no discernible “red spot” around them (perhaps because over time, it has faded into the background), there is no known example of part of a red spot peeping out from beneath the edge of a smooth plains unit. There seems to have been a change in eruptive style over time, with (small volume) explosions supplanting (large volume) effusive events.

scholarly journals Using Machine Learning to Map Western Australian Landscapes for Mineral Exploration

2021 ◽  
Vol 10 (7) ◽  
pp. 459
Author(s):  
Thomas Albrecht ◽  
Ignacio González-Álvarez ◽  
Jens Klump
Keyword(s):  
Machine Learning ◽  
Large Scale ◽  
Mineral Exploration ◽  
Climatic Conditions ◽  
Tectonic Activity ◽  
Support Vector ◽  
Near Surface ◽  
Geological Processes ◽  
Landscape Variability ◽  
Model Region

Landscapes evolve due to climatic conditions, tectonic activity, geological features, biological activity, and sedimentary dynamics. Geological processes at depth ultimately control and are linked to the resulting surface features. Large regions in Australia, West Africa, India, and China are blanketed by cover (intensely weathered surface material and/or later sediment deposition, both up to hundreds of metres thick). Mineral exploration through cover poses a significant technological challenge worldwide. Classifying and understanding landscape types and their variability is of key importance for mineral exploration in covered regions. Landscape variability expresses how near-surface geochemistry is linked to underlying lithologies. Therefore, landscape variability mapping should inform surface geochemical sampling strategies for mineral exploration. Advances in satellite imaging and computing power have enabled the creation of large geospatial data sets, the sheer size of which necessitates automated processing. In this study, we describe a methodology to enable the automated mapping of landscape pattern domains using machine learning (ML) algorithms. From a freely available digital elevation model, derived data, and sample landclass boundaries provided by domain experts, our algorithm produces a dense map of the model region in Western Australia. Both random forest and support vector machine classification achieve approximately 98% classification accuracy with a reasonable runtime of 48 minutes on a single Intel® Core™ i7-8550U CPU core. We discuss computational resources and study the effect of grid resolution. Larger tiles result in a more contiguous map, whereas smaller tiles result in a more detailed and, at some point, noisy map. Diversity and distribution of landscapes mapped in this study support previous results. In addition, our results are consistent with the geological trends and main basement features in the region. Mapping landscape variability at a large scale can be used globally as a fundamental tool for guiding more efficient mineral exploration programs in regions under cover.

Geology of Isidis based on study of mascon and chains of cones

2020 ◽  
Author(s):  
Natalia Zalewska ◽  
Leszek Czechowski ◽  
Jakub Ciążela
Keyword(s):  
Numerical Models ◽  
Thermal Conditions ◽  
Surface Structures ◽  
High Mass ◽  
Research Centre ◽  
The Moon ◽  
Geologic History ◽  
Volcanic System ◽  
Geological Processes ◽  
History Of

&lt;p&gt;&lt;strong&gt;Geology of Isidis based on study of mascon and chains of cones &lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;Leszek CZECHOWSKI&lt;sup&gt;1&lt;/sup&gt;, Natalia ZALEWSKA&lt;sup&gt;2&lt;/sup&gt;,&amp;#160; Jakub CI&amp;#260;&amp;#379;ELA&lt;sup&gt;2&lt;/sup&gt;&lt;/p&gt;&lt;p&gt;&lt;sup&gt;&amp;#160;&lt;/sup&gt;&lt;/p&gt;&lt;p&gt;1University of Warsaw, Faculty of Physics, Institute of Geophysics, ul. Pasteura 5, 02-093 Warszawa, Poland, [email protected].&lt;/p&gt;&lt;p&gt;2 Space Research Centre, Polish Academy of Sciences, ul. Bartycka 18A, 00-716 Warszawa, Poland&lt;/p&gt;&lt;p&gt;&lt;br&gt;&lt;strong&gt;Introduction:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;We consider the surface structures and geological history of Isidis Planitia on Mars. It is a plain located inside a large&amp;#160;impact basin of ~1500&amp;#160;km in diameter. Its age is ~3.8 Ga ago [1, 2]. Geologic history of Isidis Planitia (or at least some of its parts) is quite complicated and many details remain unclear. We believe that better analysis of surface structures (especially chains of cones) and large deep structures (e.g. mascon) will allow a better understanding of the origin of Isidis.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;strong&gt;Formation of basin and mascon:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;&amp;#160;One of the large Martian mascons is located under Isidis. This is an anomalously high mass concentration below the surface. Such structures were discovered during the Apollo missions on the Moon. The formation of mascon is possible only under special physical conditions. Therefore, its existence is an important source of information about past conditions and can help us determine thermal conditions in the past of the basin.&lt;/p&gt;&lt;p&gt;&amp;#160;We use numerical models to this problem. Our model is based on the equation of thermal conductivity and the equation of motion. &amp;#160;Preliminary results point that the model allows to determine thermal conditions and some tectonic processes in the period when the mascon was formed.&lt;/p&gt;&lt;p&gt;The possibility of comparing processes on different celestial bodies is important for our research. Mars is a body of intermediate mass and size between Earth and the Moon. Therefore, it can be expected that some geological processes on Mars are similar to processes on Earth (e.g. volcanism) or the Moon (e.g. mascon&amp;#8217;s formation).&lt;/p&gt;&lt;p&gt;&lt;strong&gt;Role of distributed volcanism&lt;/strong&gt; &lt;strong&gt;and chains of cones:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;We are examining the volcanic system of cones on Isidis Planitia. Many of these chain forms have a characteristic furrow through the center, suggesting that fissure volcanism along circumferential dikes was common the Isidis area. The cones have diameters of 300&amp;#8211;500 m and heights of ~30 m. These imply slopes of 7&amp;#8211;11&amp;#176; consistent with explosive type of volcanism. Similar cones are known from Iceland. Some of the Isidis cones &amp;#160;keeping the cone shape without a furrow. We recognize this type of volcanism on the volcanic archipelago of the Canary Islands and in particular on Lanzarote. The cones on Isidis have been divided into three types depending on their building. Currently, we are working on determining the duration and age of this volcanic activity, as well as the size related magma plumbing system, which might be related to Syrtis Major.&lt;/p&gt;&lt;p&gt;Instability of water in the upper layers of the regolith could cause rapid degassing of the regolith. The result may be mud volcanism or geysers [3].&lt;/p&gt;&lt;p&gt;&lt;strong&gt;&amp;#160;&lt;/strong&gt;&lt;strong&gt;References&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;[1] Ivanov, M.A., et al. 2012, Icarus.&amp;#160;&amp;#160; https://doi.org/10.1016/j.icarus.2011.11.029&lt;/p&gt;&lt;p&gt;[2] Rickman, H., et al.&amp;#160; Planetary and Space Science, 166, 70&amp;#8211;89, 2019.&lt;/p&gt;&lt;p&gt;[3] Czechowski, L., et al. 2020. Submitted for LPSC 2020 in The Woodlands, Tx&lt;/p&gt;

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