Plate Tectonic Activity Research Articles

Tectonic evolution, geomorphology and influence of bottom currents along a large submarine canyon system: The São Vicente Canyon (SW Iberian margin)

A multi-scale dataset consisting of multi-beam echo-sounder, 2D multi-channel seismic and sidescan sonar (TOBI) data allows us to identify a large variety of morphologies originating from sedimentary and tectonic processes along the São Vicente Canyon (SVC), which is the largest submarine canyon developed in the external part of the Gulf of Cadiz. The SVC is located in one of the most seismogenic areas of Western Europe. The convergence between the Eurasian and African plates has controlled the formation and evolution of the canyon. The SVC is tectonically controlled by three main thrust faults: the Marquês de Pombal Fault, the São Vicente Fault and the Horseshoe Fault. No major rivers feed sediment to the canyon head, but the main sediment source is related to the dismantling of canyon flanks and the MOW (Mediterranean Overflow Water). This current contributes sediments by two different processes: a) conturites deposition at the head and flanks of the SVC that periodically fail into the canyon; and b) the coarser-grained and denser sediment of the MOW might be trapped at the head of the canyon and could develops into hyperpycnal flows. The SVC is characterized by retrogressive erosion being submarine landslide deposits and scars the main seafloor morphologies. The tectonic and stratigraphic interpretation of seismic profiles indicate that the SVC is a clear example of a diachronous and segmented canyon developed since the Late Miocene in an area of present-day active plate tectonics. This study investigates the interaction between active tectonics, the dynamics of submarine canyons and the resulting geomorphologies.

Surface erosion events controlled the evolution of plate tectonics on Earth.

Plate tectonics is among the most important geological processes on Earth, but its emergence andevolution remain unclear. Here we extrapolate models of present-day plate tectonics to the past and propose that since about three billion years agothe rise of continents and the accumulation of sediments at continental edges and in trenches hasprovided lubrication for the stabilization of subduction and has been crucial in the developmentof plate tectonics on Earth. We conclude that the two largest surface erosion and subduction lubrication events occurred after the Palaeoproterozoic Huronian global glaciations (2.45 to 2.2 billion years ago), leading to the formation of the Columbia supercontinent, and after the Neoproterozoic 'snowball' Earth glaciations (0.75 to 0.63 billion years ago). The snowball Earth event followed the 'boring billion'-a period of reduced plate tectonic activity about 1.75 to 0.75 billion years agothat was probably caused by a shortfallof sediments in trenches-and it kick-started the modern episode of active plate tectonics.

The ability of significant tidal stress to initiate plate tectonics

Plate tectonics is a geophysical process currently unique to Earth, has an important role in regulating the Earth's climate, and may be better understood by identifying rocky planets outside our solar system with tectonic activity. The key criterion for whether or not plate tectonics may occur on a terrestrial planet is if the stress on a planet's lithosphere from mantle convection may overcome the lithosphere's yield stress. Although many rocky exoplanets closely orbiting their host stars have been detected, all studies to date of plate tectonics on exoplanets have neglected tidal stresses in the planet's lithosphere. Modeling a rocky exoplanet as a constant density, homogeneous, incompressible sphere, we show the tidal stress from the host star acting on close-in planets may become comparable to the stress on the lithosphere from mantle convection. Tidal stress of this magnitude may aid mantle convection stress in subduction of plates, or drive the subduction of plates without the need for mantle convective stresses. We also show that tidal stresses from planet-planet interactions are unlikely to be significant for plate tectonics, but may be strong enough to trigger Earthquakes. Our work may imply planets orbiting close to their host stars are more likely to experience plate tectonics, with implications for exoplanetary geophysics and habitability. We produce a list of detected rocky exoplanets under the most intense stresses. Atmospheric and topographic observations may confirm our predictions in the near future. Investigations of planets with significant tidal stress can not only lead to observable parameters linked to the presence of active plate tectonics, but may also be used as a tool to test theories on the main driving force behind tectonic activity.

Origin and evolution of the atmospheres of early Venus, Earth and Mars

We review the origin and evolution of the atmospheres of Earth, Venus and Mars from the time when their accreting bodies were released from the protoplanetary disk a few million years after the origin of the Sun. If the accreting planetary cores reached masses $$\ge 0.5 M_\mathrm{Earth}$$ before the gas in the disk disappeared, primordial atmospheres consisting mainly of H $$_2$$ form around the young planetary body, contrary to late-stage planet formation, where terrestrial planets accrete material after the nebula phase of the disk. The differences between these two scenarios are explored by investigating non-radiogenic atmospheric noble gas isotope anomalies observed on the three terrestrial planets. The role of the young Sun’s more efficient EUV radiation and of the plasma environment into the escape of early atmospheres is also addressed. We discuss the catastrophic outgassing of volatiles and the formation and cooling of steam atmospheres after the solidification of magma oceans and we describe the geochemical evidence for additional delivery of volatile-rich chondritic materials during the main stages of terrestrial planet formation. The evolution scenario of early Earth is then compared with the atmospheric evolution of planets where no active plate tectonics emerged like on Venus and Mars. We look at the diversity between early Earth, Venus and Mars, which is found to be related to their differing geochemical, geodynamical and geophysical conditions, including plate tectonics, crust and mantle oxidation processes and their involvement in degassing processes of secondary $$\hbox {N}_2$$ atmospheres. The buildup of atmospheric $$\hbox {N}_2$$ , $$\hbox {O}_2$$ , and the role of greenhouse gases such as $$\hbox {CO}_2$$ and $$\hbox {CH}_4$$ to counter the Faint Young Sun Paradox (FYSP), when the earliest life forms on Earth originated until the Great Oxidation Event $$\approx $$ 2.3 Gyr ago, are addressed. This review concludes with a discussion on the implications of understanding Earth’s geophysical and related atmospheric evolution in relation to the discovery of potential habitable terrestrial exoplanets.

The active thermogene travertine deposits along the Cameroon volcanic line (CVL), central africa: Petrology and insights for neotectonics and paleoenvironmental approach

Two main active thermogene travertine deposits along the continental part of the Cameroon Volcanic Line have been investigated petrologically and paleontologically. The Bongongo travertine in a swampy environment, near Mount Cameroon has a thickness of less than 8 m, meanwhile that of Ngol which is located near Mount Manengouba has a cascade morphology and is less than 4 m thick. Volcanic activities that made up the Cameroon Volcanic Line are related to reactivation of the Precambrian fault at the time of the evolution of the South Atlantic Ocean during the Cenozoic. The mineralogical composition in the Ngol deposit is dominated by calcite (98.5%–99.5%) associated with detrital quartz and feldspar (0.5%–1.5%) and small amount of aragonite while the Bongongo deposit is made up of calcite (99.2%–99.8%) associated with detrital quartz (0.2%–0.8%) and small quantities of aragonite. The process of precipitation of these travertines is physico-chemical essentially. The heavy minerals concentrate are made up of varied types (epidote, chlorite, tourmaline, zircon, sillimanite, etc.) suggesting that the deep water has crossed granite-gneissic basement. The abundance of Li (Lithium) in the springs is linked to lepidolite present in the Bongongo deposit, while Sr (Strontium) and Ba (Barium) are found in the hydrothermal minerals as celestite (SrSO4) and Barite (BaSO4) associated to epidote/chlorite abundant in the deposits. The evidence of the deep origin (volcanic and crustal metamorphism origin) of CO2 (500–1050 mg/L) and the temperatures (29–49 °C) of the hot springs suggest a possible mixture of endogenic and epigenic waters in the subsurface. There is abundant fossil leafs belonging to Angiosperm. The gastropod fossils (Archachatina and Helix genus) are similar to extant species. These paleontological data are indicative of tropical climatic conditions, hot and humid episodes similar to present day's but without any link to the travertine deposits. Active thermogene travertines, a product of plate tectonic activities and volcanism, are also known in Europe (France, Turkey, Greece and Italy).

Spatial modelling for tsunami evacuation route in Parangtritis Village

Tsunami is a series of huge sea waves that commonly occurs because of the oceanic plate movement or tectonic activity under the sea. As a sudden hazard, the tsunami has damaged many people over the years. Parangtritis village is one of high tsunami hazard risk area in Indonesia which needs an effective tsunami risk reduction. This study aims are modelling a tsunami susceptibility map, existing assembly points evaluation, and suggesting effective evacuation routes. The susceptibility map was created using ALOS PALSAR DEM and surface roughness coefficient. The method of tsunami modelling employed inundation model developed by Berryman (2006). The results are used to determine new assembly points based on the Sentinel 2A imagery and to determine the most effective evacuation route by using network analyst. This model can be used to create detailed scale of evacuation route, but unrepresentative for assembly point that far from road network.

Thermal Anomalies Detection Using Comparative Method for Small Earthquake

Thermal anomaly is one of the earthquake precursor in the earthquake preparatory phase. Remote sensing in thermal region has been employed based on the concept of stress accumulation in the active plate tectonics region, which may be transformed as temperature variation prior to earthquake. MODIS Land Surface Temperature has been commonly used to locate the thermal anomalies before the earthquake. Recently researches have been focusing on moderate or large magnitude earthquake events. In Thailand, small earthquake can severely damage the unprepared area. This study, the daily day- and nighttime data of MODIS MOD11A1 product for 30 days before and 15 days after the earthquake on April 22, 2007, in Wiang Pa Pao District, Chiang Rai Province, Thailand, were processed and analysed to locate possibility of thermal anomalies. Thermal anomalies before and after the earthquakes were detected using the comparative method. The result found that the thermal anomaly temperature could be high up to 4.1 - 10.9 C which occurred in 21 - 22 days prior to the earthquake. Therefore, it may conclude that small earthquake can also release energy as the detectable thermal anomaly. However, more study about the relationship between thermal precursor and earthquake is needed to continue.

Periodization and specific features of deep processes in Precambrian by example of the Ukrainian shield

Thorough information on geological structure of the Ukrainian shield (USh) allows to verify opinions existing nowadays that plume and plate tectonic activities are possible only after conclusive formation of sublithospheric mantle 2,8—2,55 Ga and plume episodes of Precambrian occurred 2,75—2,7, 2,45—2,4, 1,9, 1.8—1,75, 1,65 Ga ago. It can be proved nowadays that formation of the crust occurred before 4.0 Ga and plume events result in later transformation of not only crust but also of mantle. Isotope dating of the USh allows allocating of plume episodes in close-range time. Nevertheless these limits for the USh in many cases have connection with geological processes, because not detrite zircons are dated but those ones included in rocks. Individual episodes are united into lasting plume events (activizations) up to 3,2, 3,2—2,8, 2,7—2,3, 2,3—1,65 Ga.Special features of the structure of granite-greenstone area of the Middle Dnieper megablock of the USh support the opinion that before 2,7 Ga thick sub-continental lithosphere consisted of refractory peridotite did not exist. Crystallizable layer consists of relatively low-melt minerals and is enriched by basaltoid component. The thickness of crystallized layer reduces up to 100 and 50 km in case of addition of reheated deep matter and increases during crystallization up to 150—200 km. Asthenosphere compulsory contains the melt diluted by silicate-aqueous-carbonate fluide.After 2,7 Ga subdivision of the area into two big blocks occurred. At the mark of the Archean and Proterozoic (2,5 Ga ago) the territory of Ukraine was subdivided into blocks and territories which spatially were drawn towards suture zones. The composition of the terrains allows supposing that at the mark of the Archean and Proterozoic exarticulation of tectonic units where plume processes went in different ways occurred.The following plume event (2,3—2,65 Ga ago) was manifested as a stage of transformation of mantle and crust on all the cratons. In the structure of the USh obvious features of plate tectonic processes have been found. Movements maximal by amplitude occurred 2,0—1,8 Ga ago. During the process of this plume event abrupt change of composition of fluids and melts removed from the mantle occur. Granitization takes place with participation of aqueous chloride-potassium fluids. After granitization active dry carbonate-fluoride-sodium fluids became active. Removal of melts, fluids occurs by small portions and the regime of pulsating plume considerably specifies the composition of magmatic rocks and hydrothermal solutions.

New aragonite 87Sr/86Sr records of Mesozoic ammonoids and approach to the problem of N, O, C and Sr isotope cycles in the evolution of the Earth

New Sr isotope data from well-preserved aragonite ammonoid shell material from the Mesozoic are compared with that from a living Nautilus shell. The prominent negative Sr isotope excursions known from the Middle Permian, Jurassic and Cretaceous probably have their origins in intensive plate tectonic activity, followed by enhanced hydrothermal activity at the mid-ocean ridges (mantle volcanism) which supplied low radiogenic Sr to seawater. The maximum positive (radiogenic) shift in the lower Mesozoic Sr isotope curve (Lower Triassic peak) was likely caused by a significant expansion of dry land surfaces (Dabie-Sulu Triassic orogeny) and their intensive silicate weathering in conditions of extreme warming and aridity in the very end of the Smithian, followed by warm and humid conditions in the late Spathian, which apparently resulted in a significant oceanic input of radiogenic Sr through riverine flux. The comparatively high 87Sr/86Sr ratio obtained from the living Nautilus shell is probably a function of both the Alpine orogeny, which was accompanied by significant continental weathering and input of radiogenic Sr to the oceans, and the weakening of mantle volcanism.

Analysis of Seismicity and Earthquake Energy at Opak Oyo Fault - Yogyakarta

<em>The earthquake that occurred in the Region of Yogyakarta caused by fault activity on the surface, such as Opak-Oyo Fault, Dengkeng Fault, Menoreh Fault and plate tectonic activity in South of Java. Opak-Oyo fault activity reflected from epicenter distribution and earthquake energy. </em><em>This research aims to analyze the earthquake energy which has epicenter around the Opak-Oyo Fault in spatial and temporal. Based on earthquake catalog from 2008 – 2016, there were 66 earthquake with 11 significant event. Epicenter distribution reflected in seismicity map and for the tectonic parameter use least square method. Seismicity map of Opak Oyo Fault area show that distribution of epicenter in the East and Southeast of fault line with the calculation result of b value by least square method is 0.4. In temporal, there is an increasing trend of events in 2008-2015 and decline trend of earthquake in 2015- 2017. Earthquake energy that released in Opak Oyo Fault area has varies value about </em><em>1x10<sup>5.2</sup> – 1x10<sup>12</sup></em><em>joules. Meanwhile, the energy that associated with the existence of Opak Fault Lines has value between </em><em>1x10<sup>5.2</sup> – 1x10<sup>9.6</sup> Joule </em><em>with 10-20 km of hypocenter.The distribution energy has similar pattern with geological formations in that area.</em><p><em> </em></p><p><em><br /></em></p>

OBSERVATION AND SIMULATION OF THE VARIABLE GAMMA-RAY EMISSION FROM PSR J2021+4026

ABSTRACT Pulsars are rapidly spinning and highly magnetized neutron stars, with highly stable rotational periods and a gradual spin-down over a long timescale due to the loss of radiation. Glitches refer to events that suddenly increase the rotational speed of a pulsar. The exact causes of glitches and the resulting processes are not fully understood. It is generally believed that couplings between the normal matter and superfluid components, and starquakes, are the common causes of glitches. In this study, one famous glitching pulsar, PSR J2021+4026, is investigated. PSR J2021+4026 is the first variable gamma-ray pulsar observed by Fermi. From gamma-ray observations, it is found that the pulsar experienced a significant flux drop, an increase in the spin-down rate, a change in the pulse profile and a shift in the spectral cut-off to a lower energy, simultaneously around 2011 October 16. To explain these effects on high-energy emissions by the glitch of PSR J2021+4026, we hypothesized the glitch to be caused by the rearrangement of the surface magnetic field due to crustal plate tectonic activities on the pulsar, which was triggered by a starquake. In this glitch event, the inclination angle of the magnetic dipole axis was slightly shifted. This proposition is then tested by numerical modeling using a three-dimensional two-layer outer gap model. The simulation results indicate that a modification of the inclination angle can affect the pulse profile and the spectral properties, which can explain the observation changes after the glitch.

Population genetic diversity and structure of a dominant tropical seagrass, Cymodocea rotundata, in the Western Pacific region

AbstractCymodocea rotundata is an ecologically important tropical pioneer seagrass species distributed in the Indo‐Pacific region. The population genetic diversity and structure of this species were analysed at 46 sites spanning the Philippines, Ryukyu Islands (northern limit) and Hainan Island, by using microsatellite simple sequence repeat (SSR) markers. Analyses revealed the persistence of C. rotundata likely relies on local population dynamics and fitness influenced by environmental gradients, with sexual reproduction prevalent in the Philippines while the Ryukyu and Hainan populations were predominantly established by clonal spread. Analysis of molecular variance showed significant genetic differentiation (P < 0.001) among three geographic regions: the Philippines, Ryukyu and Hainan. Furthermore, the mean fixation index value was very high (FST = 0.36), indicating poor dispersal potential or limited gene flow. Allelic richness and heterozygosity of C. rotundata was comparable in the Philippines and Ryukyu Islands populations. More private alleles were found in the Philippines and excess heterozygotes in the Ryukyu Islands. STRUCTURE analysis revealed that the Ryukyu and Hainan populations were mosaics of admixed alleles of individuals from the Philippines. An assignment test suggested that recruitment occurs from the Northeast Philippines to Ryukyu Islands. These results suggest that the Philippine populations are tropical seagrass hotspots and perhaps the origin of the populations in the Ryukyu and Hainan Islands. This scenario is most likely driven by the Kuroshio Current and island integration events during plate tectonic activities. The Philippine Archipelago is considered of high importance for conservation objectives and management plan of seagrasses. Likewise, the Ryukyu Islands are also important in terms of conserving regional diversity because locally adapted genotypes have important evolutionary potential in the face of environmental change.

The 13 million year Cenozoic pulse of the Earth

The geomagnetic polarity reversal rate changes radically from very low to extremely high. Such process indicates fundamental changes in the Earth's core reorganization and core–mantle boundary heat flow fluctuations. However, we still do not know how critical such changes are to surface geology and climate processes. Our analysis of the geomagnetic reversal frequency, oxygen isotope record, and tectonic plate subduction rate, which are indicators of the changes in the heat flux at the core mantle boundary, climate and plate tectonic activity, shows that all these changes indicate similar rhythms on million years' timescale in the Cenozoic Era occurring with the common fundamental periodicity of ∼13 Myr during most of the time. The periodicity is disrupted only during the last 20 Myr. Such periodic behavior suggests that large scale climate and tectonic changes at the Earth's surface are closely connected with the million year timescale cyclical reorganization of the Earth's interior.

Geodynamic evolution of the Earth over the Phanerozoic: Plate tectonic activity and palaeoclimatic indicators

During the last decades, numerous local reconstructions based on field geology were developed at the University of Lausanne (UNIL). Team members of the UNIL participated in the elaboration of a 600 Ma to present global plate tectonic model deeply rooted in geological data, controlled by geometric and kinematic constraints and coherent with forces acting at plate boundaries.In this paper, we compare values derived from the tectonic model (ages of oceanic floor, production and subduction rates, tectonic activity) with a combination of chemical proxies (namely CO2, 87Sr/86Sr, glaciation evidence, and sea-level variations) known to be strongly influenced by tectonics. One of the outstanding results is the observation of an overall decreasing trend in the evolution of the global tectonic activity, mean oceanic ages and plate velocities over the whole Phanerozoic. We speculate that the decreasing trend reflects the global cooling of the Earth system. Additionally, the parallel between the tectonic activity and CO2 together with the extension of glaciations confirms the generally accepted idea of a primary control of CO2 on climate and highlights the link between plate tectonics and CO2 in a time scale greater than 107 yr. Last, the wide variations observed in the reconstructed sea-floor production rates are in contradiction with the steady-state model hypothesized by some.

Paleoproterozoic crustal growth in the North China Craton: Evidence from the Lüliang Complex

The building of continental blocks and their assembly into supercontinents are linked to episodic crustal growth through Earth history, where both vertical and horizontal accretions in convergent plate margins play a significant role. Here we investigate the Paleoproterozoic crustal growth in the North China Craton (NCC) from a traverse covering continent-trench-ocean section in the Lüliang Complex within the western margin of the Trans-North China Orogen, a major accretionary belt that sutures the Eastern and Western Blocks in the NCC. We present petrological, geochemical and zircon U–Pb and Lu–Hf data from a suite of samples including meta granitoids and gabbroic diorite that built the continental arc, and metabasalts, felsic tuff, mafic and pelitic schists, and garnet amphibolites that form part of an imbricated package of oceanic and continental material that was accreted onto the eastern margin of the Western Block in the NCC. The salient geochemical features of the magmatic suite such as high Th/Ta and La/Nb ratios, negative Nb–Ta anomalies, and high concentration of LILE as compared to HFSE suggest magma derivation from sub-continental mantle source which has undergone different degree of enrichment with crustal components or material derived from subduction-related older components. In tectonic discrimination diagrams, the granitoids show VAG affinity and all the rocks straddle the field between IAB and MORB reflecting subduction-related arc signature. The majority of zircon grains in all the rock types from the Lüliang Complex show typical magmatic crystallization textures and high Th/U values. Zircons from the meta-granitoids and diorite enclave yield upper intercept or 207Pb/206Pb mean ages in the range of 2250±20 to 2084±69Ma. Those in the mafic schist show a mean age of 2234±9Ma. In the felsic schist group, the mean ages are in the range of 2298±15 to 1933±11Ma. A minor older population of zircons with ages of 2992±28Ma and 2610±80Ma also occurs in these rocks. In the metabasalt, zircon 207Pb/206Pb mean ages are between 2391±40 and 2022±39Ma with rare magmatic xenocrysts showing Mesoarchean age of 3294±21Ma. Zircons in the felsic tuff show mean ages of 2155±25 to 1897±24Ma, with xenocryst populations yielding mean ages of 2528±31Ma and 2710±20Ma. The youngest zircons with 207Pb/206Pb mean age of ca. 1.9Ga from the felsic schist (metasediment) and felsic tuff (volcanic suite) suggest deposition within the trench of an active convergent margin at this time. In the garnet-bearing amphibolite, the zircons yield a limited age range of 1996±17Ma to 1984±12Ma. The Lu–Hf data on zircons from all samples show dominantly positive ɛHf(t) values. In the granitoid–diorite suite, the ɛHf(t) values range up to 7.6 with crustal residence ages (TDMC) of 2371–2729Ma. Zircons in the mafic and felsic schists also possess positive ɛHf(t) values (up to 9.6) with TDMC in the range of 2366–2798Ma. In the metabasalt, both positive and negative ɛHf(t) values are displayed (3.8 to −3.2) with TDMC in the range of 2495–2830Ma. Zircons in the felsic tuff also show prominent positive ɛHf(t) value (up to 7.4) and crustal residence ages range from 2274 to 2607Ma. In the garnet-bearing amphibolite, the ɛHf(t) values lie between 3.3 and 4.8 and TDMC are in the range of 2321–2413Ma. The majority of ɛHf(t) values from all the rock types in the present study are compatible with juvenile magma sources, with limited input from crustal components. Their TDMC values indicate that both Neoarchean and Paleoproterozoic components were involved in the source, attesting to a continental arc setting. The Hf data also suggest the possible presence of Mesoarchean vestiges among the dominantly Neoarchean–Paleoproterozoic basement. Our data demonstrate active plate tectonics and major crustal growth during the Paleoproterozoic history of the NCC, broadly coeval with the making of the global supercontinent Columbia, and provide insights into continent building through subduction–accretion–collision tectonics analogous to those in Phanerozoic orogenic belts.

Evidence for subduction in the ice shell of Europa

Despite widespread evidence for extension, there have been few signs of contraction on the icy surface of Jupiter’s Europa. Evidence for a subduction-like convergent boundary suggests that Europa may have active plate tectonics.

A Science Instruction for the Prevention and Reduction of 2020 Nankai Earthquake Disaster in Tokushima, Southwest Japan

Earthquakes occur in the region where plate tectonic activity is still going on, and have killed more than one million people during the past 25 years. Earthquakes are natural hazards, which cannot be stopped but the hazards can be prevented from becoming disasters by taking appropriate preventive measures. The prevention such as re-building by the implementing appropriate building code needs much time and cost. However, we can easily shift the direction of bookshelf and other shelves not to collapse. This is because the direction of S-wave vibration depends on the area of the estimated seismic center. To make a teaching material for the understanding of the direction of P- and S-waves vibration is easy and cheap, and has much effect even on primary students. The damage to be inflected by earthquakes can be reduced significantly by not only theoretical study but teaching materials for earthquakes.

Plate tectonics on super-Earths: Equally or more likely than on Earth

The discovery of extra-solar super-Earths has prompted interest in their possible mantle dynamics and evolution, and in whether their lithospheres are most likely to be undergoing active plate tectonics like on Earth, or be stagnant lids like on Mars and Venus. The origin of plate tectonics is poorly understood for Earth, likely involving a complex interplay of rheological, compositional, melting and thermal effects, which makes it challenging to make reliable predictions for other planets. Nevertheless, as a starting point it is common to parameterize the complex processes involved as a simple yield stress that is either constant or has a Byerlee's law dependence on pressure. Because the simplifying assumptions made in developing analytical scalings may not be valid over all parameter ranges, numerical simulations are needed; one numerical study on super-Earths finds that plate tectonics is less likely on a larger planet (O'Neill and Lenardic (2007)), in apparent contradiction of an analytical scaling study (Valencia et al. (2007)). To try and understand this we here present new calculations of yielding-induced plate tectonics as a function of planet size, focusing on the idealized end members of internal heating or basal heating as well as different strength profiles, and compared to analytical scalings. In the present study we model super-Earths as simple scaled up versions of Earth, i.e., assuming constant physical properties, keeping the ratio of core/mantle radii constant and applying the same temperature difference between top/bottom boundaries and the same internal heating rate. Effects that originate outside of the planet, such as tidal forces, meteor impacts and intense surface heating from a nearby star are not considered. We find that for internally-heated convection plate tectonics is equally likely for terrestrial planets of any size, whereas for basally-heated convection plate tectonics becomes more likely with increasing planet size. This is indicated both by analytical scalings and the presented numerical results, which agree with each other. When scalings are adjusted to account for increasing mean density with increasing planet size, plate tectonics becomes more likely with increasing planet size for all scenarios. The influence of the pressure variation of viscosity, thermal expansivity and conductivity may, however, act in the opposite sense and needs to be determined in future studies. At least in the simplest case, factors other than planet size, such as the presence of surface water, are likely most important for determining the presence or absence of plate tectonics.

Timing, scale and mechanism of the destruction of the North China Craton

The North China Craton (NCC) is a classical example of ancient destroyed cratons. Since the initiation of the North China Craton Destruction Project by the National Natural Science Foundation of China, numerous studies have been conducted on the timing, scale, and mechanism of this destruction through combined interdisciplinary research. Available data suggest that the destruction occurred mainly in the eastern NCC, whereas the western NCC was only locally modified. The sedimentation, magmatic activities and structural deformation after cratonization at ~1.8 Ga indicate that the NCC destruction took place in the Mesozoic with a peak age of ca 125 Ma. A global comparison suggests that most cratons on Earth are not destroyed, although they have commonly experienced lithospheric thinning; destruction is likely to occur only when the craton has been disturbed by oceanic subduction. The destruction of the NCC was coincident with globally active plate tectonics and high mantle temperatures during the Cretaceous. The subducted Pacific slab destabilized mantle convection beneath the eastern NCC, which resulted in cratonic destruction in the eastern NCC. Delamination and/or thermal-mechanical-chemical erosion resulted from the destabilization of mantle convection.

Preface to the Special Issue on Geodynamic and Climate-Change Processes over Tibet, Xinjiang and Siberia

Tibet, Xinjiang and Siberia (TibXS) are regions with active plate tectonics. Evidence from satellite gravimetry and altimetry shows the hydrological evolutions over these regions are sensitive to global climate change. For example, inter-annual lake level changes over Tibet and Xinjiang from satellite altimetry are found to be connected to the El Nino Southern Oscillation (ENSO). Lakes in central Asia, Xinjiang and Siberia show sharp changes in lake levels that can be explained by climate change. Recent terrestrial gravity, GRACE and GPS observations suggest that the crust over the Tibetan plateau is thickening, and the Himalayan glaciers appear to be thinning. Satellite altimetry is a potential tool to study vertical displacement and permafrost thawing and changes in the active layers in Siberia and Tibet. This special issue includes some of the distinguished papers presented in the “International Workshop on Gravity, GPS and Satellite Altimetry Observations of Tibet, Xinjiang and Siberia (TibXS),” held on 20 22 August 2009 in Urumqi, Xinjiang, China (http://space.cv.nctu.edu.tw/altimetryworkshop/TibXS2009/TibXS2009.htm). This special issue covers the following subjects over TibXS: (1) GPS observations and interpretations; (2) land and satellite-based gravimetry; (3) satellite altimetry observations over lake and land; and (4) data processing techniques for GPS, gravimetry and altimetry. This is the first such issue in an earth science journal dealing exclusively with observations based on GPS, gravimetry and satellite altimetry over TibXS. These papers will promote the advancement of geodynamics, climate and hydrology studies here. We are grateful to the assistance of the TAO office during the editing and review process. Special thanks go to the responsible editor Dr. Chia Chou, and Miss Mei-Ling Chen. The comments from the reviewers have significantly improved the quality of all papers. Responsible Editor: Chia Chou Research Center for Environmental Changes, Academia Sinica, Taipei, Taiwan, ROC E-mail: chiachou@rcec.sinica.edu.tw