Gamma-ray bursts from a close pulsar binary system?

The close neutron-star binary system comprised of the radio pulsars PSR J0737-3039 A,B is discussed. An analysis of the observational data indicates that the wind from pulsar A, which is more powerful than the wind from pulsar B, strongly distorts the magnetosphere of pulsar B. A shock separating the relativistic wind from pulsar A and the corotating magnetosphere of pulsar B should form inside the light cylinder of pulsar B. A weakly diverging “tail” of magnetic field is also formed, which stores a magnetic energy on the order of 10³⁰ erg. This energy could be liberated over a short time on the order of 0.1 s as a result of reconnection of the magnetic-force lines in this “tail,” leading to an outburst of electromagnetic radiation with energies near 100 keV, with an observed flux at the Earth of 4 × 10^?11 erg cm^?2 s^?2. Such outbursts would occur sporadically, as in the case of magnetic substorms in the Earth’s magnetosphere.     

Earth''s earliest continental lithosphere, hydrothermal flux and crustal recycling

The Kaapvaal craton in southern Africa and the Pilbara craton of northwestern Australia are the largest regions on Earth to have retained relatively pristine mid-Archaean rocks (3.0–4.0 Ga).The Kaapvaal craton covers about 1.2×10⁶ km², and varies in lithospheric thickness between 170 and 350 km. At surface, the craton can be subdivided into a number of Archaean sub-domains; some of the subdomains are also well defined at depth, and local variations in tomography of the lithosphere correspond closely with subdomain boundaries at surface.The Archaean history of the Kaapvaal craton spans about 1 Gyr and can be conveniently subdivided into two periods, each of about the same length as the Phanerozoic. The first period, from circa 3.7-3.1 Ga, records the initial separation of the cratonic lithosphere from the asthenosphere, terminating with a major pulse of accretion tectonics between 3.2 and 3.1 Ga, which includes the formation of “paired metamorphic belts”. This period of continental growth can be compared to plate tectonic processes occurring in modern-day oceanic basins. However, the difference is that in the mid-Archaean, these oceanic processes appear to have occurred in shallower water depths than the modern ocean basins. The second period, from circa 3.1-2.6 Ga, records intra-continental and continental-edge processes: continental growth during this period occurred predominantly through a combination of tectonic accretion of crustal fragments and subduction-related igneous processes, in much the same way as has been documented along the margins of the Pacific and Tethys oceans since the Mesozoic.The intra-oceanic processes resulted in small, but deep-rooted continental nucleii; the first separation of this early continental lithosphere could only have occurred when the mean elevation of mid-oceanicridges sank below sea-level. Substantial recycling of continental lithosphere into the mantle must have occurred during this period of Earth history. During the second period, at least two large continental nucleii amalgamated during collisional processes which, together with internal chemical differentiation processes, created the first stable continental landmass. This landmass, which is known to have been substantially bigger than its present outline, may have been part of the Earth's first supercontinent.The oldest known subdomains of the craton include the oceanic-like rocks of the Barberton greenstone belt. The comagmatic mafic-ultramafic rocks (3.48–3.49 Ga) of this belt represent a remnant of very early oceanic-like lithosphere (known as the Jamestown Ophiolite Complex), which was obducted, approximately 45 Ma after its formation, onto a volcanic arc-like terrain by processes similar to those which have emplaced modern ophiolites at convergent margins of Phanerozoic continents. The early metamorphic history, metamorphic mineralogy, oxygen isotope profiles and degree of hydration of the 3.49 Ga Jamestown Ophiolite Complex are similar to present day subseafloor hydrothermal systems. The ratio of ΔMg to ΔSi for hydrothermally altered igneous rocks, both present day and Archaean, are remarkably uniform at −5(±0.9) and the same as that of hydrothermal fluids venting on the present-day East Pacific Rise. This observation suggests that the process of Mg exchange for Si in hydrothermal systems was commonplace throughout Earth's history.The chemistry of vent fluids and hydrothermally altered igneous rocks was combined with an inventory of ³He in the mantle to model Earth's total hydrothermal flux. An Archaean flux (at 3.5 Ga) of about 10 times present day was accompanied by a correspondingly greater abundance of Mg(OH), SiO₂, carbonate and Fe---Mn metasomatic rock types as well as massive sulphides. Assuming a constant column of seawater since the Archaean, the average residence time of seawater in the oceanic crust was 1.65−8.90×10⁵ years in the Archaean. Assuming that ³He and heat are transported from the mantle in silicate melts in uniform proportions, the model stipulates that accretion of oceanic crust decreased from about 3.43−6.5×10¹⁷ g/yr to a present-day rate of 0.52−0.8×10¹⁷ g/yr, with a drop in heat flow from 1.4−2.6×10²⁰ cal/yr to 2.1−3.2×10¹⁹ cal/year.The total amounts of SiO₂ and Fe mobilised in marine hydrothermal systems since 3.5 Ga is less than their masses in the present exosphere reservoirs (crust, hydrosphere, atmosphere). The total amounts of Mg, K, CO₂, Ca and Mn are greater than their respective masses in exosphere reservoirs; therefore, they must have been recycled into mantle. The total mass of recycled hydrothermal components is small compared to the mass of the mantle. The flux of volatiles in hydrothermal systems is large compared to their volume in the atmosphere suggesting that the CO₂ and O₂ budgets of the atmosphere have been influenced by hydrothermal processes, especially in the Archaean.     

The building blocks of continental crust: Evidence for a major change in the tectonic setting of continental growth at the end of the Archean

Oceanic arcs are commonly cited as primary building blocks of continents, yet modern oceanic arcs are mostly subducted. Also, lithosphere buoyancy considerations show that oceanic arcs (even those with a felsic component) should readily subduct. With the exception of the Arabian–Nubian orogen, terranes in post-Archean accretionary orogens comprise < 10% of accreted oceanic arcs, whereas continental arcs compose 40–80% of these orogens. Nd and Hf isotopic data suggest that accretionary orogens include 40–65% juvenile crustal components, with most of these (> 50%) produced in continental arcs.Felsic igneous rocks in oceanic arcs are depleted in incompatible elements compared to average continental crust and to felsic igneous rocks from continental arcs. They have lower Th/Yb, Nb/Yb, Sr/Y and La/Yb ratios, reflecting shallow mantle sources in which garnet did not exist in the restite during melting. The bottom line of these geochemical differences is that post-Archean continental crust does not begin life in oceanic arcs. On the other hand, the remarkable similarity of incompatible element distributions in granitoids and felsic volcanics from continental arcs is consistent with continental crust being produced in continental arcs.During the Archean, however, oceanic arcs may have been thicker due to higher degrees of melting in the mantle, and oceanic lithosphere would be more buoyant. These arcs may have accreted to each other and to oceanic plateaus, a process that eventually led to the production of Archean continental crust. After the Archean, oceanic crust was thinner due to cooling of the mantle and less melt production at ocean ridges, hence, oceanic lithosphere is more subductable. Widespread propagation of plate tectonics in the late Archean may have led not only to rapid production of continental crust, but to a change in the primary site of production of continental crust, from accreted oceanic arcs and oceanic plateaus in the Archean to primarily continental arcs thereafter.     

Thermal thickness of the Earth’s lithosphere: a numerical model

A technique is suggested and the thermal thickness of the lithosphere is calculated, as well as the temperature distribution in the lithosphere on the basis of data on topography, the age of the oceanic bottom, crustal composition and structure, gravity anomalies, and mean annual surface temperatures. The bottom of the lithosphere is determined as the 1300°C isotherm. The calculation resolution is 0.5°×0.5°. All first-order tectonic structures, such as mid-ocean ridges and plume areas in oceans, continental rifts, cratons, and orogenic belts, are expressed in the computed thermal thickness. The comparative analysis of the thermal thickness of oceanic and continental lithosphere, lithosphere of cratons and young platforms, ancient and young orogens, remnant oceanic basins and adjacent continental areas can be used in geodynamical analysis of the corresponding regions.     

Recurrence of great earthquakes at subduction zones

Statistics of the recurrence times of great earthquakes at the Pacific subduction margins are made. The mean return period of great earthquakes is different from zone to zone, ranging from 27 to 117 years. The standard deviation of the return period proves to be very small, several years say, in some cases. The probabilities of a great earthquake recurring in each zone are estimated on the basis of Weibull distribution analysis.The mean return periods thus estimated are combined with the relative plate velocities at respective zones as obtained in the plate tectonics in order to estimate the ultimate displacement to rupture at the interface of the continental plate and the downgoing oceanic plate. It is presumed that great earthquakes at subduction zones occur as a result of a rebound of the continental plate at the time of rupture. The ultimate displacement thus estimated ranges from 2 to 8 m, and seems somewhat larger than that estimated on the basis of seismic observations, although the value of ultimate displacement seems to harmonize roughly with estimates based on geodetic observations on land. However, the ultimate displacement at the Aleutian—Alaska zone as estimated here seems much smaller than that estimated from actual observations.The ultimate strains, which are deduced from the displacements obtained on the assumption that the logarithmic extent of the deformed area is proportional to earthquake magnitude, are then calculated, and compared with those estimated for large inland earthquakes as revealed by repetition of geodetic surveys. The mean ultimate strain is estimated as 4.3 · 10⁻⁵ for subduction-zone earthquakes while that for inland earthquakes has been estimated as 4.7 · 10⁻⁵. As the agreement between both the ultimate strains is fairly good, it is tentatively concluded that the strength of the plate interface under the sea bottom is more or less the same as that in the crust on land.     

Gamma-ray bursts as standard-energy explosions

The distribution of observed energies for gamma-ray bursts with known redshifts can be explained as a consequence of events releasing a standard energy of E ₀=5×10⁵¹ erg. Two situations are possible: the degree of collimation could vary from burst to burst, or there could be a universal radiation pattern for all bursts, with the observed differences being due to differences in the orientation of this pattern relative to the line of sight to the Earth.     

Crustal thickness,rift‐drift and potential links to key global events

Orogenic crustal thickening leads to increased continental elevation and runoff into the oceans, but there are fundamental uncertainties in the temporal patterns of thickening through Earth history. U‐Pb age and trace element data in detrital zircons from Antarctica are consistent with recent global analyses suggesting two dominant peaks in average crustal thickness from ~2.6 to 2.0 Ga and ~0.8 to 0.5 Ga. Shifts in marine carbonate ⁸⁷Sr/⁸⁶Sr ratios show two primary peaks that post‐date these crustal thickness peaks, suggesting significant weathering and erosion of global continental relief. Both episodes correlate well with zircon trace element and isotope proxies indicating enhanced crustal and fluid input into subduction zone magmas. Increased crustal thickness correlates with increased passive margin abundance and overlaps with snowball Earth glaciations and atmospheric oxygenation, suggesting a causal link between continental rift‐drift phases and major transitions in Earth's atmospheric and oceanic evolution.     

Volcanic products in building of Earth's crust

A highly tentative analysis suggests that volcanism contributed less than 42 x 10¹⁸ but more than 14 x 10⁸ tons solid substance to the lithosphere and at least 7.2 x 10¹⁷ tons water to the hydrosphere during the entire geologic history of the Earth (4.5 x 10⁹ years). Volcanic contributions to the atmosphere are believed to be “infinitesimally small,” since the bulk of volcanic gases has been converted into solids (carbon, sulfur, etc.) or into solutes. -- V.P. Sokoloff.     

Contributions to the mineralogy of authigenic manganese phases from marine manganese deposits

The formation of authigenic manganese minerals and ores in the pelagic regions of the ocean is related to oxidation of Mn²⁺ extracted from basalts and other rocks with heated seawater. For littoral parts of the ocean and lakes mobilization of Mn²⁺ and Fe²⁺ is admitted finding its way to the bottom sediments (along with the organic substances) from land in the form of Mn⁴⁺. The main manganese mineral of oceanic and continental basins is vernadite. Its deposition is considered a result of the activity of microorganisms.     

Native iron in the sediments of Lake Baikal (borehole BDP-98): results of thermomagnetic analysis

We performed a thermomagnetic analysis of 91 samples and a probe microanalysis of five samples of sedimentary rocks from the lower zone of the borehole BDP-98 drilled at the bottom of Lake Baikal. The results show the scarcity of native iron: It was found only in five samples. Its concentration varies from ～10^–5 to 7 × 10^–4%. The distribution of native iron by content is bimodal, with a distinct “zero” mode. This scarcity of native iron in the Baikal sediments distinguishes them from continental (Eurasia) and oceanic (Atlantic) sediments of different ages. It is due to the high rate of sedimentation in the studied interval of BDP-98.     

Source mechanism of the tsunamis of 19 and 21 September 1985, in Mexico

The major earthquake measuring 8.1 on the Richter scale which struck the west coast of Mexico on Thursday 19 September 1985, generated a small tsunami. A major aftershock on 21 September, with a magnitude of 7.5 also produced a small tsunami. Both tsunamis propagated across the Pacific and were recorded by several tide stations in Central America, Colombia, Ecuador, French Polynesia, Samoa, and Hawaii. No reports of damage were received from any of the stations, and only minor damage due to the first tsunami was reported from the source region.A survey was made by the International Tsunami Information Center (ITIC) of the coastal area affected, from Manzanillo to Zihuatanejo. Tsunami runup measurements were taken and interviews with local residents in the coastal areas were conducted.A source mechanism study of the tsunamis was undertaken using seismic and geologic data and empirical relationships. Earthquake and tsunami energies were estimated and the tsunami genertion areas defined.The earthquake energies were estimated to be 5.61 × 10²⁴ erg for the 19 September event and 9.9 × 10²³ erg for the 21 September event. Tsunami energies were estimated to be 0.7 × 10²⁰ erg for the first event and 0.56 × 10²⁰ erg for the second event. The source area of the first tsunami was determined to be approximately one-half of the earthquake source area, or approximately 7500 km², while the source area of the second tsunami was estimated to be equal to the earthquake area.The relatively small tsunamis generated by these large earthquakes are attributed to the shallow angle of subduction of the Cocos plate underneath the North American plate for this particular region, and to the small vertical component of crustal displacements. However, the angle of subduction increases further south and local earthquakes from that area have the potential of producing large tsunamis on the west coast of Mexico.This paper was presented at the 4th International Symposium on Natural and Man-made Coastal Hazards held in Ensenada, Mexico, August 1988.     

A-type granites induced by a breaking-off and delamination of the subducted Junggar oceanic plate,West Junggar,Northwest China

The A-type granites with highly positive ε_Nd(t) values in the West Junggar, Central Asian Orogenic Belt (CAOB), have long been perceived as a group formed under the same tectonic and geodynamic setting, magmatic sourceq and petrogenetic model. Geological evidence shows that these granites occurred at two different tectonic units related to the southeastern subduction of Junggar oceanic plate: the Hongshan and Karamay granites emplaced in the southeast of West Junggar in the Baogutu continental arc; whereas the Akebasitao and Miaoergou granites formed in the accretionary prism. Here the authors present new bulk-rock geochemistry and Sr-Nd isotopes, zircon U-Pb ages and Hf-O isotopes data on these granites. The granites in the Baogutu continental arc and accretionary prism contain similar zircon ε_Hf(t) values (+10.9 to +16.2) and bulk-rock geochemical characteristics (high SiO₂ and K₂O contents, enriched LILEs (except Sr), depleted Sr, Ta and Ti, and negative anomalies in Ce and Eu). The Hongshan and Karamay granites in the Baogutu continental arc have older zircon U-Pb ages (315–305 Ma) and moderate ¹⁸O enrichments (δ¹⁸O_zircon=+6.41‰–+7.96‰); whereas the Akebasitao and Miaoergou granites in the accretionary prism have younger zircon U-Pb ages (305–301 Ma) with higher ¹⁸O enrichments (δ¹⁸O_zircon=+8.72‰–+9.89‰). The authors deduce that the elevated ¹⁸O enrichments of the Akebasitao and Miaoergou granites were probably inherited from low-temperature altered oceanic crusts. The Akebasitao and Miaoergou granites were originated from partial melting of low-temperature altered oceanic crusts with juvenile oceanic sediments below the accretionary prism. The Hongshan and Karamay granites were mainly derived from partial melting of basaltic juvenile lower crust with mixtures of potentially chemical weathered ancient crustal residues and mantle basaltic melt (induced by hot intruding mantle basaltic magma at the bottom of the Baogutu continental arc). On the other hand, the Miaoergou charnockite might be sourced from a deeper partial melting reservoir under the accretionary prism, consisting of the low-temperature altered oceanic crust, juvenile oceanic sediments, and mantle basaltic melt. These granites could be related to the asthenosphere’s counterflow and upwelling, caused by the break-off and delamination of the subducted oceanic plate beneath the accretionary prism Baogutu continental arc in a post-collisional tectonic setting.©2022 China Geology Editorial Office.     

Mountain building-enhanced continental weathering and organic carbon burial as major causes for climatic cooling at the Frasnian–Famennian boundary (c. 376 Ma)?

The Late Devonian was a period of drastic environmental changes, as exemplified by a major biotic crisis at the Frasnian–Famennian boundary (FFB) and the onset in Famennian times of glaciations across southern Gondwana. Worldwide evidence for the coeval development of the major Acadian–Eovariscan belt led us to propose a model relating the Late Frasnian–Famennian environmental perturbations to extensive continental uplift through two atmospheric CO₂-depleting mechanisms: (1) the intensification of silicate weathering on the continental areas as attested by a major rise in the ⁸⁷Sr/⁸⁶Sr composition of sea water at the FFB; and (2) the massive burial of organic carbon (Kellwasser events) in partially confined basins due to the collisional-induced reduction of equatorial oceanic communications between the Palaeotethysian and Panthalassic oceans. This process is also suggested to have been controlled by an important primary productivity connected to an increased nutrient availability triggered by the enhanced continental run-off.     

Manganese and copper fluxes from continental margin sediments

Total dissolvable Cu and Mn have been measured in seawaters collected from the continental shelf of the eastern Bering Sea. Copper concentrations of < 3 nmole kg⁻¹ were measured over the shelf break but concentrations increased to >4 nmole kg⁻¹ inshore of a hydrographie front over the 100 m isobath. Manganese concentrations also were low over the shelf break, <10 nmole kg⁻¹, and increased systematically to concentrations >10 nmole kg⁻¹ inshore of the hydrographic front. Depth distributions of Mn at all continental shelf stations showed gradients into the sediments, with concentrations typically >20 nmole kg⁻¹ in a bottom layer extending about 30 m off the bottom. Benthic Cu and Mn fluxes are indicated by cross-shelf pore water profiles that show interfacial concentrations more than an order of magnitude greater than in bottom water. These data and the results of a model of metal transport across the shelf suggest that Cu and Mn fluxes, estimated at 2 and 18 nmole cm⁻²y⁻¹, respectively, from continental shelf sediments may be one “source” of these metals to the deep sea.     

花岗岩:大陆地质研究的突破口以及若干关键科学问题——“岩石学报”花岗岩专辑代序

地球是宇宙中迄今唯一发现有花岗岩的星球。从物质组成而言,大洋的核心问题是玄武岩,大陆的核心问题是花岗岩。花岗岩从被发现的那一天起,围绕它的产状、成因和演化过程及其地质意义的争论就没有停止过。最早的陆壳由长英质片麻岩TTG组成,TTG不能从地幔中直接熔出,是地幔熔融的玄武岩再次熔融形成的。初始的陆壳富钠,太古宙以后的陆壳开始明显富钾。洋壳的寿命仅2~3亿年,陆壳的寿命可长达40~44亿年。花岗岩记录了大陆形成与演化的全过程,大陆演化对于认知地球具有无法替代的作用。因此,花岗岩在某种程度上可以作为陆壳的代用词。20世纪60年代兴起的板块构造理论是地球科学的一次革命,但是,板块构造理论并未解决大陆形成、演化和改造的根本问题。此外,花岗岩与大陆成矿作用关系也非常密切。花岗岩成因还存在诸多待解难题。对花岗岩的研究,只有跳出岩石学和岩石地球化学的范畴,才能真正理解大陆构造的问题。花岗岩所凝聚的科学问题是对板块构造理论的巨大挑战,也是固体地球科学理论创新的重大机遇。花岗岩研究从岩石地球化学层面跃升到陆壳演化层面,是研究思维和理论创新的突破,是21世纪花岗岩研究的重大转折。     

Fission track and fault kinematics analyses for new insight into the Late Cenozoic tectonic regime changes in West-Central Sulawesi (Indonesia)

A 3-D density model for the Cretan and Libyan Seas and Crete was developed by gravity modelling constrained by five 2-D seismic lines. Velocity values of these cross-sections were used to obtain the initial densities using the Nafe–Drake and Birch empirical functions for the sediments, the crust and the upper mantle. The crust outside the Cretan Arc is 18 to 24 km thick, including 10 to 14 km thick sediments. The crust below central Crete at its thickest section, has values between 32 and 34 km, consisting of continental crust of the Aegean microplate, which is thickened by the subducted oceanic plate below the Cretan Arc. The oceanic lithosphere is decoupled from the continental along a NW–SE striking front between eastern Crete and the Island of Kythera south of Peloponnese. It plunges steeply below the southern Aegean Sea and is probably associated with the present volcanic activity of the southern Aegean Sea in agreement with published seismological observations of intermediate seismicity. Low density and velocity upper mantle below the Cretan Sea with ρ  3.25 × 10³ kg/m³ and V_p velocity of compressional waves around 7.7 km/s, which are also in agreement with observed high heat flow density values, point out at the mobilization of the upper mantle material here. Outside the Hellenic Arc the upper mantle density and velocity are ρ ≥ 3.32 × 10³ kg/m³ and V_p = 8.0 km/s, respectively. The crust below the Cretan Sea is thin continental of 15 to 20 km thickness, including 3 to 4 km of sediments. Thick accumulations of sediments, located to the SSW and SSE of Crete, are separated by a block of continental crust extended for more than 100 km south of Central Crete. These deep sedimentary basins are located on the oceanic crust backstopped by the continental crust of the Aegean microplate. The stretched continental margin of Africa, north of Cyrenaica, and the abruptly terminated continental Aegean microplate south of Crete are separated by oceanic lithosphere of only 60 to 80 km width at their closest proximity. To the east and west, the areas are floored by oceanic lithosphere, which rapidly widens towards the Herodotus Abyssal plain and the deep Ionian Basin of the central Mediterranean Sea. Crustal shortening between the continental margins of the Aegean microplate and Cyrenaica of North Africa influence the deformation of the sediments of the Mediterranean Ridge that has been divided in an internal and external zone. The continental margin of Cyrenaica extends for more than 80 km to the north of the African coast in form of a huge ramp, while that of the Aegean microplate is abruptly truncated by very steep fractures towards the Mediterranean Ridge. Changes in the deformation style of the sediments express differences of the tectonic processes that control them. That is, subduction to the northeast and crustal subsidence to the south of Crete. Strike-slip movement between Crete and Libya is required by seismological observations.     

Tectonics and types of riftogenic basins of the Scotia Sea,South Atlantic

Western, central, and eastern provinces are recognized in the Scotia Sea. They are distinguished by their bottom topography, geophysical characteristics, and crustal structure, which record their different origin and evolution. The western province is characterized by the oceanic crust that formed on the West Scotia Ridge, where active spreading may have ceased as a result of a collision between propagating rift and the structural barrier of the thick continental lithosphere of the Falkland Plateau. The central province is a series of blocks mainly composed of continental crust that subsided to various depths depending on the degree of extension in the course of rifting. These blocks are separated by local areas with oceanic crust formed due to the breakup of the continental crust and diffusive spreading. These areas are characterized by deep bottom and high values of Bouguer anomalies. The southern framework of the central province consists of subsided continental blocks and microcontinents divided by small spreading-type basins formed by lithospheric extension complicated by strike-slip faulting. The eastern province is composed of oceanic crust formed on the backarc spreading East Scotia Ridge. The results of density analysis, analog, and numerical simulations allowed us to explain some features of the structure and evolution of these provinces. The insight into tectonic structure of the provinces and their evolution allowed us to recognize several types of riftogenic basins differing in geodynamics, age, and geological and geophysical characteristics.     

Métabasites de la cordillère occidentale d'Équateur,témoins du soubassement océanique des Andes d'Équateur

The building-up of the Andean Range is linked to the subduction of the Pacific lithosphere beneath the South American plate. However, the formation of the Central Andes is marked by continental crustal shortening, whereas accretion and underplating of exotic oceanic terranes occurred in the northern Andes. The study of various magmatic and metamorphic rocks exhumed in the Western Cordillera of Ecuador by Miocene transpressive faults enables us to constrain the nature and thermal evolution of the crustal root of this part of Ecuador. These rocks are geochemically similar to oceanic plateau basalts. The thermobarometric peak conditions of a granulite and an amphibolite indicate temperatures of 800–850?°C and pressures less than 6–9 kbar (lack of garnet). The abnormally high geothermal gradient (≈40?°C?km^?1) is probably due to the activity of the magmatic arc, which developed on the accreted oceanic terranes after Late Eocene times, and may have provoked the re-mobilisation of deeply underplated oceanic material during the genesis of the Neogene to Recent arc. To cite this article: É. Beaudon et al., C. R. Geoscience 337 (2005).     

Late Quaternary glacio- and hydro-isostasy, on a layered earth

Isostatic response of the Earth to changes in Quaternary Times of ice and water loads is partly elastic, and partly involves viscous mantle flow. The relaxation spectrum of the Earth, critical for estimation of the mantle flow component, is estimated from published determinations of Fennoscandian and Laurentide rebound, and of the nontidal acceleration of the Earth's rotation. The spectrum is consistent with an asthenosphere viscosity around 10²¹P, and a viscosity around 10²³P below 400 km depth. Calculation of relaxation effects is done by convoluting the load history with the response function in spherical harmonics for global effects, and in rectangular or cylindrical transforms for smaller regional effects. Broad-scale deformation of the globe, resulting from the last deglaciation and sea level rise, is calculated to have involved an average depression of ocean basins of about 8 m, and mean upward movement of continents of about 16 m, relative to the center of the Earth, in the last 7000 yr. Deflection in the ocean margin “hinge zone” varies with continental shelf geometry and rigidity of the underlying lithosphere: predictions are made for different model cases. The computational methods is checked by predicting Fennoscandian and Laurentide postglacial warping, from published estimates of icecap histories, with good results. The depth variations of shorelines formed around 17,000 BP (e.g., North America, 90–130 m; Australia, 130–170 m), are largely explainable in terms of combined elastic and relaxation isostasy. Differences between Holocene eustatic records from oceanic islands (Micronesia, Bermuda), and continental coasts (eastern North America, Australia), are largely but not entirely explained in the same terms.     

A correlation between the distributions of pulsars and emission measures in the galaxy

A correlation has been detected between the volume density of pulsars and the density of interstellar ionized gas on scales of more than 500 pc in Galactic longitude and 200 pc in Galactic latitude. On smaller scales, the correlation is present only for pulsars with ages less than 60000 years, which are located predominantly near supernova remnants and H II regions. This all indicates that pulsars are born in regions with high concentrations of interstellar gas. The minimum emission measures observed in the directions toward pulsars are inversely proportional to the pulsar ages. It is concluded that the ionized gas in the vicinities of a number of pulsars was formed during supernova explosions, and corresponds to Strömgren zones. The ionization of the gas in these zones requires a radiation energy on the order of 10⁵⁰–10⁵¹ erg.