bluuebunny/crossref_metadata_2025 huggingface dataset:
The application of cause‐and‐effect analysis to mathematical models of geophysical phenomena: 1. Formulation and sensitivity analysis
Authors: Andronova Natalia G. , Schlesinger Michael E.
Published: February 2008

This study examines the utility of applying the cause‐and‐effect analysis (CEA) technique to the investigation of the structure and properties of mathematical models of geophysical phenomena. The principal rules of the CEA technique are presented, and their use is illustrated by application to four formulations of the Chapman photochemical cycle for ozone. The CEA shows not only the sensitivity of these models but also how their variables interact to produce this sensitivity. It is therefore concluded that the CEA technique is a potentially powerful tool for the intercomparison of a wide variety of mathematical models of geophysical phenomena.
Vertical distribution of non methane hydrocarbons in the remote marine boundary layer
Authors: Bonsang B. , Martin D. , Lambert G. , Kanakidou M. , Le Roulley J. C. , Sennequier G.
Published: February 2008

The marine production and vertical atmospheric distribution of light nonmethane hydrocarbons (NMHC) from C2 to C6 in the marine boundary layer was studied at the Hao atoll, in the intertropical South Pacific. NMHC vertical profiles were performed up to 1600 m altitude by using balloon and remote controlled aircraft‐borne devices simultaneously with surface air and seawater samplings. Seawater was found to be supersaturated in NMHC. Despite the concentration variations of the seawater its relative composition is well reproducible, within a factor of 2. The average NMHC atmospheric composition at sea level is similar to that of seawater. However, the results obtained display a very large short time variability of the NMHC atmospheric concentrations, which seems to result mainly from variations in the marine emission rates and/or advective processes of transport. It was initially expected that the proportions of short‐lived species should rapidly decrease in altitude, because of their chemical decay, mainly by oxidation by OH radicals. However, it appeared that the proportions of the different NMHC measured remained relatively constant up to the maximum altitude sampled during the campaign, i.e., about 1600 m. This suggests that transport processes in the atmosphere were always very rapid, relative to the chemical processes, even for short‐lived NMHC. However, for reactive species, simple calculations based on the hypothesis of a steady state in thin atmospheric layers show that the photochemistry involved is consistent with usual OH concentrations varying from 1.6×107 rad cm−3 at noon to 4×104 rad cm−3 at sunset.
A high‐resolution Late Quaternary upwelling record from the anoxic Cariaco Basin, Venezuela
Authors: Peterson L. C. , Overpeck J. T. , Kipp N. G. , Imbrie J.
Published: February 2008

Results are presented of a high‐resolution study of the planktonic foraminiferal faunas from two piston cores recovered from the Cariaco Basin in the southern Caribbean Sea. The Cariaco Basin is a small anoxic marine basin on the northern continental margin of Venezuela in an area today characterized by both seasonal trade wind‐induced upwelling and pronounced dry and wet seasons. Our data indicate that large changes in the intensity of upwelling, and hence trade wind strength, occurred in this region during the last glacial‐interglacial transition and throughout the Holocene. During the last glacial lowstand of sea level, the Cariaco Basin was effectively isolated from the open Caribbean along its northern margin by the then largely emergent Tortuga Bank. Oxic conditions existed in the deep Cariaco Basin at this time, and surface productivity was low. About 12,600 years ago, the abrupt initiation of strong upwelling over the basin and the onset of permanent anoxia in the deep waters are coincident with the rapid rise of sea level that accompanied the peak interval of meltwater discharge from the Laurentide Ice Sheet into the Gulf of Mexico. Strong upwelling between 12,600 and about 10,000 years ago may be related to intensified trade winds resulting, in part, from cooler sea surface temperatures in the Caribbean and Gulf of Mexico. After about 10,000 years ago, upwelling intensity was reduced, though highly variable. A preliminary frequency domain analysis of the Holocene portion of the Cariaco Basin time series suggests that solar forcing may explain a significant component of the century‐scale variability observed in the record of upwelling and trade wind strength.
Earthquakes and sea level: Space and terrestrial metrology on a changing planet
Authors: Bilham Roger
Published: February 2008

The complacency with which Man inhabits continent‐ocean margins or plate boundaries is based on the assumption that sea level rise and periodic seismicity are acceptable risks. The forecast of future sea level or future seismicity is essential for informed assessment of these risks. The historical data from which forecasts may be derived are in each case of limited antiquity and uneven spatial distribution. Developments in space geodesy and crustal deformation metrology in the past two decades offer the means to acquire a homogeneous global data set for monitoring relative vertical and horizontal motions of the Earth's surface to within several millimeters. These new tools are reviewed in terms of their application to forecasting trends in sea level rise and forecasting damaging earthquakes.
Underplated units in an accretionary complex: Melange of the Shimanto Belt of eastern Shikoku, southwest Japan
Authors: Kimura Gaku , Mukai Atsuhiko
Published: February 2008

Imbricated thrust stacks composed of melange and oceanic slabs occur in the Shimanto Belt, eastern Shikoku, SW Japan. The melanges are divided into two types: Melange I consists of lenticular sandstone blocks surrounded by scaly shale matrix, and Melange II is composed of blocks of oceanic material, such as basalts, cherts and red shale, in a scaly matrix of shale. Melange II is observed only near the boundaries between Melange I and oceanic slabs. The fabric of Melange I indicates progressive deformation during underthrusting of originally coherent trench‐fill turbidites. Layer‐parallel extension characterizes early deformation and is divided into two stages: an early stage formed during normal faulting, and a subseguent stage formed perpendicular to the early extension. The early extension is interpreted in terms of Riedel shear associated with layer‐parallel shearing and tectonically induced loading normal to the layering. The second extension is due to sticking‐thrust movement. Late deformation of Melange I is represented by folding in association with layer‐parallel shearing. This appears to be related to compression just before or during underplating of Melange I beneath the accretionary prism. Layer‐parallel shear extends downward due to strain hardening of sheared sediments and then reaches to the base of the sediments. Subsequently, the shear zone penetrates pelagic sediments and, finally, oceanic basement. At this time, Melange II is formed by the shearing. An imbricated stack of Melanges I, II and oceanic slabs forms duplexes during the underplating process. The weak metamorphism of the melange complex in the study area suggests that underplating occurs at shallow depths where trench fill is thin.
Detachment models for the formation of passive continental margins
Authors: Lister G. S. , Etheridge M. A. , Symonds P. A.
Published: February 2008

The inherent asymmetry of extension by detachment leads to contrasting and conjugate classes of passive margins. Upper‐plate margins comprise crust above a deeper detachment. Lower‐plate margins comprise the footwall of the detachment, overlain by faulted upper plate remnants. Such margins have distinctive architectures, structural styles, uplift‐subsidence paths and thermal histories. The wide range in structural styles on passive margins is predicted by five models which incorporate detachment faults linked to flat ductile shear zones, and ductile stretching of the thermal lithosphere below the shear zones. These models provide explanations for enigmatic structural and morphological features of passive margins such as marginal plateaux, outer highs, unstructured synrift sag basins, and perched rift basins. Numerical modelling of isostatic uplift‐subsidence histories shows that different patterns of uplift‐subsidence behaviour can be explained by variations in detachment geometry and change in the amount of lithospheric stretching. Voluminous igneous underplating is predicted if anomalously hot asthenosphere is uplifted. The arrival of such mantle derived melts may cause significant additional uplift. Upper‐plate margins undergo thermally induced uplift, with permanent uplift due to igneous underplating. This uplift may be the origin of passive margin mountains in the adjacent hinterlands. Marginal plateaux are emergent or very shallowly submerged throughout the extension history, with postrift subsidence to intermediate water depths. The lithosphere is extended below a midcrustal detachment, but with little extension of the upper‐plate. The pattern of subsidence on an Atlantic margin requires an extended upper plate superimposed on progressively more stretched subdetachment lithosphere. Conjugate margins are described from the Tasman Sea, the Atlantic Ocean and the Great Southern Ocean, illustrating both the principle of complementary asymmetry and the different patterns of uplift or subsidence on opposing passive margins.
Regional differences in PB isotopic compositions of feldspars in plutonic rocks of the northern Appalachian Mountains, U.S.A., and Canada: A geochemical method of terrane correlation
Authors: Ayuso Robert A. , Bevier Mary Lou
Published: February 2008

Feldspar Pb isotopic compositions from Paleozoic tonalitic to leucogranitic Caledonian plutons from the northern Appalachian Mountains of the U.S.A. and Canada range from nonradiogenic to radiogenic relative to the evolution curve of Stacey and Kramers (1975). Pb isotopic values in the feldspars are generally independent of modal and major and trace element contents of the plutons. Plutons with the least radiogenic Pb isotopic signatures (Northern group) have intruded allochthonous rocks closest to the North American craton, and plutons with the most radiogenic Pb (Southern group) have intruded Avalonian basement. Feldspars from plutons in the Central group have intermediate Pb isotopic compositions between the Northern and Southern groups and do not define an isotopically unique group. The predominant source of the felsic magmas was the continental lithosphere as indicated by the general Pb isotopic similarity of the plutonic feldspars with either Grenville or Chain Lakes basement in the case of the Northern group and with Avalonian basement rocks in the case of the Southern group. The source region for plutons in the Central group may have contained a mixture of Grenvillian and Avalonian components. Plutons in the northern Appalachians are as a group more evolved in their Pb isotopic compositions relative to Caledonian plutons in the British Isles.
Budget of crustal shortening and subduction of continental crust in the Alps
Authors: Ménard Gilles , Molnar Peter , Platt John P.
Published: February 2008

The stratigraphy, surface structure, and deep structure of the Alps permit, but do not require, that a significant amount of European continental crust was subducted into the mantle beneath Adria, the fragment of continental lithosphere now comprising much of Italy and the Adriatic Sea floor. The present thin crust in much of Europe suggests that the crust that was stretched in Mesozoic time to form the southern margin of Europe was initially thinner than normal. The stratigraphic history of sediment deposited on that margin before its collision with Adria suggests that the crustal basement on which much of this material was deposited had become particularly thin during the formation of the margin. Most of the crustal basement underlying the European margin and involved in the collision and the formation of the chain probably was thinner than 20 km, and much of it may have been thinner than 10 km. Profiles of the present deep structure of the Alps yield a range of possible values for the the average cross‐sectional area of crust involved in the collision that permit as much as 280 km of crustal shortening, if this crust was as thin as implied by the stratigraphy. Thus, although subduction of hundreds of kilometers of continental crust into the mantle beneath Adria could have occurred, the budget of crustal material involved in the formation of the Alps does not require such crustal subduction.
The stationary Cretaceous paleomagnetic pole of Sichuan (South China Block)
Authors: Enkin R. J. , Courtillot V. , Xing L. , Zhang Z. , Zhuang Z. , Zhang J.
Published: February 2008

Upper Jurassic to lower Tertiary sites have been sampled from three localities, separated by up to 150 km, in the Sichuan Basin (∼30°N, 103°E) of the South China Block. Each locality has at least one stability test, but none alone gives a fully reliable result. When taken together, however, identical directions are found with a global average D=12.7°, I=34.2°, k=42.9°, α95=3.3° (N=44 sites) and corresponding pole 73.9°N, 234.4°E, dp=2.2°, dm=3.8°, paleolatitude λ=18.8°. There is no significant apparent polar wander (APW) with age, which is consistent with an acquisition of magnetization during the period of the stable tip of the Eurasian APW loop (∼130–70 Ma), as defined with poles from other continents transferred onto Eurasia. This age range is compatible with the available paleontological and magnetostratigraphic age constraints but is shorter than that suggested by the assigned formation ages. The paleolatitude of Sichuan is significantly lower (8.0°±4.0° at 90 Ma) than that predicted by the reference APW path, either because of northward shortening during the Tertiary or because of errors in the APW path. Cretaceous poles from other Chinese blocks are consistent with the Sichuan pole, but there is evidence that these blocks have suffered local rotations up to 10° during the Tertiary, probably as a result of the India‐Eurasia collision.
Metamorphic pressure‐temperature conditions of Indian Plate rocks south of the main mantle thrust, lower swat, Pakistan
Authors: DiPietro Joseph A.
Published: February 2008

The Lower Swat rock sequence, in northern Pakistan, is composed of greenschist and amphibolite facies Indian plate rocks that crop out in a dome directly south of the Main Mantle thrust zone and Kohistan arc terrane. The metamorphism is Eocene to Oligocene in age and records the collision of the Indian plate with the Kohistan arc. This paper presents mineral assemblage, mineral composition and garnet zoning data on the Lower Swat rock sequence in order to estimate the pressure‐temperature conditions of metamorphism and to infer a possible pressure‐temperature‐time path. The stratigraphic sequence consists of Precambrian to Cambrian(?) Manglaur formation unconformably overlain by late Paleozoic to early Mesozoic Alpurai group. The Alpurai group is further subdivided into the Marghazar, Kashala, Saidu and Nikanai Ghar formations. The Manglaur formation, in the core of the dome, is at kyanite grade. Metamorphic grade decreases in the overlying Alpurai group where a garnet “isograd” is mapped in calcareous schist of the Kashala formation. Mineral composition geothermometers and geobarometers indicate final metamorphic equilibrium conditions of about 600°–700°C and 9–11 kbar in the Manglaur and Marghazar formations. These conditions are associated with a phase of static recrystallization which postdates the main phases of deformation. Correlation of the structural‐tectonic history with the pressure‐temperature estimates, and with the garnet zoning analysis, suggests that in the Eocene the Lower Swat rock sequence was subducted to a depth of 35 to 45 km beneath the MMT suture melange. Subduction was followed immediately by exhumation. The initiation of exhumation is believed to have been triggered by a change from subduction to strike slip motion in the MMT, thereby allowing the relatively buoyant Lower Swat crust to rise. The entire metamorphic‐deformational cycle lasted from 7 to 16 m.y., ending in the late Eocene about 38 Ma when the rocks cooled through the argon blocking temperature in hornblende (≈ 550°C).
Introduction to the EXOS‐D (Akebono) Project
Authors: Tsuruda K. , Oya H.
Published: February 2008

The EXOS‐D satellite is the fourth of the EXOS (exosphere) series of satellites launched by the Institute of Space and Astronautical Science (ISAS), Japan. After the successful injection of the satellite into the designed orbit at 23:30:00 UT on February 21, 1989 from the Kagoshirna Space Center (KSC), the EXOS‐D satellite was given a Japanese name 'Akebono' which means 'the dawn'. The planning of the EXOS‐D project began shortly after the launch of the first two EXOS series satellites, EXOS‐A (Kyoko) and EXOS‐B (Jikiken).
Milankovitch Cycles in electrical resistivity logs from the Toa Baja Scientific Drillhole, Puerto Rico
Authors: Maltezou Fotini , Anderson Roger N.
Published: February 2008

Milankovitch cycles in the upper part of the Toa Baja drillhole, detected by geophysical logs, are used to estimate sedimentation rates, and to localize the depths at which sedimentation rate changes occur. The log‐derived age information is then combined with reference dates from palaeontological data and the “Vail” global sea‐level curve to build a detailed record of the chronology of the upper stratigraphic sequence in the well.
High resolution 40AR/39AR chronostratigraphy of the Late Cretaceous El Gallo Formation, Baja California del Norte, Mexico
Authors: Renne Paul R. , Fulford Madeleine M. , Busby‐Spera Cathy
Published: February 2008

Laser probe 40Ar/39Ar analyses of individual sanidine grains from four tuffs in the alluvial Late Cretaceous (Campanian) El Gallo Formation yield statistically distinct mean dates ranging from 74.87±0.05 Ma to 73.59±0.09 Ma. The exceptional precision of these dates permits calculation of statistically significant sediment accumulation rates that are much higher than passive sediment loading would cause, implying rapid tectonically induced subsidence. The dates bracket tightly the age of important dinosaur and mammalian faunas previously reported from the El Gallo Formation. The dates support an age less than 73 Ma for the Campanian/Maastrichtian stage boundary, younger than indicated by several currently used time scales. Further application of the single grain 40Ar/39Ar technique may be expected to greatly benefit stratigraphic studies of Mesozoic sedimentary basins and contribute to calibration of biostratigraphic and magnetostratigraphic time scales.
Column amounts of trace gases derived from ground‐based measurements with MIPAS during CHEOPS III
Authors: Adrian G. P. , Blumenstock T. , Fischer H. , Gerhardt L. , Gulde T. , Oelhaf H. , Thomas P. , Trieschmann O.
Published: February 2008

Infrared solar absorption spectra of the atmosphere were taken during the CHEOPS III campaign in Esrange, Sweden in January and February 1990. The MIPAS (Michelson Interferometer for Passive Atmospheric Sounding) instrument used has an unapodized spectral resolution of 0.015 cm−1. Spectra were analysed by means of the SCAIS (Simulation Code for Atmospheric Infrared Spectra) level‐by‐level and line‐by‐line algorithm for radiative transfer through the atmosphere. The time series of the retrieved zenith column amounts of O3, H2O, CH4, N2O, HNO3, NO2, HCl, and HF are presented. The stratospheric HCl/HF ratio of 1.3 at the beginning of February, 1990 points towards the conversion of a considerable portion of gaseous HCl to other chemical or physical forms in the stratosphere in this period. A significant change in the HCl column amount between February 4, 1990 and February 8, 1990 was found; this can be correlated with a stratospheric warming between these two dates. From January 27, 1990 to February 11, 1990 the derived upper limits of NO2 abundances were low (≤ 1.2 × 1015 molecules/cm2), whereas the column amounts of HNO3 were very high with 2.9 × 1016 molecules/cm2.
An anomalous radon decrease in groundwater prior to an M6.0 earthquake: A possible precursor?
Authors: Wakita Hiroshi , Igarashi George , Notsu Kenji
Published: February 2008

A. significant decrease in the radon concentration of artesian groundwater was observed at a well‐established observation site in Northeast Japan about two days before an M6.0 earthquake occurred about 200 km from the site. On the basis of a concurrent in situ (−126m) temperature drop of the groundwater, we infer that precursory changes in regional stress were locally amplified near this site and resulted in the temporary mixing of cooler, radon‐poor groundwater into the normal artesian flow.
Hydrogeology of thrust faults and crystalline thrust sheets: Results of combined field and modeling studies
Authors: Forster Craig B. , Evans James P.
Published: February 2008

Field, laboratory, and modeling studies of faulted rock yield insight into the hydraulic character of thrust faults. Late‐stage faults comprise foliated and subparallel faults, with clay‐rich gouge and fracture zones, that yield interpenetrating layers of low‐permeability gouge and higher‐permeability damage zones. Laboratory testing suggests a permeability contrast of two orders of magnitude between gouge and damage zones. Layers of differing permeability lead to overall permeability anisotropy with maximum permeability within the plane of the fault and minimum permeability perpendicular to the fault plane. Numerical modeling of regional‐scale fluid flow and heat transport illustrates the impact of fault zone hydrogeology on fluid flux, fluid pore pressure, and temperature in the vicinity of a crystalline thrust sheet.
The transition from hydrostatic to greater than hydrostatic fluid pressure in presently active continental hydrothermal systems in crystalline rock
Authors: Foumier Robert O.
Published: February 2008

Fluid flow at hydrostatic pressure (Ph) is relatively common through fractures in silicic and in mafic crystalline rocks where temperatures are less than about 350–370°C. In contrast, pore‐fluid pressure (Pf) > Ph has been encountered at the bottom of 3 geothermal exploration wells that attained temperatures >370°C (at Larderello, Italy, at Nesjavellir, Iceland, and at The Geysers, California). Chemical sealing by deposition of minerals in veins appears to have allowed the development of the high Pf encountered in the above wells. The upper limit for the magnitude of Pf that can be attained is controlled by either the onset of shear fracturing (where differential stress is relatively high) that reopens clogged veins, or the hydraulic opening of new or old fractures (at relatively low values of differential stress). The brittle‐plastic transition for silicic rocks can occur at temperatures as high as 370–400°C in tectonically active regions. In regions where high‐temperature geothermal systems develop and persist, it appears that either strain rates commonly are in the range 10−12 to 10−13, or that silicic rocks in the shallow crust generally behave rheologically more like wet quartz diorite than wet Westerly granite.
Thermal constraints on basin‐scale flow systems
Authors: Nunn Jeffrey A. , Deming David
Published: February 2008

An important constraint on basin‐wide flow systems is the thermal regime. Studies of high temperatures above fault zones which penetrate geopressured sediments and heat flow in orogenic zones have been used to document both pathways and velocities of pore fluid movement. Similarly, the high temperature (100–150°C) at shallow depths (<1.5km) inferred from studies of fluid inclusions associated with Late Paleozoic Mississippi Valley‐type (MVT) lead‐zinc deposits places a very restrictive constraint on their formation by regional fluid migration. We have used numerical models of fluid and heat transport to evaluate the viability of sediment compaction by overthrusting and topographically driven recharge as driving mechanisms for regional fluid migration. Sediment compaction by overthrusting leads to Darcy velocities on the order of cm/yr, too low to have significant effects on the temperature field unless flow is channelized. Topographically driven recharge can lead to fluid velocities on the order of m/yr. However, it is difficult to achieve the extremely high temperatures (100–150 °C) at shallow depths (<1.5km) associated with MVT deposits unless heat flow values greater than 100 mW/m2 are used. Thus, there are fundamental limitations on the ability of either mechanism to continuously transport large amounts of heat for millions of years on a basin‐wide scale. Temporal or spatial focusing of flow is likely to have played a critical role in the genesis of phenomena such as MVT deposits.
Response of the middle atmosphere to the solar proton events of August–December, 1989
Authors: Reid G. C. , Solomon S. , Garcia R. R.
Published: February 2008

Intense solar activity during the period August–December 1989 gave rise to several major energetic‐particle events, which were accompanied by greatly enhanced ionization rates and NOy production in the polar regions of both hemispheres. A two‐dimensional model of the chemistry and dynamics of the middle atmosphere has been used to calculate the production and subsequent fate of the NOy and its effect on ozone concentrations and temperatures. In the sunlit southern polar cap, NO increases as large as a factor of 20 are estimated near 60 km altitude, with column density enhancements of 55%. Corresponding peak ozone depletions of about 20% are calculated near 40km in late October 1989, with predicted temperature decreases of about 3–3.5K. Effects in the northern polar regions are considerably smaller, due to the lack of sunlight during the peak phase of the events.
Fault growth model and the universal fault length distribution
Authors: Sornette Didier , Davy Philippe
Published: February 2008

We propose and solve a simple fault growth model describing the powerlaw dependence of the fault length distribution observed both in nature and in laboratory models of the lithosphere. Starting from an arbitrary initial fault length distribution and assuming that the rate of growth of a fault is proportional to a power of its size, we show that the fault length distribution evolves towards a universal powerlaw curve. Comparison between this theory and experimental results is encouraging.
40AR/39Ar ages of six Apollo 15 impact melt rocks by laser step heating
Authors: Dalrymple G. Brent , Ryder Graham
Published: February 2008

We have obtained 15 high resolution (21–51 step) 40Ar/39 age spectra on six Apollo 15 impact melt rocks of different compositions using a continuous laser system on submilligram subsamples and on single crystal plagioclase clasts. Four of the six samples gave reproducible age spectra with well‐defined intermediate temperature plateaus over 48% or more of the 39Ar released; the plateaus are interpreted as crystallization ages. Samples 15304,7,69, 15294,6,21, and 15314,26,156 gave virtually identical plateau ages whose weighted mean is 3,870±6 Ma. These three melt rocks differ in composition and likely formed in three separate impact events. Sample 15356,9 gave replicate plateau ages that average 3,836±12 Ma and date a fourth and younger impact event. The age spectra for samples 15308,9 and 15414,3,36 increase with increasing increment temperature and may have been formed in or affected by impacts at about 2,700 Ma and 3,870 Ma, respectively. So far there continues to be no convincing evidence in the lunar record for impact melts older than about 3.9 Ga.
Spectral comparison of continuous Global Positioning System and strainmeter measurements of crustal deformation
Authors: Tralli David M.
Published: February 2008

Temporal power spectral density models of noise in continuous crustal deformation measurements obtained with the Global Positioning System (GPS) and high‐quality strainmeters are compared. The crossover frequency at which GPS measurement noise is less than that of strainmeters is determined. Assuming GPS precision of 0.1 to 1 cm in horizontal components for baselines up to 100 km in length, local deformation monitoring with GPS may be preferable to strainmeters for observations of short‐term deformation in under 6 months of continuous (at least daily) measurements. Short‐period tropospheric path delays and multipath effects, which may obscure GPS‐determined strain signals in local network measurements, also are discussed.
The Mid‐Cretaceous Super Plume, carbon dioxide, and global warming
Authors: Caldeira Ken , Rampino Michael R.
Published: February 2008

Carbon‐dioxide releases associated with a mid‐Cretaceous super plume and the emplacement of the Ontong‐Java Plateau have been suggested as a principal cause of the mid‐Cretaceous global warming. We developed a carbonate‐silicate cycle model to quantify the possible climatic effects of these CO2 releases, utilizing four different formulations for the rate of silicate‐rock weathering as a function of atmospheric CO2. We find that CO2 emissions resulting from super‐plume tectonics could have produced atmospheric CO2 levels from 3.7 to 14.7 times the modern pre‐industrial value of 285 ppm. Based on the temperature sensitivity to CO2 increases used in the weathering‐rate formulations, this would cause a global warming of from 2.8 to 7.7°C over today's global mean temperature. Altered continental positions and higher sea level may have been contributed about 4.8°C to mid‐Cretaceous warming. Thus, the combined effects of paleogeographic changes and super‐plume related CO2 emissions could be in the range of 7.6 to 12.5°C, within the 6 to 14°C range previously estimated for mid‐Cretaceous warming. CO2 releases from oceanic plateaus alone are unlikely to have been directly responsible for more than 20% of the mid‐Cretaceous increase in atmospheric CO2.
Temporal variations in the hydroxyl nightglow observed during ALOHA‐90
Authors: Turnbull D. N. , Lowe R. P.
Published: February 2008

Ground‐based observations of the hydroxyl nightglow were made with a Fourier transform spectrometer from Haleakala, Maui during the ALOHA‐90 campaign. Vibrational level populations and rotational temperatures were obtained with a temporal resolution of 1 minute. Temperature precision was ±1 K. Highly correlated in‐phase variations in temperature and population were seen on all nights. However, a long term trend in the vibrational population was not reflected in the temperature.
PC 3,4 magnetic pulsations observed simultaneously in the magnetosphere and at multiple ground stations
Authors: Odera T. J. , Van Swol D. , Russell C. T. , Green C. A.
Published: February 2008

Periods of magnetic conjugacy between ISEE and the magnetometer array of the Institute for Geological Sciences have been examined to search for the simultaneous occurrence of Pc 3,4 magnetic pulsations. When compressional waves are seen in space, waves are also observed on the ground at the same frequency and with similar waveforms. The wave amplitude on the ground at midlatitudes is similar to that in space at ISEE but at high latitudes the amplitudes are larger than in space. The one occurrence of a purely transverse signal at ISEE was not observed on the ground. These results confirm that Pc 3,4. wave energy is most readily transported through the magnetosphere by compressional fluctuations.
Distribution anisotropy: The cause of AMS in igneous rocks?
Authors: Hargraves R. B. , Johnson D. , Chan C. Y.
Published: February 2008

Understanding of AMS in pristine basic igneous rocks in terms of flow‐orientation of ellipsoidal magnetite grains is thwarted by the fact that these grains (1) typically are irregularly equant or skeletal rather than distinctly ellipsoidal, and (2) usually crystallize interstitially and late, after magma flow has ceased. However, the distribution of such grains will be relatively anisotropic if they grew in residual liquid volumes within a preferredly‐oriented (by flow) silicate “template”. This constraint may impose a slight preferred shape orientation to the irregular magnetite grains during their growth, but in addition, we suggest it is the anisotropic magnetic interaction between the grains which is the basic cause of AMS. Experiments involving the casting of magnetite‐epoxy mixtures in various foliated or lineated glass templates have yielded samples with the expected AMS symmetry, i.e. K3 perpendicular to glass plates or K1 parallel to glass rods. Slicing of near isotropic synthetic blank‐ and natural rock‐cores and interleaving with glass slides showed a progressive increase in anisotropy of the blank from ∼0.4% to 2%, and the natural rock from ∼0.9% to ∼2.9%. In both the K3 axis migrates to be perpendicular to the glass slides.
Source processes for the alkali metals in the atmosphere of Mercury
Authors: Shemansky D. E. , Morgan T. H.
Published: February 2008

A large (fivefold) increase in Mercury's potassium(K) column abundance on 14 October 1987, has been reported by Sprague et al.[199O](SKH), who attributed the enhancement to diffusion through the surface in the Caloris Basin, from depths of order 10 km. The postulated source rate is much larger than any previously estimated diffusion rate, and if true certainly affects consideration of the origin of other atmospheric species. However, Killen et al.[1991] have pointed out that the claim is not supported by the published observations of K or sodium(Na) as a whole. Sprague et al.[1991] have responded by further hypothesizing the existence of several other sources of gas diffusing out of the regolith, all of which are time variable. In any case the SKH data indicate large variations in abundance, and it is important to understand the cause. With this issue in mind we have examined the available abundance estimates for correlation with possible controlling physical parameters. We have found a significant correlation between the average zenith K column abundance and indices of solar activity, although we are left with the intrinsic uncertainty of a small data set.
The thickness of the magnetosheath: Constraints on the polytropic index
Authors: Farris M. H. , Petrinec S. M. , Russell C. T.
Published: February 2008

A statistical analysis of 351 independent bow shock crossings and 233 independent magnetopause crossings by the ISEE‐I spacecraft from 1977 to 1980 was performed to determine the average positions and shapes of the bow shock and magnetopause. The standoff distance between the magnetopause and the bow shock depends on the compressibility of the plasma which in the ‘polytropic’ approximation is related to the ratio of specific heats, γ. Standoff distances for the bow shock and magnetopause were found to be 13.7 RE (±0.2 RE) and 10.3 RE (±0.3 RE) respectively. These distances are smaller than those observed during earlier epochs. The observed thickness of the magnetosheath is that expected for the compression of a gas whose polytropic index, γ, is 1.76±0.15. This value, representative of the entire magnetosheath, is consistent with the value of 1.67 deduced from the behavior of the plasma across individual shock transitions. A value of 1.67 is expected for an adiabatic process in a collisional, monatomic gas with three degrees of freedom with lower values for non‐adiabatic processes and higher values for anisotropic heating at the shock. The observed value of 1.76 indicates that heat flux does not much affect the position of the shock while the downstream anisotropy may have a small effect.
Beam‐Stack Imaging using a small aperture array
Authors: Hedlin Michael A. H. , Minster J. Bernard , Orcutt John A.
Published: February 2008

We seek to gain a fuller understanding of seismic coda generation in the continental crust, by identifying secondary (scattering) sources illuminated by a distant primary source. We have developed a migration technique to scan seismic coda recorded by a small‐aperture seismic array for phases generated locally by scattering from large heterogeneities, or topographic undulations. We use a widely distributed suite of seismic events to illuminate the local crustal volume from different directions and produce an image of the local crust. Stable apparent secondary seismic sources are observed, and interpreted as scatterers excited by the primary events.
Genetic algorithms: An evolution from Monte Carlo Methods for strongly non‐linear geophysical optimization problems
Authors: Gallagher Kerry , Sambridge Malcolm , Drijkoningen Guy
Published: February 2008

In providing a method for solving non‐linear optimization problems Monte Carlo techniques avoid the need for linearization but, in practice, are often prohibitive because of the large number of models that must be considered. A new class of methods known as Genetic Algorithms have recently been devised in the field of Artificial Intelligence. We outline the basic concept of genetic algorithms and discuss three examples. We show that, in locating an optimal model, the new technique is far superior in performance to Monte Carlo techniques in all cases considered. However, Monte Carlo integration is still regarded as an effective method for the subsequent model appraisal.
Lunar ferroan anorthosites and mare basalt sources: The mixed connection
Authors: Ryder Graham
Published: February 2008

Global overturn of a hot, gravitationally unstable lunar mantle immediately following the solidification of a magma ocean [and essentially complete by 4.4 Ga] explains several characteristics of lunar petrology. Lunar mare basalt sources are inferred to be depleted in europium and alumina. These depletions are consensually attributed to complementary plagioclase floating from a magma ocean. However, the connection cannot be so simple and direct: in contrast to the mare basalt source parent magma, the ferroan anorthosite parent magma was more evolved by virtue of its lower Mg/Fe ratio and Ni abundances, although less evolved in its poverty of clinopyroxene constituents, flat rare earth pattern, and lower incompatible element abundances. The europium anomaly in mare sources is inferred to be present at 400 km depth, too deep to have been directly influenced by plagioclase crystallization. Massive overturning of the post‐magma ocean mantle would have carried down clinopyroxene, ilmenite, and phases containing fractionated rare earths, europium anomalies, and some heat‐producing radionuclides. These phases contributed to deep mare basalt sources. Upward‐moving phases would have been magnesian mafic minerals; their immediate melting on pressure release contributed the magnesian suite of plutonic norites and troctolites that post‐date the anorthosites in the highlands crust.
Great magnetic storms
Authors: Tsurutani Bruce T. , Gonzalez Walter D. , Tang Frances , Lee Yen Te
Published: February 2008

The five largest magnetic storms that occurred between 1971 to 1986 are studied to determine their solar and interplanetary causes. All of the events are found to be associated with high speed solar wind streams led by collisionless shocks. The high speed streams are clearly related to identifiable solar flares. It is found that: 1) it is the extreme values of the southward interplanetary magnetic fields rather than solar wind speeds that are the primary causes of great magnetic storms, 2) shocked and draped sheath fields preceding the driver gas (magnetic cloud) are at least as effective in causing the onset of great magnetic storms (3 of 5 events) as the strong fields within the driver gas itself, and 3) precursor southward fields ahead of the high speed streams allow the shock compression mechanism (item 2) to be particularly geoeffective.
Spectral analysis and mapping of palagonite tuffs of Pavant Butte, Millard County, Utah
Authors: Farrand William H. , Singer Robert B.
Published: February 2008

The Pavant Butte tuff cone in Millard County, Utah was erupted into the waters of glacial Lake Bonneville. The basaltic tephras that compose Pavant Butte are in various states of alteration; from nearly pristine to fully palagonitized. Their level of alteration is detectable by visible and near infrared reflectance spectrometry. Unaltered sideromelane has a very low reflectance and is characterized by Fe2+crystal‐field bands near 1 and 2 μm. With hydration the reflectance of the tephra increases; water and hydroxyl absorption bands at 1.4 and 1.9 μm also become prominent. The most highly altered tephras are palagonite tuffs which are characterized by a relatively high reflectance, deep H2O and OH absorptions, and a steep Fe3+absorption edge in the visible. Such altered basaltic tephras may also be good models for altered soils and dust on Mars, for which remote sensing is the primary source of data. The geologic origin of these near ubiquitous martian surface materials is still undetermined; hydrovolcanism is one possible source. The palagonite tuff deposits at Pavant Butte were remotely observed by two airborne imaging spectrometers, and the data used for compositional mapping. The palagonite tuff was used as an endmember in a linear spectral mixing model analysis. This method was also used to calibrate the remotely sensed data to reflectance. Reflectance spectra from the airborne systems validated the laboratory sample spectra and indicated the presence of both di‐ and trioctahedral clay minerals within the palagonite tuff.
On the correlation between mantle plume flux and the frequency of reversals of the geomagnetic field
Authors: Loper David E.
Published: February 2008

The validity of concept that impulsive changes in the volume flux of material rising from the base of the mantle via plumes can cause rapid changes in the heat flux from the core and in the behavior of the geomagnetic field is investigated. It is found that the natural time scale of variations in the heat flux from the core is about 109 years, a time scale far longer than that associated with the long‐term changes in the frequency of reversals of the magnetic field; following an impulsive change in plume flux, the heat flux from the core changes on a time scale of several billion years, i.e., on a time scale of the age of the earth. A harmonic variation in the volume flux up plumes results in a similar harmonic variation in the heat flux from the core, but with a phase lag of π/4 and a greatly diminished amplitude. The lack of correlation between mantle plume flux and core heat flux is due to the long natural time scale of the lower mantle and the large thermal inertia of the D″ layer (compared with the heat flux from the core). This calls into question the currently fashionable idea of a direct and immediate correlation between plume volume flux and heat flux from the core.
A two‐layer lithospheric compressional model for the tertiary uplift of the southern United Kingdom
Authors: Hillis Richard R.
Published: February 2008

Reflection seismic records show that many of the Mesozoic sedimentary basins of the southern United Kingdom were compressed and uplifted (inverted) during the Late Cretaceous‐Tertiary. Recent quantitative studies based on apatite fission track analysis and Chalk porosity data show that uplift and erosion, although concentrated in the inverted basins, was regional, and not limited to the recognized areas of crustal shortening (inversion). A two‐layer, or heterogeneous model of lithospheric compression, similar to two‐layer models of lithospheric extension, may account for this pattern of uplift. Upper‐lithospheric shortening is accommodated by reverse movement on major, reactivated, extensional detachments, causing inversion of pre‐existing basins. Pure shear shortening of the lower lithosphere is decoupled, and may be laterally displaced, from that in the upper lithosphere. Lower lithospheric shortening and thickening displaced from that in the upper lithosphere causes initial subsidence due to the submersion of cold, dense lithosphere into the surrounding asthenosphere. Subsequent thermal re‐equilibration of the lower lithosphere may have generated the uplift without attendant crustal shortening witnessed by apatite fission track and Chalk porosity data.
Mantle phase transitions and layered chaotic convection
Authors: Peltier W. R. , Solheim L. P.
Published: February 2008

We report preliminary results from a sequence of very high resolution simulations of the mantle convection process based upon an axisymmetric anelastically compressible spherical model with both Olivine‐Spinel and Spinel‐post Spinel phase transitions. Our analyses strongly suggest that at Earth‐like Rayleigh numbers near 107 the circulation may be quite strongly layered, although a very long timescale transient exists that is characterized by brief excursions into the whole mantle state. We suggest the use of a new diagnostic tool that may be employed to determine whether or not the layered state is characteristic of the present day earth.
Paleomagnetic evidence for a Pleistocene counterclockwise rotation of the Sant'Arcangelo Basin, southern Italy
Authors: Sagnotti Leonardo
Published: February 2008

New paleomagnetic results from 182 cores sampled at 15 sites in Pliocene and Pleistocene clayey units in the Sant'Arcangelo basin (southern Italy) and its surroundings are presented. They indicate that this area underwent a counterclockwise rotation of 22° after the deposition of the Lower Pleistocene clays.
A proposed super‐thick sedimentary basin, Bay of Bengal
Authors: Brune James N. , Curray Joseph , Dorman LeRoy , Raitt Russell
Published: February 2008

A super‐thick (∼22km) sedimentary basin under the northern Bay of Bengal is proposed. The hypothesis is based on data from surface wave dispersion, seismic refraction, Sn attenuation, and geology. We present new high frequency Sn data which indicate a cold upper mantle beneath the Bay of Bengal. We propose that the oceanic crust in this region is in fact nearly normal, and that the sedimentary section is at least 6 km thicker than previously thought, with velocities at the base of the sediments having been increased to near 6.5 km/sec by high pressure metamorphism. Reinterpretation of the refraction data indicate a post India‐Asia collision thickness of over 16 km.
Geomagnetic activity associated with earth passage of interplanetary shock disturbances and coronal mass ejections
Authors: Gosling J. T. , McComas D. J. , Phillips J. L. , Bame S. J.
Published: February 2008

Coronal mass ejection events (CMEs) are important occasional sources of plasma and magnetic field in the solar wind at 1 AU, accounting for approximately 10% of all solar wind measurements in the ecliptic plane during the last solar activity maximum. Previous work indicates that virtually all transient shock wave disturbances in the solar wind are driven by fast CMEs. Using a recently appreciated capability for distinguishing CMEs in solar wind data in the form of counterstreaming solar wind electron events, this paper explores the overall effectiveness of shock wave disturbances and CMEs in general in stimulating geomagnetic activity. The study is confined to the interval from mid‐August 1978 through mid‐October 1982, spanning the last solar activity maximum, when ISEE 3 was in orbit about the L1 Lagrange point 220 Re upstream from Earth. We find that all but one of the 37 largest geomagnetic storms in that era were associated with Earth passage of CMEs and/or shock disturbances, with the large majority of these storms (27 out of 37) being associated with interplanetary events where Earth encountered both a shock and the CME driving the shock (shock/CME events). Although CMEs and/or shock disturbances were increasingly the cause of geomagnetic activity as the level of geomagnetic activity increased, many smaller geomagnetic disturbances were unrelated to these events. Further, approximately half of all CMEs and half of all shock disturbances encountered by Earth did not produce any substantial geomagnetic activity as measured by the planetary geomagnetic index Kp. The geomagnetic effectiveness of Earth directed CMEs and shock wave disturbances was directly related to the flow speed, the magnetic field magnitude, and the strength of the southward (GSM) field component associated with the events. The initial speed of a CME close to the Sun appears to be the most crucial factor in determining if an earthward directed event will be effective in exciting a large geomagnetic disturbance.