Average Pole Research Articles

Seasonal CO2 rectifier effect and large‐scale extratropical atmospheric transport

In atmospheric transport models, the covariation of the atmospheric transport and annually neutral biospheric CO2 flux is usually evident as the annual zonal mean surface CO2 concentration gradient. Using the NIES transport model and CO2 flux from the Biome‐BGC model, the covariations of different transport mechanisms and CO2 flux were examined and quantified. Including the covariation of the total transport (processes included in the NIES model) and CO2 flux, the annual average pole to pole CO2 concentration gradient is 3.5 ppm and interhemispheric difference of the average extratropical surface concentration is 2.5 ppm. The conventional covariation mechanism of the seasonal variation of planetary boundary layer mixing height and CO2 flux accounts for approximately 45% of the CO2 concentration gradient. Another important contribution to the CO2 concentration gradient in this model is the covariation of the extratropical anomaly transport (mainly by cyclones and anticyclones) and the biospheric flux, which accounts for about 55%. This alternate physical mechanism is the association of stronger meridional (north–south) anomaly transport (under strong baroclinic instability condition) with higher CO2 concentration from soil respiration in the winter and weaker anomaly transport (weak baroclinic instability condition) with lower CO2 concentration from photosynthetic uptake in the summer. The net result of the meridional transport and flux covariation is a north–south annual zonal mean CO2 concentration gradient.

Taconian and Acadian transpression between the internal Humber Zone and the Gaspé Belt in the Gaspé Peninsula: tectonic history of the Shickshock Sud fault zone

The Shickshock Sud fault has a history of Ordovician (Taconian), Silurian (Salinic), and Devonian (Acadian) movements. Taconian deformation involving ductile dextral oblique-slip faulting is recorded in Cambrian rocks in the footwall of the Shickshock Sud fault. Metabasalt and metaarkose at amphibolite grade are converted into phyllonite and mylonitic schist. Shear bands, asymmetric garnet porphyroclasts, C–S fabrics, and mica-fish textures indicate dextral shearing. The regional sense of shear is top to west and southwest on generally southeast dipping shear zones. Hornblende of metabasalt yielded an 40Ar/39Ar age of 455.9 ± 2 Ma, and muscovite from the mylonitic schist yielded an 40Ar/39Ar age of 454.3 ± 0.9 Ma, which indicate metamorphism and deformation during the Taconian orogeny. Evidence for Silurian activity is indicated by the Salinic unconformity to the south related to normal block-faulting. Deformation features in the Ordovician and Silurian–Devonian rocks in the hanging wall were predominantly brittle and involved dextral transpression. Kinematic indicators point to predominantly dextral strike-slip movement. Kinematic analysis of brittle fault-slip data indicates that the shortening axis direction during strike-slip deformation was northwest–southeast and subhorizontal, which is essentially coaxial to the average pole of Acadian cleavage. Deformation in the hanging wall of the Shickshock Sud fault is Acadian-related. The irregular geometry of the Laurentian margin, including the Grenville basement, might be the cause for Taconian and Acadian transpression in the Gaspé Appalachians.

Superconducting septum magnet design for Jefferson Lab Hall A

A pair of superconducting septum magnets are required to permit hypernuclear physics experiments at JLAB's Hall A at angles to the incident beam as small as 6 degrees. A cold iron superconducting "C" magnet design has been selected. This magnet has a central field of 4.23 Tesla at a current density of 25,000 Amp/cm2, the stored energy is 0.22 Megajoules and the inductance is 1.0 Henries. The magnet has an effective field length of 0.67 meters, an average gap of 0.25 meters and an average pole width of 0.15 meters. The magnet is currently being fabricated by BWXT Inc. under contract to INFN.

Textures of tantalum metal sheets by neutron diffraction

The orientation distributions of six tantalum samples, TaPA, TaG1, TaG2, TaQ2-S1, TaQ2-S2 and TaQ2-S4, were studied by neutron diffraction and ODF analysis. The TaPA specimen is a commercial tantalum sheet with an unknown fabrication history. The TaG1 and TaG2 were fabricated from a powder metallurgical ingot by uniaxial compression, and the TaQ2 type samples were fabricated from commercial stock by similar uniaxial forging. TaQ2-S1 is the section closest to the centre of the forged disc, S2 is the intermediate section, and S4 is the section adjacent to the periphery. The texture of TaPA consisted of many components, including {014}〈100〉, {111}〈¯321〉, {100}〈010〉, and [111]/[100] double-fibre textures with the fibre axes oriented parallel to the normal direction. The two TaG-type specimens were dominated by the [111]/[100] double-fibre texture, accompanied by a weak {100}〈010〉 cube texture. The three sections of TaQ2 had much higher degrees of texture than the TaG-type samples, with an extremely strong (111) peak, which consists of (111)〈11¯2〉, (111) 〈¯1¯12〉, and [111] fibre texture. The average pole density of the three equivalent orientations of (111)〈11¯2〉 was the strongest for the S1 with over 150 multiples of random distribution (mrd), and gradually decreased with increasing radial distance to about 100 mrd for the S4 section. On the other hand, the average intensity of (111)〈¯1¯12〉 type orientations was increased from about 40 mrd at S1 to about 100 mrd for the S4 section.

Paleomagnetism of alkaline complexes and remagnetization in the Kapuskasing Structural Zone, Ontario, Canada

The Shenango and Nemegosenda alkaline complexes of the southern Kapuskasing Structural Zone (KSZ), an uplifted crustal block in northern Ontario, preserve primary thermoremanent magnetizations, with mean directions D=112°, I=−46° (k=13, α95=13°, N=9 sites) and D=304°, I=+51° ( k=31, α95=10°, N=7 sites) for Shenango and D=124°, I=−57° ( k=13, α9520°, N=4 sites) and D=312°, I=+54° (k=17, α95=13°, N=7 sites) for Nemegosenda. Their average paleomagnetic pole is 45°N, 189°E (dp=6°, dm=8°), falling on the Keweenawan track of the North American apparent polar wander path (APWP) between 1098–1107 Ma reverse‐polarity (R) and 1087–1098 Ma normal‐polarity (N) poles of Lake Superior lavas and dikes. Unlike the Keweenawan paleopoles, which have a reversal asymmetry of ≈30°, the Shenango and Nemegosenda R and N poles are almost 180° reversed, which was found also by Lewchuk and Symons (1990b). This symmetry of R and N poles casts doubt on the previously accepted predominance of asymmetric reversals of the Earth's field in Keweenawan time. The Archean Shawmere anorthosite is overprinted by a B magnetization with mean direction D=97°, I=−68° ( k=12, α95= 10°, N=18 sites). The Shawmere B paleopole at 38°N, 226°E (dp=13°, dm=l6°) falls between the carbonatite poles and ≈1850 Ma cratonic poles, and the B magnetization seems to be a composite of middle and late Proterozoic overprints. Sites in the western part of the Shawmere body close to the “carbonatite line” of faults linking the various alkaline complexes are severely altered, with an abundance of secondary magnetite and hematite. Virtual geomagnetic poles for these sites fall close to the Keweenawan track and have an average pole of 189°, 53°N (dp=15°, dm=20°) suggesting that the B NRM at these sites is an ≈1100 Ma thermochemical overprint caused by hydrothermal fluids at the time of carbonatite intrusion. More easterly sites are less altered. Their VGPs resemble ≈1850 Ma cratonic poles and average to 235°E, 30°N (dp=15°, dm=17°) These B natural remanent magnetizations are probably thermochemical remanent magnetizations impressed by middle Proterozoic hydrothermal activity associated with intrusion of early alkaline bodies, fault movement on the Ivanhoe Lake fault zone, or late‐stage uplift of the KSZ.

A biogeographic approach to estmating paleolongitude of suspect terranes in tectonic reconstructions of the Pacific region

Suspect terranes in western North America and northeastern Siberia contain Permian taxa which were endemic to the Tethyan region. According to one hypothesis, the rocks containing these faunas were transported across the Paleopacific Ocean by plate motion during the Mesozoic. An alternative explanation is that the Tethyan species crossed the Paleopacific Ocean in much the same way as modern Indo-Pacific corals migrated into central America. A third hypothesis attributes their presence in North America to dispersal through a marine corridor between the Tethys and Paleopacific oceans. Trend-surface analysis of modern and Permian biogeographic data is a new approach to understanding the origin of these exotic faunas and constraining the paleolongitude of the circum-Pacific terranes which contain them. The eastward decline in generic diversity of Recent Indo-Pacific corals and larger foraminifera across the Pacific Ocean may be used as a model for the distribution of their respective ecological and biogeographical analogs, namely, Permian Tethyan rugose corals and fusulinids in the Paleopacific Ocean.In order to test the method, data on the generic diversity of modern corals were compiled from 137 areas in the Indian and Pacific Oceans. A second-order polynomial surface was constructed from the biogeographical data. It is nearly symmetrical about the Equator, and the average pole to its plane of symmetry is located ≤1° away from the pole of the Earth's axis of rotation. It is closer to the actual pole than are mean virtual magnetic poles obtained from Quaternary lavas at three well-sampled islands: Hawaii, Tahiti and Easter Island. Trend-surface analysis of the biogeographic data on larger foraminifera yields similar results. Thus the estimate of the position of the Earth's pole of rotation using biogeography rivals that obtained from the best available palaeomagnetic data.The same kinds of data may also be used to place longitudinal constraints on paleogeographic reconstructions. The gradual decline in diversity of corals eastward across the Pacific Ocean may be used to find the location of an island if its paleomagnetically-derived latitude and the value of coral diversity are both known. In order to test this approach, the values for coral diversity at Hawaii, Tahiti, and Easter Island were removed from the data, and a second-order polynomial surface was obtained from the reduced data set. The islands were then returned to the map using their paleomagnetically-derived latitudes and the longitudes obtained from the contour lines of the diversity surface. Easter Island, Hawaii and Tahiti were placed approximately 600 km northeast, 3,700 km southeast and 600 km southeast of their actual sites, respectively. These distances are small compared with the total width of the Pacific and Indian oceans (26,000 km). Evidence that latitudinal and longitudinal gradients in faunal diversity existed during the Permian provides the rationale for the application of the proposed method to fossil data of that age.

Mesozoic paleomagnetism and northward translation of the Baja California Peninsula

Paleomagnetic data from Cretaceous igneous and sedimentary rocks of the Peninsular Ranges and Continental Borderland of the Baja California Peninsula yield an average pole position of 83°N, 344°E (A95 = 3.4°), suggesting that the peninsula as a whole has moved northward ∼11° and rotated 32° clockwise, with respect to the North American craton, since Cretaceous time. Only a small portion of this movement is due to the Neogene opening of the Gulf of California. Results from stratified rocks giving both positive and negative fold tests are included in the average Cretaceous pole. The rocks that fail fold tests have been deformed and remagnetized by nearby intrusives that are only slightly younger; unconnected directions from these sites closely match corrected directions from sites where the fold tests are positive. Oceanic rocks were also sampled in the Continental Borderland from Upper Triassic and Upper Jurassic tectonostratigraphic terranes which are apparently allochthonous with respect to the western Baja Peninsula and each other. These oceanic rocks show magnetizations indicating low paleolatitudes, although the hemisphere of origin is presently unknown. The Cretaceous rocks of the Baja California Peninsula may have originally formed adjacent to the now-truncated continental margin along the northern Middle America Trench. Northward transport of the peninsula probably occurred by transcurrent faulting associated with oblique subduction of the Farallon plate beneath western North America between Late Cretaceous and late Miocene time.

Palaeomagnetic studies of a Cretaceous molasse sequence in the central Andes (Coloso Formation, Northern Chile)

The Coloso Formation is an early Cretaceous conglomerate-dominated molasse sequence in northern Chile. The sequence was deposited rapidly and records the unroofing of granodioritic and andesitic source rocks. Thin sand units throughout the sequence have been studied palaeomagnetically; the results are complex but can be related to the diagenesis of arid-zone alluvium. Natural remanent magnetization (NRM) may be normal or reversed but is usually a combination of the two. Isolation of magnetic components by vector analysis of thermal and AF demagnetization data yields both normal and reversed components which are approximately antiparallel and yield an average pole position at 70°S, 192°E. This is consistent with late Cretaceous data from northern Chile but not with the established apparent polar wander (APW) path for South America. It may indicate late Cretaceous remagnetization but is considered to be more likely an indication that the present APW path assumes no tectonic rotation and that important relative movements have taken place between northern Chile and Argentina.

Age and magnetism of diabase dykes and tilting of the piedmont

We have conducted a paleomagnetic and radiometric study of diabase dikes in the South Carolina Piedmont where such data is lacking. Our virtual geomagnetic pole position for 20 of 24 diabase sites in the Piedmont is 83.9°E, 66.1°N and lies near the older 195 m.y. age group of Smith and Noltimier (1979). Single K-Ar apparent ages of twelve diabase sites indicate that one half of the diabase dikes studied have ages near 195 m.y. Two of the sites, whose pole positions lie well to the east of our mean value, have apparent ages in the 180 m.y. range. Thus, while two groups appear to be present in South Carolina, it is the older group that seems to predominate. We combined our pole position with other data from diabase in the southern Piedmont (Watts, 1975; Bell et al., 1979) and have calculated a mean paleopole position of 86.1°E, 66.4°N based on 50 sites in Georgia, South Carolina, and North Carolina. The southern diabase paleopole position plots slightly off the North American apparent polar wander path, but is not significantly different for the 190 m.y. average pole of Irving (1982). These results do not provide an indication of the degree of tilting of the Appalachians in post-early Mesozoic times. However, of the two possible scenarios that can be envisioned, 1. (1) injection into an updomed area or 2. (2) tilting of the Appalachian surface due to post-early Mesozoic differential erosion and isostatic rebound, adjustment to account for a 10° westerly tilting of the Piedmont surface about the Appalachian trend brings our southern pole position more nearly into coincidence with the North American cratonic pole for early Jurassic times.

Geophysical Studies of North African Cenozoic Volcanic Areas: III. Garian, Libya

Paleomagnetic and K/Ar whole rock absolute age data are described for material from the Garian area of Libya, centered at 13°E, 32°N. Within-unit cleaned paleomagnetic directions from the essentially unaltered lavas are very well defined and can almost certainly be taken as reliable measurements of the geomagnetic field direction during the initial cooling of each flow. However, the distributions of mean direction, from which the effect of repeated sampling of the field at one time has been removed, does not suggest that a reversing axial dipole field has been recorded in a representative manner. Both N and R groups of directions are azimuthally elongated, and the average poles for the N and R groups differ by 21°, or four times the 95% level uncertainty for each average pole. A number of possible physical explanations for the paleomagnetic results are discussed. The conventional overall average pole at 88°N, 123°E, δp: 3°, δm: 7 °does not differ significantly from the geographic pole, a result which agrees closely with that of Schult and Soffel (1973). However, the value of these overall average poles in estimating absolute plate motion must await an understanding of the sources of the asymmetries in the paleomagnetic data.

Geophysical Studies of North African Cenozoic Volcanic Areas: II. Jebel Soda, Libya

This study is the second of a series in which a main concern will be to try to establish the Neogene absolute motion of the African Plate. A combined paleomagnetic and K–Ar whole rock age dating study has been made of the Jebel Soda basaltic volcanic area of central Libya. Sixty basaltic flows were sampled in an area centered on 28°45′N, 15°30′E. Precisely defined paleomagnetic directions were obtained for 57 of the flows. Considerable attention has been given to the problem of data selection to obtain a best measure of the pole representing the dipole field during the period of volcanic activity. The equatorial nature of the directions, with equivalent poles extending continuously to 30°N latitude, provide a problem in data selection. Similar characteristics are apparent in the results of Schult and Soffel (1973) for the same area. A provisional average pole for the combined data sets, located at 73°N, 195°E(K: 26, A95: 5.6°) is significantly different from the geographic pole. Reasons for the 17 °divergence of paleomagnetic and geographic poles are discussed briefly.

Part 3. Present plate boundary and its evolution in the New Zealand region: Motion along the New Zealand Alpine Fault and a model for the formation of the Southern Alps

Analysis of marine geophysical data by Falconer, Geddes and Christoffel shows that the present position of the pole of rotation for motion between the Pacific and Indian Plates differs from the average pole for the past 10 million years.

Palaeomagnetism of Precambrian rocks from Southeast Norway and South Sweden

Precambrian amphibolite and hyperite rocks from the Bamble and Kongsberg areas in SE Norway, and amphibolite rocks from SW Sweden were investigated for evidence of remagnetization by the Sveconorwegian metamorphic episode. The similarity of the characteristic natural remanent magnetization directions, shown by the various rocks from the Bamble and Kongsberg areas, indeed supports the idea of remagnetization on a regional scale. Therefore the average pole position at 3°S, 153°W, determined from six sites in these areas, is considered to reflect the average virtual pole position for the post-Sveconorwegian period of uplift and cooling (1,120–975) · 10 6 year ago. The pole positions determined from the characteristic natural remanent magnetization directions of amphibolite rocks in SW Sweden are indicative of being somewhat younger. In addition, two hyperite dikes were studied near Karlshamn in SE Sweden. Their characteristic natural remanent magnetization is consistent with that of the hyperite dikes in central south Sweden (Mulder, 1971). The Precambrian apparent polar wandering path for Europe is reconstructed on the basis of twenty-three pole positions from the Baltic Shield and three pole positions from Great Britain. This pole path requires an average angular rate of apparent polar wandering of 0.2–0.3° per 10 6 year.

The Changing Catholicism in Poland

When I say in the title that Catholicism is changing in Poland, I am fully aware that the essence of the Catholic faith and the basic structure of the Catholic church cannot be changed and are not changing. But the expression of this faith, the Catholic thought, the Catholic attitudes and mentality, a language in which the Gospel is announced, can change according to changing conditions, and are changing. This is true throughout the world. The church has a mission, a role to fulfill and must make its presence effectively meaningful for the world, and consequently it must adjust to concrete changing conditions. This is the meaning of the aggriornamento proclaimed by Pope John. What is changing in Poland? First, it is necessary to present some basic information about the situation of Catholicism in Poland. Poland has been a Catholic country for over one thousand years. The Catholic church has played an enormous role in Polish history, shaping its culture, customs, social and political attitudes. Political developments in the eighteenth and nineteenth centuries have strengthened ties between religious and patriotic feelings, with all the advantages and disadvantages of this situation. The average Pole has a deep sense of attachment and fidelity to his faith and his church, characterized by traditionalism and sentimentalism. Unfortunately, we have failed to develop a more rational approach to our faith. With few exceptions we have never had in Poland in the past or in more recent times great theologians. Neither have we produced heretics. Since 1944 we have been confronted in Poland with quite a new, and in some ways, an unexpected situation. As a result of the political developments at the end of World War II, Poland joined the Eastern European bloc of socialist countries. An encounter of Catholicism and materialistic-atheistic Marxism inevitably resulted in a conflict. In fact, it was a double conflict: ideological between the two incompatible doctrines; and political between the Communist state striving to attain a monopoly of ideological influence upon its citizens on the one

Poles of rotation

One of the concepts introduced into the theory of plate tectonics is that of poles of rotation. It is supposed that the relative motion between two rigid plates can be described by the rotation of one of the plates about a pole of rotation, which shows the direction of the rotation vector. It has been pointed out that in general poles of rotation will not remain fixed. The consequences of poles of rotation which move slowly with time are examined. In particular, it is shown that fracture zones may lie very close to small circles, but that the centers of these small circles may lie as much as 20° away from the average pole of rotation. The establishment of poles of rotation from individual fracture zones is thus an inaccurate method unless it can also be shown that the pole of rotation has remained fixed.

The pole tide

About 10,000 mean monthly values of sea level from 11 tide stations have been analyzed by the method of Tukey to obtain the power spectra in the frequency range of 0.0125 to 6 cycles per year (cpy). The spectral density is on the order of 103 mm2/cpy and is remarkably uniform over this frequency range, with the following exceptions: (i) a sharp rise at the low-frequency tail, from 103 mm2/cpy at 0.1 cpy to 105 mm2/cpy at 0.0125 cpy (presumably associated with variations in recorded sea level arising from continental unrest); (ii) the line spectrum associated with the annual variation and its harmonics; and (iii) a weak peak of 0.84 cpy, barely above noise level, which is identified with the 14-month ‘pole tide’ corresponding to the earth's free nutation (Chandler wobble). The average pole tide for all stations gives an amplitude twice that predicted by equilibrium theory. The contribution to the peak of the pole tide is largely from three localities: Swinemunde, Marseille, and a combined set of Netherlands stations. Apparently the pole tide is not in accord with equilibrium theory. This raises some questions concerning the interpretation of Love numbers as derived from the period of free nutation.

THE PALAEOMAGNETISM OF THE KAINOZOIC BASALTS OF VICTORIA

Summary. The average geomagnetic pole position consistent with the magnetization of the Newer Volcanics of Victoria, which are for the most part of Pleistocene age, coincides with the present geographic pole just as do all pole determinations from Miocene and later rock formations from the Northern Hemisphere. During this time it appears that the Earth's magnetic field has approximated, on average, to that of a geocentric axial dipole and that the land masses concerned have maintained their present positions. In contrast, the pole determined from Lower Tertiary Volcanics of Victoria does not agree with the geographic pole nor with equivalent determinations from the Northern Hemisphere, suggesting that the relative positions of the continents may have been different in the past.