The Precambrian of NE Zambia in relation to the dated Kate,Mambwe and Luchewe intrusives

The Precambrian of northeastern Zambia represents a typical mid-Proterozoic granitoid basement covered by extensive subhorizontal, mainly arenitic late-Precambrian platform sediments. The roughly 4000 km² large Mambwe area contains five major regional units, namely the metamorphic series of the Bangweulu Block, the magmatic complexes, the minor granitoid intrusions, the Plateau Series and the doleritic dykes.The age of most of the granitoids, previously related to the Archean Bangweulu Block, is post-Ubendian ( 1800 Ma), while probable pre-Ubendian rocks occur only as local remnants. The Plateau Series can be correlated in age with part of the Muva system of the Copperbelt (post-Ubendian-pre-Katangan), the dolerites are of post-Kibaran age (< 1300 Ma).

---

Zusammenfassung Das PrÄkambrium Nordost-Zambias besteht aus einem mittelproterozoischen granitoiden Grundgebirge, das weitrÄumig von subhorizontalen, meist arenitischen spÄtprÄkambrischen Plattformsedimenten überlagert wird. Das etwa 4000 km² gro\e Gebiet um Mambwe wird in fünf regionale Einheiten gegliedert, nÄmlich die metamorphen Serien des Bangweulu Blocks, die magmatischen Komplexe, die granitoiden Kleinintrusionen, die Plateau Serie und die doleritischen Spaltenintrusionen.Die bisher grö\tenteils dem archaischen Bangweulu Block zugerechneten intrusiven Granitoide sind post-Ubendischen Alters ( 1800 Ma), wÄhrend vermutete prÄ-Ubendische Gesteine nur als untergeordnete, lokale Relikte vorhanden sind. Die Plateau Serie kann zeitlich mit einem Teil des Muva Systems des Copperbelt (post-Ubendian bis prÄ-Katangan) korreliert werden, die doleritischen Spaltenintrusionen sind post-Kibaran einzuordnen (< 1300 Ma).

---

Résumé Le Précaambrien du nord-est de la Zambie représente un développement de la croûte typique pour le ProtérozoÏque moyen. Il s'agit d'un socle granitique, largement recouvert par des sédiments subhorizontaux du type plateforme, essentiellement arénitiques. La région de Mambwe, couvrant une surface de 4000 km², est composée de cinq formations majeures: les formations métamorphiques du craton du Bangweulu, les complexes magmatiques, les intrusions mineures granitoÏdes, la Série du Plateau et les intrusions fissurales doléritiques.L'âge de la plupart des granitoÏdes, autrefois rapportés au socle archéen du Bangweulu, est post-Ubendien (+ ou –1800 Ma); des roches d'âge probablement pre-Ubendien sont d'extension réduite. La Série du Plateau peu correspondre dans le temps à une partie du Système de Muva du Copperbelt (post-Ubendien à pre-Katangien); les dolérites sont à rapporter au Post-Kibarien (< 1300 Ma).

---

- , , - . 4000 2 5 , : Bangweulu, , , , . , . . Bangweulu, Ubende, ca. 1800 , - , . Muva - - - -, - (< 1300 ).

     

Comparison of quartz microfabric with strain in recrystallized quartzite

The relationship between quartz c-axis microfabric and strain is examined in six specimens of recrystallized quartzite conglomerate in which strain was measured using pebble shapes. Four rocks subjected to plane strain display a direct relationship between the strength of preferred orientation and the strain intensity. The c-axis distributions in these rocks, as well as a rock subjected to moderate extensional strain, are crossed-girdles with maxima near the intermediate principal strain axis and connecting girdles at acute angles to the direction of maximum shortening. A rock subjected to moderate flattening strain has several maxima clustered near the direction of maximum shortening and a weak connecting girdle through the intermediate principal strain axis.These results are generally similar to those of other studies comparing strain and tectonite fabrics and also with experimental and computer simulation studies of fabrics. The degree of preferred orientation is related to total strain, and therefore microfabrics in quartzites may be cautiously interpreted as qualitative indicators of strain intensity. Uncertainties are greater, however, for correlations of fabric patterns with shapes of the strain ellipsoid. An observed increase in recrystallized grain sizes with increasing strain suggests that flow stress was lower in the more strained rocks.     

Mesoscale model response to random,surface-based perturbations — A sea-breeze experiment

The introduction into a mesoscale model of random (in space) variations in roughness length, or random (in space and time) surface perturbations of temperature and friction velocity, produces a measurable, but barely significant, response in the simulated flow dynamics of the lower atmosphere. The perturbations are an attempt to include the effects of sub-grid variability into the ensemble-mean parameterization schemes used in many numerical models. Their magnitude is set in our experiments by appeal to real-world observations of the spatial variations in roughness length and daytime surface temperature over the land on horizontal scales of one to several tens of kilometers. With sea-breeze simulations, comparisons of a number of realizations forced by roughness-length and surface-temperature perturbations with the standard simulation reveal no significant change in ensemble mean statistics, and only small changes in the sea-breeze vertical velocity. Changes in the updraft velocity for individual runs, of up to several cms^-1 (compared to a mean of 14 cms^-1), are directly the result of prefrontal temperature changes of 0.1 to 0.2K, produced by the random surface forcing. The correlation and magnitude of the changes are entirely consistent with a gravity-current interpretation of the sea breeze.     

Intraplate seismicity of the Pacific Basin, 1913–1988

We establish here a comprehensive database of intraplate seismicity in the Pacific Basin. Relocation and analysis of 894 earthquakes yield 403 reliable intraplate earthquakes during 1913–1988. These numbers do not include earthquake swarms, which account for another 838 events. Most of the remainder (304 events) are actually plate boundary earthquakes that have been erroneously located in intraplate regions. A significant number occur in recent years when location capabilities should have guarded against this situation. Relocations involve a careful linear inversion ofP andS arrivals, accompanied by a Monte Carlo statistical analysis. We have also attentively removed the high number of clerical errors and nuclear tests that exist in epicenter bulletins.A geographical examination of the relocated epicenters reveals several striking features. There are three NW-SE lineaments north of the Fiji Plateau and in Micronesia; diffuse seismicity and incompatible focal mechanisms argue against the southernmost, discussed byOkal et al. (1986) andKroenke andWalker (1986), as the simple relocation of the Solomon trench to the North. Besides another striking lineament, along the 130°W meridian, there is also a strong correlation between seismicity and bathymetry in certain parts of the Basin. In the Eastcentral Pacific and Nazca plates there are many epicenters on fracture zones and fossil spreading ridges, and hot spot traces like the Louisville, Nazca and Cocos Ridges also display seismicity.     

A spatial length scale analysis of turbulent temperature and velocity fluctuations within and above an orchard canopy

Turbulent flow within and above an almond orchard was measured with three-dimensional wind sensors and fine-wire thermocouple sensors arranged in a horizontal array. The data showed organized turbulent structures as indicated by coherent asymmetric ramp patterns in the time series traces across the sensor array. Space-time correlation analysis indicated that velocity and temperature fluctuations were significantly correlated over a transverse distance more than 4m. Integral length scales of velocity and temperature fluctuations were substantially greater in unstable conditions than those in stable conditions. The coherence spectral analysis indicated that Davenport's geometric similarity hypothesis was satisfied in the lower frequency region. From the geometric similarity hypothesis, the spatial extents of large ramp structures were also estimated with the coherence functions.     

Das Grundgebirge der Anden im Chonos-Archipel,Region Aisén,Chile

Zusammenfassung Im schwach bis mäßig metamorphen Grundgebirge des Chonos-Archipels in Südchile werden erstmals drei Formationen unterschieden: Die wahrscheinlich kambro-ordovizische Canal-King-Formation besteht überwiegend aus Phylliten und Glimmerschiefern mit Einlagerungen von Grünschiefern. Die schwächer metamorphe Potranca-Formation ist im wesentlichen devonisch und besteht aus Tonschiefern, unreinen Sandsteinen, Phylliten und Quarziten. Die vermutlich jungpaläozoische Canal-Pérez-Sur-Formation besteht aus Tonschiefern und Sandsteinen und zeigt fast gar keine Metamorphose.Das Gebiet ist mehrfach kompliziert gefaltet worden. Nach einer vermutlich vorvariszischen, nur noch stellenweise erkennbaren Faltung und schwachen Metamorphose folgte etwa im Unterkarbon eine kräftige variszische Faltung, die ein NNW—SSE-streichendes Gebirge schuf. Spätere, vermutlich oberpermische bis höchstens mitteltriassische Nachläufer der variszischen Faltung schufen Faltenachsen in NNE—SSW-Richtung.Das Untersuchungsgebiet stellt ein Glied in der Kette von präandinen Orogenen im südlichen Südamerika dar, deren Alter im großen ganzen gesehen nach Süden hin abnimmt.

---

Three formations are distinguished for the first time within the weakly to moderately metamorphic basement of the Chonos Archipelago in southern Chile: The probably Cambro-Ordovician Canal King Formation consists mainly of phyllites and micaschists with intercalations of greenschists. The less metamorphic Potranca Formation is essentially of Devonian age and consists of slates, impure sandstones, phyllites and quartzites. The Canal Pérez Sur Formation is probably of Upper Paleozoic age; it consists of slates and sandstones and shows nearly no metamorphism at all.The area has been folded complexly several times. After a supposed pre-Hercynian folding and metamorphism which can be recognized only in places, about in the Lower Carboniferous a strong Hercynian folding occurred, causing a NNW—SSE striking mountain chain. Possibly between Upper Permian and Middle Triassic times, late phases of the Hercynian folding created NNE—SSW striking fold axes.The investigated area forms a part of the pre-andine orogenic chains of southern South America, whose ages are on the whole decreasing from North to South.

---

Resumen En el basamento débil a moderadamente metamórfico del Archipiélago de los Chonos en Chile Austral, por primera vez se distinguen tres formaciones: La Formación Canal King, de probable edad cambroordovícica, contiene mayormente filitas y micaesquistos con algunas intercalaciones de esquistos verdes. La Formación Potranca, de edad esencialmente devónica, consiste de pizarras, areniscas impuras, filitas y cuarcitas. La Formación Canal Pérez Sur, de presunta edad permocarbonífera, consiste de pizarras y areniscas, y aparentemente no muestra metamorfismo.La región ha sido plegada varias veces y de manera compleja. Después de un plegamiento probablemente pre-varíscico y un metamorfismo débil que sólo en ciertas partes se reconocen, alrededor del Carbónico inferior un plegamiento fuerte varíscico produjo un orógeno de rumbo NNW—SSE. Fases tardías del ciclo varíscico, acontecidas probablemente entre el Pérmico superior y el Triásico medio, crearon ejes de pliegues en dirección NNE—SSW.El área investigada forma un eslabón de la cadena de orógenos pre-andinos en el cono Sur de Sudamérica cuya edad en grandes rasgos disminuye hacia el Sur.

---

, , 3 : , - , , . , , , . --, , , . . , , - , -- — . , -- — - , , -, , — — . - , .