Nonlinear Coupling of Langmuir Waves with Whistler Waves in the Solar Wind

Close temporal correlation between high-frequency Langmuir waves and low-frequency electromagnetic whistler waves has been observed recently within magnetic holes of the solar wind. In order to account for these observations, a theory is formulated to describe the nonlinear coupling of Langmuir waves and whistler waves. It is shown that a Langmuir wave can interact nonlinearly with a whistler wave to produce either right-hand or left-hand circularly polarized electromagnetic waves. Nonlinear coupling of Langmuir waves and whistler waves may lead to the formation of modulated Langmuir wave packets as well as the generation of circularly polarized radio waves at the plasma frequency in the solar wind. Numerical examples of whistler frequency, nonlinear growth rate and modulation frequency for solar wind parameters are calculated.     

A long-necked pterosaur (Pterodactyloidea,Azhdarchidae) from the Upper Cretaceous of Valencia,Spain

Fragmentary remains, including cervical vertebrae and limb bones, of a large pterosaur from the Upper Cretaceous of Tous, province of Valencia (Spain), are described. The material was recovered from lacustrine beds in the upper part of the Calizas y Margas de Sierra Perenchiza Formation, which is probably Maastrichtian in age. Six fragments of vertebrae allow a reconstruction of the anatomy of the mid-series cervicals of the animal. The general morphology of the cervical vertebrae is closely similar to that of the long-necked Azhdarchidae. Compared to other azhdarchids, the Valencia pterosaur shows minor differences from the genera Azhdarcho and Quetzalcoatlus, and is here provisionally referred to as Azhdarchidae indet. A wingspan of about 5.5 m is calculated by comparison with other known azhdarchids. This is the second azhdarchid pterosaur described from the Iberian peninsula. It confirms the wide distribution of this group of large pterosaurs at the end of the Cretaceous.     

High velocity debris avalanche at Lastarria volcano in the north Chilean Andes

A pre-historic collapse of the southeast flank of Lastarria volcano ( 5700 m) in the north Chilean Andes (25° 10 S), produced a fluidized volcanic debris avalanche whose morphology and surface structures are exceptionally well preserved. The avalanche travelled to the east-south-east, covering an area of 9.3 km², and came to rest after climbing and over-riding a 125 m high older scoria cone. The 0.091 km³ avalanche has an apparent coefficient of friction (H/L) of 0.15 and an excessive travel distance index (Le) of 5.1 km, indicating high emplacement velocity, perhaps of the order of 80 m s^–1. An important cause of the high mobility may have been the predominance of low-density, poorly cohesive scoriaceous and pumiceous layers in the source region. The flow may have had properties similar to those of a small ignimbrite.     

Spätvariszische Bruchsysteme im Hesperischen Massiv

Zusammenfassung Das Hesperische Massiv wurde von mehreren Bruchsystemen erfaßt, die durch ihre Häufigkeit und besonderen Charakter recht bedeutsam sind. Das wichtigste davon ist ein sich kreuzendes Bruchsystem mit NW-SE- und NE-SW-Streichen. Es handelt sich um spätvariszische Frakturen, die während des Mesozoikums und Tertiärs weiterhin aktiv gewesen sind. Über den ganzen variszischen Iberischen Block verbreitet findet man sehr häufig an diese Brüche gebundene Kluftsysteme.Die Störungen gaben Raum für Diabasgänge, sie haben die Intrusion von späten kalkalkalischen Graniten begünstigt, und sie haben Scherungen und Mylonitisierungen in den variszischen Gesteinen hervorgerufen.Setzt man die Lageveränderung des gesamten Hesperischen Massivs in Beziehung zum Kräftespiel an diesen Brüchen, so ist als verantwortlich für diese Deformation eine relative Drehbewegung des iberischen variszischen Sockels gegenüber dem französischen durchaus vorstellbar.

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The Hesperian Massif is affected by several systems of faults which are relevant both by their frequency and by their characteristics. Among these the most important is the system of conjugated faults striking NW-SE and NE-SW from late hercynian age which kept working during the Mesozoic and Tertiary periods. Systems of joints linked to these faults may be found very often throughout all the Iberian hercynian block.These features have originated diabasic dikes, have helped the intrusion of late calcoalcaline granite and have produced shearings and mylonitizations in the hercynian rocks.The analyse of the deformation of the Hesperian Massif as a whole in accordance with the work of these faults reveals a relative rotation of the Iberian hercynian socle by respect to the French one as the reason for this deformation.

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Resumen El Macizo hespérico se halla afectado por varios sistemas de fracturas que son importantes por su frequencia y caracteristicas. De estos el más importante es el sistema de fracturas conjugadas con direcciones NW-SE y NE-SW, de edad tardihercinica, que han seguido jugando durante el Mesozoico y el Terciario. Ligados a estas fracturas se encuentran con gran frecuencia sistemas de diaclasas distribuidos por todo el bloque hercmico ibérico. Estos accidentes han dado lugar a diques diabásicos, han favorecido la intrusión de granitos calcoalcalinos tardios y han producido cizallamientos y milonitizationes en las rocas hercínicas. Analizando la deformación del conjunto del Macizo Hespérico en función del juego de estas fracturas, puede suponerse como responsable de esta deformación una rotación relativa del zócalo hercínico ibérico respecto al francés.

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Résumé Le Massif Hespérique se trouve affecté plusieurs systèmes fractures qui sont importants par leur fréquence et par leur caractère. Parmi eux le plus important est le système de fractures conjugées en direction NW-SE et NE-SW de l'époque tardihercynienne qui s'est prolongé pendant les époques mesozoïque et tertiaire. Très souvent ces fractures sont liées à des systèmes de joints sur toute l'étendue du bloc hercynien Ibérique. Ces accidents ont été la raison de la formation de diques diabasiques, ont favorisé l'intrusion de granites calcoalcalins tardifs et ont produit des cisaillements et des mylonitisations dans les roches hercyniennes.En analysant la déformation de l'ensemble du Massif Hespérique en fonction du jeu de ces fractures, ont peut supposer comme cause de cette déformation une rotation relative du socle hercynien Ibérique par rapport au Français.

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Für die Herausgabe dieser Arbeit in deutscher Sprache ist der Autor Herrn Dr. G.Nollau in aufrichtigem Dank verbunden.     

Paleomagnetic constraints on the late Cretaceous and Cenozoic tectonics of southeastern Asia

Many features of the Cenozoic tectonic history of central and southeastern Asia can be understood as direct consequences of the thrust and penetration of India into Asia. Recent indentation experiments with plasticine (Tapponnier et al. [7]) have extended this idea and have led to the prediction of a pattern of large rotations and displacements of continental blocks that can be tested by paleomagnetism. The available Cretaceous and Cenozoic paleomagnetic data from this part of the world have been reviewed and a new APWP for Eurasia has been constructed for reference. The negligible rotation of South China and large clockwise rotation of Indochina are consistent with the model, i.e., with an history of large-scale left-lateral strike-slip motion along the Altyn Tagh and Red River faults. Data from Malaya and Borneo can be reconciled with the model, although in a less straightforward fashion. The large counter clockwise rotation of South Tibet implies that it rotated in sympathy with India during the collision and suggests that future indentation experiments should include this feature. Finally a middle Cretaceous reconstruction of the south margin of Asia is proposed. One interesting result is the restored continuity of geological features in Tibet and Indochina, with active subduction of oceanic (Indian plate) crust taking place to the south at subtropical latitudes.     

Sedimentary provenance of the Late Paleozoic metamorphic basement,south-central Chile: Implications for the evolution of the western margin of Gondwana

ABSTRACT

U-Pb detrital zircon age patterns are presented for nine samples of metapelites from the metamorphic basement of south-central Chile between 37° and 40°S, along with detrital zircon ages for a sample from the Piedra Santa metamorphic complex and a crystallization age of the Chachil plutonic complex, farther east in Argentina. Two distinct zircon age patterns are identified. One is a pattern with a dominant population of zircons at ca. 470 Ma (Ordovician), a widespread presence of Mesoproterozoic ages (1200 ? 1000 Ma), and a Carboniferous maximum deposition age indicated by the youngest zircon population. The second pattern is drastically different, with a main population of Permian zircons, a 290–250 Ma maximum deposition age, and a minor contribution of Pennsylvanian age zircons. Our results, coupled with previously reported metamorphic ages, show that the patterns reflect the presence of different tectonic blocks separated by the Mocha-Villarrica Fault Zone at 39°S. Metapelites north of this structure have the Ordovician-dominated pattern characteristic of the Western Series of the Paleozoic basement, and those south of the fault show the Permian-dominated pattern observed in the younger high-pressure metapelites from the Bahía Mansa metamorphic complex. The Piedra Santa metamorphic complex also shows the Ordovician-dominated pattern and was intruded by the Chachil plutonic complex dated here at ca. 303 Ma. Therefore, the Piedra Santa complex is interpreted as coeval with the Chilean metamorphic basement. The present dislocation of blocks with different ages is attributed to continental-scale dextral strike-slip tectonics along the Huincul Fault Zone, Argentina, which extends to the west as the Mocha-Villarrica Fault Zone in Chile.     

High-pressure,low-temperature metamorphism in Alpujarride Units of southeastern Betics (Spain)Métamorphisme de haute pression et basse température dans les unités Alpujarrides du Sud-Est de la cordillère Bétique (Espagne)

We present the first occurrences of high-pressure, low-temperature ferro-magnesiocarpholite-bearing mineral assemblages associated to quartz segregations in the Alpujarride units of southeastern Betics (Sierra de Almagro, Sierra de los Pinos and Sierra Cabrera). Thermobarometric results show that the carpholite-bearing rocks underwent the same P–T conditions in the three outcrops, i.e. 8–10 kbar, 350–400 °C. Metamorphic and structural data allow us to conclude that these rocks belong to the same Alpujarride unit. In the Sierra de Almagro, tectonic units with carpholite-bearing rocks overlie low-pressure, low-temperature Alpujarride units, then forming a stack with an inverted tectono-metamorphic sequence, as observed in the central and western part of the Alpujarride complex. The preservation of carpholite-bearing assemblages in these rocks implies that no significant temperature increase occurred during the exhumation history. To cite this article: G. Booth-Rea et al., C. R. Geoscience 334 (2002) 857–865.     

Les ensembles fluviatiles néogènes du bassin subandin d'Équateur et implications dynamiquesThe Neogene fluvial systems of the Ecuadorian foreland basin and dynamic inferences

A sedimentological study of the Neogene continental infill of the Subandean foreland basin of Ecuador led us to define an evolution of the fluvial system from an alluvial plain to an alluvial fan with an increasing slope in the same time as the drainage changed from mostly longitudinal to transverse. Combined with the data presently available on palaeotopography, exhumation, tectonic evolution and geomorphology, these results enable us to infer that, in contrast with the other Subandean foreland basins of Bolivia and Peru, the progradation of the Neogene alluvial fans proceeded by an overall expansion, associated with a relatively small tectonic shortening and not as a result of the development of successive thrust-related depocentres. This also indicates that the surrection of the Cordillera progressed in Ecuador throughout the Neogene. To cite this article: F. Christophoul et al., C. R. Geoscience 334 (2002) 1029–1037.