X-ray Jets in Interconnecting Loops

We present examples of X-ray jets, observed by the Soft X-ray Telescope on board Yohkoh, which followed trajectories of transequatorial interconnecting loops (TILs). All these TILs were preexisting, seen some time before, but were mostly invisible at the time of the onset of the jet which often made them bright along their total length. With few exceptions, these TIL-associated jets have properties very similar to other jets ejected inside active regions or along open field lines (footpoints in X-ray bright points, recurrence, strong collimation, average speed close to 350 km s⁻¹), but may reach larger lengths, in our examples up to 450 000 km. Exceptions are one jet that moved slower and one that had no brightened area at its supposed source region at the time of its origin (an X-ray bright point appeared there only 3 hours later). It appears that quite a high number of X-ray jets may be of this TIL-associated kind. Supplementary material to this paper is available in electronic form at http://dx.doi.org/10.1023/A:1014963812437     

Geochemical evidence for peat bog contribution to the streamflow generation process: case study of the Vltava River headwaters,Czech Republic

ABSTRACT

A geochemical approach using stable oxygen isotopes was used to understand streamflow generation processes in the highly peaty catchment of the Rokytka Brook in the headwaters of the Vltava River, Czech Republic. The contribution of water from peat bog areas to the total surface runoff was assessed using a hydrological time series, as well as geochemical, hydrochemical and isotope-hydrological approaches for unit hydrogram separation by means of anion deficiency. Using data from the hydrological year 2008, the role of an existing peat bog in the runoff formation dynamics of the Rokytka Brook catchment was determined, and the hydrological cycle was described and assessed using stable ¹⁸O/¹⁶O isotopes. The research findings strongly support the fact that peatland areas within the studied catchment do not significantly communicate hydraulically with surface streams, and their hydrological function in this region is insignificant.

Editor M. C. Acreman; Associate editor not assigned     

Magnetomineralogy of the cordierite gneiss from the magnetic anomaly at Humpolec,Bohemian Moldanubicum (Czech Republic)

Magnetic properties as well as the magnetomineralogy were investigated in rocks underlying a 7 km long aeromagnetic anomaly situated in the Moldanubian crystalline unit of the Bohemian Massif. The anomaly is caused by highly magnetic cordierite gneiss forming a stripe of NE — SW direction east of the town of Humpolec, eastern Bohemia. Magnetic susceptibility and its anisotropy (AMS), natural remanent magnetization, field and temperature variations of susceptibility were measured. Optical study of thin sections, electron microprobe and Mössbauer studies were also used to reveal the carrier of the high susceptibility and the high NRM. There appear to be two major generations of Fe-Ti oxides: older hematite with ilmenite exsolutions (Ti-hematite) which is the dominant remanence phase, and younger magnetite, the dominant susceptibility phase, usually associated with rutile. This indicates a reaction Hematite + Ilmenite → Magnetite + + Rutile; the trace elements in magnetite, as well as texture and morphology of the oxide grains support this assertion. An additional minor portion of maghemite is revealed by Mössbauer and thermomagnetic results. The Ti-hematite belongs to the oldest mineral assemblage in the rock, despite its anhedral morphology. Inclusions in Ti-hematite, among which corundum and abundant paragonite occur, record a strongly peraluminous and probably disequilibrium association during the crystallization of the Ti-hematite.     

Eokambrische Tillite der Železné hory,Ostböhmen

Zusammenfassung Es wird zuerst eine kurze übersicht des Algonkiums Mittelböhmens und der elezné hory (Eisengebirge, Ostböhmen) gegeben. Dem Algonkium des nördlichen Teiles der elezné hory lagert schwach diskordant eine epizonal-metamorphe eokambrische Serie auf. Sie besteht aus serizitischen Siltschiefern, normalen und konglomeratischen Grauwacken, arkosenartigen Sandsteinen, dünn gestreiften Schiefern vom warwitischen Typus, mächtigen Konglomeraten und Vulkaniten (spilitischen Porphyriten und Mandelsteinen, Tuffen und Quarzkeratophyren). Die zwei Streifen von Konglomeraten sind petrographisch ausführlicher beschrieben.Der Charakter der Sedimentgesteine, insbesondere der Konglomerate, weist auf einen raschen Ablagerungsproze\ während der starken und schnellen Denudation nach einer vorangehenden Faltungs- und Emergenzphase und unter einem kühlen Klima hin. Lithologische Eigentümlichkeiten der Konglomerate, undeutliche bis fehlende Schichtung, schlechte Sortierung, wenig abgerundetes, oft eckiges Material, unregelmä\ige Einlagerungen von Arkosegrauwacken mit zerstreuten grö\eren Geröllen, ausgezogene Flasern graphitischer Schiefer, an Frostkeile erinnernde Ausfüllungen vertikaler Klüfte, Zerdrückung einiger Gerölle sowie auffällig frische Feldspäte haben uns seinerzeit (F.Fiala, J.Svoboda 1955) zur Auffassung dieser Konglomerate als Tillite geführt. Glaziale Kritzung und Schleifung an Geschieben und auf dem Liegenden der Konglomerate wurde aber nicht festgestellt.Die behandelte eokambrische Serie haben F.Fiala und J.Svoboda 1955 als Subkambrium bezeichnet und angeführt, da\ das Böhmische Massiv nach der älteren (eisengebirgischen, H.Stille 1946) Phase der assyntischen Faltung durch eine Vereisung betroffen wurde, und da\ die subkambrischen (eokambrischen) Sedimente der elezné hory Tillite, bzw. glazimarine bis glazilakustrine warwitische Sedimente darstellen.

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Summary The Algonkian of central Bohemia and especially of the elezné hory Mts. (East Bohemia) is briefly characterized. In the northern spur of the elezné hory the Algonkian is unconformably overlain by a slightly epimetamorphosed series of Eocambrian sedimentary rocks and volcanites. The series consists of silty sericite schists, ordinary and conglomeratic greywackes, arkosic sandstones, thinly banded slates of varvitic type, conglomerates and volcanites, i. e. spilitic porphyrites and amygdaloids, tuffs and quartz keratophyres. The petrography of the two bands of conglomerates is given.The character of the sediments, especially of conglomerates, furnishes evidence of a rapid sedimentation during a strong and sudden denudation which occurred after the preceding phase of folding and emersion and under a cold climate. Lithological peculiarities of the conglomerates, the indistinct to lacking bedding, badly sorted, slightly rounded and often angular clastic material, irregular intercalations of arkosic greywackes with scarcely scattered boulders, stretched streaks of black graphitic slates, infilling of vertical cracks recalling ice-wedges, crushing of some pebbles as well as striking freshness of feldspars led F.Fiala and J.Svoboda 1955 to designate the conglomerates in question as tillites. Nevertheless, glacial striae and polishing have not be found.F.Fiala and J.Svoboda 1955 have designated the Eocambrian series under consideration as Subcambrian assuming that, after the earlier phase of Assyntian folding, the Bohemian Massif was probably affected by glaciation and that the Subcambrian (Eocambrian) sedimentary rocks of the elezné hory Mts. represent tillites, i. e. glaciomarine to glaciolacustrine varvitic sediments.

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Résumé Une vue d'ensemble de l'Algonkien de la BohÊme centrale et des elezné hory (BohÊme de l'Est) est donnée. Dans la partie nord des elezné hory une série éocambrienne des roches sédimentaires et volcaniques épi-métamorphisées est unconformablement superposée à l'Algonkien. Elle est constituée par des schistes silteux à séricite, des grauwackes ordinaires et conglomératiques, des grès arkosiques, des schistes finement laminés rappelant des types varvitiques, des conglomérats et des volcanites (des porphyrites spilitiques, des porphyrites à amygdales, des tuffs et des kératophyres quartzifères). Les caractéristiques pétrographiques des deux bandes des conglomérats sont présentées.Le caractère des sédiments, surtout des conglomérats, témoigne d'une sédimentation très active pendant la dénudation rapide suivant après une phase de plissement et d'émersion et sous un climat froid. C'est que le caractère lithologique spécial des conglomérats, leur stratification indistincte ou absente, assortiment imparfait, matériel élastique un peu roulé et souvent angulaire, les intercalations irrégulières des grauwackes à galets épars, les lambeaux étirés des schistes graphitiques, les remplissages des fentes rappelant coins de glace, le morcellement des galets et la fraÎcheur frappante des feldspaths ont amené F.Fiala et J.Svoboda (1955) à considérer ces roches comme tillites. Mais on n'a pas réussi à rencontrer des stries et des polissages glaciaires. F.Fiala et J.Svoboda (1955) ont désigné cette série pour subcambrienne en supposant qu'après la phase plus ancienne du plissement assyntien le Massif de la BohÊme a été affecté par glaciation et que les sédiments subcambriens (= éocambriens) des elezné hory correspondent aux tillites ou aux sédiments varvitiques d'origine glaciomarine jusque glacio-lacustrine.

     

Magnetic anisotropy of rocks and its application in geology and geophysics

Magnetic anisotropy in sedimentary rocks is controlled by the processes of deposition and compaction, in volcanic rocks by the lava flow and in metamorphic and plutonic rocks by ductile deformation and mimetic crystallization. In massive ore it is due to processes associated with emplacement and consolidation of an ore body as well as to ductile deformation. Hence, it can be used as a tool of structural analysis for almost all rock types. Morcover, it can influence considerably the orientation of the remanent magnetization vector as well as the configuration of a magnetic anomaly over a magnetized body. For these reasons it should be investigated in palaeomagnetism and applied geophysics as well.     

Estimate of the time interval of activity of volcanoes of the basalt formation of the lower jeseník mts. based on palaeomagnetic data

Summary Virtual geomagnetic poles, corresponding to the directions of primary remanent magnetization of the neovolcanic occurrences studied in the Lower Jeseník, form a close group which is positionally considerably removed from the present geographic pole. By comparison with some published data on the extent of the secular variation of the geomagnetic field, a conclusion was drawn that the assumption of a practically simultaneous generation of the considered volcanites (over a period of about one third of the longest secular variation cycle) is at least twice as probable as the assumption of an expressive difference in their age.