Das Nord-Süd-streichende Lineament von Elizondo in den westlichen Pyrenäen

Zusammenfassung In den spanischen Westpyrenäen läßt sich ein nord-süd-streichendes Lineament nachweisen, das sich vor allem im Aldudes-Quinto Real-Massiv zwischen Elizondo und Eugui bemerkbar macht. Die Magnesitlagerstätte von Eugui ist auf etwa 9 km nord-südlicher Erstreckung an das Lineament gebunden. Zahlreiche NW-SE streichende Diabasgänge zeigen in ihrer Gesamtheit in diesem Bereich eine lineare Anordnung von Nord nach Süd. Während des Devons und Unterkarbons bildete die Lineamentzone ein Becken mit größeren Sedimentmächtigkeiten und besonderer Fazies. Der Faltenspiegel der variszischen Strukturen fällt von Osten und Westen her in das Lineament ab. Die generell nordwestlich streichenden variszischen Faltenachsen schwenken innerhalb des Lineaments in eine nord-südliche bis rheinische Richtung ein. Bemerkenswert ist der Achsenfächer bei Berroeta.

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Near by Elizondo in the Western Pyrenees (Spain) the massiv of Aldudes-Quinto Real is crossed by a lineament of NW direction. This lineament contains the magnisite deposit of Eugui. Diabas dykes show NW-SE direction, but the prevailing direction of the series is N-S. During devonian and lower carboniferous time the region of the lineament represented a sedimentary basin of great thickness and special facies. The axis of this large synclinorium shows the same direction as the lineament. The hercynian axes of folding are striking NW in general but NS in the region of the lineament. Remarkable is the fan of axes near Berroeta.

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Compendio En los Pirineos occidentales españoles se encuentra un lineamiento con un rumbo de Norte a Sur, que se hace notable sobre todo en el macizo de Aldudes-Quinto Real entre Elizondo y Eugui. El yacimiento de magnesita de Eugui sigue este lineamiento en una extensión de 9 kms. Numerosas diques de diabasa muestran en su generalidad en esta región un orden en linea de Norte a Sur. Durante el devónico y el carbonífero inferior formaba esta zona de lineamiento una cuenca, en la que se depositaron sedimentos de gran espesor con una facies característica. Los niveles de eje de los anticlinales de las estmcturas varísticas buzan tanto del Este como del Oeste hacia el centro del lineamiento. Los ejes de los anticlinales que tienen en general un rumbo hacia el NO tuercen dentro del lineamiento en una dirección de N—S a NNE—SSO. Interesantes son los ejes en abanico cerca de Berroeta.

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Résumé Dans l'ouest des Pyrénées espagnoles on a prouvé l'éxistance d'un linéament qui se montre particulièrement dans le massif des Aldudes-Quinto Real entre Elizondo et Eugui. Le gîte de magnésite d'Eugui est attaché à cette linéament du nord au sud sur une longueur de 9 km. Dans cette région de nombreux filons basaltiques montrent dans leur totalité un arrangement linéaire du nord au sud. Durant le dévonien et le carbonifère inférieur la zone de linéament a formé une cuvette de grandes epaisseurs sédimentaires et de faciès particulier. Dans cette linéament l'axe de plissement, en général de direction NW, se dirige du N—S jusqu'à une direction rhénale. L'axe en éventail près de Berroeta est remarquable.

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Anschrift der Verfasser: Dr. K.Mohr und Professor Dr. A.Pilger, Institut für Geologie und Paläontologie der Bergakademie Clausthal — Technische Hochschule 3392 Clausthal-Zellerf eld.     

一个秃冻胀丘的热及水文动力学--关于其形成的暗示

Mud boils, classified as non-sorted circles, are a common patterned ground phenomenon of permafrost areas. They typically consist of a bare circle center of cryoturbated soil and are surrounded by vegetation on more stable soil. The objectives are to examine differences in seasonal hydrologic and thermal dynamic across this gradient of cryoturbation, i.e. the region below the organic border and the mud center. We installed instruments in a mud boil at a site close to Ny-@lesund, Spitsbergen, in September 1998. The bare soil circle center ranges about 1 m in diameter and is surrounded by a vegetated border consisting of a mixture of low vascular plants, mosses and lichens. Fine soil (>95% clay and silt) in the lower part of the profile is overlain by coarser grained material (silt and sand). The grain size distribution also suggests an upwelling of fine material in the center of the circle. Temperature and moisture sensors were installed over a vertical 1 m×1 m profile and hourly data recording started in September 1998. Surface irregularities, as well as variations of grain size and moisture, create a non-uniform thermal and hydrologic dynamic. We qualitatively analyze this dynamic with respect to the mud boils physical stability.     

Implications of Late Pleistocene Glaciation of the Tibetan Plateau for Present-Day Uplift Rates and Gravity Anomalies

Minimal and maximal models of Late Pleistocene Glaciation on the Tibetan Plateau are considered. The large ice sheet models indicate that disintegration of the ice sheet could have contributed up to 7 mm/yr of present vertical uplift and 2 mm/yr of horizontal extension. The former value can account for more than 50% of the observed uplift in central Tibet. The peak free-air gravity anomaly arising from the deglaciation would be around −5.4 mGal. In contrast, the smaller ice sheet models do not contribute significantly to the signals of present uplift and gravity anomalies. Modern geodetic measurements therefore have the potential to constrain the Late Pleistocene glaciation of the Tibetan Plateau. Assuming a large ice sheet over the Tibetan Plateau, the disintegration can contribute up to 6 m of eustatic sea-level rise.     

PT Paths from modal proportions: application to the Koralm Complex,Eastern Alps

Thermodynamic pseudosections portray those parts of a petrogenetic grid that are relevant to a given bulk composition and the reactions appearing on them can therefore be used directly to infer the PT path that the rock followed. However, for many ‘normal’ bulk compositions the use of pseudosections is hampered by the fact that they display only few large fields of high thermodynamic variance in the PT range of interest. Here it is discussed how modal information on reaction progress within these fields can be used to determine PT path information for thermodynamically high variant metamorphic assemblages. We use this information on reaction progress to contour pseudosections for modal proportions of minerals using the software package THERMOCALC. The approach is applied to di- tri- and quadrivariant assemblages from the Koralm complex in the eastern Alps. A PT path for these rocks is derived from modal considerations and compared with interpretations of mineral composition contours on the same pseudosection and with conventional thermobarometry. It is shown that at least part of the complex must have cooled initially near isobarically from prevalent peak conditions around 700°C and 14 kbar before the rocks commenced a Barroviantype decompression path.     

Last glacial maximum climate inferences from cosmogenic dating and glacier modeling of the western Uinta ice field, Uinta Mountains, Utah

During the last glacial maximum (LGM), the western Uinta Mountains of northeastern Utah were occupied by the Western Uinta Ice Field. Cosmogenic ¹⁰Be surface-exposure ages from the terminal moraine in the North Fork Provo Valley and paired ²⁶Al and ¹⁰Be ages from striated bedrock at Bald Mountain Pass set limits on the timing of the local LGM. Moraine boulder ages suggest that ice reached its maximum extent by 17.4 ± 0.5 ka (± 2σ). ¹⁰Be and ²⁶Al measurements on striated bedrock from Bald Mountain Pass, situated near the former center of the ice field, yield a mean ²⁶Al/¹⁰Be ratio of 5.7 ± 0.8 and a mean exposure age of 14.0 ± 0.5 ka, which places a minimum-limiting age on when the ice field melted completely. We also applied a mass/energy-balance and ice-flow model to investigate the LGM climate of the western Uinta Mountains. Results suggest that temperatures were likely 5 to 7°C cooler than present and precipitation was 2 to 3.5 times greater than modern, and the western-most glaciers in the range generally received more precipitation when expanding to their maximum extent than glaciers farther east. This scenario is consistent with the hypothesis that precipitation in the western Uintas was enhanced by pluvial Lake Bonneville during the last glaciation.     

Ultra-high degree spherical harmonic analysis and synthesis using extended-range arithmetic

We present software for spherical harmonic analysis (SHA) and spherical harmonic synthesis (SHS), which can be used for essentially arbitrary degrees and all co-latitudes in the interval (0°, 180°). The routines use extended-range floating-point arithmetic, in particular for the computation of the associated Legendre functions. The price to be paid is an increased computation time; for degree 3,000, the extended-range arithmetic SHS program takes 49 times longer than its standard arithmetic counterpart. The extended-range SHS and SHA routines allow us to test existing routines for SHA and SHS. A comparison with the publicly available SHS routine GEOGFG18 by Wenzel and HARMONIC SYNTH by Holmes and Pavlis confirms what is known about the stability of these programs. GEOGFG18 gives errors <1 mm for latitudes [-89°57.5′, 89°57.5′] and maximum degree 1,800. Higher degrees significantly limit the range of acceptable latitudes for a given accuracy. HARMONIC SYNTH gives good results up to degree 2,700 for almost the whole latitude range. The errors increase towards the North pole and exceed 1 mm at latitude 82° for degree 2,700. For a maximum degree 3,000, HARMONIC SYNTH produces errors exceeding 1 mm at latitudes of about 60°, whereas GEOGFG18 is limited to latitudes below 45°. Further extending the latitudinal band towards the poles may produce errors of several metres for both programs. A SHA of a uniform random signal on the sphere shows significant errors beyond degree 1,700 for the SHA program SHA by Heck and Seitz.     

Late Cretaceous exhumation history of an extensional extruding wedge (Graz Paleozoic Nappe Complex, Austria)

Late Cretaceous structures within the eastern Graz Paleozoic Nappe Complex define an extruding wedge with north-eastward directed thrusting in eastern portions and strike-slip shear along the margins. Stacking structures are overprinted by south-westward directed extension with low-grade metamorphic rocks in the hangingwall and high-grade basement rocks in the footwall. Pressure–temperature and structural data are obtained from successively opening quartz veins that record various stages of progressive deformation and metamorphism. Fluid inclusion data and related structures show that during extension isothermal decompression from ca. 550°C and 8 kbar down to ca. 450°C and 2 kbar was related to exhumation of rocks from deep crustal levels. The data point to a high geothermal gradient and explain condensed paleo-isotherms due to ductile normal faulting in the eastern areas of the Graz Paleozoic Nappe Complex. The investigated Late Cretaceous structural elements suggest that the Graz Paleozoic Nappe Complex decoupled from the surrounding basement units and operated as a large-scale extension–extrusion corridor that evolved prior to Miocene extrusion tectonics in the Eastern Alps.