Isobaric cooling and anti-clockwise P–T paths in the Variscan Odenwald Crystalline Complex, Germany

Mineral assemblages in Al₂O₃‐rich, SiO₂‐ and K₂O‐poor metapelitic rocks from the western Odenwald Crystalline Complex (Variscan Mid‐German Crystalline Rise, southern Germany) include corundum, spinel, cordierite, sillimanite, garnet and staurolite. Quartz is absent from almost all samples. Therefore, the applicability of conventional geothermobarometry is very limited or even impossible. Detailed petrographic investigation on selected samples permits inference of the sequence of appearance and disappearance of several mineral assemblages. The recognition of such partial re‐equilibration stages and their associated mineral assemblages, together with mineral stabilities predicted from KFMASH pseudosections, enables the determination of the pressure‐temperature (P–T) trajectories experienced by these rocks during the Variscan metamorphism. The rocks were metamorphosed under low‐P/high‐T conditions and underwent an anti‐clockwise P–T evolution. A pressure increase from about 2 kbar to 4 ± 0.5 kbar was accompanied by heating. Peak metamorphic conditions were reached at pressures of 4 ± 0.5 kbar and temperatures of at least 640 °C, probably even higher. The retrograde evolution is characterised by near‐isobaric cooling from ≥ 640 °C to approximately 550 °C. The rocks underwent the anti‐clockwise evolution in a subduction‐related magmatic arc setting. The close spatial association of the low‐P/high‐T rocks with recently discovered metabasic eclogites in the eastern part of the Odenwald Crystalline Complex may indicate a fossil paired metamorphic belt in the Central European Variscides.     

Paleostress-tensor analysis of late deformation events in the Odenwald Crystalline Complex and comparison with other units of the Mid-German Crystalline Rise, Germany

Summary Geometric data of fault planes and fault plane lineations, together with the observed sense of shear on the slip planes, were used to calculate paleostress tensors and fields responsible for the post metamorphic peak D3 and D4 deformation events in the four Odenwald units sensu Krohe (1991). The paleostress fields were calculated using the method of Will and Powell (1991). As inferred from the paleostress analysis, the D3 strike-slip deformation west of the Otzberg fault zone was caused by a, ± N-S directed, compressional regional stress field, with shallowly plunging σ₁ axes and σ₃ directions that plunge at shallow to moderate angles to the E or W; the calculated mean orientations are: σ₁ 06 → 350, σ₂ 77 → 234 and σ₃ 12 → 085. The B?llsteiner Odenwald east of the Otzberg fault zone was not affected by this stress field. This implies that the Bergstr?sser and B?llsteiner Odenwald were spatially separated and formed independent crustal blocks during D3. The D4 faulting event is recognised in all areas investigated, even though most prominently in units III and IV, and juxtaposed the Bergstr?sser and B?llsteiner Odenwald. This faulting episode was caused by a paleostress field with a steeply westerly plunging σ₁ axis and a shallowly southsoutheasterly plunging σ₃ axis. The orientations of the principal stresses are: σ₁ 52 → 270, σ₂ 38 → 085 and σ₃ 06 → 174. With continued deformation from D3 to D4, there was a progressive change in the orientation of the stress field indicating a change from a N-S compressional to extensional stress field, accompanied by the progressive development of strike-slip faults and late normal faults. Paleostress field orientations in the Pfalz Forest, SW of the Odenwald, determined by Fl?ttmann and Oncken (1992) are very similar to those obtained for the Odenwald region and indicate a regionally consistent stress pattern in the southwestern part of the Mid-German Crystalline Rise (MGCR) during strike-slip and normal faulting deformations.

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Zusammenfassung Paleostress-Tensor Analyse sp?ter Deformationsereignisse im Odenwald-Kristallin und ein Vergleich mit anderen Einheiten der Mitteldeutschen Kristallinzone, Deutschland Für die vier Odenwald-Einheiten im Sinne von Krohe (1991) wurden Pal?ostressfelder für die Blattverschiebungs- und Abschiebungsereignisse D3 und D4 mit der Methode von Will und Powell (1991) berechnet. Die Analyse ergibt, da? das regionale Spannungsfeld, das westlich der Otzberg-Zone im Bergstr?sser Odenwald zum D3-Ereignis führte, ein ± N-S gerichtetes kompressives Stresssfeld war. Die σ₁-Achse f?llt flach nach N bzw. S ein, die σ₃-Achse mit kleinen bis moderaten Winkeln nach E bzw. W; die berechneten Orientierungen der Hauptspannungsrichtungen sind: σ₁ 08 → 350, σ₂ 77 → 234 and σ₃ 12 → 085. Der B?llsteiner Odenwald, ?stlich der Otzberg-Zone, wurde von diesem Spannungsfeld nicht erfa?t. Dies impliziert, da? Bergstr?sser und B?llsteiner Odenwald w?hrend des D3-Ereignisses voneinander getrennt waren und separate Krusteneinheiten darstellten. Auswirkungen der D4-Deformation k?nnen im gesamten Untersuchungsgebiet erkannt werden, am st?rksten jedoch in den Einheiten III und IV. Dieses Ereignis wurde von einem Pal?ostressfeld mit einer steil nach W einfallenden σ₁- und einer flach nach SSE einfallenden σ₃-Achse verursacht und führte zum Zusammenschlu? von Bergstr?sser und B?llsteiner Odenwald. Die berechneten Orientierungen der Hauptspannungsrichtungen sind: σ₁ 52 → 270, σ₂ 38 → 085 und σ₃ 06 → 174. Die Rotation der Hauptspannungsrichtungen war mit einer ?nderung von einem kompressionalen N-S gerichteten (D3) hin zu einem extensionalen (D4) Stressfeld verbunden. Die erzielten Ergebnisse sind sehr ?hnlich mit Resultaten, die Fl?ttmann und Oncken (1992) im Pf?lzer Wald ermittelten. Dies weist auf ein regional übereinstimmendes Spannungsfeld im SW-Teil der Mitteldeutschen Kristallinzone hin.

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Received July 8, 1999; revised version accepted March 28, 2000     

Simulating the moderating effect of a lake on downwind temperatures

A steady-state, two-dimensional numerical model is used to simulate air temperatures and humidity downwind of a lake at night. Thermal effects of the lake were modelled for the case of moderate and low surface winds under the cold-air advective conditions that occur following the passage of a cold front. Surface temperatures were found to be in good agreement with observations. A comparison of model results with thermal imagery indicated the model successfully predicts the downwind distance for which thermal effects due to the lake are significant.     

The IRAS PSCz dipole

We use the PSC z IRAS galaxy redshift survey to analyse the cosmological galaxy dipole out to a distance of 300  h ¹ Mpc. The masked area is filled in three different ways, first by sampling the whole sky at random, secondly by using neighbouring areas to fill a masked region, and thirdly using a spherical harmonic analysis. The method of treatment of the mask is found to have a significant effect on the final calculated dipole.
The conversion from redshift space to real space is accomplished by using an analytical model of the cluster and void distribution, based on 88 nearby groups, 854 clusters and 163 voids, with some of the clusters and all of the voids found from the PSC z data base.
The dipole for the whole PSC z sample appears to have converged within a distance of 200  h ¹ Mpc and yields a value for , consistent with earlier determinations from IRAS samples by a variety of methods. For b =1, the 2 range for ₀ is 0.431.02.
The direction of the dipole is within 13° of the cosmic microwave background (CMB) dipole, the main uncertainty in direction being associated with the masked area behind the Galactic plane. The improbability of further major contributions to the dipole amplitude coming from volumes larger than those surveyed here means that the question of the origin of the CMB dipole is essentially resolved.     

Living on the margin: Ethnoecological insights from Marshall Islanders at Rongelap atoll

Pacific Islanders who live on atolls are among the first people who have begun to be seriously impacted by the effects of global climate change. These are the people whose entire landscape is typically no higher than one meter above sea level. Extreme environmental changes are nothing new to these communities. Over many generations these atoll cultures have survived major, unpredictable and locally devastating changes that are of the same magnitude as those expected from climate changes. An examination of traditional ecological knowledge of Marshall Islanders at Rongelap atoll serves to illustrate some of the coping strategies that have enabled these people to be resilient in the past and in the current environmental crisis. Interviews revealed that these atoll dwellers actively manage the resources that are most likely to be impacted by climate change.