Petrology and geochronology of eclogites from the Variscan Schwarzwald (F.R.G.)

The Moldanubian basement of the Schwarzwald contains basic to ultrabasic rocks of both crustal and mantle origin which display high-pressure mineral assemblages or relics of such. In order to constrain the P-T-t evolution of the crustal high-pressure rocks, petrological and geochronological studies have been carried out on three eclogite samples. Geothermobarometric estimations indicate minimum metamorphic pressures of 1.6 GPa and equilibration temperatures of 670 750°C. Reaction textures document various metamorphic stages during exhumation of the high-pressure rocks. The age of high-pressure metamorphism is constrained by Sm-Nd isochrons of 332±13 Ma, 334±11 Ma, and 337±6 Ma defined by garnet, whole rock and clinopyroxene. For one sample, large garnets show prominent growth zoning in terms of major elements, Sm, Nd, and inclusions, dividing the grains into two growth stages. Sm-Nd isotope analyses on these garnets indicate that the time span between the two growth stages is too small to be resolved, reflecting a rather rapid metamorphic evolution. This result is further constrained by a Rb-Sr isochron age of 325±6 Ma on retrograde biotite and whole rock on the same sample. For one of the studied eclogites, formation of the magmatic precursor rocks is possibly approximated by the Ordovician U-Pb upper intercept age of a discordia from zircons.     

Active Galactic Nuclei

D01 Direct evidence of the receding ‘torus’ around active galactic nuclei of FRII radio galaxies and quasars D02 Infrared emission from a clumpy and dusty torus around AGN D03 Size and properties of AGN narrow–line regions from emission–line diagnostics D04 Structural Variability of Intraday Variable Sources D05 Stability of self‐gravitating accretion disks in galactic centers D06 Supermassive Binary Black Holes in AGN D07 The extreme flare in III Zw 2: Evolution of a radio jet in a Seyfert galaxy D08 Radio Linear and Circular Polarization from M81* D09 A fundamental relation between Supermassive Black Holes and Dark Matter Haloes D10 Hunting for radio‐quiet BL Lacs – the 2dF BL Lac survey D11 The Eddington limit in accretion discs D12 Molecular Tori in AGN: A search using excited states of OH D13 The X‐Ray Properties of Radio‐Loud Core‐Dominated AGN: The 2 cm‐X‐Sample D14 The X‐Ray Properties of Radio‐Loud Core‐Dominated AGN: Extension to the High Redshift Regime D15 Line Profile Variability in AGN D16 Jet Superwind Interaction D17 Radio Interferometric Observations of AGN – Probing the Nucleus of M87 with 20 Schwarzschild radii resolution D18 The ISO–2MASS AGN survey D19 Supermassive binary black holes driving the activity of galactic nuclei D20 Proton acceleration at quasi‐perpendicular shocks: A case study for Active Galactic Nuclei D21 Super‐luminal shocks in Active Galactic Nuclei D22 Unconventional quasars from the variability and proper motion survey D23 Radio observations of starburst and AGN activity in Ultraluminous Infrared Galaxies D24 Kinematics in Active Galactic Nuclei at Parsec Scales: the VLBA 2cm Survey D25 Three‐dimensional models of clumpy tori in Seyfert galaxies D26 Silicate emission in active galaxies ‐ From LINERs to QSOs D27 Discovery of 10 µm silicate emission in quasars. – Evidence of the AGN unification scheme. D28 Near‐IR adaptive optics imaging of luminous infrared galaxies D29 Interferometric observations of the Circinus galaxy with MIDI D30 Infrared Interferometry of the Seyfert Galaxy NGC 1068     

Soil hydraulic conductivities of latosols under pasture,forest and teak in Rondonia,Brazil

We investigated the changes of saturated hydraulic conductivity, K_sat , with depth of latosols developed on Precambrian basement rocks under primary rainforest, pasture and teak. In all cases, K_sat decreased with depth, with most of the decrease occurring between the surface and a depth of 30 cm. In conjunction with prevailing rainfall intensities and frequencies, this anisotropy supports a pronounced lateral component of hillslope flow paths, and also of overland flow under pasture. Our results are at variance with data from other latosols where K_sat tends to increase with depth, and hence suggest that considerable restraint is needed in generalization and extrapolation until results from a co‐ordinated effort at hydrology‐oriented data collection become available. Copyright © 1999 John Wiley & Sons, Ltd.     

The Bronze Age occupation of the Black Sea coast of Georgia—New insights from settlement mounds of the Colchian plain

Along the lower course of the Rioni and several minor rivers, more than 70 settlement mounds (local name: Dikhagudzuba) have been identified by field surveys and remote sensing techniques. They give evidence of a formerly densely populated landscape in the coastal lowlands on the Colchian plain (western Georgia) and have been dated to the Bronze Age. As yet, limited information is available on their internal architecture, the chronology of the different layers and their palaeoenvironmental context. Based on archaeological sources, remote sensing measurements of three mounds and sediment cores from one mound and its closer surroundings, our study presents a review of the relevant literature and reveals the internal structure, distribution and spatial extent of the mounds. Geochemical and sedimentological analyses of element contents (X-ray fluorescence) and granulometry helped to identify different stratigraphical layers and differentiate between natural facies and anthropogenic deposits; using the Structure-from-Motion technique the mounds' dimensions were calculated. The studied settlement mounds had relatively small dimension (varying from 30 to 100 m in diameter) and were similar in their stratigraphy. Measurement of elements that can identify types of human activity, notably metals and phosphorus, suggest changing intensities of human occupation, pastoral agriculture and metalworking through the occupation sequence. According to the ¹⁴C chronology, the formation of the settlements occurred during the first half of the second millennium B.C., which confirms the archaeological interpretation of their Bronze Age origin. The narrow age difference between the lowermost and uppermost anthropogenic layers indicates an intentional construction of the mounds, rather than a successive accumulation of construction debris due to the disintegration of loam bricks by weathering. Therefore, they are indeed mounds and not tells. It is most likely that the characteristic circular moats that surround them were the source of their construction material. Fluvial and alluvial processes in a warm and humid climate dominated the environment of the mounds.     

The Rapid Retreat of Jakobshavns Isbræ, West Greenland: Field Observations of 2005 and Structural Analysis of its Evolution

Jakobshavns Isbræ in West Greenland (terminus at ≈69° 10′ N/50° W), a major outlet glacier of the Greenland Ice Sheet and a continuously fast-moving ice stream, has long been the fastest moving and one of the most productive glaciers on Earth. It had been moving continuously at speeds of over 20 m/day with a stable front position throughout most of the latter half of the twentieth century, except for relatively small seasonal changes. In 2002, the ice stream apparently suddenly entered a phase of rapid retreat. The ice front started to break up, the floating tongue disintegrated, and the production of icebergs increased. In July 2005, we conducted an extensive aerial survey of Jakobshavns Isbræ to measure and document the present state of retreat compared to our previous field observations since 1996. We use an approach that combines structural analysis of deformation features with continuum mechanics to assess the kinematics and dynamics of glaciers, based on aerial imagery, satellite data and GPS measurements. Results from interpretation of ERS-SAR and ASTER data from 1995 to 2005 in combination with aerial imagery from 1996 to 2005 shed light on the question of changes versus stability and their causes in the Jakobshavns Isbræ dynamical system. The recently observed retreat of Jakobshavns Isbræ is attributed to climatic warming, rather than to an inherent change in the glaciodynamic system. Close to the retreating front, deformation structures are characteristic of extension and disintegration. Deformation provinces that do not border the retreating front have had the same deformation characteristics throughout the past decade (1996–2005).     

Pb/Pb age determinations on the Newania and Sevattur carbonatites of India: evidence for multi-stage histories

The ages of Indian carbonatites are still controversial. Most of the earlier datings were done by K/Ar methods. We therefore analysed Pb/Pb ratios in carbonatites from carbonatite-alkalic complexes of Newania (NW India, Rajasthan State) and Sevattur (SW India, Tamil Nadu State) to constrain the age and geological history of these rocks. Newania carbonatites are intrusive into Precambrian Untala granite-gneiss and mainly dolomitic in composition (rauhaugite) followed by a later phase of ankerite carbonatite, while thin calcite carbonatite (sövite) dykelets are the youngest in the sequence. The analysed whole-rock samples are characterised by ²⁰⁶Pb/²⁰⁴Pb ratios between 60 and 176 and ²⁰⁷Pb/²⁰⁴Pb ratios between 22 and 40, which are extremely high in comparison to common igneous rocks and even for carbonatite compositions. One sample, New 37, shows the extreme ratios of ²⁰⁶Pb/²⁰⁴Pb = 574 and ²⁰⁷Pb/²⁰⁴Pb = 73. This requires a μ-value of about 2000 for the last 1550 Ma. If the samples are classified according to their petrographic/geochemical characteristics this results in an isochron age of 1551 ± 46 Ma for the ankerite carbonatites (six samples). The dolomites (6 samples) yield an isochron age of 2.27 Ga. Although these results fit quite well into the geological evolution scheme of the area, the extreme long age hiatus between dolomite carbonatite and ferrocarbonatite formation events raises severe problems for their petrologic interpretation.

The Proterozoic Sevattur carbonatite complex (SCC, Tamil Nadu) was emplaced contemporaneously with a large number of carbonatite complexes within the Precambrian gneissic terrane of the Eastern Ghats Mobile Belt. The main mass is composed of dolomite carbonatite (rauhaugite) with a few dikes of calcite carbonatite (sövite) and ankerite carbonatite within it. All eight samples together yield an isochron of 805 ± 10 Ma. This isochron is mainly determined on ankerite carbonatites with μ-values up to 1900 for the last 800 Ma. Taking only ankerite carbonatites into account, the resulting age is 801 ± 11 Ma. The ²⁰⁶Pb/²⁰⁴Pb and ²⁰⁷Pb/²⁰⁴Pb ratios of these samples are similar to the main group of Newania and far beyond the isotopic composition of common igneous rocks.

Our investigations show that in carbonatitic rock systems extremely high lead isotopic ratios can be established due to the crystallization of uranium-rich mineral phases. In both cases the observed high to extremely high initial Pb isotope ratios require the residence of the lead in intermediate high-μ reservoirs either within the upper mantle or the crust prior to the carbonatite formation. A high-temperature event, which completely reset the Rb/Sr and K/Ar isotopic systems of Nevania carbonatites, seems to have no influence on the lead isotopic systematics.     

藏南定日剖面晚白垩世菊石和叠瓦蛤类的首次发现:生物地层和古环境意义(英文)

藏南定日遮普惹山剖面主要是Albian 晚期到古近纪海相沉积, Willems 等( 1996 )对岩石地层和沉积微相进行了详细研究,并通过浮游有孔虫研究建立生物地层格架。在与岗巴地区地层对比基础上,该剖面被认为是整个藏南地区白垩纪—古近纪海相地层的标准剖面。2004 年我们与中国、德国同行一道对该剖面上白垩统地层进行再考察,重点对无脊椎动物化石样品进行采集和研究。与西藏大多数白垩纪剖面一样,尽管沉积环境为陆棚环境,该剖面以前却几乎没有菊石和叠瓦蛤类化石的报道,而同样环境下的世界其他地区剖面含有大量的菊石和叠瓦蛤类化石。藏南定日剖面重新调查后发现了少量的菊石和叠瓦蛤类化石。化石数量少一方面是由于灰泥质灰岩和泥灰质灰岩内化石保存状况差,另一方面采样条件也不理想。还有,当时的环境条件可能不利于大多数无脊椎动物类群的生存,这一点或许从大量存在于岗巴群上部的小个体双壳类碎片可以得到证实。尽管获得的化石分散并且保存差,本次研究仍获得了一些有价值的生物地层数据。岗巴群上部发现的化石Calycoceras?,指示其时代为Cenomanian 晚期,随后出现不能鉴定的desmoceratids类的幼体。之上,菊石Forresteria sp.的发现表明岗巴群顶部地层属于Coniacian下部,这被同一地层内发现的其他化石所支?