The transition from passive to active margin tectonics: a case study from the zone of Samedan (eastern Switzerland)

The Zone of Samedan is part of a fossil, early Mesozoic rift system originally situated in the distal, Lower Austro-Alpine domain of the Adriatic passive continental margin. An early Mesozoic configuration of asymmetrical rift basins bounded by relative structural highs compartmentalized Late Cretaceous active margin tectonics; Jurassic half-grabens were folded into arcuate synclines, whereas relative structural highs engendered thin, imbricated thrust sheets. West-directed thrusting and folding initiated at the surface and continued to depths favoring mylonitization under lower greenschist-facies conditions. At this time Liguria-Piemontese ophiolites were accreted to Lower Austro-Alpine units directly underlying the Zone of Samedan. Late Cretaceous orogenic collapse of the Adriatic active margin involved the reactivation of west-directed thrusts as low-angle, top-to-the-east, normal faults. These faults accommodated extensional uplift of Liguria-Piemontese ophiolites and Lower Austro-Alpine units beneath and within the Zone of Samedan. During Paleogene collision, some Late Cretaceous faults in the Zone of Samedan were reactivated under lower anchizonal conditions as north-directed thrusts. The latter stages of this early Tertiary thickening were transitional to brittle, high-angle normal faulting associated with top-to-the-east extension and spreading above the warm, uplifting Lepontine dome.     

Osmium Isotopic Evidence for Crust-Mantle Interaction in the Genesis of Continental Intraplate Basalts from the Newer Volcanics Province, Southeastern Australia

Basalts from the Quaternary Newer Volcanics Province in southeasternAustralia have a large diversity in their chemical and Nd, Srand Os isotopic compositions. Plains series olivine tholeiitesand Cones series nepheline hawaiites have distinctive isotopiccompositions and are clearly not related to each other by asimple genetic process. The Cones series nepheline hawaiiteshave trace element abundances and Nd (     

Glyptograptus? persculptus (Salter), its tectonic deformation,and its stratigraphic significance for the Carys Mills Formation of N.E. Maine,U.S.A.

The Carys Mills Formation of NE Maine represents the SW extension of the Matapedia Group and the White Head Formation of southern Gaspé, Quebec. This formation has yielded two main collections, one hitherto considered of Middle Ordovician age (zone 13 of Berry's 1960 Marathon, Texas, zonation) with 7 species referred to 4 genera, and one of the Early Silurian age. A revision of the supposed Middle Ordovician collections reveals that the graptolites are basal Silurian and consist of only one species, Glyptograptus? persculptus. Several hundred specimens, preserved both flattened and in three dimensions, the latter in iron pyrites, allow an analysis of both the rhabdosome changes wrought by diagenetic flattening and those caused by severe tectonic deformation. It is shown that those specimens lying parallel to the bedding plane lineation caused by a high-angle main cleavage have a silhouette appearance close to Glyptograptus tamariscus (Nicholson), whilst those at right angles to this direction superficially resemble robust Amplexograptus spp., or Diplograptus s.s., or Diplograptus s.l. spp., thus explaining the stratigraphic assignment of earlier workers. An analogue video reshaper confirms the above conclusions. This determination assigns the whole Carys Mills Formation to the Lower Silurian, but the possibility that part of the formation is of Late Ordovician age cannot be excluded. This much is suggested by the Matapedia Group and the White Head Formation which are of Late Ordovician to Early Silurian age, and the Honorat Group, which has yielded graptolites of late Middle Ordovician age.     

Isotopic composition of oxygen and hydrogen in mud-volcanic waters from Taman (Russia) and Kakhetia (Eastern Georgia)

The ¹⁸O and D values in mud-volcanic waters of the Taman Peninsula and Kakhetia vary from +0.7 to +10.0 and from –37 to –13 , respectively. These values increase as the Greater Caucasus is approached. The increase in 18O and D also positively correlates with fluid generation temperatures based on hydrochemical geothermometers. This is accompanied by changes in the chemical composition of waters, in which contents of alkali metals, HCO^– ₃ ion, and boron increase, while the content of halogen ions (Cl, Br, J) decreases. Changes in the isotopic composition of water are also accompanied by the increase of ¹³ in methane and decrease of ¹¹ B in clays. Analysis of formal models of the evolution of isotopic composition of mud-volcanic waters showed that mud volcanoes are recharged by freshened water from the Maikop paleobasin with an inferred isotopic composition of D –40 and ¹⁸ O –6. Based on this assumption, the ¹⁸O and D values observed in mud-volcanic waters can be explained not only by processes of distillation and condensation in a closed system, but also by combined processes of isotopic reequilibration in the water-illite-methane system.Translated from Litologiya i Poleznye Iskopaemye, No. 2, 2005, pp. 143–158.Original Russian Text Copyright © 2005 by Lavrushin, Dubinina, Avdeenko.     

Discovery of Arundian and Holkerian faunas from a Dinantian platform succession in North Wales

For the first time Arundian and Holkerian faunas have been recognized from the lower part of the Dinantian succession in North Wales. These limestones and sandstones, hitherto regarded as Asbian, have a macrofauna and microfauna confirming their older age, and this discovery' has necessitated a revision of the palaeogeography in the North Wales region. Biostratigraphical correlations have been made with contemporaneous platform successions in the Central, Northern, and Southwest Provinces of Britain. A new genus and species of foraminifer, Groessensella moldensis, is described.     

Mechanism of arrested charnockite formation at Nemmara, Palghat region, southern India

The formation of arrested charnockite is an excellent example of structurally controlled channellised fluid flow along specific sites accompanied by selective elemental mobility and mineralogical changes. The present paper recognises and focuses study on three types of arrested charnockite formation from Palghat region, namely, shear-controlled, foliation parallel and boudin-neck types, and address their spatio-temporal relations to regional-scale charnoenderbite. The shear-controlled and foliation parallel types post-date deformation and migmatisation. The boudin-neck type, on the contrary, is coeval with partial melting and followed the path of cooling and decreasing water activity in the gneiss. K-feldspar veining around plagioclase and quartz, symplectitic intergrowth of biotite+quartz after orthopyroxene and K-feldspar, and fluid inclusion data suggests the presence of alkalic supercritical brine and low-density CO₂-rich fluid during charnockite formation. Charnockite domains developed following the breakdown of hornblende, biotite and quartz are characterised by a more or less pronounced depletion of Fe, Ca, Mg and Ti and trace elements Y and Zr, compared to their counterpart gneiss. REE spectra indicate a subtle depletion in the HREE near the centre of the charnockite domain. Although close-pair samples of gneiss–charnockite are isochemical, on a scale of a few millimetres, bi-directional element movement, related to the formation of new mineral was noted. It is postulated that arrested charnockite formation developed in situ on local scale within the granitic domains of the hornblende-biotite gneiss, in the presence of CO₂-rich fluids and alkalic supercritical saline brine. This process post-dated the time of regional granulite (charnoenderbite) and large regional scale retrogression and migmatisation.     

Environmental Models and Public Stakeholders in the Chesapeake Bay Watershed

The Chesapeake Bay is not only North America's largest estuary, but it is also home to one of most comprehensive computational modeling efforts that seeks to study and integrate a very large range of the complex socio-ecological dynamics within its watershed. Known as the Chesapeake Bay Modeling System (CBMS), this suite of models are invaluable to scientists, environmental policymakers, resource managers, and local government and community leaders, all of whom are engaged in efforts to reduce the negative impacts of population growth and development in the watershed on the ecosystems and living resources of the Chesapeake Bay. Until recently, the results of the CBMS were used to guide voluntary efforts to reduce nutrient and sediment runoff into the Chesapeake Bay. However, the results are now being used to guide and evaluate the implementation of Watershed Implementation Plans at the state and county levels, which in turn are based on CBMS estimates of total maximum daily loads (TMDLs) for these sub-watershed regions. The use of the CBMS for these regulatory efforts has also increased the number of public stakeholders who are now able to directly inquire about the how the CBMS works and raise questions about its ability to accurately represent their land use decisions and practices. This "going public" of the CBMS has raised many societal and cultural issues, including the articulation of local expert and scientific knowledge, and modelers, scientists, policymakers, and resource managers are now realizing the need to understand more of the human dimensions arising from the translation and implementation of the CBMS. A multidisciplinary approach is needed to understand these rapidly emerging societal and cultural dimensions of the expanded use of the CBMS. In this paper, we draw upon our collective experience as social and natural scientists, with modeling experience, to describe a range of social, economic, political, and cultural issues that have emerged as a result of the CBMS being used to support mandatory nutrient reduction regulations (TMDL).