Cretaceous-Tertiary geodynamics: a North Atlantic exercise

New reconstructions are presented for the Cretaceous–Early Tertiary North Atlantic using a combination of palaeomagnetic, hotspot and magnetic anomaly data. We utilize these reconstructions in an analysis of previously described misfits between the North Atlantic Plate elements at successive intervals during this time period. We are able to achieve reasonable overlap between the hotspot and palaeomagnetic reconstructions between 40 and 95 Ma and thus are able to support the idea that the Indo–Atlantic hotspots are relatively stationary. Small, but systematic discrepancies for this time interval can readily be modelled with a long-term, octopole non-dipole field contribution (G3 = g₃⁰/g₁⁰ = 0.08). However, hotspot and palaeomagnetic reconstructions for the Early Cretaceous North Atlantic show substantial differences that cannot be explained by constant, non-dipole fields and we favour an explanation for these discrepancies in terms of true polar wander (TPW) triggered by mantle instabilities between 125 and 95 Ma; this constitutes the only identifiable event of significant TPW since the Early Cretaceous. Taken in the context of available geochronological and geological data and seismic tomography from the region, the 95–40 Ma reconstructions and their time-consequent geological products are interpreted in terms of specific conditions of mantle-crust coupling and global plate motions/tectonic activity. Highlights from these reconstructions show uniform NE movement of the coupled North American, Greenland and Eurasian plates from 95 to 80 Ma; a marked cusp in the paths for all three elements at 80 Ma where the three plates simultaneously change direction and follow a uniform NW-directed motion until c. 20 Ma when Eurasia diverges NE, away from the still-NW-moving Greenland and North American elements. Positioning of the Iceland plume beneath the spreading-ridge at 20 Ma may have increased upwelling below the ridge, increased the ridge-push, and caused a NE shift in the absolute direction of Eurasia

Zinc-Regulated DNA Binding of the Yeast Zap1 Zinc-Responsive Activator

The Zap1 transcription factor of Saccharomyces cerevisiae plays a central role in zinc homeostasis by controlling the expression of genes involved in zinc metabolism. Zap1 is active in zinc-limited cells and repressed in replete cells. At the transcriptional level, Zap1 controls its own expression via positive autoregulation. In addition, Zap1's two activation domains are regulated independently of each other by zinc binding directly to those regions and repressing activation function. In this report, we show that Zap1 DNA binding is also inhibited by zinc. DMS footprinting showed that Zap1 target gene promoter occupancy is regulated with or without transcriptional autoregulation. These results were confirmed using chromatin immunoprecipitation. Zinc regulation of DNA binding activity mapped to the DNA binding domain indicating other parts of Zap1 are unnecessary for this control. Overexpression of Zap1 overrode DNA binding regulation and resulted in constitutive promoter occupancy. Under these conditions of constitutive binding, both the zinc dose response of Zap1 activity and cellular zinc accumulation were altered suggesting the importance of DNA binding control to zinc homeostasis. Thus, our results indicated that zinc regulates Zap1 activity post-translationally via three independent mechanisms, all of which contribute to the overall zinc responsiveness of Zap1

Explanatory pluralism in the medical sciences: theory and practice

Explanatory pluralism is the view that the best form and level of explanation depends on the kind of question one seeks to answer by the explanation, and that in order to answer all questions in the best way possible, we need more than one form and level of explanation. In the first part of this article, we argue that explanatory pluralism holds for the medical sciences, at least in theory. However, in the second part of the article we show that medical research and practice is actually not fully and truly explanatory pluralist yet. Although the literature demonstrates a slowly growing interest in non-reductive explanations in medicine, the dominant approach in medicine is still methodologically reductionist. This implies that non-reductive explanations often do not get the attention they deserve. We argue that the field of medicine could benefit greatly by reconsidering its reductive tendencies and becoming fully and truly explanatory pluralist. Nonetheless, trying to achieve the right balance in the search for and application of reductive and non-reductive explanations will in any case be a difficult exercise

Greenland – Norway separation: A geodynamic model for the North Atlantic

Combining information from onshore and offshore Mid-Norway, we propose a structural model for the Scandinavian North Atlantic passive margin from Permo- Carboniferous through Present. We re-examine the role of post-Permo-Carboniferous normal faults and define an innermost boundary fault system forming the continentward limit of the rifted margin. Crustal-scale cross-sections of the Greenland- Norway passive margins show the asymmetric nature of crustal extension between the two conjugate margins. On both margins the upper plate/lower plate geometry and the dip of major extensional normal faults change across the broad width of the Jan Mayen Fracture Zone. South of this zone on the Møre Margin (Norway), the dip of the major faults is towards the west, defining a lower plate – tilted block margin. North of the transform on the Vøring-Trøndelag Margin (Norway), the major faults dip to the east, defining an upper plate or flexural margin. In the Norwegian passive margin, the transition occurs as a progressive change of vergence of normal faults between the northern Vøring-Trøndelag Platform area and the Møre Basin. The model shows continuous separation between the two conjugate margins of Greenland and Norway, starting with a very tight fit in Late Permian time. The rifting events between Late Permian and Late Cretaceous are associated with a broadly WSW-ENE- to W-E- oriented extension while Late Cretaceous to Early Tertiary extension directions are oriented NNW-SSE. These plate separation directions and the subsequent plate motion can be related to the important basin development within, and probably, to the structural evolution and geometry of, the conjugate passive margins

The Nesna Shear Zone, north-central Norway: An 40Ar/ 39Ar record of Early Devonian -Early Carboniferous ductile extension and unroofing

In north-central Norway, Ar/Ar ages from a profile through the Nesna Shear Zone (NSZ) and into the underlying Sjona window, a gneiss-cored culmination, document time of onset of ductile shearing and two episodes of unroofing for the crustal package. A progressive decrease in white mica and biotite ages from 397.8 ± 1.0 to 378.3 ± 0.9 Ma, downward through the tectonostratigraphy, conforms to an overall pattern of cooling and argon retention as the crustal section was progressively unroofed. The age differences between the NSZ and Sjona window micas allow us further to distinguish two kinematically distinct events. White mica and biotite ages within the NSZ fall between 397.8 ± 1.0 and 387.1 ± 0.8 Ma and correspond closely to time of genesis of the ductile, top-WSW stretching fabrics within the shear zone. Biotites within the Sjona window lack the same ductile fabric and instead record younger cooling largely between 384.3 ± 1.0 and 378.3 ± 0.9 Ma. Sjona window biotites passed through closure temperatures similar to those in the NSZ, but under conditions dominated by positive buoyancy of the Sjona gneisses, aided by shortening normal to the top-WSW stretching direction. Unroofing or 'doming' of the Sjona window was almost certainly promoted, and perhaps accelerated, by earlier, NSZ-related extension in the overlying nappe pile. Extension had waned by latest Mid Devonian time when the shear-zone system was overtaken by activity on younger, steeper, ductile-to-brittle extensional faults. K-feldspar ages from the Sjona window yield a pronounced Early Carboniferous signature (335-346 Ma) that we attribute to a second episode of rapid cooling and unroofing, after top-WSW ductile motion on the NSZ had ceased. We relate unroofing to motion on the steeper and younger faults that cut low-angle ductile shear zones like the NSZ. Early Carboniferous unroofing in north-central Norway would have been contemporaneous with widespread, Late Devonian-Early Carboniferous tectonic activity documented around the Caledonian perimeter. These mica and K-feldspar ages are the first published from north-central Norway and promote a picture of widespread, Early-Mid Devonian top-W to -SW ductile extension and latest Devonian-Early Carboniferous unroofing, operating at several tectonostratigraphic levels within the disintegrating Scandinavian Caledonide orogen

Modern techniques and Old Red problems - Determining the age of continental sedimentary deposits with40Ar/39Ar provenance analysis in west-central Norway

Ages of continental 'Old Red Sandstone' (ORS) deposits in Norway have been notoriously difficult to obtain due to the paucity of fossil-bearing horizons. In general, Ar/Ar ages from detrital mica and K-feldspar from unmetamorphosed, first-cycle sedimentary units yield maximum ages for sediment deposition since the detrital grains retain the ages of their crystalline basement provenance. To determine the maximum age for a presumed Lower-Middle Devonian ORS sequence in west-central Norway - the Asenoya basin - we applied Ar/Ar geochronology to detrital white micas in red sandstone, and to white mica, biotite and K-feldspar from three different whole-rock clasts in an overlying conglomerate. Single-grain laser fusion of white mica from the sandstone yielded ages ranging between 416 ±4 and 386 ±1 Ma, with the majority of grains between ca. 400 and 392 Ma. Furnace step-heating of white mica, biotite and K-feldspar from the three rock clasts yielded weighted-mean ages of 410.2 ±3.5 Ma, 402.7 ±3.5 Ma and 371.0 ±3.2 Ma, respectively. Published white mica and biotite Ar/Ar cooling ages from the Central Norway basement window (CNBW), to the east and north of Asenoya, range from ca. 398 to 388 Ma; white mica and biotite Ar/Ar cooling ages from the Seve and Köli Nappes, above the CNBW, range from ca. 432 to 402 Ma. Both of these primary source regions-the CNBW and the nappes-are thus represented in the red sandstone and conglomerate detritus. K-feldspar Ar/Ar ages from local, CNBW basement (published age of 371 ±8 Ma) and from orthogneiss in an offshore, in situ basement horst (377.3 ±3.4 Ma, this study) further confirm the presence of appropriately-aged, proximal basement sources of CNBW type for some of the ORS conglomerate clasts. The new provenance age data demonstrate that some of the west-central Norway ORS units are younger than ca. 371 Ma-or a minimum of Late Devonian to Early Carboniferous age if time for unroofing/erosion of the basement provenance is allowed. The Asenoya sedimentary deposits are, thus, the youngest yet documented in the Norway ORS and are the last remnants of the Paleozoic sedimentary deposits of the Norwegian Caledonides that subsequently became recycled in offshore Mesozoic sedimentary basins

Compilation and appraisal of geochronological data from the North Atlantic Igneous Province (NAIP)

NAG-TEC Geochronological Databas