Triassic pegmatites in the Mesozoic middle crust of the Southern Alps (Italy): Fluid inclusions, radiometric dating and tectonic implications

The schists in the northern part of the South-Alpine crystalline basement along Lake Como record Barrovian syn-kinematic metamorphism of Variscan age. They cooled below the Rb-Sr whole rock closing temperature at ca. 300 Ma and were exhumed by ca. 6-7 km before the Late Permian. In the Middle Triassic a thermal perturbation affected the South-Alpine middle crust leading to the widespread transformation of garnets into biotite + sillimanite aggregates under static conditions. Anatectic pegmatites were emplaced roughly contemporaneous with the peak temperature conditions. Rb-Sr mineral ages on pegmatites, schists and marbles between 229 and 194 Ma show the crust was again cooling during the Late Triassic, when continental rifting started. Stretching leading eventually to the opening of the Ligurian-Piemont ocean continued until Middle Jurassic times. Fluid inclusion data from the pegmatites establish that only limited decompression took place during Late Triassic to Early Cretaceous cooling. As a result of Alpine shortening, the rocks were eventually exhumed to the surface

Integrated stratigraphy and 40Ar/39Ar chronology of the Early to Middle Miocene Upper Freshwater Molasse in eastern Bavaria (Germany)

A detailed integrated stratigraphic study was carried out on middle Miocene fluvial successions of the Upper Freshwater Molasse (OSM) from the North Alpine Foreland Basin, in eastern Bavaria, Germany. The biostratigraphic investigations yielded six new localities thereby refining the OSM biostratigraphy for units C to E (sensu; Heissig, Actes du Congres BiochroM'1997) and further improving biostratigraphic correlations between the different sections throughout eastern Bavaria. Radioisotopic ages of 14.55 ± 0.19 and 14.88 ± 0.11 Ma have been obtained for glass shards from the main bentonite horizon and the Ries impactite: two important stratigraphic marker beds used for confirming our magnetostratigraphic calibration to the Astronomical Tuned Neogene Time Scale (ATNTS04; Lourens et al. in Geologic Time Scale 2004, Cambridge University Press, 2004). Paleomagnetic analysis was performed using alternating field (AF) and thermal (TH) demagnetization methods. The AF method revealed both normal and reverse polarities but proofs to yield unreliable ChRM directions for the Puttenhausen section. Using the biostratigraphic information and radioisotopic ages, the magnetostratigraphic records of the different sections are tentatively correlated to the Astronomical Tuned Neogene Time Scale (ATNTS04; Lourens et al. in Geologic Time Scale 2004, Cambridge University Press, 2004). This correlation implies that the main bentonite horizon coincides to chron C5ADn, which is corroborated by its radioisotopic age of 14.55 Ma, whereas the new fossil locality Furth 460, belonging to OSM unit E, probably correlates to chron C5Bn.1r. The latter correlation agrees well with the Swiss Molasse locality Frohberg. Correlations of the older sections are not straightforward. The Brock horizon, which comprises limestone ejecta from the Ries impact, possibly correlates to C5ADr (14.581 ± 14.784 Ma), implying that, although within error, the radioisotopic age of 14.88 ± 0.11 Ma is somewhat too old. The fossil localities in Puttenhausen, belonging to the older part of OSM unit C, probably coincide with chron C5Cn.2n or older, which is older than the correlations established for the Swiss Molasse. © Springer-Verlag 2007

40Ar/39Ar geochronology of Holocene basalts; examples from Stromboli, Italy

Absolute chronologies of active volcanoes and consequently timescales for eruptive behaviour and magma production form a quantitative basis for understanding the risk of volcanoes. Surprisingly, the youngest records in the geological timescale often prove to be the most elusive when it comes to isotopic dating. Absolute Holocene volcanic records almost exclusively rely on 14C ages measured on fossil wood or other forms of biogenic carbon. However, on volcanic flanks, fossil carbon is often not preserved, and of uncertain origin when present in paleosols. Also, low 14C-volcanic CO2 may have mixed with atmospheric and soil 14C-CO2, potentially causing biased ages. Even when reliable data are available, it is important to have independent corroboration of inferred chronologies as can be obtained in principle using the 40K/40Ar decay system. Here we present results of a 40Ar/39Ar dating study of basaltic groundmass in the products from the Pleistocene – Holocene boundary until the beginning of the historic era for the north-northeastern flank of Stromboli, Aeolian Islands, Italy, identifying a short phase of intensified flank effusive activity 7500±500 yrs ago, and a maximum age of 4000±900 yr for the last flank collapse event that might have caused the formation of the Sciara del Fuoco depression. We expect that under optimum conditions 40Ar/39Ar dating of basaltic groundmass samples can be used more widely for dating Holocene volcanic events

When did the Indus River of South-Central Asia take on its “modern” drainage configuration?

For sedimentary archives to be used as a record of hinterland evolution, the factors affecting the archive must be known. In addition to tectonics, a number of factors, such as changes in climate and paleodrainage, as well as the degree of diagenesis, influence basin sediments. The Indus River delta-fan system of South-Central Asia records a history of Himalayan evolution, and both the onshore and offshore sedimentary repositories have been studied extensively to research orogenesis. However, a number of unknowns remain regarding this system. This paper seeks to elucidate the paleodrainage of the Indus River, in particular when it took on its modern drainage configuration with respect to conjoinment of the main Himalayan (Punjabi) tributary system with the Indus trunk river. We leverage the fact that the Punjabi tributary system has a significantly different provenance signature than the main trunk Indus River, draining mainly the Indian plate. Therefore, after the Punjabi tributary system joined the Indus River, the proportion of Indian plate material in the repositories downstream of the confluence should have been higher than in the upstream repository. We compared bulk Sr-Nd data and detrital zircon U-Pb data from the Cenozoic upstream peripheral foreland basin and downstream Indus delta and Indus Fan repositories. We determined that throughout Neogene times, repositories below the confluence had a higher proportion of material from the Indian plate than those above the confluence. Therefore, we conclude that the Indus River took on its current configuration, with the Punjabi tributary system draining into the Indus trunk river in the Paleogene, early in the history of the orogen. The exact time when the tributary system joined the Indus should correlate with a shift to more Indian plate input in the downstream repositories only. While the upstream repository records no change in Indian plate input from Eocene to Neogene times, a shift to increased material from the Indian plate occurs at the Eocene−Oligocene boundary in the delta, but sometime between 50 Ma and 40 Ma in the fan. Though further work is required to understand the discrepancy between the two downstream repositories, we can conclude that the tributary system joined the Indus trunk river at or before the start of the Oligocene

Large scale pantelleritic ash flow eruptions during the Late Miocene in central Kenya and evidence for significant environmental impact

In the area south-east of Mount Kenya, four previously unrecorded peralkaline rhyolitic (pantelleritic) ash flow tuffs have been located. These predominantly greyish welded and non-welded tuffs form up to 12 m thick units, which are sometimes characterized by a basal vitrophyre. The four flow units yielded 40Ar/39Ar ages ranging from 6.36 to 8.13 Ma, indicating a period of ~ 1.8 Ma of pantelleritic volcanic activity during the Late Miocene in central Kenya. Tentative compositional and age correlations with other known tuff deposits suggest that the pantelleritic tuffs originally covered 40,000 km2 in central Kenya, extending much further than earlier recorded Pliocene tuffs. This newly identified magmatic phase occurred between the phonolitic flood eruptions (16–8 Ma) and the Pliocene tuff eruptions (6–4 Ma). The occurrence of multiple ash flow tuff deposits up to 150 km away from the inferred eruptive center(s) in the central sector of the Kenya Rift, indicates multi-cyclic peralkaline supereruptions during the Late Miocene. By analogy with more recent pantelleritic eruptions, the tuffs are thought to have been sulfur-rich; during eruption, they formed stratospheric aerosols, with significant environmental impact. The timing of the eruptions coincides with the shift towards more savannah-dominated environments in East Africa

Automatic generation of scheduling and communication code in real-time parallel programs

Inter-process communication and scheduling are notorious problem areas in the design of real-time systems. Using CASE tools, the system design phase will in general result in a system description in the form of parallel processes. Manual allocation of these processes to processors may result in error prone and/or slow communication code. Scheduling of the processes, necessary to meet timing constraints, is also a tedious task that takes many iterations. The described design tools result in code that is comparable in quality and performance with expert manual realization. Many network layers have been implemented to relieve the user from the low-level programming of communication software. However, the increase in user-friendliness is usually paid with performance degradation. The proposed approach combines user-friendliness with high performance by generating communication software that is tailor-made for the application. A similar approach is followed with the scheduling software. Schedulers in the form of a built-in a kernel are available all the time and cause overhead all the time. The proposed preprocessor tool generates scheduling software after analyzing the timing requirements of the particular application. This results in simple code for simple timing requirements and more complicated code for complex timing requirements. The tools have been implemented in Occam for use on a transputer. However, the results are valid for any distributed memory machine

Interpreting and reporting ⁴⁰Ar/³⁹Ar geochronologic data

The ⁴⁰Ar/³⁹Ar dating method is among the most versatile of geochronometers, having the potential to date a broad variety of K-bearing materials spanning from the time of Earth’s formation into the historical realm. Measurements using modern noble-gas mass spectrometers are now producing ⁴⁰Ar/³⁹Ar dates with analytical uncertainties of ∼0.1%, thereby providing precise time constraints for a wide range of geologic and extraterrestrial processes. Analyses of increasingly smaller subsamples have revealed age dispersion in many materials, including some minerals used as neutron fluence monitors. Accordingly, interpretive strategies are evolving to address observed dispersion in dates from a single sample. Moreover, inferring a geologically meaningful “age” from a measured “date” or set of dates is dependent on the geological problem being addressed and the salient assumptions associated with each set of data. We highlight requirements for collateral information that will better constrain the interpretation of ⁴⁰Ar/³⁹Ar data sets, including those associated with single-crystal fusion analyses, incremental heating experiments, and in situ analyses of microsampled domains. To ensure the utility and viability of published results, we emphasize previous recommendations for reporting ⁴⁰Ar/³⁹Ar data and the related essential metadata, with the amendment that data conform to evolving standards of being findable, accessible, interoperable, and reusable (FAIR) by both humans and computers. Our examples provide guidance for the presentation and interpretation of ⁴⁰Ar/³⁹Ar dates to maximize their interdisciplinary usage, reproducibility, and longevity