Migmatization of Archean aluminous metasediments from the eastern Beartooth Mountains, Montana, U.S.A.

Geothermobarometry, mineral compositions and textures, and thermodynamic models suggest biotite dehydration melting occurred in the peraluminous rocks of the eastern Beartooth Mountains. These Archean metapelitic migmatites are metatexites and diatexites, and have typical metamorphic assemblages of Qtz + Pl + Kfs + Bt + Sil +/- Grt +/- Crd. The subsequent in situ crystallization of the magma derived from the biotite dehydration created migmatitic leucosomes in the rocks. These leucosomes are primarily composed of quartz, plagioclase and potassium feldspar. Water derived from the dehydration of biotite was dissolved in the melted phase. Crystallization of the magma reintroduced this water to the system, allowing reversal of the biotite dehydration melting reactions on the retrograde pressure/temperature path. This rehydration event produced melanosomes, primarily composed of biotite, sillimanite and garnet. The volumetric and conceptual significance of theses melanosomes suggest that retrograde processes are of major importance to the formation of textures in pelitic migmatites. Geothermobarometry suggests that these rocks attained peak conditions of 795° +/- 42° C and 7.0 +/- 0.9 kbar. The interpreted pressure/temperature path is isobaric heating above four kilobars to 795°. At peak temperature, a nearly isothermal compression occurred, raising the pressure to seven kilobars. This roughly counterclockwise (in P/T space) trajectory is consistent with a thermal event due to local emplacement of granitic plutons, subsidence due to magmatic thickening, and later uplift and unroofing. Trace element heterogeneities in sillimanite, revealed by Scanning Electron Microscopy-Cathodoluminescence Imaging (SEM-CL), suggest multiple stages of growth and dissolution of this mineral throughout the metamorphic cycle. The interpretation of these heterogeneities involves initial prograde production of sillimanite, and subsequent dissolution during the biotite dehydration melting reactions. Further sillimanite and biotite is formed during retrograde metamorphism, and enriched in chromium by a late-stage hydration event

Standardisation of data collection in traumatic brain injury: key to the future?

Great variability exists in data collection and coding of variables in studies on traumatic brain injury (TBI). This confounds comparison of results and analysis of data across studies. The difficulties in performing a meta-analysis of individual patient data were recently illustrated in the IMPACT project (International Mission on Prognosis and Clinical Trial Design in TBI): merging data from 11 studies involved over 10 person years of work. However, these studies did confirm the great potential for advancing the field by this approach. Although randomized controlled trials remain the prime approach for investigating treatment effects, these can never address the many uncertainties concerning multiple treatment modalities in TBI. Pooling data from different studies may provide the best possible source of evidence we can get in a cost efficient way. Standardisation of data collection and coding is essential to this purpose. Recommendations hereto have been proposed by an interagency initiative in the US. These proposals deserve to be taken forward at an international level. This initiative may well constitute one of the most important steps forwards, paving the road for harvesting successful results in the near future

Monitoring prognosis in severe traumatic brain injury

The choice of disease-specific versus generic scales is common to many fields of medicine. In the area of traumatic brain injury, evidence is coming forward that disease-specific prognostic models and disease-specific scoring systems are preferable in the intensive care setting. In monitoring prognosis, the use of a calibration belt in validation studies potentially provides accurate and intuitively attractive insight into performance. This approach deserves further empirical evaluation of its added value as well as its limitations

Cerebrospinal fluid enzymes in acute brain injury

Severe brain injury is a major cause of death, especially in young men. In 1972, over 20% of all deaths occurring in England and Wales in men aged 15-25 years were due to head injury (Field, 1976). The mortality rate after severe brain injuries is higb. Jennett et al. (1977) reporting on a large international study comprising 700 patients describe a 53% mortality rate. In this study patients with brain injuries were studied in whom consciousness was suppressed for a period of at least six hours to a degree that inability to obey commands, to speak, or to open the eyes existed. Studies reported from different parts of Europe show a similar mortality rate (table 1 ). Not only do severe brain injuries call a large death toll, but many of the patients who survive remain disabled, often for life. Of 65 patients who were admitted to the University Hospital of Rotterdam in the period 1974-1976 with severe brain injury and were still alive after 6 months, 24 (37%) were disabled at that time. Disability may be due to physical sequelae, to disturbances of mental function, which are especially common following head injuries, or to difficulties arising when social reintegration is attempted