9,784 research outputs found
Geology of the Snap Lake kimberlite intrusion, Northwest Territories, Canada: field observations and their interpretation
The Cambrian (523 Ma) Snap Lake hypabyssal kimberlite intrusion, Northwest Territories, Canada, is a complex segmented diamond-bearing ore-body. Detailed geological investigations suggest that the kimberlite is a multi-phase intrusion with at least four magmatic lithofacies. In particular, olivine-rich (ORK) and olivine-poor (OPK) varieties of hypabyssal kimberlite have been identified. Key observations are that the olivine-rich lithofacieshas a strong tendency to be located where the intrusion is thickest and that there is a good correlation between intrusion thickness, olivine crystal size and crystal content. Heterogeneities in the lithofacies are attributed to variations in intrusion thickness and structural complexities. The geometry and distribution of lithofacies points to magmaticco-intrusion, and flow segregation driven by fundamental rheological differences between the two phases. We envisage that the low-viscosity OPK magma acted as a lubricant for the highly viscous ORK magma. The presenceof such low-viscosity, crystal-poor magmas may explain how crystal-laden kimberlite magmas (>60 vol.%) are able to reach the surface during kimberlite eruptions. We also document the absence of crystal settling and the development of an unusual subvertical fabric of elongate olivine crystals, which are explained by rapid degassing-induced quench crystallization of the magmas during and after intrusio
The extended Main Sequence Turn Off cluster NGC1856: rotational evolution in a coeval stellar ensemble
Multiple or extended turnoffs in young clusters in the Magellanic Clouds have
recently received large attention. A number of studies have shown that they may
be interpreted as the result of a significant age spread (several 10^8yr in
clusters aged 1--2 Gyr), while others attribute them to a spread in stellar
rotation. We focus on the cluster NGC 1856, showing a splitting in the upper
part of the main sequence, well visible in the color m_{F336W}-m_{F555W}$, and
a very wide turnoff region. Using population synthesis available from the
Geneva stellar models, we show that the cluster data can be interpreted as
superposition of two main populations having the same age (~350Myr), composed
for 2/3 of very rapidly rotating stars, defining the upper turnoff region and
the redder main sequence, and for 1/3 of slowly/non-rotating stars. Since rapid
rotation is a common property of the B-A type stars, the main question raised
by this model concerns the origin of the slowly/non-rotating component. Binary
synchronization is a possible process behind the slowly/non-rotating
population; in this case, many slowly/non-rotating stars should still be part
of binary systems with orbital periods in the range from 4 to 500 days. Such
periods imply that Roche lobe overflow occurs, during the evolution of the
primary off the main sequence, so most primaries may not be able to ignite core
helium burning, consistently why the lack of a red clump progeny of the slowly
rotating population.Comment: 8 pages 4 figures, accepted for publication on Monthly Notices of the
R.A.
Métodos para coleta de parasitos de peixes
Insensibilização dos peixes; Dados biométricos; Sequência de procedimentos para coleta de parasitos de peixe; Detecção e métodos de fixação de parasitos de peixes; Preparação dos reagentes fixadores de parasitos;bitstream/item/46620/1/AP-2011-Metodos-coleta-Circular.pd
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