On aluminous and edenitic hornblendes

1971 ◽  
Vol 38 (296) ◽  
pp. 389-407 ◽  
Author(s):  
Bernard E. Leake
Keyword(s):  
High Pressure ◽  
Low Temperatures ◽  
Metamorphic Rocks ◽  
Critical Examination ◽  
Increase With Increase ◽  
Calciferous Amphibole

SummaryBased on nearly 1500 published amphibole analyses the maximum possible Alvi in hornblendes is shown to increase with increase of Aliv. New analyses of hornblendes from amphibole-corundum rocks, with and without anorthite, are given and after critical examination of the available data it is concluded that the maximum verified Alvi-rich calciferous amphibole that approaches the closest to hypothetical tschermakite comes from a kyanite-bearing aluminous high-pressure-crystallized schist from Lukmanier, Switzerland. Pure natural edenite or ferroedenite is unknown, but a new analysis of the nearest known natural edenite, from Mysore, India, agrees with the postulated view that extraordinarily low temperatures are needed for edenite-ferroedenite crystallization, much below that possible in magmas and only rarely achieved in metamorphic rocks containing amphiboles. The limit of the approach of igneous hornblendes to edenite-ferroedenite and tremolite-ferroactinolite is outlined.At least 1100 °C is required for complete expulsion of water from some amphiboles.

Sulphur at High Pressure and Low Temperatures

1991 ◽  
pp. 143-160 ◽  
Author(s):  
B. Eckert ◽  
H. J. Jodl ◽  
H. O. Albert ◽  
P. Foggi
Keyword(s):  
High Pressure ◽  
Low Temperatures

Under Pressure: High-Pressure Metamorphism in the Alps

Elements ◽  
2021 ◽  
Vol 17 (1) ◽  
pp. 17-22 ◽  
Author(s):  
Lucie Tajčmanová ◽  
Paola Manzotti ◽  
Matteo Alvaro
Keyword(s):  
High Pressure ◽  
Structural Data ◽  
Metamorphic Rocks ◽  
Lithostatic Pressure ◽  
Mineral Inclusion ◽  
Crustal Material ◽  
Local Pressure ◽  
Ultra High Pressure ◽  
Mechanical Models ◽  
The Alps

The mechanisms attending the burial of crustal material and its exhumation before and during the Alpine orogeny are controversial. New mechanical models propose local pressure perturbations deviating from lithostatic pressure as a possible mechanism for creating (ultra-)high-pressure rocks in the Alps. These models challenge the assumption that metamorphic pressure can be used as a measure of depth, in this case implying deep subduction of metamorphic rocks beneath the Alpine orogen. We summarize petro-logical, geochronological and structural data to assess two fundamentally distinct mechanisms of forming (ultra-)high-pressure rocks: deep subduction; or anomalous, non-lithostatic pressure variation. Furthermore, we explore mineral-inclusion barometry to assess the relationship between pressure and depth in metamorphic rocks.

scholarly journals Subduction of trench-fill sediments beneath an accretionary wedge: Insights from sandbox analogue experiments

Geosphere ◽  
2020 ◽  
Vol 16 (4) ◽  
pp. 953-968 ◽  
Author(s):  
Atsushi Noda ◽  
Hiroaki Koge ◽  
Yasuhiro Yamada ◽  
Ayumu Miyakawa ◽  
Juichiro Ashi
Keyword(s):  
High Pressure ◽  
Side Wall ◽  
Metamorphic Rocks ◽  
Accretionary Wedge ◽  
Seafloor Topography ◽  
Subduction Channel ◽  
Hp Metamorphism ◽  
Analogue Experiments ◽  
Topographic High

Abstract Sandy trench-fill sediments at accretionary margins are commonly scraped off at the frontal wedge and rarely subducted to the depth of high-pressure (HP) metamorphism. However, some ancient exhumed accretionary complexes are associated with high-pressure–low-temperature (HP-LT) metamorphic rocks, such as psammitic schists, which are derived from sandy trench-fill sediments. This study used sandbox analogue experiments to investigate the role of seafloor topography in the transport of trench-fill sediments to depth during subduction. We conducted two different types of experiments, with or without a rigid topographic high (representing a seamount). We used an undeformable backstop that was unfixed to the side wall of the apparatus to allow a seamount to be subducted beneath the overriding plate. In experiments without a seamount, progressive thickening of the accretionary wedge pushed the backstop down, leading to a stepping down of the décollement, narrowing of the subduction channel, and underplating of the wedge with subducting sediment. In contrast, in experiments with a topographic high, the subduction of the topographic high raised the backstop, leading to a stepping up of the décollement and widening of the subduction channel. These results suggest that the subduction of stiff topographic relief beneath an inflexible overriding plate might enable trench-fill sediments to be deeply subducted and to become the protoliths of HP-LT metamorphic rocks.

Studies on the manufacture of sweet cream starter butter: II. Effect of variation in proportion of starter added to cream

1960 ◽  
Vol 27 (1) ◽  
pp. 91-102 ◽  
Author(s):  
F. H. McDowall ◽  
J. A. Singleton ◽  
B. S. Le Heron
Keyword(s):  
Lactic Acid ◽  
Low Temperatures ◽  
Starter Culture ◽  
Skim Milk ◽  
Ph Values ◽  
Commercial Scale ◽  
Increase With Increase ◽  
Keeping Quality ◽  
Higher Temperature

SummaryProduction of diacetyl and acetoin by starters in cold skim-milk and cream was shown to increase with increase in the proportion of starter culture added, with some limitations at the higher rates of starter addition.With Streptococcus diacetilactis starter in skim-milk at 50°F the relation between proportion of starter added and production of diacetyl was linear up to addition at the 4% level, whereas at 43°F it was approximately linear up to the 10% level. At both 50 and 43°F the relation between the proportion of starter added and the production of acetoin was linear up to the 10% level.With Camb starter in skim-milk at both 50 and 43°F there were regular increases in production of diacetyl up to the 4% level of addition, but only minor changes thereafter with increase in the proportion of starter added up to 10%. At both temperatures the maximum production of acetoin was reached with the 7% rate of addition.Production of diacetyl and acetoin in skim-milk was greater at 50°F than at 43°F with both starters for all proportions up to 10%, and it was greater for Str. diacetilactis than for the mixed cultures.Except at the higher rates of addition of starter and at the higher temperature there were no concomitant increases in the acidity of the milk or lowering of the pH values. It appears that at low temperatures production of diacetyl by starters in sweet milk and cream proceeds independently of production of lactic acid.Similar results were obtained in a series of experimental buttermaking trials and some small commercial-scale trials, in which varying proportions of starter were added to creams after pasteurizing and before holding overnight for churning. With the cream-holding temperatures used, mainly 40–50°F, the pH values of the butters were not appreciably lowered by the starter additions to the cream. At all the rates of addition there were with Str. diacetilactis starter higher contents of diacetyl in the butter than with Camb starter. There was no indication of any relationship between the proportion of starter added and the keeping quality of the butter.

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