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1.
John F. Rudge Marian B. Holness Graham C. Smith 《Contributions to Mineralogy and Petrology》2008,156(4):413-429
The spatial distribution of grains in a solidifying igneous rock controls the physical properties of the crystal mush, and
in turn is controlled by the rate of crystal growth and accumulation. A predominant non-spherical habit for igneous minerals
brings into question the use of spherical particles in reference packings used for quantification of spatial distribution.
Furthermore, variations of crystal clustering/ordering with length scale require spatial statistics which take into account
the distribution of particles beyond nearest neighbours. Using random close packings of spherocylinders, we demonstrate the
importance of aspect ratio for the aggregation index (usually known as R) and show that packings of spherical particles have more structure than packings of rods. The spatial distribution functions
demonstrate that the plagioclase grains in the colonnade from the Holyoke basalt are clustered on a length scale of 0.5 mm.
Understanding the controls on grain spatial distribution in igneous rocks will depend on the application of these techniques
to well-understood environments. 相似文献
2.
Marian B. Holness M. J. Bickle Colin M. Graham 《Contributions to Mineralogy and Petrology》1991,108(3):356-367
In the aureole of the Beinn an Dubhaich granite, Skye, the minimum observed median forsterite-calcite-calcite dihedral angle
varies from 110° at the olivinein isograd to about 165° (the equilibrium value) at the granite-limestone contact. Laboratory
experiments were performed to investigate the kinetics of this textural change. It was found that the rate of change of the
forsterite-calcite-calcite dihedral angle followed approximately first-order kinetics with an activation energy of 48±4 kJ
mol-1 for fluid-present conditions, and 90 ±4 kJ mol-1 for fluid-absent conditions. Scanning ion imaging demonstrated that, at least in the early stages of textural change, solution-reprecipitation
of the calcite was the rate determining step in the fluid-present runs. The latter result and the value of the activation
energy are both consistent with the activation energy found by previous authors for (albeit zeroth order) silicate-aqueous
solution solution-reprecipitation reactions. The value of activation energy for the dry data does not correspond to those
for either grain boundary or volume diffusion of oxygen or magnesium in forsterite. The mechanism for textural equilibration
in the fluid-absent runs is uncertain. Application of the experimentally-derived rate equation to the Beinn an Dubhaich marbles
gave activation energies higher than those obtained experimentally. It is concluded from consideration of grain growth effects
that activation energies derived from the Beinn an Dubhaich marbles probably reflect textural equilibration under predominantly
fluid-absent conditions. 相似文献
3.
Infiltration Metasomatism of Cumulates by Intrusive Magma Replenishment: the Wavy Horizon, Isle of Rum, Scotland 总被引：4，自引：0，他引：4
The Eastern Layered Intrusion of the Rum Layered Suite comprisespaired peridotite and allivalite (troctolite and gabbro) layersforming 16 macro-rhythmic units. Whereas the majority of thesemacro-units are believed to have formed by a process of crystal–liquiddifferentiation involving successive accumulation of crystalsfrom multiple picritic replenishments of the chamber, the Unit9 peridotite is interpreted as a layer-parallel picrite intrusion.Closely correlated with this discontinuous peridotite body isa distinctive feature generally known as the Wavy Horizon, whichdivides the overlying allivalite into a lower troctolite andan upper gabbro along a well-defined undulating contact. Wepropose that the Wavy Horizon is a metasomatic feature formedconsequent to the removal of clinopyroxene from an originalgabbroic mush. Foundering of the mush into the picritic sillresulted in the replacement of the original interstitial liquidby one saturated only in olivine (± plagioclase). Progressivethrough-flow of this liquid resulted in the stripping out ofclinopyroxene from the lower parts of the allivalite. We interpretthe Wavy Horizon as a reaction front, representing the pointat which the invading liquid became saturated in clinopyroxene.The distinctive pyroxene-enriched zone immediately above theWavy Horizon could have formed when mixing of the interstitialliquids on either side of the reaction front formed a supercooledliquid oversaturated in pyroxene, as a result of the curvatureof the olivine–plagioclase–clinopyroxene cotectic.The presence of many such approximately layer-parallel features,defined by differences in pyroxene content, in the Eastern LayeredIntrusion of Rum suggests that such an infiltration–reactionprocess was not unique to Unit 9. KEY WORDS: cumulate; infiltration metasomatism; Rum; Eastern Layered Intrusion 相似文献
4.
Stephen D. Holness 《地球表面变化过程与地形》2001,26(1):77-89
The orientation of sorted stripes developed in glacial deposits on Marion Island is examined. This study confirms earlier reports of preferential occurrence of sorted stripes on windward slopes. However, sorted stripes were also found to occur on low angle leeward slopes. Mechanisms for the orientation of sorted stripes by wind action are discussed. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
5.
Fluid-calcite-calcite dihedral angles have been measured for fluids in the system H2O−CO2−NaCl, between 1 and 2 kbar, and 550–750° C. It is found that the calcite-calcite-H2O dihedral angle decreases steadily with addition of NaCl from a value of about 80° (pure water) to 44° (60 wt% NaCl). The
CO2−H2O system displays a well-defined minimum at
, with a dihedral angle of 50°, in contrast to those of pure CO2 and H2O which are 90° and 80° respectively. Experiments containing fluids which are immiscible at run conditions showed a bimodal
distribution of dihedral angles in the CO2−H2O−NaCl system, which can be approximately correlated with the compositions of the two fluid phases. Such bimodality was only
observed for immiscible fluids in the H2O−NaCl system if the quench rate exceeded about 200°C per min. This is probably due to the extremely rapid establishment of
the single phase dihedral angle on quenching. The fluid phase topology in devolatilising marbles will only be a connected
network for very saline brines and fluids with
close to 0.5. Fluids trapped in fluid inclusions in calcite grains in marbles may be predominantly H2O-rich or CO2-rich, and of low salinity. All other fluid compositions in the H2O−CO2−NaCl-calcite system will occupy isolated pores, the largest of which will grow at the expense of the smallest. Escape of
fluid produced during devolatilisation reactions under such conditions will occur by fluid overpressuring and hydrofracture.
In contrast, previous experimental studies of quartz-fluid dihedral angles between 950° and 1100° C (Watson and Brenan 1987)
predict that quartz-dominated lithologies will permit pervasive flow of H2O−NaCl fluids, but not of H2O−CO2 fluids. Documented geological examples of differences in permeability and fluid flow mechanism between metamorphic argillites,
psammites and limestones which support the results of the experimental studies are discussed. 相似文献
6.
M. B. Holness 《Contributions to Mineralogy and Petrology》1998,131(1):86-94
The Ballachulish igneous complex in the Scottish Highlands, part of a widespread group of late Caledonian calcalkaline intrusions,
was emplaced at a depth of 10 km into Dalradian metasediments resulting in melting of the country rocks near the intrusive
contact. The greatest extent of melting occurred in the Leven schist in the 400 m wide so-called Chaotic Zone which experienced
infiltration of aqueous fluids from the pluton. In contrast, adjacent to the Chaotic Zone, the feldspar-bearing Appin quartzite
underwent significant melting only within a few metres of the intrusion, despite both being in contact with the same fluid
source as the Leven schist and having a similar (wet) melting point. The permeability of the Appin quartzite and quartz horizons
in the Leven schist to pervasive grain-edge infiltration of aqueous fluids was determined by measuring the equilibrium quartz-H2O dihedral angle for the P-T conditions of contact metamorphism. Addition of powdered samples of both rock types to the pure quartz-H2O system results in a linear decrease of the quartz-H2O dihedral angle with increasing temperature. The rate of this decrease for the Leven schist is greater than that for the
Appin quartzite, and the angle decreases below 60° some 30 °C below the wet solidus (670 °C at 0.3 GPa). Charges bearing Appin
quartzite had dihedral angles greater than 60° at all temperatures below the wet solidus (690 °C at 0.3 GPa). These results
demonstrate that quartz-rich horizons in the Leven schist would have been permeable to infiltration of aqueous fluids close
to the solidus, permitting extensive H2O-fluxed melting to occur. The Appin quartzite would have remained impermeable to grain-edge flow, consistent with the observed
differences in the extent of partial melting of the two lithologies.
Received: 25 November 1996 / Accepted: 29 October 1997 相似文献
7.
Rais Latypov Tony Morse Brian Robins Richard Wilson Grant Cawthorn Christian Tegner Marian Holness Charles Lesher Steve Barnes Brian O’Driscoll Ilya Veksler Michael Higgins Allan Wilson Olivier Namur Sofya Chistyakova Richard Naslund Peter Thy 《Contributions to Mineralogy and Petrology》2015,169(2):1-10
8.
Successive episodes of reactive liquid flow through a layered intrusion (Unit 9, Rum Eastern Layered Intrusion,Scotland) 总被引：2，自引：2，他引：0
J. Leuthold J. D. Blundy M. B. Holness R. Sides 《Contributions to Mineralogy and Petrology》2014,168(1):1-27
We present a detailed microstructural and geochemical study of reactive liquid flow in Unit 9 of the Rum Eastern Layered Intrusion, Scotland. Unit 9 comprises an underlying lens-like body of peridotite overlain by a sequence of troctolite and gabbro (termed allivalite), with some local and minor anorthosite. The troctolite is separated from the overlying gabbro by a distinct, sub-horizontal, undulose horizon (the ‘major wavy horizon’). Higher in the stratigraphy is another, similar, horizon (the ‘minor wavy horizon’) that separates relatively clinopyroxene-poor gabbro from an overlying gabbro. To the north of the peridotite lens, both troctolite and gabbro grade into poikilitic gabbro. Clinopyroxene habit in the allivalite varies from thin rims around olivine in troctolite to equigranular crystals in gabbro and to oikocrysts in poikilitic gabbro. The poikilitic gabbros contain multiple generations of clinopyroxene, with Cr-rich (~1.1 wt% Cr2O3) anhedral cores with moderate REE concentrations (core1) overgrown by an anhedral REE-depleted second generation with moderate Cr (~0.7 wt% Cr2O3) (core2). These composite cores are rimmed by Cr-poor (~0.2 wt% Cr2O3) and REE-poor to -moderate clinopyroxene. We interpret these microstructures as a consequence of two separate episodes of partial melting triggered by the intrusion of hot olivine-phyric picrite to form the discontinuous lenses that comprise the Unit 9 peridotite. Loss of clinopyroxene-saturated partial melt from the lower part of the allivalite immediately following the early stages of sill intrusion resulted in the formation of clinopyroxene-poor gabbro. The spatial extent of clinopyroxene loss is marked by the minor wavy horizon. A second partial melting event stripped out almost all clinopyroxene from the lowest allivalite to form a troctolite, with the major wavy horizon marking the extent of melting during this episode. The poikilitic gabbro formed from clinopyroxene-saturated melt moving upwards and laterally through the remobilized cumulate pile and precipitating clinopyroxene en route. This process, called reactive liquid flow, is potentially important in open magma chambers. 相似文献
9.
10.
Andy?McMillan Nigel?B.?W.?HarrisEmail author Marian?Holness Lewis?Ashwal Simon?Kelley Roger?Rambeloson 《Contributions to Mineralogy and Petrology》2003,145(5):585-599
The Ranomandry Complex is a Neoproterozoic, nested intrusion from central Madagascar composed of a gabbroic core within a coeval peraluminous granite ring intruding pelitic metasediments. Although xenocryst entrainment and magma mixing have both contributed to marginal phases of the granite, the primary melt is characterised by steep LREE/HREE ratios and negligible, or slightly positive, Eu anomalies. Both isotopic and trace element systematics preclude an origin from either partial melting of the metapelitic country rock or from fractional crystallisation of the gabbroic magma. However, trace-element modelling suggests an origin from the dehydration melting of a plagioclase-poor, garnet-bearing metagreywacke at temperatures of 850–900 °C and at lower crustal pressures (>10 kbar). Melting of an enriched subcontinental mantle generated gabbroic magmas that caused advective heating and anatexis at the base of thickened continental crust during their ascent. Transport of the resulting granite magma was facilitated by the pre-existing plumbing system that overcame thermal and mechanical problems associated with both diapirism and self-propagating dykes as mechanisms for long-distance transport of granite magmas. The nested geometry of the intrusions is an indication of a structurally homogeneous lower crust that contains no pre-existing shear zones or fault systems. 相似文献