Disequilibrium dihedral angles in dolerite sills: A new proxy for cooling rate

Holness, Marian B.; Richardson, Chris N.; Helz, Rosalind Tuthill

doi:10.1130/g33119.1

Cited by 30 publications

(65 citation statements)

References 17 publications

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“…Miyamoto & Takeda, 1994), crystal grain size (e.g. Cashman, 1993) or the geometry of three-grain junctions (Holness et al, 2012). Studies of well-exposed contact aureoles can also be used to constrain thermal time-scales (e.g.…”

Section: Introductionmentioning

confidence: 99%

Contact Metamorphism of Precambrian Gneiss by the Skaergaard Intrusion

Bufe

Holness

Humphreys

2014

Journal of Petrology

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Section: Introductionmentioning

confidence: 99%

Contact Metamorphism of Precambrian Gneiss by the Skaergaard Intrusion

Bufe

Holness

Humphreys

2014

Journal of Petrology

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“…Such infiltration would require high porosity over this distance, since the microstructural evidence they present is not consistent with interfacial energy-driven infiltration of sub-solidus cumulates (e.g. Holness et al 2012b). The evidence of Hayes et al (2017) relates to an upward increase in the Mg# in mafic minerals associated with plagioclase of a constant An content: an alternative explanation for this feature was offered by Cawthorn (2015) who suggested it is due to the trapped liquid shift effect.…”

Section: Implications Of Results For Magma Chamber Processesmentioning

confidence: 89%

Section: Mush Thickness From Dihedral Angle Stepsmentioning

confidence: 99%

“…The creation of threegrain junctions is a gradual process, with the progressive filling of increasingly narrow pores as solidification proceeds: all clinopyroxene-plagioclase-plagioclase dihedral angles are formed when the rock is > 90 vol.% solidified (Holness et al 2012b). Because the melt topology in solidifying gabbros is unlikely to be in textural equilibrium (Holness et al 2012b), there is a finite porosity (the percolation threshold) below which the remaining melt no longer forms an interconnected network. Cheadle et al (2004) showed that the percolation threshold occurs at 8-11 vol.% for non-texturally equilibrated systems, suggesting that once solidification has proceeded sufficiently to result in the completion of all dihedral angles (at least in gabbros which are not undergoing deformation) any remaining liquid is essentially immobile.…”

Section: Mush Thickness From Dihedral Angle Stepsmentioning

confidence: 99%

“…All possible angles will be formed in solidifying orthocumulates (i.e. those cumulates initially containing abundant interstitial liquid, similar to the basalts of the Kilauea Iki crust) when all but ~ 10 vol.% of the interstitial liquid has solidified (Holness et al 2012b); in rocks with more adcumulate character, dihedral angle formation will be complete only when the rock is closer to 100% solidification. In all cases, the base of the step corresponds to the horizon at which the volume of remaining liquid had dropped below the permeability threshold (c.f.…”

Section: Mush Thickness From Dihedral Angle Stepsmentioning

confidence: 99%

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The thickness of the crystal mush on the floor of the Bushveld magma chamber

Holness

Cawthorn

Roberts

2017

Contrib Mineral Petrol

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The thickness of the crystal mush on magma chamber floors can be constrained using the offset between the step-change in the median value of dihedral angles formed at the junctions between two grains of plagioclase and a grain of another phase (typically clinopyroxene, but also orthopyroxene and olivine) and the first appearance or disappearance of the liquidus phase associated with the step-change in median dihedral angle. We determined the mush thickness in the Rustenburg Layered Suite of the Bushveld Complex at clinopyroxene-in (in Lower Main Zone) and magnetite-in (in Upper Zone). We also examined an intermittent appearance of cumulus apatite in Upper Zone, using both the appearance and disappearance of cumulus apatite. In all cases, the mush thickness does not exceed 4 m. These values are consistent with field observations of a mechanically rigid mush at the bases of both magnetitite and chromitite layers overlying anorthosite. Mush thickness of the order of a few metres suggests that neither gravitationally-driven compaction nor compositional convection within the mush layer is likely to have been important processes during solidification: adcumulates in the Bushveld are most likely to have formed at the top of the mush during primary crystallisation. Similarly, it is unlikely either that migration of reactive liquids occurs through large stretches of stratigraphy, or that layering is formed by mechanisms other than primary accumulation.

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Intrusive large igneous provinces below sedimentary basins: An example from the Exmouth Plateau (NW Australia)

Rohrman

2013

JGR Solid Earth

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[1] Large igneous provinces (LIPs) are commonly characterized by extrusion of huge outpourings of flood basalts. However, some LIPs associated with thick sedimentary basins display mainly intrusive sill and dike complexes and a relative absence of extrusives as evidenced on the Exmouth Plateau. Here a breakup-related 150 km × 400 km sill complex imaged on seismic reflection data intruded mainly Triassic sedimentary rocks between the Late Jurassic and the Early Cretaceous. The sill complex is most likely sourced by a mafic or an ultramafic magma chamber, seismically imaged as a high-velocity body (HVB) and covering~16 × 10 4 km 2 . This magma chamber is located at the base of the crust and did not generate extrusives. Simple hydrostatic calculations suggest that melt became vertically arrested in the basin sediments, primarily owing to a reduction in the magmatic overpressure gradient as a result of the differences between fracture and melt gradients controlled by upward decreasing densities of the basin fill. Furthermore, magma overpressures at the source between 5 and 20 MPa are required to explain the presence of sill complexes at 4-11 km depth, indicating that the HVB is the source of the sill/dike complex on the Exmouth Plateau. The extent and outline of the HVB places constraints on the origin of magmatism and LIP formation. In combination with published data, the results suggest a thermal anomaly (upwelling or plume) source for the observed magmatism.

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Disequilibrium dihedral angles in dolerite sills: A new proxy for cooling rate

Cited by 30 publications

References 17 publications

Contact Metamorphism of Precambrian Gneiss by the Skaergaard Intrusion

Contact Metamorphism of Precambrian Gneiss by the Skaergaard Intrusion

The thickness of the crystal mush on the floor of the Bushveld magma chamber

Intrusive large igneous provinces below sedimentary basins: An example from the Exmouth Plateau (NW Australia)

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