Distribution of Ca in highly fractionated peralkaline magmas
- Authors: Marsh, Julian S
- Date: 1976
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132974 , vital:36914 , https://doi.org/10.1016/0012-821X(76)90106-0
- Description: Many peralkaline rhyolites and granites contain less than 0.15 wt.% CaO. In contrast, strongly fractionated peralkaline nepheline syenites and phonolites usually contain greater than 0.5 wt.% CaO. Consideration of known distributions of Ca between crystals and liquid in conjunction with crystal fractionation does not provide an adequate explanation of the contrasting levels of Ca depletion observed. Examination of the suites of late-crystallizing accessory phases in peralkaline rocks suggests that Ca is more soluble in undersaturated magmas than in over-saturated magmas. Activities for CaO in silicic and phonolitic rocks are calculated and the latter have higher CaO activities than the former and this may manifest itself in the different suites of accessory phases and levels of Ca depletion noted in natural rocks.
- Full Text: false
- Date Issued: 1976
- Authors: Marsh, Julian S
- Date: 1976
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132974 , vital:36914 , https://doi.org/10.1016/0012-821X(76)90106-0
- Description: Many peralkaline rhyolites and granites contain less than 0.15 wt.% CaO. In contrast, strongly fractionated peralkaline nepheline syenites and phonolites usually contain greater than 0.5 wt.% CaO. Consideration of known distributions of Ca between crystals and liquid in conjunction with crystal fractionation does not provide an adequate explanation of the contrasting levels of Ca depletion observed. Examination of the suites of late-crystallizing accessory phases in peralkaline rocks suggests that Ca is more soluble in undersaturated magmas than in over-saturated magmas. Activities for CaO in silicic and phonolitic rocks are calculated and the latter have higher CaO activities than the former and this may manifest itself in the different suites of accessory phases and levels of Ca depletion noted in natural rocks.
- Full Text: false
- Date Issued: 1976
The Lüderitz alkaline province, South West Africa, III: the Pomona and Drachenberg Syenite Complexes
- Authors: Marsh, Julian S
- Date: 1976
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132984 , vital:36915 , https://hdl.handle.net/10520/AJA10120750_2853
- Description: The Pomona ring complex consists of several intrusive masses of syenitic magma that define a differentiation trend towards silica oversaturation. Volume relations, sequence of intrusion, and broad chemical characteristics are consistent with the syenites being derived by feldspar fractionation from an immediate syenitic parent. A plug of nepheline syenite and tinguaite dykes indicate the availability of silica-undersaturated magma generally in the Luderitz Province.
- Full Text:
- Date Issued: 1976
The Lüderitz alkaline province, South West Africa, III: the Pomona and Drachenberg Syenite Complexes
- Authors: Marsh, Julian S
- Date: 1976
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132984 , vital:36915 , https://hdl.handle.net/10520/AJA10120750_2853
- Description: The Pomona ring complex consists of several intrusive masses of syenitic magma that define a differentiation trend towards silica oversaturation. Volume relations, sequence of intrusion, and broad chemical characteristics are consistent with the syenites being derived by feldspar fractionation from an immediate syenitic parent. A plug of nepheline syenite and tinguaite dykes indicate the availability of silica-undersaturated magma generally in the Luderitz Province.
- Full Text:
- Date Issued: 1976
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