The petrology and significance of a stratiform mafic segregation pegmatite in a Karoo-aged dolerite sheet
- Mitchell, Andrew A, Naicker, S B, Marsh, Julian S, Dunlevey, J N
- Authors: Mitchell, Andrew A , Naicker, S B , Marsh, Julian S , Dunlevey, J N
- Date: 1997
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149496 , vital:38858 , https://hdl.handle.net/10520/EJC-9293fd659
- Description: A sub-horizontal stratiform mafic segregation pegmatite, of the order of 30 cm thick, occurs within 25 m of the top contact of a Karoo-aged dolerite sheet at Pietermaritzburg, South Africa. The host rock is an orthopyroxene-rich dolerite containing 5 - 8% interstitial granophyre. The pegmatite is similar to the host dolerite in many respects, except that the granophyre content is higher, and acicular augite is the only pyroxene. At its upper contact, a laterally continuous sub-horizontal joint forms a sharp boundary to the pegmatite, whilst the lower contact is gradational over a few millimetres. Low MgO and chalcophiles, and elevated incompatible element contents, are the main geochemical attributes of the pegmatite.
- Full Text:
- Authors: Mitchell, Andrew A , Naicker, S B , Marsh, Julian S , Dunlevey, J N
- Date: 1997
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/149496 , vital:38858 , https://hdl.handle.net/10520/EJC-9293fd659
- Description: A sub-horizontal stratiform mafic segregation pegmatite, of the order of 30 cm thick, occurs within 25 m of the top contact of a Karoo-aged dolerite sheet at Pietermaritzburg, South Africa. The host rock is an orthopyroxene-rich dolerite containing 5 - 8% interstitial granophyre. The pegmatite is similar to the host dolerite in many respects, except that the granophyre content is higher, and acicular augite is the only pyroxene. At its upper contact, a laterally continuous sub-horizontal joint forms a sharp boundary to the pegmatite, whilst the lower contact is gradational over a few millimetres. Low MgO and chalcophiles, and elevated incompatible element contents, are the main geochemical attributes of the pegmatite.
- Full Text:
A laterally extensive geochemical discontinuity in the subcontinental Gondwana Lithosphere
- Erlank, Anthony J, Duncan, Andrew R, Marsh, Julian S, Sweeney, R J, Hawkesworth, C J, Milner, Simon C, Miller, R McG, Rogers, N W
- Authors: Erlank, Anthony J , Duncan, Andrew R , Marsh, Julian S , Sweeney, R J , Hawkesworth, C J , Milner, Simon C , Miller, R McG , Rogers, N W
- Date: 1988
- Language: English
- Type: text , abstracts
- Identifier: http://hdl.handle.net/10962/131678 , vital:36710
- Description: Cox et al. (1967) first delineated the existence of two major geochemical provinces in the Karoo basalts of southern Africa. Tholeiitic basalts in Zimbabwe are highly enriched in incompatible trace elements and constitute the "northern province". In contrast, basalts from Lesotho and from the southern segment of the Lebombo monocline have lower or “normal” abundances of these elements and were regarded as a "southern province'. Recent work has established that this change in composition takes place relatively rapidly in the Central Lebombo.
- Full Text:
- Authors: Erlank, Anthony J , Duncan, Andrew R , Marsh, Julian S , Sweeney, R J , Hawkesworth, C J , Milner, Simon C , Miller, R McG , Rogers, N W
- Date: 1988
- Language: English
- Type: text , abstracts
- Identifier: http://hdl.handle.net/10962/131678 , vital:36710
- Description: Cox et al. (1967) first delineated the existence of two major geochemical provinces in the Karoo basalts of southern Africa. Tholeiitic basalts in Zimbabwe are highly enriched in incompatible trace elements and constitute the "northern province". In contrast, basalts from Lesotho and from the southern segment of the Lebombo monocline have lower or “normal” abundances of these elements and were regarded as a "southern province'. Recent work has established that this change in composition takes place relatively rapidly in the Central Lebombo.
- Full Text:
Aenigmatite stability in silica-undersaturated rocks
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132942 , vital:36911 , https://doi.org/10.1007/BF00373333
- Description: Aenigmatite is common in many trachytes, phonolites and agpaitic nepheline syenites. Petrographic evidence suggests that the aenigmatite in these rocks arises by the reaction of Ti-magnetite with a peralkaline silica-undersaturated liquid, and it is postulated that a no-oxide field, where aenigmatite is stable, exists in alkaline undersaturated magmas.
- Full Text: false
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132942 , vital:36911 , https://doi.org/10.1007/BF00373333
- Description: Aenigmatite is common in many trachytes, phonolites and agpaitic nepheline syenites. Petrographic evidence suggests that the aenigmatite in these rocks arises by the reaction of Ti-magnetite with a peralkaline silica-undersaturated liquid, and it is postulated that a no-oxide field, where aenigmatite is stable, exists in alkaline undersaturated magmas.
- Full Text: false
The Luderitz Alkaline Province, South West Africa I: descriptive petrology of the Granitberg Foyaite Complex
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132951 , vital:36912
- Description: The Granitberg foyaite complex is one of three known alkaline igneous complexes, which, together with a dyke swarm, constitute the Liüderitz Alkaline Province of Lower Cretaceous age. The near-circular complex is emplaced into dolomites and sandstones of the Bogenfels Formation. A large fragment of these sedimentary rocks, originally forming the roof of the intrusion, is preserved in the centre of the complex.
- Full Text:
- Authors: Marsh, Julian S
- Date: 1975
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/132951 , vital:36912
- Description: The Granitberg foyaite complex is one of three known alkaline igneous complexes, which, together with a dyke swarm, constitute the Liüderitz Alkaline Province of Lower Cretaceous age. The near-circular complex is emplaced into dolomites and sandstones of the Bogenfels Formation. A large fragment of these sedimentary rocks, originally forming the roof of the intrusion, is preserved in the centre of the complex.
- Full Text:
- «
- ‹
- 1
- ›
- »