Asthenospheric and lithospheric sources for Mesozoic dolerites from Liberia (Africa): trace element and isotopic evidence
- Dupuy, C, Marsh, Julian S, Dostal, J, Michard, A, Testa, S
- Authors: Dupuy, C , Marsh, Julian S , Dostal, J , Michard, A , Testa, S
- Date: 2002
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140422 , vital:37887 , https://doi.org/10.1016/0012-821X(88)90067-2
- Description: Combined elemental, and Sr and Nd isotopic data are presented for Mesozoic dolerite dikes of Liberia (Africa) which are related to the initial stage of opening of the Atlantic Ocean.
- Full Text: false
- Date Issued: 2002
- Authors: Dupuy, C , Marsh, Julian S , Dostal, J , Michard, A , Testa, S
- Date: 2002
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140422 , vital:37887 , https://doi.org/10.1016/0012-821X(88)90067-2
- Description: Combined elemental, and Sr and Nd isotopic data are presented for Mesozoic dolerite dikes of Liberia (Africa) which are related to the initial stage of opening of the Atlantic Ocean.
- Full Text: false
- Date Issued: 2002
Geochemical constraints on coupled assimilation and fractional crystallization involving upper crustal compositions and continental tholeiitic magma
- Authors: Marsh, Julian S
- Date: 2002
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140432 , vital:37888 , https://doi.org/10.1016/0012-821X(89)90021-6
- Description: The commonly analyzed trace elements in tholeiites can be subdivided into three groups depending on their sense of enrichment or depletion in upper continental crust in relation to fractional crystallization. Lithophile incompatible elements are enriched in crustal rocks and by fractional crystallization, whereas compatible transition elements such as Ni and Cr are depleted. A small third group comprising Ti, V, Fe, and sometimes P, enrich with crystallization but are depleted in the crust.
- Full Text: false
- Date Issued: 2002
- Authors: Marsh, Julian S
- Date: 2002
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/140432 , vital:37888 , https://doi.org/10.1016/0012-821X(89)90021-6
- Description: The commonly analyzed trace elements in tholeiites can be subdivided into three groups depending on their sense of enrichment or depletion in upper continental crust in relation to fractional crystallization. Lithophile incompatible elements are enriched in crustal rocks and by fractional crystallization, whereas compatible transition elements such as Ni and Cr are depleted. A small third group comprising Ti, V, Fe, and sometimes P, enrich with crystallization but are depleted in the crust.
- Full Text: false
- Date Issued: 2002
Magma flow inferred from AMS fabrics in a layered mafic sill, Insizwa, South Africa
- Ferré, Eric C, Bordarier, Cecile, Marsh, Julian S
- Authors: Ferré, Eric C , Bordarier, Cecile , Marsh, Julian S
- Date: 2002
- Language: English
- Type: Article
- Identifier: vital:6733 , http://hdl.handle.net/10962/d1007543
- Description: The Insizwa sill, is a 25-km-diameter, >1000-m-thick layered mafic intrusion, part of the Karoo Igneous Province in South Africa. The peridotitic and gabbronoritic rocks are undeformed and mineral fabrics demonstrably result from magma flow. A horizontal, centimeter-scale model layering is visible in numerous outcrops. Plagioclase crystals are both tabular and elongated. Their preferred orientation, parallel to the layering, forms a foliation and a NW–SE lineation, respectively interpreted as the magma flow plane and flow direction. Throughout the 78 stations of this study (699 specimens), magnetic susceptibilities (K[subscript m]) range from 750 to 10,000×10[superscript (−6)] SI. The magnetic anisotropy (P[subscript j]) ranges from 1.03 to 1.08. Magnetic ellipsoids are both prolate and oblate (average T[subscript j]≈0). Anisotropy of magnetic susceptibility (AMS) fabrics are dominated by multidomain to pseudo-single domain magnetite. High-field magnetic experiments indicate that the paramagnetic contribution from the mafic silicates is less than 50 percentage for low susceptibility rock types. The anisotropy results from magnetite grain shape solely as shown by no significant increase in P[subscript j] with increasing K[subscript m]. The magnetic lineation (305°, 05°) is consistent throughout the sill at various scales and coincides with the mineral lineation in average. In contrast, the magnetic foliation (125° NE 10°) is generally perpendicular to the mineral foliation and to the layering. Several explanations for this odd configuration are discussed. The variations of magnetic parameters across the layering and field observations point to a multiple injection. The magnetic lineation is consistent with the presence of a single feeder dike situated to the SE of the sill.
- Full Text:
- Date Issued: 2002
- Authors: Ferré, Eric C , Bordarier, Cecile , Marsh, Julian S
- Date: 2002
- Language: English
- Type: Article
- Identifier: vital:6733 , http://hdl.handle.net/10962/d1007543
- Description: The Insizwa sill, is a 25-km-diameter, >1000-m-thick layered mafic intrusion, part of the Karoo Igneous Province in South Africa. The peridotitic and gabbronoritic rocks are undeformed and mineral fabrics demonstrably result from magma flow. A horizontal, centimeter-scale model layering is visible in numerous outcrops. Plagioclase crystals are both tabular and elongated. Their preferred orientation, parallel to the layering, forms a foliation and a NW–SE lineation, respectively interpreted as the magma flow plane and flow direction. Throughout the 78 stations of this study (699 specimens), magnetic susceptibilities (K[subscript m]) range from 750 to 10,000×10[superscript (−6)] SI. The magnetic anisotropy (P[subscript j]) ranges from 1.03 to 1.08. Magnetic ellipsoids are both prolate and oblate (average T[subscript j]≈0). Anisotropy of magnetic susceptibility (AMS) fabrics are dominated by multidomain to pseudo-single domain magnetite. High-field magnetic experiments indicate that the paramagnetic contribution from the mafic silicates is less than 50 percentage for low susceptibility rock types. The anisotropy results from magnetite grain shape solely as shown by no significant increase in P[subscript j] with increasing K[subscript m]. The magnetic lineation (305°, 05°) is consistent throughout the sill at various scales and coincides with the mineral lineation in average. In contrast, the magnetic foliation (125° NE 10°) is generally perpendicular to the mineral foliation and to the layering. Several explanations for this odd configuration are discussed. The variations of magnetic parameters across the layering and field observations point to a multiple injection. The magnetic lineation is consistent with the presence of a single feeder dike situated to the SE of the sill.
- Full Text:
- Date Issued: 2002
New views on the Jurassic Clarens Formation: volcano-sedimentary interaction
- Holzforster, Frank, Holzforster, Heike W, Marsh, Julian S
- Authors: Holzforster, Frank , Holzforster, Heike W , Marsh, Julian S
- Date: 2002
- Language: English
- Type: text , abstract
- Identifier: http://hdl.handle.net/10962/132716 , vital:36874
- Description: The Lower Jurassic Clarens Formation of the Great Karoo Basin is usually viewed in the literature as a aeolian and, in places, fluvio-aeolian deposit of tremendous thickness variation form 0-250 m thickness. Interaction with the overlying Karoo Flood Basalts, particularly in the Eastern Cape area and in Lesotho, has been noted but was never a major topic. Relatively widespread pyroclastic deposits sandwiched between the Clarens Formation and the Karoo Flood Basalts have been interpreted as flood-lahars.
- Full Text:
- Date Issued: 2002
- Authors: Holzforster, Frank , Holzforster, Heike W , Marsh, Julian S
- Date: 2002
- Language: English
- Type: text , abstract
- Identifier: http://hdl.handle.net/10962/132716 , vital:36874
- Description: The Lower Jurassic Clarens Formation of the Great Karoo Basin is usually viewed in the literature as a aeolian and, in places, fluvio-aeolian deposit of tremendous thickness variation form 0-250 m thickness. Interaction with the overlying Karoo Flood Basalts, particularly in the Eastern Cape area and in Lesotho, has been noted but was never a major topic. Relatively widespread pyroclastic deposits sandwiched between the Clarens Formation and the Karoo Flood Basalts have been interpreted as flood-lahars.
- Full Text:
- Date Issued: 2002
The distribution of platinum group elements in the Insizwa lobe, Mount Ayliff Complex, South Africa: implications for Ni-Cu-PGE sulfide exploration in the Karoo igneous province
- Maier, W D, Marsh, Julian S, Barnes, Sarah-Jane, Dodd, D C
- Authors: Maier, W D , Marsh, Julian S , Barnes, Sarah-Jane , Dodd, D C
- Date: 2002
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150353 , vital:38969 , https://0-doi.org.wam.seals.ac.za/10.2113/gsecongeo.97.6.1293
- Description: The Mount Ayliff Complex of the Eastern Cape province of South Africa is a layered intrusion of some 800 km2 surface area and up to 1,200 m thickness. On the basis of compositional similarities and spatial association, it is generally interpreted to form part of the Karoo igneous province. Similarities between the Mount Ayliff Complex and the staging chambers and feeder conduits to flood basalts that host magmatic sulfide ores elsewhere in the world suggest that the Mount Ayliff Complex may have an enhanced potential for Noril’sk-Talnakh–type massive Ni-Cu sulfide ores, an idea that is supported by the well-known sulfide occurrence at Waterfall Gorge.
- Full Text: false
- Date Issued: 2002
- Authors: Maier, W D , Marsh, Julian S , Barnes, Sarah-Jane , Dodd, D C
- Date: 2002
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/150353 , vital:38969 , https://0-doi.org.wam.seals.ac.za/10.2113/gsecongeo.97.6.1293
- Description: The Mount Ayliff Complex of the Eastern Cape province of South Africa is a layered intrusion of some 800 km2 surface area and up to 1,200 m thickness. On the basis of compositional similarities and spatial association, it is generally interpreted to form part of the Karoo igneous province. Similarities between the Mount Ayliff Complex and the staging chambers and feeder conduits to flood basalts that host magmatic sulfide ores elsewhere in the world suggest that the Mount Ayliff Complex may have an enhanced potential for Noril’sk-Talnakh–type massive Ni-Cu sulfide ores, an idea that is supported by the well-known sulfide occurrence at Waterfall Gorge.
- Full Text: false
- Date Issued: 2002
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