The Experts below are selected from a list of 46206 Experts worldwide ranked by ideXlab platform
D. I. Groves - One of the best experts on this subject based on the ideXlab platform.
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The Bushveld Complex, South Africa: formation of platinum–palladium, chrome- and vanadium-rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large, relatively slowly cooling, subsiding magma chamber
Mineralium Deposita, 2013Co-Authors: W. D. Maier, S.-j. Barnes, D. I. GrovesAbstract:Platinum-group element (PGE) deposits in the Bushveld Complex and other layered intrusions form when large, incompletely solidified magma chambers undergo central subsidence in response to crustal loading, resulting in slumping of semi-consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides, oxides, olivine and pyroxene and less dense layers enriched in plagioclase. The most economic PGE, Cr and V reefs form in large, multiple-replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification. The depth of emplacement has to be relatively shallow as, otherwise, ductile crust would not be able to flex and collapse. In smaller intrusions, cooling rates are faster, subsidence is less pronounced and, where it occurs, the cumulate may be largely solidified, resulting in insignificant mush mobility and mineral sorting. Layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower, but the reefs can be relatively thicker. An additional factor controlling the PGE, Cr and V prospectivity of intrusions is their location within cratons. Intra-cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large, layered igneous bodies. Furthermore, intrusions sited within cratons are more readily preserved because cratons are underlain by thick, buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust.
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The Bushveld Complex, South Africa: formation of platinum–palladium, chrome- and vanadium-rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large, relatively slowly cooling, subsiding magma chamber
Mineralium Deposita, 2013Co-Authors: W. D. Maier, S.-j. Barnes, D. I. GrovesAbstract:Platinum-group element (PGE) deposits in the Bushveld Complex and other layered intrusions form when large, incompletely solidified magma chambers undergo central subsidence in response to crustal loading, resulting in slumping of semi-consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides, oxides, olivine and pyroxene and less dense layers enriched in plagioclase. The most economic PGE, Cr and V reefs form in large, multiple-replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification. The depth of emplacement has to be relatively shallow as, otherwise, ductile crust would not be able to flex and collapse. In smaller intrusions, cooling rates are faster, subsidence is less pronounced and, where it occurs, the cumulate may be largely solidified, resulting in insignificant mush mobility and mineral sorting. Layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower, but the reefs can be relatively thicker. An additional factor controlling the PGE, Cr and V prospectivity of intrusions is their location within cratons. Intra-cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large, layered igneous bodies. Furthermore, intrusions sited within cratons are more readily preserved because cratons are underlain by thick, buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust.
W. D. Maier - One of the best experts on this subject based on the ideXlab platform.
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The Bushveld Complex, South Africa: formation of platinum–palladium, chrome- and vanadium-rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large, relatively slowly cooling, subsiding magma chamber
Mineralium Deposita, 2013Co-Authors: W. D. Maier, S.-j. Barnes, D. I. GrovesAbstract:Platinum-group element (PGE) deposits in the Bushveld Complex and other layered intrusions form when large, incompletely solidified magma chambers undergo central subsidence in response to crustal loading, resulting in slumping of semi-consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides, oxides, olivine and pyroxene and less dense layers enriched in plagioclase. The most economic PGE, Cr and V reefs form in large, multiple-replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification. The depth of emplacement has to be relatively shallow as, otherwise, ductile crust would not be able to flex and collapse. In smaller intrusions, cooling rates are faster, subsidence is less pronounced and, where it occurs, the cumulate may be largely solidified, resulting in insignificant mush mobility and mineral sorting. Layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower, but the reefs can be relatively thicker. An additional factor controlling the PGE, Cr and V prospectivity of intrusions is their location within cratons. Intra-cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large, layered igneous bodies. Furthermore, intrusions sited within cratons are more readily preserved because cratons are underlain by thick, buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust.
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The Bushveld Complex, South Africa: formation of platinum–palladium, chrome- and vanadium-rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large, relatively slowly cooling, subsiding magma chamber
Mineralium Deposita, 2013Co-Authors: W. D. Maier, S.-j. Barnes, D. I. GrovesAbstract:Platinum-group element (PGE) deposits in the Bushveld Complex and other layered intrusions form when large, incompletely solidified magma chambers undergo central subsidence in response to crustal loading, resulting in slumping of semi-consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides, oxides, olivine and pyroxene and less dense layers enriched in plagioclase. The most economic PGE, Cr and V reefs form in large, multiple-replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification. The depth of emplacement has to be relatively shallow as, otherwise, ductile crust would not be able to flex and collapse. In smaller intrusions, cooling rates are faster, subsidence is less pronounced and, where it occurs, the cumulate may be largely solidified, resulting in insignificant mush mobility and mineral sorting. Layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower, but the reefs can be relatively thicker. An additional factor controlling the PGE, Cr and V prospectivity of intrusions is their location within cratons. Intra-cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large, layered igneous bodies. Furthermore, intrusions sited within cratons are more readily preserved because cratons are underlain by thick, buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust.
Natsuko Adachi - One of the best experts on this subject based on the ideXlab platform.
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late early cambrian archaeocyath reefs in hubei province south china modes of construction during their period of demise
Facies, 2014Co-Authors: Natsuko Adachi, Yoichi Ezaki, Takashi Nakai, Jianbo LiuAbstract:The Lower Cambrian (lower Toyonian) Tianheban Formation of Hubei Province, South China, includes small archaeocyath–calcimicrobial reefs that formed by combinations of archaeocyaths (e.g., Archaeocyathus yichangensis) and calcimicrobes (including Epiphyton, Renalcis, and Girvanella). The archaeocyaths provided substrates onto which the calcimicrobes became attached. In particular, Girvanella encrusts directly upon the surfaces of archaeocyaths, and bush-shaped aggregations of Epiphyton, growing downward, spread over the Girvanella. The remaining spaces among these reef framework-builders are infilled by chambered forms of Epiphyton and/or Renalcis. These calcimicrobes made a strong contribution to reinforcement of the reef frameworks. The archaeocyath-bearing reefs in South China first appeared during the Atdabanian and are last seen in the early Toyonian Tianheban Formation in Hubei Province. Subsequent reefs are purely microbial reefs without archaeocyaths. The Tianheban reefs are therefore the last representatives of archaeocyath-bearing reefs in South China. These reefs, reported herein, record the transition from archaeocyath–calcimicrobial reefs to purely microbial reefs during the Toyonian. Further studies involving integrated geobiological and geochemical analyses are needed to identify the factors that led to the demise of archaeocyath-bearing reefs and that subsequently hindered the development of skeletal-dominated reefs for 40 million years.
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EARLY ORDOVICIAN SHIFT IN REEF CONSTRUCTION FROM MICROBIAL TO METAZOAN REEFS
PALAIOS, 2011Co-Authors: Natsuko Adachi, Yoichi Ezaki, Jianbo LiuAbstract:The Ordovician is a period when novel reef ecosystems appeared along with new reef constructors and skeletal-dominated reefs. The Lower Ordovician (late Tremadocian) Fenhsiang Formation of the Three Gorges area in South China contains the oldest known bryozoan reefs (lithistid sponge–bryozoan and bryozoan–pelmatozoan reefs) alongside lithistid sponge–microbial reefs. The latter are characterized by the dominance of microbialites that encrusted and bound the frame-building sponges and inter-sponge sediments. In contrast, the lithistid sponge–bryozoan and bryozoan–pelmatozoan reefs are generally characterized by bryozoans that encrusted the frame-building sponges or pelmatozoans and grew to fill the inter-frameworks. These sponges and pelmatozoans did not construct the rigid frameworks unaided; their association with bryozoans enabled the development of small skeletal-dominated reefs with rigid frameworks. Skeletal-dominated reefs, for which frame-constructing and encrusting roles are conspicuous, were largely unknown before the Early Ordovician. The appearance of skeletal organisms (specifically colonial, encrusting bryozoans) enabled the development of skeletal-dominated reefs, which were pioneers in the rise of Middle–Late Ordovician reefs. The Early Ordovician establishment of skeletal-dominated reefs at the earliest stages of the Great Ordovician Biodiversification Event would have created novel niches and biological interactions that further promoted the evolution of reef-building and -dwelling organisms, as well as ensuing reef ecosystems.
Jianbo Liu - One of the best experts on this subject based on the ideXlab platform.
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late early cambrian archaeocyath reefs in hubei province south china modes of construction during their period of demise
Facies, 2014Co-Authors: Natsuko Adachi, Yoichi Ezaki, Takashi Nakai, Jianbo LiuAbstract:The Lower Cambrian (lower Toyonian) Tianheban Formation of Hubei Province, South China, includes small archaeocyath–calcimicrobial reefs that formed by combinations of archaeocyaths (e.g., Archaeocyathus yichangensis) and calcimicrobes (including Epiphyton, Renalcis, and Girvanella). The archaeocyaths provided substrates onto which the calcimicrobes became attached. In particular, Girvanella encrusts directly upon the surfaces of archaeocyaths, and bush-shaped aggregations of Epiphyton, growing downward, spread over the Girvanella. The remaining spaces among these reef framework-builders are infilled by chambered forms of Epiphyton and/or Renalcis. These calcimicrobes made a strong contribution to reinforcement of the reef frameworks. The archaeocyath-bearing reefs in South China first appeared during the Atdabanian and are last seen in the early Toyonian Tianheban Formation in Hubei Province. Subsequent reefs are purely microbial reefs without archaeocyaths. The Tianheban reefs are therefore the last representatives of archaeocyath-bearing reefs in South China. These reefs, reported herein, record the transition from archaeocyath–calcimicrobial reefs to purely microbial reefs during the Toyonian. Further studies involving integrated geobiological and geochemical analyses are needed to identify the factors that led to the demise of archaeocyath-bearing reefs and that subsequently hindered the development of skeletal-dominated reefs for 40 million years.
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EARLY ORDOVICIAN SHIFT IN REEF CONSTRUCTION FROM MICROBIAL TO METAZOAN REEFS
PALAIOS, 2011Co-Authors: Natsuko Adachi, Yoichi Ezaki, Jianbo LiuAbstract:The Ordovician is a period when novel reef ecosystems appeared along with new reef constructors and skeletal-dominated reefs. The Lower Ordovician (late Tremadocian) Fenhsiang Formation of the Three Gorges area in South China contains the oldest known bryozoan reefs (lithistid sponge–bryozoan and bryozoan–pelmatozoan reefs) alongside lithistid sponge–microbial reefs. The latter are characterized by the dominance of microbialites that encrusted and bound the frame-building sponges and inter-sponge sediments. In contrast, the lithistid sponge–bryozoan and bryozoan–pelmatozoan reefs are generally characterized by bryozoans that encrusted the frame-building sponges or pelmatozoans and grew to fill the inter-frameworks. These sponges and pelmatozoans did not construct the rigid frameworks unaided; their association with bryozoans enabled the development of small skeletal-dominated reefs with rigid frameworks. Skeletal-dominated reefs, for which frame-constructing and encrusting roles are conspicuous, were largely unknown before the Early Ordovician. The appearance of skeletal organisms (specifically colonial, encrusting bryozoans) enabled the development of skeletal-dominated reefs, which were pioneers in the rise of Middle–Late Ordovician reefs. The Early Ordovician establishment of skeletal-dominated reefs at the earliest stages of the Great Ordovician Biodiversification Event would have created novel niches and biological interactions that further promoted the evolution of reef-building and -dwelling organisms, as well as ensuing reef ecosystems.
S.-j. Barnes - One of the best experts on this subject based on the ideXlab platform.
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The Bushveld Complex, South Africa: formation of platinum–palladium, chrome- and vanadium-rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large, relatively slowly cooling, subsiding magma chamber
Mineralium Deposita, 2013Co-Authors: W. D. Maier, S.-j. Barnes, D. I. GrovesAbstract:Platinum-group element (PGE) deposits in the Bushveld Complex and other layered intrusions form when large, incompletely solidified magma chambers undergo central subsidence in response to crustal loading, resulting in slumping of semi-consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides, oxides, olivine and pyroxene and less dense layers enriched in plagioclase. The most economic PGE, Cr and V reefs form in large, multiple-replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification. The depth of emplacement has to be relatively shallow as, otherwise, ductile crust would not be able to flex and collapse. In smaller intrusions, cooling rates are faster, subsidence is less pronounced and, where it occurs, the cumulate may be largely solidified, resulting in insignificant mush mobility and mineral sorting. Layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower, but the reefs can be relatively thicker. An additional factor controlling the PGE, Cr and V prospectivity of intrusions is their location within cratons. Intra-cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large, layered igneous bodies. Furthermore, intrusions sited within cratons are more readily preserved because cratons are underlain by thick, buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust.
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The Bushveld Complex, South Africa: formation of platinum–palladium, chrome- and vanadium-rich layers via hydrodynamic sorting of a mobilized cumulate slurry in a large, relatively slowly cooling, subsiding magma chamber
Mineralium Deposita, 2013Co-Authors: W. D. Maier, S.-j. Barnes, D. I. GrovesAbstract:Platinum-group element (PGE) deposits in the Bushveld Complex and other layered intrusions form when large, incompletely solidified magma chambers undergo central subsidence in response to crustal loading, resulting in slumping of semi-consolidated cumulate slurries to the centres of the intrusions and hydrodynamic unmixing of the slurries to form dense layers enriched in sulfides, oxides, olivine and pyroxene and less dense layers enriched in plagioclase. The most economic PGE, Cr and V reefs form in large, multiple-replenished intrusions because these cool relatively slowly and their central portions subside prior to termination of magmatism and complete cumulate solidification. The depth of emplacement has to be relatively shallow as, otherwise, ductile crust would not be able to flex and collapse. In smaller intrusions, cooling rates are faster, subsidence is less pronounced and, where it occurs, the cumulate may be largely solidified, resulting in insignificant mush mobility and mineral sorting. Layering is thus less pronounced and less regular and continuous and the grades of the reefs are lower, but the reefs can be relatively thicker. An additional factor controlling the PGE, Cr and V prospectivity of intrusions is their location within cratons. Intra-cratonic environments offer more stable emplacement conditions that are more amenable to the formation of large, layered igneous bodies. Furthermore, intrusions sited within cratons are more readily preserved because cratons are underlain by thick, buoyant keels of harzburgite that prevent plate tectonic recycling and destruction of crust.
