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Basalt

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K. D. Spinks – 1st expert on this subject based on the ideXlab platform

  • Influence of the crust and crustal structure on the location and composition of high-alumina Basalts of the Taupo Volcanic Zone, New Zealand
    New Zealand Journal of Geology and Geophysics, 2007
    Co-Authors: J. Hieß, J W Cole, K. D. Spinks

    Abstract:

    High-alumina Basalts (HABs) that occur throughout the central part of the Taupo Volcanic Zone (TVZ) are associated particularly with faulting, and many occur where faults intersect caldera margins. For convenience, the Basalts are described in terms of three geographic-tectonic segments: Okataina in the north, Kapenga in the middle, and Taupo in the south. Evidence for mixing and mingling between rising Basaltic magmas and rhyolitic rocks and magmas is common, including the frequent occurrence of xenocrysts and xenoliths, quench textures, and melting around the rims of inclusions. Chemically, the Basalts are similar in terms of major element compositions, suggesting relatively homogeneous PT conditions in the mantle source, but variation between some trace elements suggests different processes are operating in the crust with variable degrees of contamination. The model presented for HAB generation in the TVZ is for partial melting of mantle peridotite in the upper mantle, with the melt rising into the lower crust via dike swarms. In the upper crust, the distribution of HAB is strongly influenced by location and structure. In the Kapenga segment, there is little evidence for interaction between Basaltic and rhyolitic magma, other than at very shallow levels, perhaps because the rhyolitic magma chambers (or pods) were solid, allowing brittle deformation and rapid intrusion of Basalt dikes. At Okataina there is much greater mixing and mingling, suggesting there was still partially molten rhyolitic magma chambers beneath this area during Basalt intrusion. Basalt in the Taupo segment occurs outside the Taupo caldera complex and may be related to the earlier Whakamaru caldera complex. The Basalt is thought to rise through the crust as a network of unrelated melt batches into a plexus of discrete magma chambers and conduits, many of which are sited along fault zones causing fissure eruptions at the surface.

J. Hieß – 2nd expert on this subject based on the ideXlab platform

  • Influence of the crust and crustal structure on the location and composition of high-alumina Basalts of the Taupo Volcanic Zone, New Zealand
    New Zealand Journal of Geology and Geophysics, 2007
    Co-Authors: J. Hieß, J W Cole, K. D. Spinks

    Abstract:

    High-alumina Basalts (HABs) that occur throughout the central part of the Taupo Volcanic Zone (TVZ) are associated particularly with faulting, and many occur where faults intersect caldera margins. For convenience, the Basalts are described in terms of three geographic-tectonic segments: Okataina in the north, Kapenga in the middle, and Taupo in the south. Evidence for mixing and mingling between rising Basaltic magmas and rhyolitic rocks and magmas is common, including the frequent occurrence of xenocrysts and xenoliths, quench textures, and melting around the rims of inclusions. Chemically, the Basalts are similar in terms of major element compositions, suggesting relatively homogeneous PT conditions in the mantle source, but variation between some trace elements suggests different processes are operating in the crust with variable degrees of contamination. The model presented for HAB generation in the TVZ is for partial melting of mantle peridotite in the upper mantle, with the melt rising into the lower crust via dike swarms. In the upper crust, the distribution of HAB is strongly influenced by location and structure. In the Kapenga segment, there is little evidence for interaction between Basaltic and rhyolitic magma, other than at very shallow levels, perhaps because the rhyolitic magma chambers (or pods) were solid, allowing brittle deformation and rapid intrusion of Basalt dikes. At Okataina there is much greater mixing and mingling, suggesting there was still partially molten rhyolitic magma chambers beneath this area during Basalt intrusion. Basalt in the Taupo segment occurs outside the Taupo caldera complex and may be related to the earlier Whakamaru caldera complex. The Basalt is thought to rise through the crust as a network of unrelated melt batches into a plexus of discrete magma chambers and conduits, many of which are sited along fault zones causing fissure eruptions at the surface.

Chongjin Pang – 3rd expert on this subject based on the ideXlab platform

  • origin of arc like continental Basalts implications for deep earth fluid cycling and tectonic discrimination
    Lithos, 2016
    Co-Authors: Xuance Wang, Simon A Wilde, Bei Xu, Chongjin Pang

    Abstract:

    Abstract Continental Basalts generally display enrichment of fluid-mobile elements and depletion of high-field-strength elements, similar to those that evolved in the subduction environment, but different from oceanic Basalts. Based on the continental flood Basalt database for six large igneous provinces, together with rift-related Basalt data from the Basin and Range Province, this study aimed to test the validity of geochemical tectonic discrimination diagrams in distinguishing arc-like intra-continental Basalts from arc Basalts and to further investigate the role of deep-Earth water cycling in producing arc-like signatures in large-scale intra-continental Basalts. Our evaluation shows that arc-like intra-continental Basalts can be distinguished from arc Basalts by integrating the following factors: (1) the FeO, MgO, and Al 2 O 3 concentrations of the primary melt; (2) Ti V, Zr Zr/Y, Zr Ti, and Ti/V Zr/Sm Sr/Nd discrimination diagrams; (3) the coexistence of arc-like and OIB-like subtype Basalts within the same province; (4) primitive mantle-normalized trace element distribution patterns. The similarity of enrichment in fluid-mobile elements (Ba, Rb, Sr, U, and K) between arc-like and true arc Basalts suggests the importance of water flux melting in producing arc-like signatures in continental Basalts. Experimentally determined liquid lines of descent (LLD) imply high magma water concentrations for continental flood Basalts (CFBs) and the Basin and Range Basalts. Furthermore, estimates based on the Al 2 O 3 –LLD method indicates 4.0–5.0 wt% pre-eruptive magma H 2 O concentration for CFBs and the Basin and Range Basalts. The tight relationships between H 2 O/Ce and Ba/La, Ba/Nb and Rb/Nb based on global arc Basalt data were further used to estimate the primary H 2 O concentrations. With the exception of the Emeishan CFBs (mainly containing 4.0–5.6 wt% H 2 O), all other CFBs investigated have similar estimated primary H 2 O contents, with values ranging from 1.0 to 2.0 wt%. The estimated primary H 2 O content of the Basin and Range Basalts is extremely high and up to 10.0 wt%. Thus, this study demonstrates that water flux melting played an important role in the generation of many intra-continental igneous provinces. This new finding was further employed to investigate the tectonic setting of 320–270 Ma Basalts in Inner Mongolia, North China. Most Basalts from three key rock units (i.e. Amushan, Benbatu, and Dashizhai formations) from the Central Asian Orogenic belt are classified as non-arc types. The estimated magma H 2 O concentrations suggest a strong link between H 2 O content and arc-like geochemical signatures. Together with established geological evidence, we proposed that these 320–270 Ma Basaltic rocks were most likely produced in a post-orogenic extensional environment facilitated by subducted slab-driven deep-Earth fluid cycling. We propose a mantle transition zone water-filtering model that links deep-Earth fluid cycling, large-scale intra-continental Basaltic magmatism, and supercontinent cycles into a self-organized system.