Interaction of magma and wet unconsolidated sediments ...
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63 Interaction of magma and wet unconsolidated sediments: case study from Byers Peninsula, Livingston Island, Antarctica Взаимодействие между магма и неконсолидирани седименти: пример от п-в Байерс, о-в Ливингстън, Антарктика Stefan Velev 1 , Docho Dochev 2 , Kamen Bonev 3 Стефан Велев 1 , Дочо Дочев 2 , Камен Бонев 3 1 Sofia University “St. Kliment Ohridski”, National Center for Polar Studies, 1504 Sofia; E-mail: [email protected] 2 Sofia University “St. Kliment Ohridski”, Faculty of Geology and Geography, 1504 Sofia; E-mail: [email protected] 3 Bulgarian Antarctic Institute, 1504 Sofia; E-mail: [email protected] Keywords: subaqueous cryptodomes, peperites, magma, Antarctica. Interaction between magma and wet unconsolidated sediments is common in environments where sedi- mentation accompanies volcanism and magmatism, especially in subaqueous settings where large volumes of magma are emplaced as syn-volcanic intrusion. In this work we describe and interpret a case study of non-explosive magma-water interaction developed in subaqueous environment in the Byers Peninsula. Byers Peninsula is the largest ice-free area of Livingston Island, South Shetland Islands, Antarctica. Exposed Upper Jurassic–Lower Cretaceous sedimen- tary and volcanic rocks are included in Byers Group. The basaltic cryptodomes crop out in several places on the Byers Peninsula. They are intruded in uncon- solidated sediment rocks (alternation of sandstones and siltstones). The cryptodomes have irregular fin- gershaped contacts (Fig. 1a). The penetration of the basalts in the wet unconsolidated sediments results in quench fragmentation and generation of in situ hyaloclastite. The low viscosity magma is influxed in the sediments and peperites (White et al., 2000) are formed due to temperature differences and the fluidi- zation effect. In peperitic facies, sandstones or siltstones fill joints and fractures that define pseudo-pillows (Fig. 1b), lobe-like bodies (Fig. 1e), polyhedral joint blocks and closely packed fabric (Fig. 1c) or sediment, matrix-rich breccia (Fig. 1d), contains fragments and apophyses of basalts (dispersed fabric). Often the ba- salt fragments show jigsaw-fit texture and some of the direct contacts with the sediments have chilled margins. Along some contacts, peperite with dispersed fab- ric passes through a zone of closely packed peperite into coherent facies. Alternatively, closely packed pe- perite passes directly into coherent facies. Examples of peperite with more than one clast type (globular, blocky and platy), and involving sedimentary matrix are common (Doyle, 2000). The complexities of peperite in respect to clast types, abundances and distribution, as well as grain- size and structures in the sedimentary component, suggest that a spectrum of fragmentation and mixing processes were involved in fragmenting the sheets. At Byers Peninsula, peperite developed by one or a com- bination of: (i) non-explosive oscillation of vapour films at the magma-sediment interface; (ii) non-explo- sive expansion of pore water following enclosure of sediment in the magma or entrapment of sediment at the magma-sediment contacts. References Doyle, M. G. 2000. Clast shape and textural associations in peperite as a guide to hydromagmatic interactions: Upper Permian basaltic and basaltic andesite examples from Kiama, Australia. – Australian J. of Earth Sci., 47, 167–177. White, J. D. L., J. McPhie, I. Skiling. 2000. Peperite: a usefull genetic term. – Bull. Volcanol., 62, 65–66. СПИСАНИЕ НА БЪЛГАРСКОТО ГЕОЛОГИЧЕСКО ДРУЖЕСТВО, год. 79, кн. 3, 2018, с. 63–64 REVIEW OF THE BULGARIAN GEOLOGICAL SOCIETY, vol. 79, part 3, 2018, p. 63–64 National Conference with international participation “GEOSCIENCES 2018”
Transcript of Interaction of magma and wet unconsolidated sediments ...
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Interaction of magma and wet unconsolidated sediments: case study from Byers Peninsula, Livingston Island, AntarcticaВзаимодействие между магма и неконсолидирани седименти: пример от п-в Байерс, о-в Ливингстън, АнтарктикаStefan Velev1, Docho Dochev2, Kamen Bonev3
Стефан Велев1, Дочо Дочев2, Камен Бонев3
1 Sofia University “St. Kliment Ohridski”, National Center for Polar Studies, 1504 Sofia; E-mail: [email protected] Sofia University “St. Kliment Ohridski”, Faculty of Geology and Geography, 1504 Sofia; E-mail: [email protected] Bulgarian Antarctic Institute, 1504 Sofia; E-mail: [email protected]
Keywords: subaqueous cryptodomes, peperites, magma, Antarctica.
Interaction between magma and wet unconsolidated sediments is common in environments where sedi-mentation accompanies volcanism and magmatism, especially in subaqueous settings where large volumes of magma are emplaced as syn-volcanic intrusion. In this work we describe and interpret a case study of non-explosive magma-water interaction developed in subaqueous environment in the Byers Peninsula.
Byers Peninsula is the largest ice-free area of Livingston Island, South Shetland Islands, Antarctica. Exposed Upper Jurassic–Lower Cretaceous sedimen-tary and volcanic rocks are included in Byers Group. The basaltic cryptodomes crop out in several places on the Byers Peninsula. They are intruded in uncon-solidated sediment rocks (alternation of sandstones and siltstones). The cryptodomes have irregular fin-gershaped contacts (Fig. 1a). The penetration of the basalts in the wet unconsolidated sediments results in quench fragmentation and generation of in situ hyaloclastite. The low viscosity magma is influxed in the sediments and peperites (White et al., 2000) are formed due to temperature differences and the fluidi-zation effect.
In peperitic facies, sandstones or siltstones fill joints and fractures that define pseudo-pillows (Fig. 1b), lobe-like bodies (Fig. 1e), polyhedral joint blocks and closely packed fabric (Fig. 1c) or sediment, matrix-rich breccia (Fig. 1d), contains fragments and apophyses of basalts (dispersed fabric). Often the ba-
salt fragments show jigsaw-fit texture and some of the direct contacts with the sediments have chilled margins.
Along some contacts, peperite with dispersed fab-ric passes through a zone of closely packed peperite into coherent facies. Alternatively, closely packed pe-perite passes directly into coherent facies. Examples of peperite with more than one clast type (globular, blocky and platy), and involving sedimentary matrix are common (Doyle, 2000).
The complexities of peperite in respect to clast types, abundances and distribution, as well as grain-size and structures in the sedimentary component, suggest that a spectrum of fragmentation and mixing processes were involved in fragmenting the sheets. At Byers Peninsula, peperite developed by one or a com-bination of: (i) non-explosive oscillation of vapour films at the magma-sediment interface; (ii) non-explo-sive expansion of pore water following enclosure of sediment in the magma or entrapment of sediment at the magma-sediment contacts.
ReferencesDoyle, M. G. 2000. Clast shape and textural associations in
peperite as a guide to hydromagmatic interactions: Upper Permian basaltic and basaltic andesite examples from Kiama, Australia. – Australian J. of Earth Sci., 47, 167–177.
White, J. D. L., J. McPhie, I. Skiling. 2000. Peperite: a usefull genetic term. – Bull. Volcanol., 62, 65–66.
СПИСАНИЕ НА БЪЛГАРСКОТО ГЕОЛОГИЧЕСКО ДРУЖЕСТВО, год. 79, кн. 3, 2018, с. 63–64REVIEW OF THE BULGARIAN GEOLOGICAL SOCIETY, vol. 79, part 3, 2018, p. 63–64National Conference with international participation “GEOSCIENCES 2018”
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Fig. 1. Intrusion of cryptodomes in nonconsolidated sediments: a, idealized sketch; b, pseudo-pillows; c, closely packed peperites; d, sediment matrix-rich breccias; e, lobe-like platy body
