Research Article| January 01, 2012 Interconnected sills and inclined sheet intrusions control shallow magma transport in the Ferrar large igneous province, Antarctica James D. Muirhead; James D. Muirhead † 1School of Environment, University of Auckland, Private Bag 92019, Auckland, New Zealand †E-mail: jmuirhead@ymail.com Search for other works by this author on: GSW Google Scholar Giulia Airoldi; Giulia Airoldi 2Geology Department, University of Otago, Leith Street, P.O. Box 56, Dunedin 9054, New Zealand Search for other works by this author on: GSW Google Scholar Julie V. Rowland; Julie V. Rowland 1School of Environment, University of Auckland, Private Bag 92019, Auckland, New Zealand Search for other works by this author on: GSW Google Scholar James D.L. White James D.L. White 2Geology Department, University of Otago, Leith Street, P.O. Box 56, Dunedin 9054, New Zealand Search for other works by this author on: GSW Google Scholar GSA Bulletin (2012) 124 (1-2): 162–180. https://doi.org/10.1130/B30455.1 Article history received: 20 Nov 2010 rev-recd: 25 Mar 2011 accepted: 06 Apr 2011 first online: 08 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation James D. Muirhead, Giulia Airoldi, Julie V. Rowland, James D.L. White; Interconnected sills and inclined sheet intrusions control shallow magma transport in the Ferrar large igneous province, Antarctica. GSA Bulletin 2012;; 124 (1-2): 162–180. doi: https://doi.org/10.1130/B30455.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract Field observations and structural data from intrusive complexes at Allan Hills and Terra Cotta Mountain, South Victoria Land, Antarctica, demonstrate that interconnected sills and inclined sheets transported magma through the shallow subsurface. These sills and sheets represent the upper-crustal (top 4 km) plumbing system of the 183 Ma Ferrar large igneous province. The sheets are short in length (<1500 m), are moderately inclined (47° and 51° means), and show meter-scale variations in attitude; in places, they intruded bedding planes, resulting in stepped sheet-sill geometries. Sheet geometries and their relationship to the surrounding country rock are consistent with peripheral sheet intrusion under local magmatic stresses arising from roof-lift during sill injection. The sheet intrusions thus reflect the intrusive process itself rather than a far-field tectonic stress regime. The sills and sheets, together with local dolerite masses, formed the intrusive network that supplied magma to the Mawson Formation pyroclastic rocks in various parts of South Victoria Land and, by inference, the Kirkpatrick flood basalt lavas. The predominance of inclined sheets rather than steeply dipping dikes indicates a magmatic environment that is unlike the Jurassic rift arm inferred by previous authors. This could be explained using any of the following three scenarios. (1) The axis of the rift, and hence any rift-hosted dikes, lies beyond the current exposure area. (2) The regionally extensive Ferrar sills may have provided rheologically weak horizons that limited mechanical coupling of the basement rocks and overlying Beacon Supergroup, locally detaching the upper 4 km of the crust from possible synmagmatic basement extension below. (3) The Ferrar large igneous province was emplaced in a neutral tectonic setting. In this scenario, broad-scale distribution of magma through the province was controlled by preexisting structure in the basement, and local intrusion geometries reflect the physical interaction of intruding magma with bedding anisotropy of the Beacon Supergroup. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.
Abstract Allan Hills nunatak, south Victoria Land, Antarctica, exposes an exceptional example of a shallow depth (< 500 m) intrusive complex formed during the evolution of the Ferrar large igneous province (LIP). Dyke distribution, geometries and relationships allow reconstruction of its history and mechanics of intrusion. Sills interconnect across host sedimentary layers, and a swarm of parallel inclined dolerite sheets is intersected by a radiating dyke-array associated with remnants of a phreatomagmatic vent, where the dolerite is locally quenched and mixed to form peperite. Intrusion geometries, and lack of dominant rift-related structures in the country rock indicate that magma overpressure, local stresses between mutually interacting dykes and vertical variations of host rock mechanical properties controlled the intrusive process throughout the thick and otherwise undeformed pile of sedimentary rocks (Victoria Group). Dolerite sills connected to one another by inclined sheets are inferred to record the preferred mode of propagation for magma-carrying cracks that represent the shallow portions of the Ferrar LIP plumbing system.
We analyse 10 representative intrusions from two sets of inclined diabase (Ferrar Dolerite) sheets exposed at Allan Hills (South Victoria Land, Antarctica), using petrographic and rock magnetic methods to determine microfabrics and infer magma flow directions. At least one diabase sample was collected at the margins of each intrusion. Magnetite and pyrrhotite contribute to magnetic fabrics of the samples. Thirty-six magnetic fabric directions, inferred from the mutual arrangement of either the magnetic lineation, or the magnetic foliation plane and local macroscopic flow indicators (e.g. horn-shaped apophyses and kinks) at the tips and margins of each intrusion reveal composite (i.e. both lateral and vertical) flow paths recorded along each intrusive segment. Petrographic textures and multiple flow directions inferred at sheet-segment tips reveal that 'passive' injection of magma via hydrofracturing produced the local shallow large igneous province plumbing as a sill-dominated intrusive complex very close to, or intersecting the palaeosurface. This contrasts with 'classic' arrays of either vertically or laterally injected blade-like dykes.
Abstract The thermoelectric power of the alloy Cu3Au has been measured in the range of temperature 180°K < T < 1000°K both for samples at equilibrium and for samples disordered by quenching. The thermoelectric power depends remarkably upon the degree of order: the disordered samples present a behaviour quite similar to that of Cu and Au, whilst the samples at equilibrium show a drastic change near the critical temperature Tc and a different behaviour as a function of temperature for T < Tc . A comparison is made with the theoretical curves previously obtained and the results are discussed in connection with the modifications of the Brillouin zones consequent to the order–disorder transition.
Abstract The temperature dependence of the thermoelectric power of the Au 3 Cu alloy was measured for different states of order. While the disordered and the long‐range ordered states show qualitatively the same trend as the Cu 3 Au alloy, the short‐range ordered state shows different behaviour and a certain analogy with the long‐range ordered states. These results are discussed in connection with the new Bragg planes induced by the superlattice.
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