Emplacement mechanisms of sill complexes: Information from the geochemical architecture of the Golden Valley Sill Complex, South Africa

Galerne, Christophe; Neumann, Else-Ragnhild; Planke, Sverre

doi:10.1016/j.jvolgeores.2008.06.004

Cited by 84 publications

(61 citation statements)

References 64 publications

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“…7A, 7B; Galerne et al, 2008;Leat, 2008;Polteau et al, 2008b;Airoldi et al, 2012;Muirhead et al, 2012Muirhead et al, , 2014Svensen et al, 2012;Scheiber-Enslin et al, 2014). In the Ferrar magmatic province specifically, the role of sills in facilitating extensive lateral magma flow is supported by: (1) observed sill-sill feeding relationships (Muirhead et al, , 2014; (2) decreasing Mg# and MgO contents along the length of the Ferrar magmatic province that are consistent with fractional crystallization during lateral magma flow as far as 4100 km from the Weddell Sea region (Elliot et al, 1999;Elliot and Fleming, 2000;Leat, 2008); and (3) the consistent orientation of bridge and/or broken bridge structure long axes and magnetic lineations within sills and interconnected sheets across Antarctica (e.g., in the Theron Mountains, Antarctica) (Dragoni et al, 1997;Hutton, 2009;Airoldi et al, 2012).…”

Section: Karoo-ferrar Lipmentioning

confidence: 99%

Lateral Magma Flow in Mafic Sill‐complexes

Magee

Muirhead

Karvelas

et al. 2016

Acta Geologica Sinica (Eng)

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The structure of upper crustal magma plumbing systems controls the distribution of volcanism and influences tectonic processes. However, delineating the structure and volume of plumbing systems is difficult because (1) active intrusion networks cannot be directly accessed; (2) field outcrops are commonly limited; and (3) geophysical data imaging the subsurface are restricted in areal extent and resolution. This has led to models involving the vertical transfer of magma via dikes, extending from a melt source to overlying reservoirs and eruption sites, being favored in the volcanic literature. However, while there is a wealth of evidence to support the occurrence of dike-dominated systems, we synthesize field-and seismic reflection-based observations and highlight that extensive lateral magma transport (as much as 4100 km) may occur within mafic sill complexes. Most of these mafic sill complexes occur in sedimentary basins (e.g., the Karoo Basin, South Africa), although some intrude crystalline continental crust (e.g., the Yilgarn craton, Australia), and consist of interconnected sills and inclined sheets. Sill complex emplacement is largely controlled by host-rock lithology and structure and the state of stress. We argue that plumbing systems need not be dominated by dikes and that magma can be transported within widespread sill complexes, promoting the development of volcanoes that do not overlie the melt source. However, the extent to which active volcanic systems and rifted margins are underlain by sill complexes remains poorly constrained, despite important implications for elucidating magmatic processes, melt volumes, and melt sources.

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Section: Karoo-ferrar Lipmentioning

confidence: 99%

Lateral Magma Flow in Mafic Sill‐complexes

Magee

Muirhead

Karvelas

et al. 2016

Acta Geologica Sinica (Eng)

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“…These weighted variables are combined in n − 1 basis functions (assuming that n < m). An example of such statistical analysis can be found in Table 3 in Galerne et al (2008). The general formulation of the discriminant (or principal component) function is:…”

Section: Methodsmentioning

confidence: 99%

“…The statistical method has the advantage that it can deal with large data sets and produce quick and robust results (see Fig. 11 in Galerne et al 2008).…”

Section: Methodsmentioning

confidence: 99%

“…sills and dykes, each represented by a specific sample population), may be easily distinguished in a map view, but their genetic relationships are unknown. Few physical contacts exist between sills and dykes in the GVSC, thus numerous genetic relationships may be imagined: from (a) all units originate in the same, or identical, magma batches, to (b) all units are derived from separate magma batches (Galerne et al 2008(Galerne et al , 2010. The genetic relationship has important bearing on our understanding of the intrusion mechanisms and feeding systematics of sill complexes.…”

Section: Methodsmentioning

confidence: 99%

“…The GVSC is located in the southern part of the Karoo Basin, SW of the Lesotho Lava Plateau, and consists of four major elliptical saucer-shaped sills and a major dyke ( Fig. 5a; Galerne et al 2008). The GVSC area also includes the Golden Valley Dyke (GVD; ≤15 m thick, 17 km long) and several small dykes (d1-d4) and short sill segments (e.g., L1, L2 and L3).…”

Section: Methodsmentioning

confidence: 99%

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Geochemical Fingerprinting and Magmatic Plumbing Systems

Galerne

Neumann

2014

Physical Geology of Shallow Magmatic Systems

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Subvolcanic systems are characterized by complex combinations of intrusive units (dykes, sills, saucer-shaped sills, cone sheets, etc.) for which genetic relationships are unclear. This chapter explains how whole-rock geochemistry may be used to resolve the genetic relationships of such subvolcanic (and volcanic) systems. We start with a short introduction of the geochemical fingerprinting method with particular emphasis on the statistical refinement method called Forward Stepwise-Discriminant Function Analysis (FS-DFA). Combined with field mapping and structural analysis, geochemical fingerprinting based on major and trace elements and isotope ratios, is a very powerful tool to distinguish between igneous units (lavas, sills, dykes) with subtle (or not so subtle) geochemical differences. Different geochemical fingerprinting or signatures indicate derivation from distinct magma batches. The results from FS-DFA analyses may be used to reveal genetic relationships between geological units, or lack of such, which again may be used to throw light on subvolcanic plumbing systems, the feeding system in sill-dyke complexes, as well as other problems. The method is illustrated by studies of the Golden Valley Sill Complex in the Karoo Basin (South Africa).

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Modeling fluid flow in sedimentary basins with sill intrusions: Implications for hydrothermal venting and climate change

Iyer¹,

Rüpke²,

Galerne

2013

Geochem Geophys Geosyst

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[1] Large volumes of magma emplaced within sedimentary basins have been linked to multiple climate change events due to release of greenhouse gases such as CH 4 . Basin-scale estimates of thermogenic methane generation show that this process alone could generate enough greenhouse gases to trigger global incidents. However, the rates at which these gases are transported and released into the atmosphere are quantitatively unknown. We use a 2D, hybrid FEM/FVM model that solves for fully compressible fluid flow to quantify the thermogenic release and transport of methane and to evaluate flow patterns within these systems. Our results show that the methane generation potential in systems with fluid flow does not significantly differ from that estimated in diffusive systems. The values diverge when vigorous convection occurs with a maximum variation of about 50%. The fluid migration pattern around a cooling, impermeable sill alone generates hydrothermal plumes without the need for other processes such as boiling and/or explosive degassing. These fluid pathways are rooted at the edges of the outer sills consistent with seismic imaging. Methane venting at the surface occurs in three distinct stages and can last for hundreds of thousands of years. Our simulations suggest that although the quantity of methane potentially generated within the contact aureole can cause catastrophic climate change, the rate at which this methane is released into the atmosphere is too slow to trigger, by itself, some of the negative d 13 C excursions observed in the fossil record over short time scales (<10,000 years).

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Emplacement mechanisms of sill complexes: Information from the geochemical architecture of the Golden Valley Sill Complex, South Africa

Cited by 84 publications

References 64 publications

Lateral Magma Flow in Mafic Sill‐complexes

Lateral Magma Flow in Mafic Sill‐complexes

Geochemical Fingerprinting and Magmatic Plumbing Systems

Modeling fluid flow in sedimentary basins with sill intrusions: Implications for hydrothermal venting and climate change

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