The Subvolcanic Units of the Late Paleozoic Halle Volcanic Complex, Germany: Geometry, Internal Textures and Emplacement Mode

Breitkreuz, Christoph; Ehling, Bodo-Carlo; Pastrik, Nicole

doi:10.1007/11157_2014_2

Cited by 6 publications

(5 citation statements)

References 28 publications

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“…The values of Π 4 for our model sills (0.014 to 0.02) are in the range, close to the upper bound, of those for sills in nature (0.0001 to 0.05) (Bunger & Cruden, ; Cruden et al, ; Hansen & Cartwright, ; Schmiedel et al, ). This suggests that our models simulate the emplacement of magmas that are more viscous than mafic magmas, e.g., andesite to rhyolite sills (Breitkreuz et al, , and references therein). Other possibilities are that neither the elastic properties of the silica flour, i.e., it is too soft with respect to natural rocks, nor do the properties of intrusion‐induced dilation or compaction of the host material properly simulate those of natural rocks.…”

Section: Discussionmentioning

confidence: 87%

Dynamics of Sill and Laccolith Emplacement in the Brittle Crust: Role of Host Rock Strength and Deformation Mode

2017

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Igneous intrusions in sedimentary basins exhibit a great diversity of shapes from thin sheets (e.g., dikes, sills and cone sheets) to massive intrusions (e.g., laccoliths and plugs). Presently, none of the established models of magma emplacement have the capability to simulate this diversity because they account for either purely elastic or purely plastic or purely viscous host rocks, whereas natural rocks are complex visco‐elasto‐plastic materials. In this study, we investigate the effects of elasto‐plastic properties of host rock on magma emplacement using laboratory experiments made of dry granular materials of variable cohesion. Our results show how the deformation mechanism of the host rock controls the emplacement of magma: thin sheet sills form in high‐cohesion materials, which dominantly deform by elastic bending, whereas massive intrusions such as punched laccoliths form in low‐cohesion materials, which dominantly deform by shear failure. Our models also suggest that combined elastic/shear failure deformation modes likely control the emplacement of cone sheets. Our experiments are the first to spontaneously produce diverse, geologically relevant intrusion shapes. Our models show that accounting for the elasto‐plastic behavior of the host rock is essential to filling the gap between the established elastic and plastic models of magma emplacement, and so to reveal the dynamics of magma emplacement in the Earth's brittle crust.

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Section: Discussionmentioning

confidence: 87%

Dynamics of Sill and Laccolith Emplacement in the Brittle Crust: Role of Host Rock Strength and Deformation Mode

2017

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“…At local scale, that is, intrusion tip scale, significant brittle shear and/or ductile shear has been documented to accommodate the propagation of intrusion tips (e.g., Agirrezabala, ; Pollard, ; Schofield et al, ; Wilson et al, ; Spacapan et al, ). At larger scale, that is, at intrusion scale, some authors argue that shear failure controls, at least partly, the emplacement of magma or fluidized sediments into conical intrusions (Galland et al, ; Guldstrand et al, ; Phillips, ; Schmiedel, Galland, & Breitkreuz, ), saucer‐shaped intrusions (Galland et al, ; Haug et al, ; Muirhead et al, ), or laccoliths (Breitkreuz et al, ; Corry, ; de Saint‐Blanquat et al, ; Schmiedel et al, ; Schmiedel, Galland, & Breitkreuz, ). The resulting host rock deformation pattern and associated damage likely have important implications for fluid flow through intruded sedimentary basins (Senger et al, , ).…”

Section: Introductionmentioning

confidence: 99%

Shear Versus Tensile Failure Mechanisms Induced by Sill Intrusions: Implications for Emplacement of Conical and Saucer‐Shaped Intrusions

et al. 2018

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Sills, saucer‐shaped sills, and cone sheets are fundamental magma conduits in many sedimentary basins worldwide. Models of their emplacement usually approximate the host rock properties as purely elastic and consider the plastic deformation to be negligible. However, many field observations suggest that inelastic damage and shear fracturing play a significant role during sill emplacement. Here we use a rigid plasticity approach, through limit analysis modeling, to study the conditions required for inelastic deformation of sill overburdens. Our models produce distinct shear failure structures that resemble intrusive bodies, such as cone sheets and saucer‐shaped sills. This suggests that shear damage greatly controls the transition from flat sill to inclined sheets. We derive an empirical scaling law of the critical overpressure required for shear failure of the sill's overburden. This scaling law allows to predict the critical sill diameter at which shear failure of the overburden occurs, which matches the diameters of natural saucer‐shaped intrusions' inner sills. A quantitative comparison between our shear failure model and the established sill's tensile propagation mechanism suggests that sills initially propagate as tensile fractures, until reaching a critical diameter at which shear failure of the overburden controls the subsequent emplacement of the magma. This comparison also allows us to predict, for the first time, the conditions of emplacement of both conical intrusions, saucer‐shaped intrusions, and large concordant sills. Beyond the application to sills, our study suggests that shear failure significantly controls the emplacement of igneous sheet intrusions in the Earth's brittle crust.

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“…The Halle sample represented fully crystalline subvolcanic rhyolite from the Halle Volcanic Complex (located within the Saale Basin). The Halle Complex comprises several fine-grained and coarse-grained laccoliths [19,20] emplaced from 291.7 ± 1.8 to 301 ± 3 Ma [19]. The individual laccoliths were formed by several successive magma pulses with evidence of the prolonged laccolith formation being consistent with structural, petrological, and geochemical data [15,21,22].…”

Section: Geological Settingmentioning

confidence: 55%

Towards Identification of Zircon Populations in Permo-Carboniferous Rhyolites of Central Europe: Insight from Automated SEM-Mineral Liberation Analyses

et al. 2020

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Zircon is a main mineral used for dating rhyolitic magmas as well as reconstructing their differentiation. It is common that different populations of zircon grains occur in a single rhyolitic sample. The presence of both autocrystic and antecrystic zircon grains is reflected in their strongly varied chemical compositions and slight spread of ages. However, postmagmatic processes may induce lead loss, which is also recorded as a spread of zircon ages. Therefore, new approaches to identify different zircon populations in rhyolitic rocks are needed. In this study, we suggest that detailed examination of zircon positions in the thin sections of rhyolitic rocks provides valuable information on zircon sources that can be used to identify autocrystic and antecrystic zircon populations. Automated Scanning Electron Microscope (SEM) analyses are of great applicability in determining this, as they return both qualitative and quantitative information and allow for quick comparisons between different rhyolite localities. Five localities of Permo-Carboniferous rhyolites related to post-Variscan extension in Central Europe (Organy, Bieberstein, Halle, Chemnitz, Krucze) were analyzed by automated SEM (MLA-SEM). The samples covered a range of Zr whole rock contents and displayed both crystalline and glassy groundmass. Surprisingly, each locality seemed to have its own special zircon fingerprint. Based on comparisons of whole rocks, modal composition and SEM images Chemnitz ignimbrite was interpreted as containing mostly (or fully) antecrystic zircon, whereas the Bieberstein dyke was shown to possibly contain both types, with the antecrystic zircon being associated with disturbed cumulates. On the other hand, Organy was probably dominated by autocrystic zircon, and Krucze contained dismembered, subhedral zircon in its matrix, whereas Halle zircon was located partly in late veins, filling cracks in laccolith. Both localities may, therefore, contain zircon populations that represent later stages than the crystallization of the main rhyolitic body.

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The Subvolcanic Units of the Late Paleozoic Halle Volcanic Complex, Germany: Geometry, Internal Textures and Emplacement Mode

Cited by 6 publications

References 28 publications

Dynamics of Sill and Laccolith Emplacement in the Brittle Crust: Role of Host Rock Strength and Deformation Mode

Dynamics of Sill and Laccolith Emplacement in the Brittle Crust: Role of Host Rock Strength and Deformation Mode

Shear Versus Tensile Failure Mechanisms Induced by Sill Intrusions: Implications for Emplacement of Conical and Saucer‐Shaped Intrusions

Towards Identification of Zircon Populations in Permo-Carboniferous Rhyolites of Central Europe: Insight from Automated SEM-Mineral Liberation Analyses

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